- Email: [email protected]
Slow diffusion co-assembly as an efficient tool to tune colour emission in alkynyl benzoazoles
Journal Pre-proof Slow diffusion co-assembly as an efficient tool to tune colour emission in alkynyl benzoazoles R. Martín, I. Torres-Moya, B. Donoso, J.R. Carrillo, J.M. González-Domínguez, J. Frontiñan-Rubio, P. Prieto, A. Díaz-Ortiz PII:
S0143-7208(19)32694-4
DOI:
https://doi.org/10.1016/j.dyepig.2020.108246
Reference:
DYPI 108246
To appear in:
Dyes and Pigments
Received Date: 19 November 2019 Revised Date:
23 January 2020
Accepted Date: 26 January 2020
Please cite this article as: Martín R, Torres-Moya I, Donoso B, Carrillo JR, González-Domínguez JM, Frontiñan-Rubio J, Prieto P, Díaz-Ortiz A, Slow diffusion co-assembly as an efficient tool to tune colour emission in alkynyl benzoazoles, Dyes and Pigments (2020), doi: https://doi.org/10.1016/ j.dyepig.2020.108246. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.
CRediT author statement Raul Martín: Methodology, Visualization, Investigation, Writing-Original Draft, Writing-Review & Editing. Iván Torres-Moya: Resources. Beatriz Donoso: Resources. José R. Carrillo: Formal analysis. José M. González-Domínguez: Formal analysis. Javier Frontiñan-Rubio: Formal analysis. Pilar Prieto: Supervision, Project administration, Writing-Review & Editing. Angel Díaz-Ortiz: Conceptualization, Supervision, Writing-Original Draft.
1
Slow Diffusion Co-Assembly as an Efficient Tool to Tune Colour
2
Emission in Alkynyl Benzoazoles
3
R. Martín,a,b I. Torres-Moya,a B. Donoso,a J. R. Carrillo,a J. M. González-Domínguez,c J.
4
Frontiñan-Rubio,d P. Prieto,a,* A. Díaz-Ortiz.a,*
5
a
6
Chemical Technologies, University of Castilla-La Mancha-IRICA, 13071 Ciudad Real, Spain
7
b
8
Castilla- La Mancha, 13071 Ciudad Real, Spain
9
c
Department of Inorganic, Organic Chemistry and Biochemistry, Faculty of Science and
Research Institute for Chemical and Environmental Technology (ITQUIMA), University of
Group of Carbon Nanostructures and Nanotechnology, Institute of Carbon Chemistry (ICB-
10
CSIC), c/ Miguel Luesga Castán 4, 50018 Zaragoza, Spain
11
d
12
IRICA, 13071 Ciudad Real, Spain
13
E-mail: [email protected] [email protected]
Instituto Regional de Investigación Científica Aplicada, University of Castilla-La Mancha-
14 15
Abstract
16
We report here the preparation of co-assembled microcrystals by employing an easy,
17
reproducible and cost-effective technique, namely slow diffusion. 2H-Benzo[d][1,2,3]triazole
18
and benzo[c][1,2,5]thiadiazole were chosen as host and guest skeletons, respectively. Structural
19
similarities allowed the correct co-assembly of the two structures. The co-assemblies were
20
studied by different techniques that included Raman spectroscopy and X-ray diffraction,
21
amongst others. The waveguiding properties and the emission colour of the doped organic
22
microcrystals were also investigated. It was found that changes in the molar ratio of the
23
different doping agents could tune the light emission. Fluorescence microscopy images of the
24
co-assembled microcrystals revealed light colour changes from green to whitish, up to CIE
25
coordinates of (0.370, 0.385). These tunable colour-active materials could be useful in the fields
26
of optoelectronics or lab-on-a-chip for integrated optical circuits at micro-/nanoscale.
27 28
Keywords
29
2H-benzo[d][1,2,3]triazole, benzo[c][1,2,5]thiadiazole, co-assembly, slow diffusion, organic
30
optical waveguide, tuning colour emission
31 32
1. Introduction
33
Organic semiconductor micro-/nanocrystals with regular shapes have attracted a great deal of
34
attention in recent years for many applications, such as Organic Field-Effect Transistors
35
(OFETs),1 organic waveguide devices,2 and Organic Solid-State Lasers (OSSL).3 As a
1
36
consequence, these systems are inherently ideal building blocks for key circuits in the next
37
generation of miniaturised optoelectronic devices.4
38
Nevertheless, one of the main problems with organic molecules used in the solid state for
39
optoelectronics is their low fluorescence quantum efficiency, which is due in part to the
40
aggregation-induced quenching (AIQ) phenomenon.5 This problem can be solved by using co-
41
assembled structures6 formed by one (or more) molecule(s), one of which acts as a dopant and
42
the other(s) as a guest. According to Förster's resonance energy transfer (FRET) mechanism,7
43
the energy absorbed by the host molecules can be transferred to the guest molecule, thus leading
44
to light emission and possibly avoiding reabsorption by the organic materials. This process has
45
been shown to be particularly efficient in supramolecular aggregates and it is often used as a
46
tool to tune the emission of individual particles.8 In this way, different emission colours can be
47
obtained in co-assembled structures by simply adjusting the molar ratio between host and
48
dopant materials, since even small quantities of the latter dispersed in aggregates are sufficient
49
to modify the emission spectrum and confirm an efficient energy transfer.9
50
The next generation of optoelectonic devices will be based on nanophotonics, a discipline in
51
which the aim is to control and manipulate photons and/or optical energy in nanometer-scale
52
matter. Optical waveguides are one of the essential components of these new devices.10 Doping
53
systems can be excellent candidates to be part of these devices. However, to date the most
54
widely reported organic doping systems are amorphous.11 Since the crystallinity of
55
nanomaterials can improve their charge carrier transport and enhance the performance of optical
56
and optoelectronic devices,12 the development of organised co-systems is essential for
57
optoelectronic applications. Different approaches have been employed to obtain organised co-
58
assembled systems, including electrospinning13 and template-assisted,8 adsorbent-assisted
59
physical vapour deposition (PVD) methods,14 vapour epitaxy growth,15 and light mediated
60
heterostructures16 and self-assembled heterostructures.17 These methods are often tedious and
61
require specific instrumentation. Solution-based methods are a suitable alternative to overcome
62
these drawbacks.18,19 Slow diffusion is an easy, reproducible and cost-effective technique that
63
can produce organised structures without specialised equipment.
64
It is well known that organic white-light emission (WLE) materials are essential for full-colour
65
displays and the backlight of portable display devices.20 For this reason, modulation of colour
66
emission is a crucial factor in current research. Several supramolecular approaches have been
67
reported for WLE generation by self-assembly21 or gelation22 of molecular building blocks that
68
emit the three primary colours, i.e., red, green, and blue.
69
In the last few years our ongoing research line has been based on the design and preparation of
70
new organic optical waveguides based on azole and benzoazole derivatives.23 In this respect, we
71
recently described the doping of a 2H-benzo[d][1,2,3]triazole derivative with graphene. This
72
strategy allowed us to modulate the emission colour of the graphene-modified aggregate.24
2
73
In the work described here we studied different co-assembled structures from derivatives 1 and
74
2 (Figure 1) previously prepared by our research group by means of Sonogashira C–C cross-
75
coupling reactions between the dibromobenzotriazole or dibromobenzothiadiazole derivative
76
and the corresponding arylacetylene.23c-e The 2H-benzo[d][1,2,3]triazole core was selected as
77
the donor host skeleton due to its exceptional ability to form well-defined rod-like self-
78
assembled aggregates.23c This core is able to emit in the blue and near green regions. Doping of
79
the benzotriazole 1 with the green and red dye derivatives of benzo[c][1,2,5]thiadiazole 2 as
80
guest molecules24 allows the light emission to be successfully tuned from the green to the
81
orange region and the colour can be adjusted by simply modifying the molar ratio. The similar
82
structures of the host and guest molecules ensure the confinement and proximity of donor and
83
acceptor molecules in co-assembled microstructures, thus resulting in efficient FRET in the
84
donor-acceptor system.7
85 86
Figure 1. Structures of derivatives 1 and 2 used as host and guest materials, respectively.
87 88
2. Results and Discussion
89
2.1 Self-assembly behaviour
90
Organised supramolecular co-assembled structures were obtained by the slow diffusion
91
technique. Thus, 10−3 M stock solutions of 1 and 2 were prepared in THF. Five different doping
92
ratios 1:2 were chosen as follows: 1:0.1; 1:0.3; 1:1; 1:3; 1:9. The specific compositions 1:2 were
93
obtained by mixing the appropriate volumes to form 1 mL of THF solution. An open sample
94
vial containing the mixed solutions was gently placed in a vessel containing MeOH as the poor
95
solvent and the system was sealed. After several days of slow diffusion, a uniform precipitate
96
was observed in the inner vial. It is interesting to note that co-assembled structures are only
97
formed up to 1:0.3 molar ratios. In order to avoid false luminescence emission signals arising
98
from remaining solutions of doping agents that could coat the co-assembled crystals, the
99
crystals were washed with two different solvents: hexane and methanol. Despite the fact that
3
100
both solvents removed the coating products, methanol, being a more polar solvent, could
101
dissolve some of the crystal and it was found that hexane was the best option to ensure the
102
integrity of the crystal (compare Figures 2 and S1–S2).
103
Visual changes confirmed that a co-assembly process had taken place and dye leakage was not
104
observed during the preparation process. Co-assembled crystals were formed with a different
105
colour from the pure host. Whereas pure 1 forms clear yellow crystals with an intense yellow
106
emission under 365 nm (Figure 2A,B), the colour of doped 2a and 2b crystals were clear orange
107
(Figure 2I,J) and red (Figure 2K,L), respectively, due to the incorporation of the doping
108
compound into the host structure. More strikingly, 2c-doped crystals were dark brown when the
109
co-assembly process was completed (Figure 2M,N), thus providing evidence that all of the
110
acceptor dyes 2 had been doped into the organic microcrystals of 1. It is worth noting that in
111
cases where the slow diffusion conditions were not satisfactory (solvent, temperature,
112
proportions, time etc.), co-assembled crystals did not form and separate precipitates of pure host
113
and guest molecules were observed (Figure S3). In order to ascertain whether co-assembled
114
structures were formed in the slow diffusion process, 1 mL of a pure solution of 2a and 2c was
115
added to pure microcrystals of 1. After several days neither visual changes nor different
116
emission were observed in the crystals of 1 (Figure S4). Thus, the co-assembly process only
117
takes place if slow diffusion is carried out.
118 119 120
Figure 2. Pure self-assembled crystals of 1 (A,B), 2a (C,D), 2b (E,F) and 2c (G,H) under natural light and irradiated at 365 nm. Pictures of the co-assembled structures (I–N) with the
4
121 122 123
doping agents represented. All structures were removed from their original solution and washed with hexane in order to avoid false emission signals.
124
The resulting morphologies of the co-assembled crystals were visualised by scanning electron
125
microscopy (SEM) on glass substrates (Figure 3). Pure benzotriazole 1 produced well-defined
126
rod-like aggregates that were hundreds of micrometres in length by slow diffusion using
127
chloroform (CHCl3) as the good solvent and acetonitrile (CH3CN) as the poor solvent.23c
128
However, the use of THF/MeOH as solvents in the slow diffusion process gave ultra-long self-
129
assembled needle-like crystals that were several millimetres in length – a process that could
130
facilitate their use in optoelectronic devices (Figure S5).
131
It was found that the percentage of doping agents must be less than 25% in order to favour
132
crystal growth by the slow diffusion technique. In general, when compared with pure
133
microcrystals of 1, the co-assembled structures had very few morphological differences, which
134
indicates that the host (1) has a greater tendency to aggregate than the guest (2) and the acceptor
135
organic molecules will not affect the macroscopic crystallinity of the as-prepared organic
136
microstructures (Figure 3). In the case of 2c only a 1:0.1 host:guest ratio afforded co-assembled
137
structures.
138
In general, co-assembled structures are less thick than pure self-assembled 1 (Figure 3E-I vs. A)
139
and this is especially noteworthy in the case of 2c-doped crystals (Figure 3I).
5
140 141 142 143 144 145
Figure 3. SEM images of pure self-assembled 1 and 2, and the resulting morphologies of 1:0.1 and 1:0.3 molar ratio co-assembled structures obtained by slow diffusion of MeOH vapour into dilute THF solutions.
146
NMR spectroscopy was employed in an effort to confirm further that the co-assembly process
147
of both derivatives occurred effectively. Hexane-washed co-assembled crystals 1:2a (1:0.3)
148
were dissolved in 600 µL of CDCl3. The proton signals of both 1 and 2 were observed in the
149
NMR spectra and this confirmed that the two molecules coexist in the crystal (Figure S6).
150
Furthermore, other spectroscopic techniques were applied to obtain information about the co-
151
assembled system and these are discussed in the following sections.
152 153
2.2 Raman analysis
154
A Raman spectroscopy study was performed on selected samples. After an initial screening it
155
was only possible to carry out Raman spectroscopy on compound 2c. The high fluorescence of
156
derivatives 2a and 2b precluded their study by this technique. The identification of each
157
component was made on the basis of the intensity of a specific peak. The peak at 1416 cm−1 was
158
chosen for compound 1 and for compound 2c the peak at 1334 cm−1 was selected as a
159
representative feature.
6
160
Representative Raman spectra for organic compounds 1 and 2c are shown in Figure 4. Given
161
the vibrational nature of Raman spectroscopy, the different peaks can be ascribed to specific
162
vibrations according to the molecular structure. Compound 1 presented the alkyne stretching
163
band at 2200 cm–1 as the most prominent feature. Furthermore, aromatic ring vibrations also had
164
a strong presence in the spectrum, namely the N=N and C=C stretchings at 1416 cm–1 and 1572
165
cm–1, respectively. Compound 2c had a Raman profile that was similar to that of the host (1) in
166
terms of the alkyne and aromatic C=C bands, while other bands related to other carbon bonds,
167
such as C–C stretching (1283 cm–1) and methyl bending (1334 and 1481 cm–1), were observed.
2c
168 169 170 171 172 173 174 175 176
Figure 4. a) Raman spectra (532 nm laser) of compounds 1, 2c, and the mixture of 1:2c (1:0.1 ratio). The assignments of the main vibrational bands are depicted. Dashed vertical lines indicate the peaks used in the two-dimensional mapping to identify each compound: green for compound 1 and red for compound 2c, with interference not observed between the two sets of signals. b) Inset of the lower part of the spectra, for the sake of clarity, showing the selected 1334 cm−1 band belonging to compound 2c.
177
to each peak (red for 1334 cm−1 and green for 1416 cm−1) and these were plotted
178
simultaneously, using Wire 4.4 software, according to the intensity of the respective peaks. This
179
process allowed us to ascertain the relative disposition of each compound in the mixtures.
180
In general terms, it can be seen how the co-assembled crystals 1:2c (1:0.1) present an uneven
181
distribution of the two components within the crystal. Thus, by Raman spectroscopy it was
182
determined that these crystals are formed by a matrix of aggregated 1 with small clusters of 2c
183
randomly scattered across the structure (Figure 5). This trend was still visible after the crystals
184
were washed with hexane (Figure 5 and S1). However, a different situation was observed when
185
the crystals were washed with methanol (Figure S2). In this case, the distribution of 2c islands
186
within 1 became unclear and the resulting colour mapping suggested that a merging of the two
In the two-dimensional Raman mappings (Figures 5, S1 and S2) specific colours were assigned
7
187
compounds had taken place. This finding is in good agreement with the experimental
188
observations that methanol is able to partially dissolve the crystalline structure of this mixture.
189
190 191 192 193 194
Figure 5. 2D Raman mapping (532 nm laser) of a selected region of a co-assembled crystal 1:2c (1:0.1) from characteristic bands of 1 (in green) and 2c (in red). Numbers in the coloured bars are arbitrary.
195
2.3 X-ray diffraction analysis
196
The crystal structures of the binary nanomaterials were studied by X-ray diffraction (XRD) and
197
the profiles of the pure and doped nanowires were obtained. For the different compounds the
198
diffraction pattern of the binary nanowires shows diffraction peaks for the host and guest
199
compounds. This indicates that 1 is also crystalline in the doped nanomaterials but the
200
formation of a co-crystal or superlattice-type composite crystal did not occur (Figures 6, S7 and
201
S8). Furthermore, a significant displacement of the peak at 2θ = 15.00º of the structure of 1 can
202
be observed (which corresponds to an interplanar spacing of 5.90 Å) to 2θ = 14.68º (interplanar
203
spacing of 6.03 Å) in the doped structure. This may indicate that for molecules of 1 the
204
interplanar spacing along the b-axis increases in order to accommodate molecules of 2a. This
205
peak displacement appears in the three doped nanowires, probably due to the similar structures
206
of the doping agents.
8
207 208 209 210 211 212 213
Figure 6. XRD patterns of the pure compounds 1 (green) and 2a (blue), and the doped organic microcrystal with 1:2a (1:0.3) (red). The stars indicate the diffraction peak of 2θ = 14.68º for 1, which exhibits a significant displacement in the doped structures. The numbers ‘1’ and ‘2a’ indicate the diffraction peaks of the pure structures 1 and 2a, respectively. Crystal planes were assigned from the X-ray structures of the pure compounds.
214
2.4 Photophysical features
215
The optical spectra of compounds 1 and 2 were experimentally measured in tetrahydrofuran
216
(THF) (Figure 7). Only a slight overlap between the emission band of 1 and the absorption band
217
of 2a can be seen in Figure 7A. However, it should be noted that the emission spectrum of 1
218
shows a good overlap with the absorption spectra of 2b and 2c in the wavelength range 450–600
219
nm (Figures 7B and 7C, respectively), which may result in efficient energy transfer from the
220
host 1 to the guest 2 in the doped system. Doping organic derivatives 2 as acceptors into a donor
221
host matrix of benzotriazole 1 ensures confinement and proximity of the two molecules within
222
self-assembled microstructures, and could tentatively result in efficient IFRET (Intermolecular
223
Fluorescence Resonance Energy Transfer) in the donor-acceptor system.18,25 We hope that
224
further experiments with analogous substrates currently underway in our laboratory can clarify
225
this transfer mechanism.
226
9
227 228 229 230 231 232 233 234 235
Figure 7. Absorption and emission spectra of pure 1 (green), 2a (yellow), 2b (red) and 2c (purple). Overlap between the emission spectrum of 1 and the absorption spectrum of 2 is denoted with grey lines. All spectra were measured in THF solution. PL spectra were measured after excitation at the maximum absorption peak of the corresponding compounds (1, λex=290 nm; 2a λex=310 nm; 2b, λex=320 nm; 2c, λex=350 nm). Absorption spectra of compounds 2 were normalised to its ICT band and emission spectra have been corrected to eliminate the solvent interferences.
236
2.5 Optical waveguiding properties
237
Considering the previously reported results on the optical waveguiding features of the related
238
pure compounds 123c and 2a,23e we investigated the propagation of light in the aggregates
239
formed from co-assembled structures. These studies were carried out by fluorescence
240
microscopy with a mercury lamp capable of excitation at any wavelength. Pure 1 aggregates
241
exhibited blue and green bright luminescence spots at the opposite ends and a relatively weak
242
emission from the body when it was irradiated at one end (Figure S9).
243
The co-structures discussed above were irradiated with a laser beam at different λ values and
244
the resulting fluorescence images were recorded with a camera (Figure 8). When benzotriazole
245
1 was doped with 10% of 2a (1:0.1 molar ratio) only green light was propagated through the
246
structure (Figure 8A). Interestingly, when the proportion of the doping agent 2a was 25%
247
(doping ratio 1:0.3), the structure was also able to propagate red light (Figure 8B). This finding
248
provides evidence that changes in the doping agent ratio can modify the propagated light. A
249
similar result has been reported previously in the literature.20d
250
Co-assembled structures containing compound 2c only propagated red light when they were
251
irradiated at one end (Figure 8D). This characteristic could due to the large overlap between the
10
252
emission band of 1 and the absorption band of 2c at 430–570 nm (Figure 7C), which could
253
favour the light reabsorption processes described previously in the literature.4g When the host
254
structure was doped with 2b both green and red light were propagated through the structure
255
(Figure 8C). A lower level of overlap between the emission band of 1 and the absorption band
256
of 2b is observed in the PL spectra of pure compounds, which could indicate that the possible
257
reabsorption phenomenon would be less effective (Figure 7B). These results show that the
258
presence of different doping agents can modify the emission colour of the molecular aggregate
259
with waveguide properties. In this specific case, the dopant dyes cause a bathochromic shift in
260
the emission colour of 1, which changes from blue and green emission to green-red or red
261
emission with the appropriate ratio of doping agent.
262
263 264 265 266 267 268 269
Figure 8. Fluorescence images of the co-assembled aggregates 1:2a 1:0.1 molar ratio (A), 1:0.3 molar ratio (B), 1:2b 1:0.3 molar ratio (C), and 1:2c 1:0.1 molar ratio (D) obtained by irradiating a portion of the aggregate at 320–380 nm (blue), 450–490 nm (green), and 515–565 nm (red). The propagated light at the end of the crystal is shown with a white dashed circle and the direction of the light with a dashed arrow.
270
2.6 White light-emission
271
It is well known that a mixture of blue, green and red chromophores can afford structures that
272
emit white light.20 Bearing this in mind, it was decided to carry out a photophysical study on
11
273
mixtures of compound 1 with different compositions of the three doping agents. The
274
fluorescence emission spectra of solutions are shown in Figure 9.
275
In mixtures with 2a only one broad emission band can be observed due to the low Stokes shift
276
(79 nm) between the emission bands of 1 and 2a (Figure 7A and 9A). Mixtures made with
277
derivative 2c showed very poor emission in solution (Photoluminescence Quantum Yield,
278
PLQY = 8%),26 so an emission band corresponding to this compound was not observed in the
279
fluorescence spectra of the mixture (Figure 9C) and only a decrease in the intensity of the band
280
due to 1 was observed as its molar ratio decreased.
281
In the case of 2b, for which the PLQY was 67%26 and where the Stokes shift between the
282
emission bands of 1 and 2b was 127 nm, the mixed solution of compounds showed two
283
dominant emission bands located at around 500 and 600 nm. These bands can be attributed to
284
molecules of compound 1 and the dopant 2b, respectively (Figure 9B).
285
The emission wavelengths of both 1 and 2 did not show any obvious differences from those of
286
the monomers, so the emission colour of the as-prepared binary 1D microstructures was mainly
287
dependent on the doping ratio. Luminescence photographs of the solutions upon increasing the
288
dopant ratio with excitation 365 nm are shown in Figure 9. The colours of the solutions are
289
consistent with the corresponding emission spectra. In general, the presence of higher levels of
290
doping agent (2) gave rise to lower emission of the host (1).
291
It is worth noting the presence of a broad emission band (450–700 nm) and a visual white
292
emission of the solution 1:2b when the doping ratio was 1:0.3 (Figure 9B), which hints at a
293
possible white emission in the solid state for the crystal with this doping ratio.
12
294 295 296 297 298
Figure 9. Fluorescence spectra and luminescence photographs of 10−3 M THF solutions of 1 upon increasing the dopant ratio of 2a (A), 2b (B) and 2c (C). Luminescence photographs were taken under natural light (above) and 365 nm light (below).
299
The optical properties of the co-assembled structures with different doping ratios were also
300
investigated and the PL spectra of the as-prepared microcrystals are shown in Figure 10c.
301
The confocal microscopy images (Figure 10a) of the co-assembled microrods reveal only slight
302
colour changes from green to whitish upon increasing the molar doping ratio – an observation
303
that indicates the successful modulation of the light emission of the organic microcrystals. The
304
uniform emission colour of each single wire reveals that the guest molecules of 2 are dispersed
305
very uniformly in the matrix 1, which is in good agreement with Raman spectroscopy data
306
(Figure 5). The CIE coordinates of these pure and co-assembled structures are presented in
307
Figure 10b. The CIE coordinates (0.370, 0.385) of the microcrystals with a 2b doping ratio of
308
1:0.3 correspond to the white-emissive region in the CIE chromaticity diagram.
13
309
Doping ratios of 1:0.2 and 1:0.5 were also tested with 2b as the doping agent (Figures S10 and
310
S11). It was found that a 1:0.2 ratio was not sufficient to achieve white emission and pale-
311
yellow crystals were obtained. In contrast, a 1:0.5 ratio gave green-yellow crystals.
312
313 314 315 316 317 318 319
Figure 10. a) Fluorescence microscopy images of the microcrystals containing different doping ratios of 2 upon excitation at 425–650 nm; b) The emission colours corresponding to the organic microcrystals shown in (a) the CIE chromaticity diagram. The white emission colour is marked as a red circle in the CIE chromaticity diagram; c) Emission spectra of the microcrystals shown in (a) deposited onto quartz wafers.
320
3. Conclusions
321
The 2H-benzo[d][1,2,3]triazole core has been employed as a host skeleton to prepare well-
322
defined co-assembled microcrystals. The exceptional ability to form well-defined rod-like self-
323
assembled aggregates and the blue and near-green emission of this compound has been
324
successfully combined with the intense green and red emissions of benzo[c][1,2,5]thiadiazole
325
guest molecules.
326
The co-assembled microcrystals were obtained by the slow diffusion technique, which is an
327
easy, reproducible and cost-effective approach. Five doping ratios were tested and it was found
328
that the percentage of doping agent must be lower than 25% in order to favour crystal growth.
329
All of the co-assembled microcrystals prepared in this study showed impressive visual colour
330
changes from the pure host, thus confirming that a co-assembly process had successfully taken
14
331
place. The arrangement of the co-assembled structures was analysed by different spectroscopic
332
and microscopic techniques.
333
SEM analysis did not indicate any significant morphological differences in the structures of the
334
co-assembled microcrystals when compared to pure 1. This finding indicates that the host
335
material drives the formation of the organised co-assembled structures.
336
X-ray diffraction analysis revealed that the crystallinity of the host material (1) remains
337
unaltered when the guest material (2) is incorporated, and a co-crystal or superlattice-type
338
composite crystal is therefore not formed. However, it was found that molecules of 1 increase
339
their interplanar spacing along the b-axis probably in order to accommodate molecules 2.
340
Evidence for a randomly scattered distribution of the guest molecule (2c) in the matrix structure
341
of the host molecule (1) was provided by Raman spectroscopy.
342
The co-assembled microcrystals can act as optical organic waveguides and the propagation of
343
the light in the resulting aggregates could be modulated by altering both the doping agent and
344
the doping ratio. The light reabsorption process must be avoided in order to allow propagation
345
of light with a different wavelength along the co-assembled microcrystals.
346
The emission spectra of the mixed solution of 1:2b with a 1:0.3 molar doping ratio revealed the
347
presence of a broad emission band (450–700 nm) and a visible white emission from the
348
solution. The CIE coordinates of this solid co-assembled aggregate were (0.370, 0.385). Colour
349
changes in the light from green to orange were observed for the rest of co-assembled
350
microcrystals and this indicates successful modulation of the light emission of the organic
351
microcrystals.
352
The results presented herein offer a versatile approach towards affordable white emissive
353
materials for future applications in the field of optoelectronics or for integrated optical chips.
354 355
4. Experimental details
356
Compounds 1 and 2a-c were prepared according to experimental procedures described by our
357
research group.23e,c, 26
358
SEM images were obtained on a JEOL JSM 6335F microscope working at 15 kV. The samples
359
for SEM imaging were prepared by slow diffusion by mixing the appropriate proportions of
360
compounds 1 and 2. The corresponding solids were washed with hexane and deposited onto a
361
glass substrate, with the remaining solvent evaporated at room temperature.
362
Raman spectra were recorded on a Renishaw inVia™ microspectrophotometer using a 532 nm
363
wavelength laser (85 mW effective output power), with the system coupled to an optical
364
microscope. The sample preparation for Raman measurements was performed by drop casting a
365
THF solution onto a clean piece of SiO2/Si wafer (WRS Materials) and leaving the solvent to
366
evaporate in the open air. Point-based spectra were collected using the 100× objective (N.A. =
367
0.85), 0.1% of the maximum laser power, and 1 second of exposure time at each pulse, in order
15
368
to avoid thermal damage to the sample and interference by fluorescent emission. Each spectrum
369
was baseline-corrected and normalised (to its own highest intensity band) using the Renishaw
370
Wire 4.4 software tool. As regards to two-dimensional mappings, a line-based laser option was
371
used (streamline). The experimental conditions were set up in the range of 0.1–1 seconds
372
exposure time and 0.05–0.1% of the maximum laser power. The probed areas were
373
approximately 20–25 mm2.
374
The XRD patterns were obtained on a PANalytical X'Pert X-ray diffractometer with Cu-Kα
375
radiation (λ = 1.54056 Å). For this study the optimal parameters were run with an increment
376
size of 0.01° and an increment scan time of 1 second over a scan range of 3–40 2θ.
377
Powdery crystals of pure and doped compounds were deposited on a Si zero diffraction plate.
378
This kind of sample holder has no background noise from 20 to 120 degrees and ensures that
379
diffraction peaks are obtained from the sample.
380
Crystal planes of 1 and 2a were assigned for comparison with the corresponding XRD pattern
381
simulated from their X-ray structures.23b,c,e, 24
382
UV-vis spectra were recorded on a Jasco V-530 spectrophotometer. Fluorescence spectra were
383
recorded on a Jasco FP-750 spectrophotometer. In both cases standard quartz cells (1 cm width)
384
were used. Spectra were recorded at room temperature using solvents of spectroscopic grade.
385
Fluorescence images for waveguide behaviour were recorded on a ZEISS Axioplan-2
386
fluorescence microscope with a mercury lamp capable of excitation at any wavelength.
387
However, a series of filters was used to select the excitation wavelength and absorption. These
388
correspond to wavelengths in the blue (λexc = 320–380 nm, λem = 410–510 nm), green (λexc =
389
450–490 nm, λem = 515–565 nm) or red (λexc = 475–495 nm, λem = 520–570 nm). This
390
microscope was fitted with a shutter that allowed the light to be focused on the desired part of
391
the crystal.
392
A Zeiss LSM 800 confocal microscope (Zeiss, Jenna, Germany) with a 10× objective (Plan-
393
Apochromat 10×/0.45 M27) equipped with the ZEN imaging software was used to collect RGB
394
and spectral images of the microcrystals containing different doping ratios of 2. RGB images
395
were obtained using three diode lasers (405, 488 and 561) for blue, green and red fluorescence.
396
Spectral imaging was carried out with laser excitation in the 425–650 nm emission range. A set
397
of 26 images was obtained, with each image acquired with a separate narrow bandwidth of 8
398
µM, thus representing the complete spectral distribution of the fluorescence signals.
399 400
Acknowledgements
401
This
402
SBPLY/17/180501/000189) and MINECO of Spain (projects CTQ2017-88158-R, CTQ2017-
403
84825-R and RED2018-102331-T). R. Martín and B. Donoso are indebted to MEC for a FPU
404
studentship. We thank Mr. Carlos Rivera for his help in the X-ray analysis.
work
has
been
financially
supported
16
by
JCCM-FEDER
(project
405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464
References 1.
2.
3.
4.
a) Shin H, Kumar A, Chao H, Yang D, Palai AK, Pyo S. Laterally-Stacked, solution-processed organic microcrystal with ambipolar charge transport behavior. ACS Appl Mater Interfaces 2014;6:17804-14. http://dx.doi.org/10.1021/am5044505; b) Kabe R, Nakanotani H, Sakanoure T, Yahiro M, Adachi C. Effect of molecular morphology on amplified spontaneous emission of bis‐styrylbenzene derivatives. Adv Mater 2009;21:4034-8. http://dx.doi.org/ 10.1002/adma.200803588; c) Mas-Torrent M, Hadley P, Bromley ST, Ribas X, Tarres J, Mas M, Molins E, Veciana J, Rovira C. Correlation between crystal structure and mobility in organic field-effect transistors based on single crystals of tetrathiafulvalene derivatives. J Am Chem Soc 2004;126:8546-53. http://dx.doi.org/10.1021/ja048342i; d) Wang Y, Guo H, Ling S, ArrecheaMarcos I, Wang Y, Lopez Navarrete JT, Ponce Ortiz R, Guo X. Ladder-type heteroarenes: up to 15 rings with five imide groups. Angew Chem Int Ed 2017;56:9924-9. http://dx.doi.org/10.1002/anie.201702225. a) Chandrasekar R. Organic photonics: prospective nano/micro scale passive organic optical waveguides obtained from π-conjugated ligand molecules. Phys Chem Chem Phys 2014;16:7173-83. http://dx.doi.org/10.1039/C3CP54994A; b) Gu X, Yao J, Zhang G, Yan Y, Zhang C, Peng Q, Liao Q, Wu Y, Xu Z, Zhao Y, Fu H, Zhang D. Influence of alkyl chain lengths on the properties of iridium(III)-based piezochromic luminescent dyes with triazolepyridine type ancillary ligands. Adv Funct Mater 2012;22:4862-72. http://dx.doi.org/10.1016/j.dyepig.2013.08.015; c) Guo Z-H, Lei T, Jin Z-X, Wang J-Y, Pei J. Tshaped donor–acceptor lolecules for Low-loss red-emission optical waveguide. Org Lett 2013;15:3530-3. http://dx.doi.org/10.1021/ol4012025; d) Li Q, Jia Y, Dai L, Yang Y, Li J. Controlled rod nanostructured assembly of diphenylalanine and their optical waveguide properties. ACS Nano 2015;9:2689-95. http://dx.doi.org/10.1021/acsnano.5b00623; e) Wang X, Han Y, Liu Y, Zou G, Gao Z, Wang F. Cooperative supramolecular polymerization of fluorescent platinum acetylides for optical waveguide applications. Angew Chem Int Ed 2017;56:12466-70. http://dx.doi.org/10.1002/anie.201704294; h) Li Y, Ma Z, Li A, Xu W, Wang Y, Jiang H, Wang K, Zhao Y, Jia X. A single crystal with multiple functions of optical waveguide, aggregation-induced emission, and mechanochromism. ACS Appl Mater Interfaces 2017;9:8910-8. http://dx.doi.org/10.1021/acsami.7b00195; i) Basak S, Chandrasekar R. Passive optical waveguiding organic rectangular tubes: tube cutting, controlling light propagation distance and multiple optical out-puts. J Mater Chem C 2014;2:1404-8. https://doi.org/10.1039/C3TC31576B; j) Mitetelo N, Venkatakrishnarao D, Ravi J, Popov M, Mamonov E, Murzina TV, Chandrasekar R. Chirality‐controlled multiphoton luminescence and second‐harmonic generation from enantiomeric organic micro‐optical waveguides. Adv Optical Mater 2019;7:1801775. https://doi.org/10.1002/adom.201801775; k) Chandrasekhar N, Mohiddon MA, Chandrasekar R. Organic submicro tubular optical waveguides: self‐assembly, diverse geometries, efficiency, and remote sensing properties. Adv Optical Mater 2013;1:30511. https://doi.org/10.1002/adom.201200067. a) Wang X, Li H, Wu Y, Fu H. Tunable morphology of the self-assembled organic microcrystals for the efficient laser optical resonator by molecular modulation. J Am Chem Soc 2014;136:16602-8. http://dx.doi.org/10.1021/ja5088503; b) Wang X, Liao Q, Kong Q, Zhang Y, Xu Z, Lu X, Fu H. Whispering‐gallery‐mode microlaser based on self‐assembled organic single‐ crystalline hexagonal microdisks. Angew Chem Int Ed 2014;53:5863-7. http://dx.doi.org/ 10.1002/anie.201310659; c) Wang X, Liao Q, Xu Z, Wu Y, Wei L, Lu X, Fu H. Excitonpolaritons with size-tunable coupling strengths in self-assembled organic microresonators. ACS Photonics 2014;1:413-20. http://dx.doi.org/10.1021/ph400160v. a) Zhao YS, Fu H, Hu F, Peng A, Yao. Multicolor emission from ordered assemblies of organic 1D nanomaterials. J. Adv Mater 2007;19:3554-8. http://dx.doi.org/10.1002/adma.200701513; b) Ong BS, Wu YL, Liu P, Gardner S. High-performance semiconducting polythiophenes for organic thin-film transistors. J Am Chem Soc 2004;126:3378-9. http://dx.doi.org/10.1021/ja039772w; c) Wang ZL. Nanobelts, Nanowires, and nanodiskettes of semiconducting oxides-from materials to nanodevices. Adv Mater 2003;15:432-6. http://dx.doi.org/10.1002/adma.200390100; d) Law M, Greene LE, Johnson JC, Saykally R, Yang P. Nanowire dye-sensitized solar cells. Nat Mater 2005;4:455-9. http://dx.doi.org/10.1038/nmat1387; e) Liu H, Li Y, Jiang L, Luo H, Xiao S, Fang H, Li H, Zhu D, Yu D, Xu J, Xiang B. Imaging as-grown [60]Fullerene nanotubes by template technique. J Am Chem Soc 2002;124:13370-1. http://dx.doi.org/10.1021/ja0280527; f) Li X, Gu H, Chen K,
17
465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Song L, Hao Q. STorus: A new topology for optical network-on-chip. Optical Switching and Networking (OSN) 2016;22:77-85. http://dx.doi.org/10.1016/j.osn.2016.04.004; g) Chandrasekhar N, Basak S, Mohiddon MA, Chandrasekar R. Planar active organic waveguide and wavelength filter: self-assembled meso-tetratolylporphyrin hexagonal nanosheet. ACS Appl Mater Interfaces 2014;6:1488-94. https://doi.org/10.1021/am4039163. a) Birks JB. Photophysics of Aromatic Molecules; Wiley: New York, 1970; b) Yuang Z, Liu P, Chen S, Lam JWY, Wang Z, Liu Y, Kwok HS, Ma Y, Tang BZ. Changing the behavior of chromophores from aggregation-caused quenching to aggregation-induced emission: development of highly efficient light emitters in the solid state. Adv Matter 2010;22:2159-63. http://dx.doi.org/10.1002/adma.200904056; c) Huang Y, Xing J, Gong Q, Chen L-C, Liu G, Yao C, Wang Z, Zhang H-L, Chen Z, Zhang Q. Reducing aggregation caused quenching effect through co-assembly of PAH chromophores and molecular barriers Nature Commun 2019;10:art. nº 169. http://dx.doi.org/10.1038/s41467-018-08092-y. a) Mendez H, Heimel G, Optiz A, Sauer K, Barjowski P, Oehzelt M, Soeda J, Okamoto T, Takeya J, Arlin JB, Balandier JY, Geerts Y, Koch N, Salzmann I. Doping of organic semiconductors: impact of dopant strength and electronic coupling. Angew Chem Int Ed 2013;52:7751-55. http://dx.doi.org/10.1002/anie.201302396; b) Huang D, Wang C, Zou Y, Zhen X, Zang Y, Shen H, Gao X, Yi Y, Xu W, Di C-A, Zhu D. Bismuth interfacial doping of organic small molecules for high performance n‐type thermoelectric materials. Angew Chem 2016;128:10830-3. http://dx.doi.org/10.1002/ange.201604478. a) Förster, T. Intermolecular energy migration and fluorescence. Ann Phys 1948;2:55–75. http://dx.doi.org/10.1002/andp.19484370105; b) Hohng S, Lee J, Lee S. Single-Molecule ThreeColor FRET with Both Negligible Spectral Overlap and Long Observation Time. PLOS ONE 2010;5:e12270. http://dx.doi.org/10.1371/journal.pone.0012270; c) Jones GA, Bradshaw DS. Resonance energy transfer: From fundamental theory to recent applications. Frontiers in Physics. 2019;7:100. http://dx.doi.org/10.3389/fphy.2019.00100. Tseng K-P, Tsai Y-T, Shyue J-J, Raffy G, del Guerzo A, Wong K-T, Bassini DM. Emissive nanotubes from templated self-assembly of small molecules. Chem Phys Lett 2017;683:43-8. http://dx.doi.org/10.1016/j.cplett.2017.04.005. a) Xu Z, Liao Q, Shi X, Li H, Zhang H, Fu H. Full-color tunable organic nanoparticles with FRET-assisted enhanced two-photon excited fluorescence for bio-imaging. J Mater Chem B 2013;1:6035-41. http://dx.doi.org/10.1039/C3TB20841A; b) Fang H-H, Lu S-Y, Wang L, Ding R, Wang H-Y, Feng J, Chen Q-D, Sun H-B. Preparation and time-resolved fluorescence study of RGB organic crystals. Org Electron 2013;14:389-95. http://dx.doi.org/10.1016/j.orgel.2012.10.028. a) Zhang W, Zhao YS. Organic nanophotonic materials: the relationship between excited-state processes and photonic performances. Chem Commun 2016;52:8906-17. http://dx.doi.org/ 10.1039/C6CC00018E; b) Zhang C, Zhou C-L, Zhao Y, Dong C-H, Wei C, Wang H, Liu Y, Guo G-C, Yao J, Zhao YS. Organic printed photonics: From microring lasers to integrated circuits. Science Adv 2015;1:e1500257. http://dx.doi.org/10.1126/sciadv.1500257; c) Zhao G, Dong H, Liao Q, Jiang J, Luo Y, Fu H, Hu W. Organic field-effect optical waveguides. Nature Commun 2018;9:art nº 4790. http://dx.doi.org/10.1038/s41467-018-07269-9. a) Peng A, Xiao D, Ma Y, Yang W, Yao J. Tunable emission from doped 1,3,5‐triphenyl‐2‐ pyrazoline organic nanoparticles. Adv Mater 2005;17:2070-3. http://dx.doi.org/10.1002/adma.200401989; b) Tang CW, van Slyke SA, Chen CH. Electroluminescence of doped organic thin films. J Appl Phys 1989;65:3610-16. http://dx.doi.org/10.1063/1.343409; c) Kido J, Kimura K, Nagai K. Multilayer white lightemitting organic electroluminescent device. Science 1995;267:1332-34. http://dx.doi.org/ 10.1126/science.267.5202.1332. a) Zhao YS, Di C, Yang W, Yu G, Liu Y, Yao. Photoluminescence and electroluminescence from tris(8‐hydroxyquinoline)aluminum nanowires prepared by adsorbent‐assisted physical vapor deposition. J. Adv Funct Mater 2006;16:1985-91. http://dx.doi.org/10.1002/adfm.200600070; b) Qu L, Shi G. Crystalline oligopyrene nanowires with multicolored emission. Chem Commun 2004:2800-1. http://dx.doi.org/10.1039/B412638F. Ishii Y, Omori K, Satozono S, Fukuda M. Dye-doped submicron fiber waveguides composed of hole- and electron-transport materials. Org Electron Physics Mater Appl 2017;41:215–20. http://dx.doi.org/10.1016/j.orgel.2016.11.007. Liao Q, Fu H, Yao. Waveguide modulator by energy remote relay from binary organic crystalline microtubes. J. Adv Mater 2009;21:4153–7. http://dx.doi.org/10.1002/adma.200900997.
18
525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583
15. Pradeep VV, Annadhasan M, Chandrasekar R. Vapour‐phase epitaxial growth of dual‐ colour‐emitting DCM‐perylene micro‐heterostructure optical waveguides. Chem Asian J 2019;14:4577-81. https://doi.org/10.1002/asia.201901221. 16. Venkatakrishnarao D, Mohiddon MA, Chandrasekhar N, Chandrasekar R. Photonic microrods composed of photoswitchable molecules: erasable heterostructure waveguides for tunable optical modulation. Adv Optical Mater 2015;3:1035-40. https://doi.org/10.1002/adom.201500106. 17. a) Li Z-Z, Tao Y-C, Wang X-D, Liao LS. Organic nanophotonics: self-assembled singlecrystalline homo-/heterostructures for optical waveguides. ACS Photonics 2018;5:3763-71. https://doi.org/10.1021/acsphotonics.8b00815; b) Lei Y, Sun Y, Liao L, Lee S-T, Wong W-Y. Facet-selective growth of organic heterostructured architectures via sequential crystallization of structurally complementary π-conjugated molecules. Nano Lett 2017;17:695-701. https://doi.org/10.1021/acs.nanolett.6b03778; c) Yang C, Gu L, Ma C, Gu M, Xie X, Shi H, Ma H, Yao W, An Z, Huang W. Controllable co-assembly of organic micro/nano heterostructures from fluorescent and phosphorescent molecules for dual anti-counterfeiting. Mater Horiz 2019;6: 984-9. https://doi.org/10.1039/C8MH01582A. 18. Li ZZ, Liang F, Zhuo MP, Shi YL, Wang XD, Liao LS. White-Emissive Self-Assembled Organic Microcrystals. Small 2017;13:1–6. http://dx.doi.org/10.1002/smll.201604110. 19. Zhang J, Wang J, Xu X, Chen S, Zhang Q, Yao C, Zhuang X, Pan A, Li L. An air-stable microwire radial heterojunction with high photoconductivity based on a new building block. J Mater Chem C 2015;3:5933–9. http://dx.doi.org/10.1039/C5TC01050K. 20. a) D’Andrade BW, Forrest SR. White organic light‐emitting devices for solid‐state lighting. Adv Mater 2004;16:1585-95. http://dx.doi.org/10.1002/adma.200400684; b) Kubo Y, Nishiyabu R. White-light emissive materials based on dynamic polymerization in supramolecular chemistry. Polymer 2017;128:257-75. http://dx.doi.org/10.1016/j.polymer.2016.12.082; c) Zhao YS, Fu H, Hu H, Peng A, Yang W, Yao. Tunable emission from binary organic one‐dimensional nanomaterials: an alternative approach to white‐light emission. J Adv Mater 2008;20:79-83. http://dx.doi.org/10.1002/adma.200700542; d) Lei Y, Liao Q, Fu H, Yao J. Orange−blue−orange triblock one-dimensional heterostructures of organic microrods for white-light emission. J Am Chem Soc 2010;132:1742-3. http://dx.doi.org/10.1021/ja9084435. 21. Abbel R, Grenier C, Pouderoijen MJ, Stouwdam JW, Leclêre PELG. White-light emitting hydrogen-bonded supramolecular copolymers based on π-conjugated oligomers. J Am Chem Soc 2009;131:833-44. http://dx.doi.org/10.1021/ja807996y. 22. Vijayakumar C, Praveen VK, Ajayaghost A. RGB emission through controlled donor self‐ assembly and modulation of excitation energy transfer: a novel strategy to white‐light‐emitting organogels. Adv Mater 2009;21:2059-63. http://dx.doi.org/10.1002/adma.200802932. 23. a) Cáceres D, Cebrián C, Rodríguez AM, Carrillo JR, Díaz-Ortiz A, Prieto P, Aparicio F, García F, Sánchez L. Optical waveguides from 4-aryl-4H-1,2,4-triazole-based supramolecular structures. Chem Commun 2013;49:621-3. http://dx.doi.org/10.1039/C2CC37381E; b) Pastor MJ, Torres I, Cebrián C, Carrillo JR, Díaz-Ortiz A, Matesanz E, Buendía J, García F, Barberá J, Prieto P, Sánchez L. 4‐aryl‐3,5‐bis(arylethynyl)aryl‐4H‐1,2,4‐triazoles: multitasking skeleton as a self‐assembling unit. Chem Eur J 2015;21:1795-802. http://dx.doi.org/10.1002/chem.201404243; c) Torres I, Carrillo JR, Díaz-Ortiz A, Martín R, Gómez MV, Stegemann L, Strassert CA, Orduna J, Buendía J, Greciano EE, Valera JS, Matesanz E, Sánchez L, Prieto P. Self-assembly of T-shape 2H-benzo[d][1,2,3]-triazoles. Optical waveguide and photophysical properties. RSC Adv 2016;6:36544-53. http://dx.doi.org/10.1039/c6ra02473d; d) Torres I, Díaz-Ortiz A, Sánchez L, Orduna J, Blesa MJ, Carrillo JR, Prieto P. Tunable emission in aggregated T-Shaped 2H-Benzo[d][1,2,3]triazoles with waveguide behaviour. Dyes Pigments 2017;142:212-25. http://dx.doi.org/10.1016/j.dyepig.2017.02.048; e) Martín R, Prieto P, Carrillo JR, Torres I, Strassert CA, Soloviova K, Rodríguez AM, Sánchez L, Díaz-Ortiz A. Colored optical waveguides in self-assembled thiadiazole-based materials. Dyes Pigments 2018;151:327-34. http://dx.doi.org/10.1016/j.dyepig.2018.01.001. 24. Torres I, González-Domínguez JM, Díaz-Ortiz A, Romero-Nieto C, Rominger F, Vázquez E, Carrillo JR, Prieto P. Modulation of Waveguide Behaviour of an ICT 2HBenzo[d][1,2,3]Triazole Derivative with Graphene. Org Electron 2019;68:1-8. http://dx.doi.org/10.1016/j.orgel.2019.01.033. 25. a) Lakowicz JR. Principles of Fluorescence Spectroscopy; Springer Science & Business Media, Germany, 2013; b) Chemla DS, Zyss J. Nonlinear Optical Properties of Organic Molecules and Crystals; Elsevier, The Netherlands, 2001.
19
584 585 586 587
26. Martín R, Prieto P, Carrillo JR, Rodríguez AM, de Cózar A, Boj PG, Díaz-García MA, Ramírez MG. Design, synthesis and amplified spontaneous emission of 1,2,5-benzothiadiazole derivatives. J Mater Chem C 2019;7:9996-10007. http://dx.doi.org/10.1039/C9TC03148K.
20
Some benzotriazoles and thiadiazoles can act as host and guest co-assembled skeletons Slow diffusion, an easy and cost-effective technique to form co-assembled aggregates Tunable colour-active materials could be useful in the fields of optoelectronics Changes in the molar ratio of the different doping agents can tune the light emission Co-assembled microcrystals can act as optical waveguide
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
ID. DOCUMENTO
Página: 1 / 1
Xuoo7yVCcG FIRMADO POR
FECHA FIRMA
ID. FIRMA
DIAZ ORTIZ ANGEL
23-01-2020 17:03:14
1579795401899
Xuoo7yVCcG Calle Altagracia número 50 - Ciudad Real - 13071. Tfno.: 902204100 Fax.: 902204130 - https://www.sede.uclm.es - Soporte a usuarios: https://cau.uclm.es Copia de documento electrónico. Para verificar su autenticidad y la validez de su firma, acceda a https://www.sede.uclm.es/verificadorfirmas/uclm
S0143-7208(19)32694-4
DOI:
https://doi.org/10.1016/j.dyepig.2020.108246
Reference:
DYPI 108246
To appear in:
Dyes and Pigments
Received Date: 19 November 2019 Revised Date:
23 January 2020
Accepted Date: 26 January 2020
Please cite this article as: Martín R, Torres-Moya I, Donoso B, Carrillo JR, González-Domínguez JM, Frontiñan-Rubio J, Prieto P, Díaz-Ortiz A, Slow diffusion co-assembly as an efficient tool to tune colour emission in alkynyl benzoazoles, Dyes and Pigments (2020), doi: https://doi.org/10.1016/ j.dyepig.2020.108246. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.
CRediT author statement Raul Martín: Methodology, Visualization, Investigation, Writing-Original Draft, Writing-Review & Editing. Iván Torres-Moya: Resources. Beatriz Donoso: Resources. José R. Carrillo: Formal analysis. José M. González-Domínguez: Formal analysis. Javier Frontiñan-Rubio: Formal analysis. Pilar Prieto: Supervision, Project administration, Writing-Review & Editing. Angel Díaz-Ortiz: Conceptualization, Supervision, Writing-Original Draft.
1
Slow Diffusion Co-Assembly as an Efficient Tool to Tune Colour
2
Emission in Alkynyl Benzoazoles
3
R. Martín,a,b I. Torres-Moya,a B. Donoso,a J. R. Carrillo,a J. M. González-Domínguez,c J.
4
Frontiñan-Rubio,d P. Prieto,a,* A. Díaz-Ortiz.a,*
5
a
6
Chemical Technologies, University of Castilla-La Mancha-IRICA, 13071 Ciudad Real, Spain
7
b
8
Castilla- La Mancha, 13071 Ciudad Real, Spain
9
c
Department of Inorganic, Organic Chemistry and Biochemistry, Faculty of Science and
Research Institute for Chemical and Environmental Technology (ITQUIMA), University of
Group of Carbon Nanostructures and Nanotechnology, Institute of Carbon Chemistry (ICB-
10
CSIC), c/ Miguel Luesga Castán 4, 50018 Zaragoza, Spain
11
d
12
IRICA, 13071 Ciudad Real, Spain
13
E-mail: [email protected] [email protected]
Instituto Regional de Investigación Científica Aplicada, University of Castilla-La Mancha-
14 15
Abstract
16
We report here the preparation of co-assembled microcrystals by employing an easy,
17
reproducible and cost-effective technique, namely slow diffusion. 2H-Benzo[d][1,2,3]triazole
18
and benzo[c][1,2,5]thiadiazole were chosen as host and guest skeletons, respectively. Structural
19
similarities allowed the correct co-assembly of the two structures. The co-assemblies were
20
studied by different techniques that included Raman spectroscopy and X-ray diffraction,
21
amongst others. The waveguiding properties and the emission colour of the doped organic
22
microcrystals were also investigated. It was found that changes in the molar ratio of the
23
different doping agents could tune the light emission. Fluorescence microscopy images of the
24
co-assembled microcrystals revealed light colour changes from green to whitish, up to CIE
25
coordinates of (0.370, 0.385). These tunable colour-active materials could be useful in the fields
26
of optoelectronics or lab-on-a-chip for integrated optical circuits at micro-/nanoscale.
27 28
Keywords
29
2H-benzo[d][1,2,3]triazole, benzo[c][1,2,5]thiadiazole, co-assembly, slow diffusion, organic
30
optical waveguide, tuning colour emission
31 32
1. Introduction
33
Organic semiconductor micro-/nanocrystals with regular shapes have attracted a great deal of
34
attention in recent years for many applications, such as Organic Field-Effect Transistors
35
(OFETs),1 organic waveguide devices,2 and Organic Solid-State Lasers (OSSL).3 As a
1
36
consequence, these systems are inherently ideal building blocks for key circuits in the next
37
generation of miniaturised optoelectronic devices.4
38
Nevertheless, one of the main problems with organic molecules used in the solid state for
39
optoelectronics is their low fluorescence quantum efficiency, which is due in part to the
40
aggregation-induced quenching (AIQ) phenomenon.5 This problem can be solved by using co-
41
assembled structures6 formed by one (or more) molecule(s), one of which acts as a dopant and
42
the other(s) as a guest. According to Förster's resonance energy transfer (FRET) mechanism,7
43
the energy absorbed by the host molecules can be transferred to the guest molecule, thus leading
44
to light emission and possibly avoiding reabsorption by the organic materials. This process has
45
been shown to be particularly efficient in supramolecular aggregates and it is often used as a
46
tool to tune the emission of individual particles.8 In this way, different emission colours can be
47
obtained in co-assembled structures by simply adjusting the molar ratio between host and
48
dopant materials, since even small quantities of the latter dispersed in aggregates are sufficient
49
to modify the emission spectrum and confirm an efficient energy transfer.9
50
The next generation of optoelectonic devices will be based on nanophotonics, a discipline in
51
which the aim is to control and manipulate photons and/or optical energy in nanometer-scale
52
matter. Optical waveguides are one of the essential components of these new devices.10 Doping
53
systems can be excellent candidates to be part of these devices. However, to date the most
54
widely reported organic doping systems are amorphous.11 Since the crystallinity of
55
nanomaterials can improve their charge carrier transport and enhance the performance of optical
56
and optoelectronic devices,12 the development of organised co-systems is essential for
57
optoelectronic applications. Different approaches have been employed to obtain organised co-
58
assembled systems, including electrospinning13 and template-assisted,8 adsorbent-assisted
59
physical vapour deposition (PVD) methods,14 vapour epitaxy growth,15 and light mediated
60
heterostructures16 and self-assembled heterostructures.17 These methods are often tedious and
61
require specific instrumentation. Solution-based methods are a suitable alternative to overcome
62
these drawbacks.18,19 Slow diffusion is an easy, reproducible and cost-effective technique that
63
can produce organised structures without specialised equipment.
64
It is well known that organic white-light emission (WLE) materials are essential for full-colour
65
displays and the backlight of portable display devices.20 For this reason, modulation of colour
66
emission is a crucial factor in current research. Several supramolecular approaches have been
67
reported for WLE generation by self-assembly21 or gelation22 of molecular building blocks that
68
emit the three primary colours, i.e., red, green, and blue.
69
In the last few years our ongoing research line has been based on the design and preparation of
70
new organic optical waveguides based on azole and benzoazole derivatives.23 In this respect, we
71
recently described the doping of a 2H-benzo[d][1,2,3]triazole derivative with graphene. This
72
strategy allowed us to modulate the emission colour of the graphene-modified aggregate.24
2
73
In the work described here we studied different co-assembled structures from derivatives 1 and
74
2 (Figure 1) previously prepared by our research group by means of Sonogashira C–C cross-
75
coupling reactions between the dibromobenzotriazole or dibromobenzothiadiazole derivative
76
and the corresponding arylacetylene.23c-e The 2H-benzo[d][1,2,3]triazole core was selected as
77
the donor host skeleton due to its exceptional ability to form well-defined rod-like self-
78
assembled aggregates.23c This core is able to emit in the blue and near green regions. Doping of
79
the benzotriazole 1 with the green and red dye derivatives of benzo[c][1,2,5]thiadiazole 2 as
80
guest molecules24 allows the light emission to be successfully tuned from the green to the
81
orange region and the colour can be adjusted by simply modifying the molar ratio. The similar
82
structures of the host and guest molecules ensure the confinement and proximity of donor and
83
acceptor molecules in co-assembled microstructures, thus resulting in efficient FRET in the
84
donor-acceptor system.7
85 86
Figure 1. Structures of derivatives 1 and 2 used as host and guest materials, respectively.
87 88
2. Results and Discussion
89
2.1 Self-assembly behaviour
90
Organised supramolecular co-assembled structures were obtained by the slow diffusion
91
technique. Thus, 10−3 M stock solutions of 1 and 2 were prepared in THF. Five different doping
92
ratios 1:2 were chosen as follows: 1:0.1; 1:0.3; 1:1; 1:3; 1:9. The specific compositions 1:2 were
93
obtained by mixing the appropriate volumes to form 1 mL of THF solution. An open sample
94
vial containing the mixed solutions was gently placed in a vessel containing MeOH as the poor
95
solvent and the system was sealed. After several days of slow diffusion, a uniform precipitate
96
was observed in the inner vial. It is interesting to note that co-assembled structures are only
97
formed up to 1:0.3 molar ratios. In order to avoid false luminescence emission signals arising
98
from remaining solutions of doping agents that could coat the co-assembled crystals, the
99
crystals were washed with two different solvents: hexane and methanol. Despite the fact that
3
100
both solvents removed the coating products, methanol, being a more polar solvent, could
101
dissolve some of the crystal and it was found that hexane was the best option to ensure the
102
integrity of the crystal (compare Figures 2 and S1–S2).
103
Visual changes confirmed that a co-assembly process had taken place and dye leakage was not
104
observed during the preparation process. Co-assembled crystals were formed with a different
105
colour from the pure host. Whereas pure 1 forms clear yellow crystals with an intense yellow
106
emission under 365 nm (Figure 2A,B), the colour of doped 2a and 2b crystals were clear orange
107
(Figure 2I,J) and red (Figure 2K,L), respectively, due to the incorporation of the doping
108
compound into the host structure. More strikingly, 2c-doped crystals were dark brown when the
109
co-assembly process was completed (Figure 2M,N), thus providing evidence that all of the
110
acceptor dyes 2 had been doped into the organic microcrystals of 1. It is worth noting that in
111
cases where the slow diffusion conditions were not satisfactory (solvent, temperature,
112
proportions, time etc.), co-assembled crystals did not form and separate precipitates of pure host
113
and guest molecules were observed (Figure S3). In order to ascertain whether co-assembled
114
structures were formed in the slow diffusion process, 1 mL of a pure solution of 2a and 2c was
115
added to pure microcrystals of 1. After several days neither visual changes nor different
116
emission were observed in the crystals of 1 (Figure S4). Thus, the co-assembly process only
117
takes place if slow diffusion is carried out.
118 119 120
Figure 2. Pure self-assembled crystals of 1 (A,B), 2a (C,D), 2b (E,F) and 2c (G,H) under natural light and irradiated at 365 nm. Pictures of the co-assembled structures (I–N) with the
4
121 122 123
doping agents represented. All structures were removed from their original solution and washed with hexane in order to avoid false emission signals.
124
The resulting morphologies of the co-assembled crystals were visualised by scanning electron
125
microscopy (SEM) on glass substrates (Figure 3). Pure benzotriazole 1 produced well-defined
126
rod-like aggregates that were hundreds of micrometres in length by slow diffusion using
127
chloroform (CHCl3) as the good solvent and acetonitrile (CH3CN) as the poor solvent.23c
128
However, the use of THF/MeOH as solvents in the slow diffusion process gave ultra-long self-
129
assembled needle-like crystals that were several millimetres in length – a process that could
130
facilitate their use in optoelectronic devices (Figure S5).
131
It was found that the percentage of doping agents must be less than 25% in order to favour
132
crystal growth by the slow diffusion technique. In general, when compared with pure
133
microcrystals of 1, the co-assembled structures had very few morphological differences, which
134
indicates that the host (1) has a greater tendency to aggregate than the guest (2) and the acceptor
135
organic molecules will not affect the macroscopic crystallinity of the as-prepared organic
136
microstructures (Figure 3). In the case of 2c only a 1:0.1 host:guest ratio afforded co-assembled
137
structures.
138
In general, co-assembled structures are less thick than pure self-assembled 1 (Figure 3E-I vs. A)
139
and this is especially noteworthy in the case of 2c-doped crystals (Figure 3I).
5
140 141 142 143 144 145
Figure 3. SEM images of pure self-assembled 1 and 2, and the resulting morphologies of 1:0.1 and 1:0.3 molar ratio co-assembled structures obtained by slow diffusion of MeOH vapour into dilute THF solutions.
146
NMR spectroscopy was employed in an effort to confirm further that the co-assembly process
147
of both derivatives occurred effectively. Hexane-washed co-assembled crystals 1:2a (1:0.3)
148
were dissolved in 600 µL of CDCl3. The proton signals of both 1 and 2 were observed in the
149
NMR spectra and this confirmed that the two molecules coexist in the crystal (Figure S6).
150
Furthermore, other spectroscopic techniques were applied to obtain information about the co-
151
assembled system and these are discussed in the following sections.
152 153
2.2 Raman analysis
154
A Raman spectroscopy study was performed on selected samples. After an initial screening it
155
was only possible to carry out Raman spectroscopy on compound 2c. The high fluorescence of
156
derivatives 2a and 2b precluded their study by this technique. The identification of each
157
component was made on the basis of the intensity of a specific peak. The peak at 1416 cm−1 was
158
chosen for compound 1 and for compound 2c the peak at 1334 cm−1 was selected as a
159
representative feature.
6
160
Representative Raman spectra for organic compounds 1 and 2c are shown in Figure 4. Given
161
the vibrational nature of Raman spectroscopy, the different peaks can be ascribed to specific
162
vibrations according to the molecular structure. Compound 1 presented the alkyne stretching
163
band at 2200 cm–1 as the most prominent feature. Furthermore, aromatic ring vibrations also had
164
a strong presence in the spectrum, namely the N=N and C=C stretchings at 1416 cm–1 and 1572
165
cm–1, respectively. Compound 2c had a Raman profile that was similar to that of the host (1) in
166
terms of the alkyne and aromatic C=C bands, while other bands related to other carbon bonds,
167
such as C–C stretching (1283 cm–1) and methyl bending (1334 and 1481 cm–1), were observed.
2c
168 169 170 171 172 173 174 175 176
Figure 4. a) Raman spectra (532 nm laser) of compounds 1, 2c, and the mixture of 1:2c (1:0.1 ratio). The assignments of the main vibrational bands are depicted. Dashed vertical lines indicate the peaks used in the two-dimensional mapping to identify each compound: green for compound 1 and red for compound 2c, with interference not observed between the two sets of signals. b) Inset of the lower part of the spectra, for the sake of clarity, showing the selected 1334 cm−1 band belonging to compound 2c.
177
to each peak (red for 1334 cm−1 and green for 1416 cm−1) and these were plotted
178
simultaneously, using Wire 4.4 software, according to the intensity of the respective peaks. This
179
process allowed us to ascertain the relative disposition of each compound in the mixtures.
180
In general terms, it can be seen how the co-assembled crystals 1:2c (1:0.1) present an uneven
181
distribution of the two components within the crystal. Thus, by Raman spectroscopy it was
182
determined that these crystals are formed by a matrix of aggregated 1 with small clusters of 2c
183
randomly scattered across the structure (Figure 5). This trend was still visible after the crystals
184
were washed with hexane (Figure 5 and S1). However, a different situation was observed when
185
the crystals were washed with methanol (Figure S2). In this case, the distribution of 2c islands
186
within 1 became unclear and the resulting colour mapping suggested that a merging of the two
In the two-dimensional Raman mappings (Figures 5, S1 and S2) specific colours were assigned
7
187
compounds had taken place. This finding is in good agreement with the experimental
188
observations that methanol is able to partially dissolve the crystalline structure of this mixture.
189
190 191 192 193 194
Figure 5. 2D Raman mapping (532 nm laser) of a selected region of a co-assembled crystal 1:2c (1:0.1) from characteristic bands of 1 (in green) and 2c (in red). Numbers in the coloured bars are arbitrary.
195
2.3 X-ray diffraction analysis
196
The crystal structures of the binary nanomaterials were studied by X-ray diffraction (XRD) and
197
the profiles of the pure and doped nanowires were obtained. For the different compounds the
198
diffraction pattern of the binary nanowires shows diffraction peaks for the host and guest
199
compounds. This indicates that 1 is also crystalline in the doped nanomaterials but the
200
formation of a co-crystal or superlattice-type composite crystal did not occur (Figures 6, S7 and
201
S8). Furthermore, a significant displacement of the peak at 2θ = 15.00º of the structure of 1 can
202
be observed (which corresponds to an interplanar spacing of 5.90 Å) to 2θ = 14.68º (interplanar
203
spacing of 6.03 Å) in the doped structure. This may indicate that for molecules of 1 the
204
interplanar spacing along the b-axis increases in order to accommodate molecules of 2a. This
205
peak displacement appears in the three doped nanowires, probably due to the similar structures
206
of the doping agents.
8
207 208 209 210 211 212 213
Figure 6. XRD patterns of the pure compounds 1 (green) and 2a (blue), and the doped organic microcrystal with 1:2a (1:0.3) (red). The stars indicate the diffraction peak of 2θ = 14.68º for 1, which exhibits a significant displacement in the doped structures. The numbers ‘1’ and ‘2a’ indicate the diffraction peaks of the pure structures 1 and 2a, respectively. Crystal planes were assigned from the X-ray structures of the pure compounds.
214
2.4 Photophysical features
215
The optical spectra of compounds 1 and 2 were experimentally measured in tetrahydrofuran
216
(THF) (Figure 7). Only a slight overlap between the emission band of 1 and the absorption band
217
of 2a can be seen in Figure 7A. However, it should be noted that the emission spectrum of 1
218
shows a good overlap with the absorption spectra of 2b and 2c in the wavelength range 450–600
219
nm (Figures 7B and 7C, respectively), which may result in efficient energy transfer from the
220
host 1 to the guest 2 in the doped system. Doping organic derivatives 2 as acceptors into a donor
221
host matrix of benzotriazole 1 ensures confinement and proximity of the two molecules within
222
self-assembled microstructures, and could tentatively result in efficient IFRET (Intermolecular
223
Fluorescence Resonance Energy Transfer) in the donor-acceptor system.18,25 We hope that
224
further experiments with analogous substrates currently underway in our laboratory can clarify
225
this transfer mechanism.
226
9
227 228 229 230 231 232 233 234 235
Figure 7. Absorption and emission spectra of pure 1 (green), 2a (yellow), 2b (red) and 2c (purple). Overlap between the emission spectrum of 1 and the absorption spectrum of 2 is denoted with grey lines. All spectra were measured in THF solution. PL spectra were measured after excitation at the maximum absorption peak of the corresponding compounds (1, λex=290 nm; 2a λex=310 nm; 2b, λex=320 nm; 2c, λex=350 nm). Absorption spectra of compounds 2 were normalised to its ICT band and emission spectra have been corrected to eliminate the solvent interferences.
236
2.5 Optical waveguiding properties
237
Considering the previously reported results on the optical waveguiding features of the related
238
pure compounds 123c and 2a,23e we investigated the propagation of light in the aggregates
239
formed from co-assembled structures. These studies were carried out by fluorescence
240
microscopy with a mercury lamp capable of excitation at any wavelength. Pure 1 aggregates
241
exhibited blue and green bright luminescence spots at the opposite ends and a relatively weak
242
emission from the body when it was irradiated at one end (Figure S9).
243
The co-structures discussed above were irradiated with a laser beam at different λ values and
244
the resulting fluorescence images were recorded with a camera (Figure 8). When benzotriazole
245
1 was doped with 10% of 2a (1:0.1 molar ratio) only green light was propagated through the
246
structure (Figure 8A). Interestingly, when the proportion of the doping agent 2a was 25%
247
(doping ratio 1:0.3), the structure was also able to propagate red light (Figure 8B). This finding
248
provides evidence that changes in the doping agent ratio can modify the propagated light. A
249
similar result has been reported previously in the literature.20d
250
Co-assembled structures containing compound 2c only propagated red light when they were
251
irradiated at one end (Figure 8D). This characteristic could due to the large overlap between the
10
252
emission band of 1 and the absorption band of 2c at 430–570 nm (Figure 7C), which could
253
favour the light reabsorption processes described previously in the literature.4g When the host
254
structure was doped with 2b both green and red light were propagated through the structure
255
(Figure 8C). A lower level of overlap between the emission band of 1 and the absorption band
256
of 2b is observed in the PL spectra of pure compounds, which could indicate that the possible
257
reabsorption phenomenon would be less effective (Figure 7B). These results show that the
258
presence of different doping agents can modify the emission colour of the molecular aggregate
259
with waveguide properties. In this specific case, the dopant dyes cause a bathochromic shift in
260
the emission colour of 1, which changes from blue and green emission to green-red or red
261
emission with the appropriate ratio of doping agent.
262
263 264 265 266 267 268 269
Figure 8. Fluorescence images of the co-assembled aggregates 1:2a 1:0.1 molar ratio (A), 1:0.3 molar ratio (B), 1:2b 1:0.3 molar ratio (C), and 1:2c 1:0.1 molar ratio (D) obtained by irradiating a portion of the aggregate at 320–380 nm (blue), 450–490 nm (green), and 515–565 nm (red). The propagated light at the end of the crystal is shown with a white dashed circle and the direction of the light with a dashed arrow.
270
2.6 White light-emission
271
It is well known that a mixture of blue, green and red chromophores can afford structures that
272
emit white light.20 Bearing this in mind, it was decided to carry out a photophysical study on
11
273
mixtures of compound 1 with different compositions of the three doping agents. The
274
fluorescence emission spectra of solutions are shown in Figure 9.
275
In mixtures with 2a only one broad emission band can be observed due to the low Stokes shift
276
(79 nm) between the emission bands of 1 and 2a (Figure 7A and 9A). Mixtures made with
277
derivative 2c showed very poor emission in solution (Photoluminescence Quantum Yield,
278
PLQY = 8%),26 so an emission band corresponding to this compound was not observed in the
279
fluorescence spectra of the mixture (Figure 9C) and only a decrease in the intensity of the band
280
due to 1 was observed as its molar ratio decreased.
281
In the case of 2b, for which the PLQY was 67%26 and where the Stokes shift between the
282
emission bands of 1 and 2b was 127 nm, the mixed solution of compounds showed two
283
dominant emission bands located at around 500 and 600 nm. These bands can be attributed to
284
molecules of compound 1 and the dopant 2b, respectively (Figure 9B).
285
The emission wavelengths of both 1 and 2 did not show any obvious differences from those of
286
the monomers, so the emission colour of the as-prepared binary 1D microstructures was mainly
287
dependent on the doping ratio. Luminescence photographs of the solutions upon increasing the
288
dopant ratio with excitation 365 nm are shown in Figure 9. The colours of the solutions are
289
consistent with the corresponding emission spectra. In general, the presence of higher levels of
290
doping agent (2) gave rise to lower emission of the host (1).
291
It is worth noting the presence of a broad emission band (450–700 nm) and a visual white
292
emission of the solution 1:2b when the doping ratio was 1:0.3 (Figure 9B), which hints at a
293
possible white emission in the solid state for the crystal with this doping ratio.
12
294 295 296 297 298
Figure 9. Fluorescence spectra and luminescence photographs of 10−3 M THF solutions of 1 upon increasing the dopant ratio of 2a (A), 2b (B) and 2c (C). Luminescence photographs were taken under natural light (above) and 365 nm light (below).
299
The optical properties of the co-assembled structures with different doping ratios were also
300
investigated and the PL spectra of the as-prepared microcrystals are shown in Figure 10c.
301
The confocal microscopy images (Figure 10a) of the co-assembled microrods reveal only slight
302
colour changes from green to whitish upon increasing the molar doping ratio – an observation
303
that indicates the successful modulation of the light emission of the organic microcrystals. The
304
uniform emission colour of each single wire reveals that the guest molecules of 2 are dispersed
305
very uniformly in the matrix 1, which is in good agreement with Raman spectroscopy data
306
(Figure 5). The CIE coordinates of these pure and co-assembled structures are presented in
307
Figure 10b. The CIE coordinates (0.370, 0.385) of the microcrystals with a 2b doping ratio of
308
1:0.3 correspond to the white-emissive region in the CIE chromaticity diagram.
13
309
Doping ratios of 1:0.2 and 1:0.5 were also tested with 2b as the doping agent (Figures S10 and
310
S11). It was found that a 1:0.2 ratio was not sufficient to achieve white emission and pale-
311
yellow crystals were obtained. In contrast, a 1:0.5 ratio gave green-yellow crystals.
312
313 314 315 316 317 318 319
Figure 10. a) Fluorescence microscopy images of the microcrystals containing different doping ratios of 2 upon excitation at 425–650 nm; b) The emission colours corresponding to the organic microcrystals shown in (a) the CIE chromaticity diagram. The white emission colour is marked as a red circle in the CIE chromaticity diagram; c) Emission spectra of the microcrystals shown in (a) deposited onto quartz wafers.
320
3. Conclusions
321
The 2H-benzo[d][1,2,3]triazole core has been employed as a host skeleton to prepare well-
322
defined co-assembled microcrystals. The exceptional ability to form well-defined rod-like self-
323
assembled aggregates and the blue and near-green emission of this compound has been
324
successfully combined with the intense green and red emissions of benzo[c][1,2,5]thiadiazole
325
guest molecules.
326
The co-assembled microcrystals were obtained by the slow diffusion technique, which is an
327
easy, reproducible and cost-effective approach. Five doping ratios were tested and it was found
328
that the percentage of doping agent must be lower than 25% in order to favour crystal growth.
329
All of the co-assembled microcrystals prepared in this study showed impressive visual colour
330
changes from the pure host, thus confirming that a co-assembly process had successfully taken
14
331
place. The arrangement of the co-assembled structures was analysed by different spectroscopic
332
and microscopic techniques.
333
SEM analysis did not indicate any significant morphological differences in the structures of the
334
co-assembled microcrystals when compared to pure 1. This finding indicates that the host
335
material drives the formation of the organised co-assembled structures.
336
X-ray diffraction analysis revealed that the crystallinity of the host material (1) remains
337
unaltered when the guest material (2) is incorporated, and a co-crystal or superlattice-type
338
composite crystal is therefore not formed. However, it was found that molecules of 1 increase
339
their interplanar spacing along the b-axis probably in order to accommodate molecules 2.
340
Evidence for a randomly scattered distribution of the guest molecule (2c) in the matrix structure
341
of the host molecule (1) was provided by Raman spectroscopy.
342
The co-assembled microcrystals can act as optical organic waveguides and the propagation of
343
the light in the resulting aggregates could be modulated by altering both the doping agent and
344
the doping ratio. The light reabsorption process must be avoided in order to allow propagation
345
of light with a different wavelength along the co-assembled microcrystals.
346
The emission spectra of the mixed solution of 1:2b with a 1:0.3 molar doping ratio revealed the
347
presence of a broad emission band (450–700 nm) and a visible white emission from the
348
solution. The CIE coordinates of this solid co-assembled aggregate were (0.370, 0.385). Colour
349
changes in the light from green to orange were observed for the rest of co-assembled
350
microcrystals and this indicates successful modulation of the light emission of the organic
351
microcrystals.
352
The results presented herein offer a versatile approach towards affordable white emissive
353
materials for future applications in the field of optoelectronics or for integrated optical chips.
354 355
4. Experimental details
356
Compounds 1 and 2a-c were prepared according to experimental procedures described by our
357
research group.23e,c, 26
358
SEM images were obtained on a JEOL JSM 6335F microscope working at 15 kV. The samples
359
for SEM imaging were prepared by slow diffusion by mixing the appropriate proportions of
360
compounds 1 and 2. The corresponding solids were washed with hexane and deposited onto a
361
glass substrate, with the remaining solvent evaporated at room temperature.
362
Raman spectra were recorded on a Renishaw inVia™ microspectrophotometer using a 532 nm
363
wavelength laser (85 mW effective output power), with the system coupled to an optical
364
microscope. The sample preparation for Raman measurements was performed by drop casting a
365
THF solution onto a clean piece of SiO2/Si wafer (WRS Materials) and leaving the solvent to
366
evaporate in the open air. Point-based spectra were collected using the 100× objective (N.A. =
367
0.85), 0.1% of the maximum laser power, and 1 second of exposure time at each pulse, in order
15
368
to avoid thermal damage to the sample and interference by fluorescent emission. Each spectrum
369
was baseline-corrected and normalised (to its own highest intensity band) using the Renishaw
370
Wire 4.4 software tool. As regards to two-dimensional mappings, a line-based laser option was
371
used (streamline). The experimental conditions were set up in the range of 0.1–1 seconds
372
exposure time and 0.05–0.1% of the maximum laser power. The probed areas were
373
approximately 20–25 mm2.
374
The XRD patterns were obtained on a PANalytical X'Pert X-ray diffractometer with Cu-Kα
375
radiation (λ = 1.54056 Å). For this study the optimal parameters were run with an increment
376
size of 0.01° and an increment scan time of 1 second over a scan range of 3–40 2θ.
377
Powdery crystals of pure and doped compounds were deposited on a Si zero diffraction plate.
378
This kind of sample holder has no background noise from 20 to 120 degrees and ensures that
379
diffraction peaks are obtained from the sample.
380
Crystal planes of 1 and 2a were assigned for comparison with the corresponding XRD pattern
381
simulated from their X-ray structures.23b,c,e, 24
382
UV-vis spectra were recorded on a Jasco V-530 spectrophotometer. Fluorescence spectra were
383
recorded on a Jasco FP-750 spectrophotometer. In both cases standard quartz cells (1 cm width)
384
were used. Spectra were recorded at room temperature using solvents of spectroscopic grade.
385
Fluorescence images for waveguide behaviour were recorded on a ZEISS Axioplan-2
386
fluorescence microscope with a mercury lamp capable of excitation at any wavelength.
387
However, a series of filters was used to select the excitation wavelength and absorption. These
388
correspond to wavelengths in the blue (λexc = 320–380 nm, λem = 410–510 nm), green (λexc =
389
450–490 nm, λem = 515–565 nm) or red (λexc = 475–495 nm, λem = 520–570 nm). This
390
microscope was fitted with a shutter that allowed the light to be focused on the desired part of
391
the crystal.
392
A Zeiss LSM 800 confocal microscope (Zeiss, Jenna, Germany) with a 10× objective (Plan-
393
Apochromat 10×/0.45 M27) equipped with the ZEN imaging software was used to collect RGB
394
and spectral images of the microcrystals containing different doping ratios of 2. RGB images
395
were obtained using three diode lasers (405, 488 and 561) for blue, green and red fluorescence.
396
Spectral imaging was carried out with laser excitation in the 425–650 nm emission range. A set
397
of 26 images was obtained, with each image acquired with a separate narrow bandwidth of 8
398
µM, thus representing the complete spectral distribution of the fluorescence signals.
399 400
Acknowledgements
401
This
402
SBPLY/17/180501/000189) and MINECO of Spain (projects CTQ2017-88158-R, CTQ2017-
403
84825-R and RED2018-102331-T). R. Martín and B. Donoso are indebted to MEC for a FPU
404
studentship. We thank Mr. Carlos Rivera for his help in the X-ray analysis.
work
has
been
financially
supported
16
by
JCCM-FEDER
(project
405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464
References 1.
2.
3.
4.
a) Shin H, Kumar A, Chao H, Yang D, Palai AK, Pyo S. Laterally-Stacked, solution-processed organic microcrystal with ambipolar charge transport behavior. ACS Appl Mater Interfaces 2014;6:17804-14. http://dx.doi.org/10.1021/am5044505; b) Kabe R, Nakanotani H, Sakanoure T, Yahiro M, Adachi C. Effect of molecular morphology on amplified spontaneous emission of bis‐styrylbenzene derivatives. Adv Mater 2009;21:4034-8. http://dx.doi.org/ 10.1002/adma.200803588; c) Mas-Torrent M, Hadley P, Bromley ST, Ribas X, Tarres J, Mas M, Molins E, Veciana J, Rovira C. Correlation between crystal structure and mobility in organic field-effect transistors based on single crystals of tetrathiafulvalene derivatives. J Am Chem Soc 2004;126:8546-53. http://dx.doi.org/10.1021/ja048342i; d) Wang Y, Guo H, Ling S, ArrecheaMarcos I, Wang Y, Lopez Navarrete JT, Ponce Ortiz R, Guo X. Ladder-type heteroarenes: up to 15 rings with five imide groups. Angew Chem Int Ed 2017;56:9924-9. http://dx.doi.org/10.1002/anie.201702225. a) Chandrasekar R. Organic photonics: prospective nano/micro scale passive organic optical waveguides obtained from π-conjugated ligand molecules. Phys Chem Chem Phys 2014;16:7173-83. http://dx.doi.org/10.1039/C3CP54994A; b) Gu X, Yao J, Zhang G, Yan Y, Zhang C, Peng Q, Liao Q, Wu Y, Xu Z, Zhao Y, Fu H, Zhang D. Influence of alkyl chain lengths on the properties of iridium(III)-based piezochromic luminescent dyes with triazolepyridine type ancillary ligands. Adv Funct Mater 2012;22:4862-72. http://dx.doi.org/10.1016/j.dyepig.2013.08.015; c) Guo Z-H, Lei T, Jin Z-X, Wang J-Y, Pei J. Tshaped donor–acceptor lolecules for Low-loss red-emission optical waveguide. Org Lett 2013;15:3530-3. http://dx.doi.org/10.1021/ol4012025; d) Li Q, Jia Y, Dai L, Yang Y, Li J. Controlled rod nanostructured assembly of diphenylalanine and their optical waveguide properties. ACS Nano 2015;9:2689-95. http://dx.doi.org/10.1021/acsnano.5b00623; e) Wang X, Han Y, Liu Y, Zou G, Gao Z, Wang F. Cooperative supramolecular polymerization of fluorescent platinum acetylides for optical waveguide applications. Angew Chem Int Ed 2017;56:12466-70. http://dx.doi.org/10.1002/anie.201704294; h) Li Y, Ma Z, Li A, Xu W, Wang Y, Jiang H, Wang K, Zhao Y, Jia X. A single crystal with multiple functions of optical waveguide, aggregation-induced emission, and mechanochromism. ACS Appl Mater Interfaces 2017;9:8910-8. http://dx.doi.org/10.1021/acsami.7b00195; i) Basak S, Chandrasekar R. Passive optical waveguiding organic rectangular tubes: tube cutting, controlling light propagation distance and multiple optical out-puts. J Mater Chem C 2014;2:1404-8. https://doi.org/10.1039/C3TC31576B; j) Mitetelo N, Venkatakrishnarao D, Ravi J, Popov M, Mamonov E, Murzina TV, Chandrasekar R. Chirality‐controlled multiphoton luminescence and second‐harmonic generation from enantiomeric organic micro‐optical waveguides. Adv Optical Mater 2019;7:1801775. https://doi.org/10.1002/adom.201801775; k) Chandrasekhar N, Mohiddon MA, Chandrasekar R. Organic submicro tubular optical waveguides: self‐assembly, diverse geometries, efficiency, and remote sensing properties. Adv Optical Mater 2013;1:30511. https://doi.org/10.1002/adom.201200067. a) Wang X, Li H, Wu Y, Fu H. Tunable morphology of the self-assembled organic microcrystals for the efficient laser optical resonator by molecular modulation. J Am Chem Soc 2014;136:16602-8. http://dx.doi.org/10.1021/ja5088503; b) Wang X, Liao Q, Kong Q, Zhang Y, Xu Z, Lu X, Fu H. Whispering‐gallery‐mode microlaser based on self‐assembled organic single‐ crystalline hexagonal microdisks. Angew Chem Int Ed 2014;53:5863-7. http://dx.doi.org/ 10.1002/anie.201310659; c) Wang X, Liao Q, Xu Z, Wu Y, Wei L, Lu X, Fu H. Excitonpolaritons with size-tunable coupling strengths in self-assembled organic microresonators. ACS Photonics 2014;1:413-20. http://dx.doi.org/10.1021/ph400160v. a) Zhao YS, Fu H, Hu F, Peng A, Yao. Multicolor emission from ordered assemblies of organic 1D nanomaterials. J. Adv Mater 2007;19:3554-8. http://dx.doi.org/10.1002/adma.200701513; b) Ong BS, Wu YL, Liu P, Gardner S. High-performance semiconducting polythiophenes for organic thin-film transistors. J Am Chem Soc 2004;126:3378-9. http://dx.doi.org/10.1021/ja039772w; c) Wang ZL. Nanobelts, Nanowires, and nanodiskettes of semiconducting oxides-from materials to nanodevices. Adv Mater 2003;15:432-6. http://dx.doi.org/10.1002/adma.200390100; d) Law M, Greene LE, Johnson JC, Saykally R, Yang P. Nanowire dye-sensitized solar cells. Nat Mater 2005;4:455-9. http://dx.doi.org/10.1038/nmat1387; e) Liu H, Li Y, Jiang L, Luo H, Xiao S, Fang H, Li H, Zhu D, Yu D, Xu J, Xiang B. Imaging as-grown [60]Fullerene nanotubes by template technique. J Am Chem Soc 2002;124:13370-1. http://dx.doi.org/10.1021/ja0280527; f) Li X, Gu H, Chen K,
17
465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Song L, Hao Q. STorus: A new topology for optical network-on-chip. Optical Switching and Networking (OSN) 2016;22:77-85. http://dx.doi.org/10.1016/j.osn.2016.04.004; g) Chandrasekhar N, Basak S, Mohiddon MA, Chandrasekar R. Planar active organic waveguide and wavelength filter: self-assembled meso-tetratolylporphyrin hexagonal nanosheet. ACS Appl Mater Interfaces 2014;6:1488-94. https://doi.org/10.1021/am4039163. a) Birks JB. Photophysics of Aromatic Molecules; Wiley: New York, 1970; b) Yuang Z, Liu P, Chen S, Lam JWY, Wang Z, Liu Y, Kwok HS, Ma Y, Tang BZ. Changing the behavior of chromophores from aggregation-caused quenching to aggregation-induced emission: development of highly efficient light emitters in the solid state. Adv Matter 2010;22:2159-63. http://dx.doi.org/10.1002/adma.200904056; c) Huang Y, Xing J, Gong Q, Chen L-C, Liu G, Yao C, Wang Z, Zhang H-L, Chen Z, Zhang Q. Reducing aggregation caused quenching effect through co-assembly of PAH chromophores and molecular barriers Nature Commun 2019;10:art. nº 169. http://dx.doi.org/10.1038/s41467-018-08092-y. a) Mendez H, Heimel G, Optiz A, Sauer K, Barjowski P, Oehzelt M, Soeda J, Okamoto T, Takeya J, Arlin JB, Balandier JY, Geerts Y, Koch N, Salzmann I. Doping of organic semiconductors: impact of dopant strength and electronic coupling. Angew Chem Int Ed 2013;52:7751-55. http://dx.doi.org/10.1002/anie.201302396; b) Huang D, Wang C, Zou Y, Zhen X, Zang Y, Shen H, Gao X, Yi Y, Xu W, Di C-A, Zhu D. Bismuth interfacial doping of organic small molecules for high performance n‐type thermoelectric materials. Angew Chem 2016;128:10830-3. http://dx.doi.org/10.1002/ange.201604478. a) Förster, T. Intermolecular energy migration and fluorescence. Ann Phys 1948;2:55–75. http://dx.doi.org/10.1002/andp.19484370105; b) Hohng S, Lee J, Lee S. Single-Molecule ThreeColor FRET with Both Negligible Spectral Overlap and Long Observation Time. PLOS ONE 2010;5:e12270. http://dx.doi.org/10.1371/journal.pone.0012270; c) Jones GA, Bradshaw DS. Resonance energy transfer: From fundamental theory to recent applications. Frontiers in Physics. 2019;7:100. http://dx.doi.org/10.3389/fphy.2019.00100. Tseng K-P, Tsai Y-T, Shyue J-J, Raffy G, del Guerzo A, Wong K-T, Bassini DM. Emissive nanotubes from templated self-assembly of small molecules. Chem Phys Lett 2017;683:43-8. http://dx.doi.org/10.1016/j.cplett.2017.04.005. a) Xu Z, Liao Q, Shi X, Li H, Zhang H, Fu H. Full-color tunable organic nanoparticles with FRET-assisted enhanced two-photon excited fluorescence for bio-imaging. J Mater Chem B 2013;1:6035-41. http://dx.doi.org/10.1039/C3TB20841A; b) Fang H-H, Lu S-Y, Wang L, Ding R, Wang H-Y, Feng J, Chen Q-D, Sun H-B. Preparation and time-resolved fluorescence study of RGB organic crystals. Org Electron 2013;14:389-95. http://dx.doi.org/10.1016/j.orgel.2012.10.028. a) Zhang W, Zhao YS. Organic nanophotonic materials: the relationship between excited-state processes and photonic performances. Chem Commun 2016;52:8906-17. http://dx.doi.org/ 10.1039/C6CC00018E; b) Zhang C, Zhou C-L, Zhao Y, Dong C-H, Wei C, Wang H, Liu Y, Guo G-C, Yao J, Zhao YS. Organic printed photonics: From microring lasers to integrated circuits. Science Adv 2015;1:e1500257. http://dx.doi.org/10.1126/sciadv.1500257; c) Zhao G, Dong H, Liao Q, Jiang J, Luo Y, Fu H, Hu W. Organic field-effect optical waveguides. Nature Commun 2018;9:art nº 4790. http://dx.doi.org/10.1038/s41467-018-07269-9. a) Peng A, Xiao D, Ma Y, Yang W, Yao J. Tunable emission from doped 1,3,5‐triphenyl‐2‐ pyrazoline organic nanoparticles. Adv Mater 2005;17:2070-3. http://dx.doi.org/10.1002/adma.200401989; b) Tang CW, van Slyke SA, Chen CH. Electroluminescence of doped organic thin films. J Appl Phys 1989;65:3610-16. http://dx.doi.org/10.1063/1.343409; c) Kido J, Kimura K, Nagai K. Multilayer white lightemitting organic electroluminescent device. Science 1995;267:1332-34. http://dx.doi.org/ 10.1126/science.267.5202.1332. a) Zhao YS, Di C, Yang W, Yu G, Liu Y, Yao. Photoluminescence and electroluminescence from tris(8‐hydroxyquinoline)aluminum nanowires prepared by adsorbent‐assisted physical vapor deposition. J. Adv Funct Mater 2006;16:1985-91. http://dx.doi.org/10.1002/adfm.200600070; b) Qu L, Shi G. Crystalline oligopyrene nanowires with multicolored emission. Chem Commun 2004:2800-1. http://dx.doi.org/10.1039/B412638F. Ishii Y, Omori K, Satozono S, Fukuda M. Dye-doped submicron fiber waveguides composed of hole- and electron-transport materials. Org Electron Physics Mater Appl 2017;41:215–20. http://dx.doi.org/10.1016/j.orgel.2016.11.007. Liao Q, Fu H, Yao. Waveguide modulator by energy remote relay from binary organic crystalline microtubes. J. Adv Mater 2009;21:4153–7. http://dx.doi.org/10.1002/adma.200900997.
18
525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583
15. Pradeep VV, Annadhasan M, Chandrasekar R. Vapour‐phase epitaxial growth of dual‐ colour‐emitting DCM‐perylene micro‐heterostructure optical waveguides. Chem Asian J 2019;14:4577-81. https://doi.org/10.1002/asia.201901221. 16. Venkatakrishnarao D, Mohiddon MA, Chandrasekhar N, Chandrasekar R. Photonic microrods composed of photoswitchable molecules: erasable heterostructure waveguides for tunable optical modulation. Adv Optical Mater 2015;3:1035-40. https://doi.org/10.1002/adom.201500106. 17. a) Li Z-Z, Tao Y-C, Wang X-D, Liao LS. Organic nanophotonics: self-assembled singlecrystalline homo-/heterostructures for optical waveguides. ACS Photonics 2018;5:3763-71. https://doi.org/10.1021/acsphotonics.8b00815; b) Lei Y, Sun Y, Liao L, Lee S-T, Wong W-Y. Facet-selective growth of organic heterostructured architectures via sequential crystallization of structurally complementary π-conjugated molecules. Nano Lett 2017;17:695-701. https://doi.org/10.1021/acs.nanolett.6b03778; c) Yang C, Gu L, Ma C, Gu M, Xie X, Shi H, Ma H, Yao W, An Z, Huang W. Controllable co-assembly of organic micro/nano heterostructures from fluorescent and phosphorescent molecules for dual anti-counterfeiting. Mater Horiz 2019;6: 984-9. https://doi.org/10.1039/C8MH01582A. 18. Li ZZ, Liang F, Zhuo MP, Shi YL, Wang XD, Liao LS. White-Emissive Self-Assembled Organic Microcrystals. Small 2017;13:1–6. http://dx.doi.org/10.1002/smll.201604110. 19. Zhang J, Wang J, Xu X, Chen S, Zhang Q, Yao C, Zhuang X, Pan A, Li L. An air-stable microwire radial heterojunction with high photoconductivity based on a new building block. J Mater Chem C 2015;3:5933–9. http://dx.doi.org/10.1039/C5TC01050K. 20. a) D’Andrade BW, Forrest SR. White organic light‐emitting devices for solid‐state lighting. Adv Mater 2004;16:1585-95. http://dx.doi.org/10.1002/adma.200400684; b) Kubo Y, Nishiyabu R. White-light emissive materials based on dynamic polymerization in supramolecular chemistry. Polymer 2017;128:257-75. http://dx.doi.org/10.1016/j.polymer.2016.12.082; c) Zhao YS, Fu H, Hu H, Peng A, Yang W, Yao. Tunable emission from binary organic one‐dimensional nanomaterials: an alternative approach to white‐light emission. J Adv Mater 2008;20:79-83. http://dx.doi.org/10.1002/adma.200700542; d) Lei Y, Liao Q, Fu H, Yao J. Orange−blue−orange triblock one-dimensional heterostructures of organic microrods for white-light emission. J Am Chem Soc 2010;132:1742-3. http://dx.doi.org/10.1021/ja9084435. 21. Abbel R, Grenier C, Pouderoijen MJ, Stouwdam JW, Leclêre PELG. White-light emitting hydrogen-bonded supramolecular copolymers based on π-conjugated oligomers. J Am Chem Soc 2009;131:833-44. http://dx.doi.org/10.1021/ja807996y. 22. Vijayakumar C, Praveen VK, Ajayaghost A. RGB emission through controlled donor self‐ assembly and modulation of excitation energy transfer: a novel strategy to white‐light‐emitting organogels. Adv Mater 2009;21:2059-63. http://dx.doi.org/10.1002/adma.200802932. 23. a) Cáceres D, Cebrián C, Rodríguez AM, Carrillo JR, Díaz-Ortiz A, Prieto P, Aparicio F, García F, Sánchez L. Optical waveguides from 4-aryl-4H-1,2,4-triazole-based supramolecular structures. Chem Commun 2013;49:621-3. http://dx.doi.org/10.1039/C2CC37381E; b) Pastor MJ, Torres I, Cebrián C, Carrillo JR, Díaz-Ortiz A, Matesanz E, Buendía J, García F, Barberá J, Prieto P, Sánchez L. 4‐aryl‐3,5‐bis(arylethynyl)aryl‐4H‐1,2,4‐triazoles: multitasking skeleton as a self‐assembling unit. Chem Eur J 2015;21:1795-802. http://dx.doi.org/10.1002/chem.201404243; c) Torres I, Carrillo JR, Díaz-Ortiz A, Martín R, Gómez MV, Stegemann L, Strassert CA, Orduna J, Buendía J, Greciano EE, Valera JS, Matesanz E, Sánchez L, Prieto P. Self-assembly of T-shape 2H-benzo[d][1,2,3]-triazoles. Optical waveguide and photophysical properties. RSC Adv 2016;6:36544-53. http://dx.doi.org/10.1039/c6ra02473d; d) Torres I, Díaz-Ortiz A, Sánchez L, Orduna J, Blesa MJ, Carrillo JR, Prieto P. Tunable emission in aggregated T-Shaped 2H-Benzo[d][1,2,3]triazoles with waveguide behaviour. Dyes Pigments 2017;142:212-25. http://dx.doi.org/10.1016/j.dyepig.2017.02.048; e) Martín R, Prieto P, Carrillo JR, Torres I, Strassert CA, Soloviova K, Rodríguez AM, Sánchez L, Díaz-Ortiz A. Colored optical waveguides in self-assembled thiadiazole-based materials. Dyes Pigments 2018;151:327-34. http://dx.doi.org/10.1016/j.dyepig.2018.01.001. 24. Torres I, González-Domínguez JM, Díaz-Ortiz A, Romero-Nieto C, Rominger F, Vázquez E, Carrillo JR, Prieto P. Modulation of Waveguide Behaviour of an ICT 2HBenzo[d][1,2,3]Triazole Derivative with Graphene. Org Electron 2019;68:1-8. http://dx.doi.org/10.1016/j.orgel.2019.01.033. 25. a) Lakowicz JR. Principles of Fluorescence Spectroscopy; Springer Science & Business Media, Germany, 2013; b) Chemla DS, Zyss J. Nonlinear Optical Properties of Organic Molecules and Crystals; Elsevier, The Netherlands, 2001.
19
584 585 586 587
26. Martín R, Prieto P, Carrillo JR, Rodríguez AM, de Cózar A, Boj PG, Díaz-García MA, Ramírez MG. Design, synthesis and amplified spontaneous emission of 1,2,5-benzothiadiazole derivatives. J Mater Chem C 2019;7:9996-10007. http://dx.doi.org/10.1039/C9TC03148K.
20
Some benzotriazoles and thiadiazoles can act as host and guest co-assembled skeletons Slow diffusion, an easy and cost-effective technique to form co-assembled aggregates Tunable colour-active materials could be useful in the fields of optoelectronics Changes in the molar ratio of the different doping agents can tune the light emission Co-assembled microcrystals can act as optical waveguide
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
ID. DOCUMENTO
Página: 1 / 1
Xuoo7yVCcG FIRMADO POR
FECHA FIRMA
ID. FIRMA
DIAZ ORTIZ ANGEL
23-01-2020 17:03:14
1579795401899
Xuoo7yVCcG Calle Altagracia número 50 - Ciudad Real - 13071. Tfno.: 902204100 Fax.: 902204130 - https://www.sede.uclm.es - Soporte a usuarios: https://cau.uclm.es Copia de documento electrónico. Para verificar su autenticidad y la validez de su firma, acceda a https://www.sede.uclm.es/verificadorfirmas/uclm