Towards better understanding of photophysical properties of rhenium(I) tricarbonyl complexes with terpy-like ligands

Journal Pre-proof Towards better understanding of photophysical properties of rhenium(I) tricarbonyl complexes with terpy-like ligands

Magdalena Małecka, Barbara Machura, Anna Świtlicka, Sonia Kotowicz, Grażyna Szafraniec-Gorol, Mariola Siwy, Marcin Szalkowski, Sebastian Maćkowski, Ewa Schab-Balcerzak PII:

S1386-1425(20)30101-3

DOI:

https://doi.org/10.1016/j.saa.2020.118124

Reference:

SAA 118124

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received date:

2 January 2020

Revised date:

31 January 2020

Accepted date:

1 February 2020

Please cite this article as: M. Małecka, B. Machura, A. Świtlicka, et al., Towards better understanding of photophysical properties of rhenium(I) tricarbonyl complexes with terpylike ligands, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy(2020), https://doi.org/10.1016/j.saa.2020.118124

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© 2020 Published by Elsevier.

Journal Pre-proof Towards better understanding of photophysical properties of rhenium(I) tricarbonyl complexes with terpy-like ligands

Magdalena Małecka a, Barbara Machura* a, Anna Świtlickaa, Sonia Kotowicza, Grażyna Szafraniec-Gorola, Mariola Siwyb, Marcin Szalkowskic, Sebastian Maćkowskic, Ewa

of

Schab-Balcerzak*a,b

Institute of Chemistry, University of Silesia, 9th Szkolna Street, 40006 Katowice, Poland

b

Centre of Polymer and Carbon Materials, Polish Academy of Sciences, 34 M.

ro

a

c

-p

Curie-Sklodowska Str., 41-819 Zabrze, Poland

Nanophotonics Group, Institute of Physics, Faculty of Physics, Astronomy and Informatics,

re

Nicolaus Copernicus University, 5 Grudziadzka Str., 87-100 Torun, Poland

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*Corresponding authors: e-mail: [email protected], [email protected]

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Abstract: Series of Re(I) carbonyls complexes were designed and synthesized to explore the impact of the triimine skeleton and number of methoxy groups attached to aryl substituents on their optoelectronic and thermal properties. The chemical structures of the prepared complexes were confirmed by 1H and 13C NMR spectroscopy, HR-MS, elemental anlsysis, and X-ray measurements. DSC measuremtns showed that they melted in the range of 198–325 C. Some of them form stable molecular glasses with high glass transition temperatures (158–173C). Experimentally obtained optical properties were supported by DFT calculations. The UV-Vis spectra display a series of overlapping absorption bands in the range 200–350 nm, and much weaker broad band in the visible spectral region, due to intraligand and charge transfer transitions, respectively. All synthesized complexes were emissive in solution and in solid state as powder. Moreover, when applied in diodes, some of them exhibited ability for emission of light under external voltage with maximum of electroluminescence band located at 591–630 nm. Keywords: Re(I) carbonyl • terpy-like ligands • photoluminescence • electroluminescence

Journal Pre-proof Introduction Re(I) carbonyls [ReL(CO)3(NN)]n+ (n = 0 or 1, L - ancillary ligand) with derivatives of 1,10-phenanthroline and 2,2-bipyridine (NN) have received widespread scientific attention since 1974, when Wrighton and Morse first examined the luminescence behavior of [ReCl(CO)3(4,7-(Ph)2phen)] and [ReCl(CO)3(5-R-phen)] (R – H, CH3, Cl, Br, NO2) [1]. It has been demonstrated that the character and energies of HOMO and LUMO, and hence photo- and electroluminescent properties of [ReL(CO)3(NN)]n+, may be fine-tuned by varying the ancillary ligand (L) and introducing electron withdrawing or donating groups into the diimine skeleton [2-42]. The development in this area has been mostly driven by the potential

of

application of [ReL(CO)3(NN)]n+ in photocatalysis [43-47], biological imaging [48-57], and

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organic light-emitting devices [14, 58-65].

The related [ReCl(CO)3(terpy-κ2N)] compound, first examined in 1988 by Juris et al. [66],

-p

was found to be non-emissive in solution at room temperature, which limited further studies of Re(I) tricabonyls with 2,2′:6′,2′′-terpyridines. Scientific interest in these systems was renewed

re

in the early 2000s [67-72], especially when Wang and co-workers demonstrated that

lP

introduction of hole-transporting moieties, carbazole or diphenylamine-based substituents, into 2,2′:6′,2′′-terpyridine at 4-position, leads to significantly enhanced phosphorescence of

na

[ReCl(CO)3(4′-R-terpy-κ2N)] compared to [ReCl(CO)3(terpy-κ2N)] [70]. Additionally, theoretical investigations based on the density functional theory (DFT) performed for these compounds, revealed that they facilitate electron transfer and hole extraction, making them

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very attractive as electrophosphorescence materials for organic light emitting diodes (OLEDs) construction [73]. Potential usefulness of [ReCl(CO)3(L-2N)] with modified terpyridine-like ligands for use in the OLED technology was further verified by the research results obtained in our group [74-79].

In the current work, series of phenyl and naphthyl-substituted 2,2′:6′,2′′-terpyridine (terpy), 2,6-di(thiazol-2-yl)pyridine (dtpy) and 2,6-di(pyrazin-2-yl)pyridine (dppy) derivatives decorated with methoxy groups (scheme 1) were used for the synthesis of [ReCl(CO)3(L-2N)]. Beneficial role of a single methoxy group attached to aryl substituents was proved by our previous studies. In solid state, the Re(I) complex with 2,2′:6′,2′′-terpyridine substituted with 4-methoxy-1-phenyl exhibited a remarkably enhanced photoluminescence quantum yield of ∼30% in relation to other [ReCl(CO)3(4-R-terpy-κ2N)] with 4-Cl-phenyl (∼21%), 4-Br-phenyl (∼17%),

4-biphenyl

(∼12%)

substituents

[75,78].

The

Re(I)

complexes

with

Journal Pre-proof 2,2′:6′,2′′-terpyridine or 2,6-di(thiazol-2-yl)pyridine functionalized with 4-methoxy-1-phenyl and 6-methoxy-2-naphthyl were also found to be very promising for OLED fabrication [78]. The aim of the current was to explore the impact of additional methoxy groups attached to the phenyl or naphthyl-substituent of terpy, dtpy and dppy on the thermal, spectral and electrochemical properties of the rhenium(I) carbonyls [ReCl(CO)3(Ln-2N)] (scheme 1). As the methoxy unit is known to lower oxidation potential and enhance the electrochemical stability, its presence in compounds designed for optoelectronic can be beneficial [80]. The presence of methoxy substituent at the para position of the phenyl ring adds electron density into the triimine skeleton, while meta-positioned methoxy groups withdraw electron density

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from the trisheterocyclic moiety [81-82].

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The photophysical properties of 1–9 were explored by carrying out absorption and emission studies in solution and solid state, as well as a possibility of light emission under

-p

external voltage in diodes with configuration ITO/PEDOT:PSS/compound/Al and

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na

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compounds was investigated using DSC.

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ITO/PEDOT:PSS/PVK:PBD:compound/Al was tested. The thermal behavior of the prepared

Journal Pre-proof O

O

H3C

O CH3

H3C

N L

N L

CH3

CH3

O

O

O

H3C

CH3

3

O

CH3

O

H3C

CH3

S

4

N

L

7

N

re

5

L

lP

O

na

N

N

N

CH3

O

6

CH3

O

O

O

CH3

CH3

CH3

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N

N

N

L

CH3

O

N

-p

N

N

L

S

N

N N

ro

of

H3C

N L

O

O

N

N

2

CH3

O

N

N

1

O

CH3

N

S

N

O

H3C

CH3

S

N N

O

O

S

S

N N

N

N L

8

N

N

N

N L

9

Scheme 1. Ligands employed in this study.

Results and Discussion Synthesis, structural and thermal characterisation The complexes [ReCl(CO)3(Ln-2N)] (1–9) were prepared according to the standard procedure via direct exchange of two carbonyl ligands in Re(CO)5Cl by the corresponding L1-9 ligand (Scheme 1). The molecular formulae of 1–9 were confirmed by elemental analysis, HRMS (ESI) spectrometry, as well as NMR and IR spectroscopy. In the IR spectra, a sharp and intense high-energy carbonyl stretching band (2019–2029 cm–1) accompanied with two

Journal Pre-proof overlapping lower-energy (CO) absorptions (1955–1864 cm–1) (Figures S1-S9) is supportive of facial arrangement of CO groups in the moiety [Re(CO)3]+. Consistent with the bidentate coordination mode of Ln, the protons of the outer pirydyl/thiazolyl/pyrazinyl rings are magnetically inequivalent, showing separate signals in the 1H NMR spectra of 1–9, each integrated for 1 proton (Figures S10S19). Using the multidimensional techniques 1H–13C HMBC, 1H–13C HMQC, 1H–1H COSY, the full assignment of the signals in the 1H and

13

C

NMR spectra was performed for 1, 4, 7 (Figure S20). Crystals suitable for X-ray diffraction studies were obtained for the complexes 5, 7 and 9, and the structural analysis confirmed distorted octahedral geometry of Re(I) ion, defined by three

na

lP

re

-p

ro

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fac-arranged carbonyl groups, two nitrogen atoms of Ln, and one chlorine atom (Figure 1).

7

9

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5

Figure 1. Molecular structures of 5, 7 and 9 with thermal ellipsoids set at 50% probability for non-hydrogen atoms.

As expected for [ReCl(CO)3(4′-R-terpy-κ2N)] and related systems [74-79], the complexes 5, 7 and 9 show a small bite angle N(2)–Re(1)–N(1) angle of 74.91(12) in 5, 74.87(11) in 7, 74.50 (13)° in 9, significant enlargement of C(1)–Re(1)–N(2) angle of 100.37(16) in 5, 99.98(15) in 7 and 102.53(17)° in 9 as well as elongation of Re(1)–N(2) bond length to the central pyridine ring [2.250(3)Å for 5, 2.204(3)Å for 7, 2.207(3) Å for 9] in comparison with Re(1)–N(1) distance to the peripheral pyridine ring [2.165(3)Å in 5, 2.165(3)Å in 7, 2.148(4) Å in 9]. All these structural features are attributed to κ2N-coordination of the tiiminie moiety and steric interaction of the uncoordinated heterocycle ring with the carbonyl group C(1)–O(1). The non-coordinated peripheral ring is inclined to the central pyridine at 41.622(3) in 5, 50.96(15) in 7 and 54.69(17) in 9, while the dihedral angle between the central pyridine and pendant

Journal Pre-proof phenyl ring ring is 10.4465(7)° in 5, 19.95(14)° in 7 and 15.19(14) in 9. Additional structural data of 5, 7 and 9 are included in Tables S1–S5 and shown in Figure S21 (in ESI). Thermal properties of the prepared 1–9 complexes were investigated using differential scanning calorimetry (DSC). The registered temperatures of melting (Tm), crystallization (Tc), and glass transition (Tg) are presented in Experimental section. During the first heating scan in DSC thermograms only the melting endotherm with maximum between 198 and 325 C was seen, except for complex 9. In the case of 9, apart from Tm at 233 C, also crystallization exotherm giving new crystals, which melted with degradation at 287 C were observed. It was found that the presence of three methoxy substituents raises the melting temperature of the

of

complexes (4–6). Moreover, these complexes (4–6) melted with thermal decomposition. Other

ro

complexes, that is, with two methoxy groups (1, 3, 7) formed amorphous material after rapid cooling with Tg in the range of 158 – 173 C, which is beneficial for formation of

-p

morphologically stable thin films. Complexes 3 and 7 form stable molecular glasses, because they do not undergo crystallization even upon heating above their Tg, contrary to 1, which

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during further heating above Tg crystallized and again formed crystalline material. The results

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indicate that all of the investigated complexes exhibited high enough Tm values from the point

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of view of applications in optoelectronic devices.

DFT evaluation of the electronic structures and transport properties To gain better understanding of the photophysical properties of 1–9, the frontier molecular

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orbitals and their energy levels have been calculated at DFT/PBE1PBE/DEF2– TZVPD/6-31+G** level theory, and the results are presented in Figures 2-3 and S22-S24. Geometry optimization yielded bond angles and lengths in good agreement with crystal structures (Table S1). For all of the compounds, the LUMO and LUMO+1 are composed predominantly of π* orbitals localized on the triimine skeleton, and the energies of these orbitals are essentially influenced by the type of the triimine ligand, decreasing in the order terpy  dtpy  dppy. The HOMOs of 7–9 are energetically destabilized relative to the respective 1–6 and previously reported Re(I) tricarbonyls with the corresponding triimines substituted with 4-methoxy-1-naphthyl [78]. The HOMO energy levels of 7–9, raised by the attachment of 4,7-dimethoxy-1-naphthyl unit to the triimine moiety (terpy, dtpy and dppy) seem to be favorable for hole-transporting ability of the resulting complexes. On the other hand, decrease of the LUMO energy levels of the Re(I) complexes with dtpy- and dppy-based ligands relative to those bearing terpy derivatives is expected to improve the electron injection ability [83]. On

Journal Pre-proof the contrary, introduction of additional methoxy groups into the phenyl group attached to the central pyridine of terpy, dtpy and dppy leads to stabilization of the HOMO energy level of 1– 6 relative to the corresponding Re(I) tricarbonyls with 4-MeO-phenyl-subsitued triimines, which results in higher HOMO–LUMO energy gaps. Structural modifications of the triimine ligand also tune the distribution of the HOMO orbitals, which can result in differences of electronic transition character upon excitation. The HOMOs of 1, 3 and 7–9 are principally centered on the substituent part of the organic ligand, while 5d rhenium, *CO and Cl make a major contribution into the HOMO of 2. The HOMOs of 4, 5

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na

lP

re

-p

ro

of

and 6 spread over the whole molecule, except the peripheral triimine ring orbitals.

Figure 2. Partial molecular orbital energy DFT/PBE1PBE/DEF2–TZVPD/6-31+G** level.

levels

of

1–9

computed

at

the

Journal Pre-proof Compound

1

2

3

4

5

6

7

HOMO

f o

LUMO

n r u

l a

Figure 3. Frontier molecular orbitals of the complexes 1–9.

o J

r P

e

o r p

8

9

Journal Pre-proof The values of ionization potential (IP) and electronic affinity (EA) were computed to estimate energy barriers for injecting holes and electrons, while reorganization energies (λhole and λelectron), which reflect the geometric relaxation associated with transition between neutral and ionized states, were calculated to estimate the charge transport properties of 1–9 (Table 1). For photoluminescent materials, lower IP values mean the easier injection of holes from the hole-transporting layer to the emitter. On the contrary, the higher EA, the easier the entrance of electrons from the electron-transporting layer. The low reorganization energies are required for efficient charge transporting process [84-85].

of

Compared to the Re(I) tricarbonyls bearing the terpy/dtpy/dppy ligands substituted with 4-methoxy-1-naphthyl [78], the compounds 7–9 showed lower IP values, which may

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imply improved hole injection abilities. The reorganization energies (λhole and λelectron)

-p

were found to be almost unchanged after the introduction of additional methoxy groups into the naphthyl ring. Most importantly however, the values of λhole and λelectron are

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comparable, which may make the complexes 7–9 good ambipolar materials, likewise as systems with terpy/dtpy/dppy substituted with 4-methoxy-1-naphthyl [78]. The

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introduction of additional methoxy groups into the phenyl group attached to the terpy, dtpy and dppy effectively lowers the values of λhole, but it was found unfavourable for

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hole-transporting ability of 1–6, leading to the increase of IP values relative to the Re(I) tricarbonyls bearing the corresponding triimines with 4-methoxy-1-phenyl substituent

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[78]. For all three series 1–3, 4–6 and 7–9, the calculated EAs and EEPs values increase in the following order terpy  dtpy  dppy.

Table 1. Calculated ionization potentials and electron affinities (vertical and adiabatic), energy gap, as well as hole and electrons reorganization energies and extraction potentials (DFT/PBE1PBE/DEF2-TZVPD/DEF2-TZVP) of 1–9 in acetonitrile. Complex

IP(v) [eV]

IP(a) [eV]

EA(v) [eV]

EA(a) [eV]

λhole [eV]

λelectron [eV]

HEP [eV]

EEP [eV]

energy gap(a) [eV]

1

6.26

5.93

2.79

2.96

0.71

0.34

5.55

3.13

2.96

2

6.30

5.97

3.04

3.21

0.70

0.33

5.60

3.38

2.76

3

6.40

6.09

3.19

3.36

0.68

0.32

5.72

3.52

3.52

4

6.26

5.92

2.81

2.97

0.72

0.33

5.54

3.14

2.95

5

6.29

5.96

3.03

3.20

0.49

0.34

5.59

3.37

2.76

Journal Pre-proof 6

6.33

5.84

3.19

3.35

0.77

0.32

5.56

3.51

2.49

7

5.77

5.63

2.74

2.92

0.27

0.36

5.49

3.10

2.71

8

5.81

5.68

2.98

3.16

0.27

0.35

5.54

3.34

2.52

9

5.81

5.67

3.15

3.32

0.27

0.34

5.54

3.49

2.35

;

;

;

Absorption properties and TDDFT calculations Absorption properties of 1–9 were investigated in solid state and two solvents of

of

different polarity, chloroform (ε = 4.8) and acetonitrile (ε = 37.5) (Table S6 and Figures S25-S27). The absorption profiles of 1–9 in acetonitrile are shown in Figure 4. The

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electronic spectra of 1–9 display a series of overlapping intense absorption bands in the

-p

range 200–350 nm, which is typical of intraligand transitions, and much weaker and

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na

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broader bands extending well into the visible region (Figure 4).

(a)

(b) Figure 4.The UV-Vis absorption spectra for 1–9 in (a) acetonitrile and (b) thin films on glass. Right y axis in Fig. 4b is referred to compounds 2 and 5. According to the TDDFT calculations, the low-energy absorption bands of 1–9 are composed of several transitions of different origins (Table 2 and Figure S28). In addition to the metal-to-ligand charge transfer (1MLCT) and ligand-to-ligand charge transfer (1LLCT), assigned as metal-ligand-to-ligand charge transfer (1MLLCT) transitions, also intraligand charge transfer (1ILCT) transitions make contributions into

Journal Pre-proof the visible absorption spectra. The latter ones are the prevailing components for compounds bearing 4,7-dimethoxy-1-naphthyl substituent (7–9). The visible absorption spectra of these compounds (7–9) are principally contributed by HOMOLUMO and HOMO LUMO+1 transitions, which can be interpreted as charge delocalization from the 4,7-dimethoxy-1-naphthyl unit to π-conjugated trisheterocyclic acceptor moiety (1ILCT). For complexes 1–6, the transitions the transitions assigned to the lowest wavelength absorption are of 1MLLCT origin or mixed 1MLLCT/1ILCT character (Table 3). With respect to the corresponding Re(I) tricarbonyls with metoxyphenyl-substituted

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triimines (1–6), the lowest energy absorption bands of 7–9 are bathochromically

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shifted, consistent with extension of π conjugation of the substituent. Conversely, substituent pattern (1–3 in relation to the corresponding 4–6) has little impact on the

-p

location of the longest-wavelength absorption. The effect of the triimine skeleton is seen in the bathochromic shift of the lowest energy absorption band in the order terpy 

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tpy  dppy for all three series 1–3, 4–6 and 7–8 (Figure S27). The absorption profiles of 1–9 are also affected by the changes in the solvent polarity. Typically for Re(I)

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carbonyls[ReL(CO)3(NN)]n+, the longest wavelength absorption band in the spectra of

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1–9 is negatively solvatochromic, with maxima blue-shifted of 25 nm for 1, 22 nm for 2, 24 nm for 3, 17 nm for 4, 28 nm for 5, 21 nm for 6, 12 nm for 7, 17 nm for 8, and 18 nm for 9.

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In solid state as powder, the absorption spectra of 1–9 are bathochromically shifted in comparison with those obtained in solution, most likely due to stronger intermolecular interactions in the solid state (Figure S25). On the other hand, complexes as thin film on glass substrate showed absorption range similar to those in solution (Figure 4). Table 2. The energies and characters of spin-allowed electronic transitions assigned to the lowest wavelength absorption band of complexes 1-9 in MeCN. Experimental absorption ; nm/eV

Calculated transitions Major contribution (%)

Character

E [eV]

λ [nm]

Oscillator strength

3.05 3.19 3.24 3.51

406.4 389.0 383.0 353.4

0.0112 0.0046 0.1278 0.0071

1

370 (3.35)

H-1→L (98%) H→L (98%) H-2→L (97%) H-3→L (94%)

MLLCT ILCT MLLCT MLLCT

Journal Pre-proof 2 MLLCT MLLCT/ILCT ILCT MLLCT 3

2.86 3.05 3.21 3.32

434.1 406.5 385.9 373.8

0.0034 0.1426 0.0041 0.0216

MLLCT ILCT MLLCT MLLCT ILCT MLLCT 4

2.77 2.97

447.4 417.1

0.0131 0.0627

401 (3.09)

H-1→L (94%) H→L (51%) H-2→L (45%) H-2→L (48%) H→L (45%) H-4→L (96%)

3.00

413.6

0.0543

3.25

381.1

0.0068

376 (3.30)

H→L (94%) H-1→L (89%) H-3→L (92%)

MLLCT MLLCT/ILCT MLLCT 5

3.05 3.22 3.50

406.8 385.2 353.8

0.0144 0.1851 0.0122

MLLCT ILCT/MLLCT ILCT/MLLCT MLLCT/ILCT MLLCT ILCT MLLCT/ILCT ILCT/MLLCT ILCT MLLCT/ILCT MLCT 6

2.87

432.6

0.0041

3.03

408.5

0.2174

387 (3.20)

H-1→L (73%) H→L (23%) H→L (41%) H-3→L (35%) H-1→L (22%) H-2→L (54%) H-3→L (21%) H→L (19%) H-2→L (44%) H-3→L (35%) H-4→L (86%)

3.26

380.6

0.0475

3.28

378.3

0.0468

3.34

371.1

0.0168

H-1→L (64%) H→L (32%) H-2→L (36%) H→L (32%) H-1→L (29%) H-2→L (57%) H→L (34%)

MLLCT ILCT/MLLCT MLLCT/ILCT ILCT/MLLCT MLLCT MLLCT/ILCT ILCT/MLLCT 7

2.77

447.8

0.0234

2.96

419.2

0.1745

3.14

394.8

0.038

ILCT MLLCT MLLCT/ILCT ILCT ILCT MLCT ILCT MLLCT/ILCT 8

2.86 3.10 3.31

433.3 399.3 374.7

0.2119 0.0171 0.0391

389 (3.19)

H→L (97%) H-1→L (97%) H-2→L (80%) H-3→L (17%) H→L+1 (96%) H-4→L(96%) H-3→L (77%) H-2→L (17%)

3.47 3.55 3.63

357.3 349.2 341.5

0.1386 0.0058 0.0349

402 (3.08)

H→L (98%) H-1→L (98%) H-2→L (78%) H-3→L (19%)

ILCT MLLCT ILCT MLLCT

2.69 2.91 3.13

461.2 426.33 395.65

0.2315 0.011 0.0419

ro

-p

re

lP

na

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399 (3.11)

of

391 (3.17)

H→L (98%) H-2→L (78%) H-1→L (87%) H-4→L (83%)

Journal Pre-proof

408 (3.04)

H→L+1 (98%) H-4→L (90%) H-3→L (78%) H-2→L (19%)

ILCT MLLCT/IL ILCT MLLCT 9

3.25 3.37 3.42

381.35 368.08 362.26

0.1356 0.0119 0.0236

H→L (97%) H-1→L (96%) H-2→L (83%) H→L+1 (95%) H-4→L (98%) H-3→L (81%) H→L+2 (95%)

ILCT MLLCT MLLCT ILCT MLLCT ILCT ILCT

2.49 2.76 3.01 3.18 3.24 3.39 3.47

497.2 450.0 412.4 390.0 382.2 365.3 356.9

0.1464 0.0118 0.0607 0.1637 0.0043 0.0247 0.0421

Emission properties

of

Photoluminescence behavior of 1–9 was studied in solution and in solid state as

ro

powder, as well as in the form of a thin film on a glass substrate. The relevant photophysical data are summarized in Table 3, and excitation and emission spectra of

-p

1–9 are shown in Figure S29.

Upon excitation in the lowest-energy absorption band, the Re(I) complexes 1–9 exhibit

re

emission band with the maximum falling in the range 654 – 744 nm in solution, and

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580 – 686 in solid state as powder. Upon varying the solvent polarity from chloroform to more polar acetonitrile, the shift of the emission is smaller than 15 nm (Table 3). Consistent with the rigidochromic effect leading to raising the energy of the emissive

na

CT states due the lack of solvent mobility following excitation, the emission maxima of 1–9 in solid state as powder occur in higher energies in relation to the corresponding

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solutions. The blue-shift of emission when going from solution to the solid state is accompanied by the increase of lifetimes, which are significantly longer in solid state as compared to those in solution. Upon excitation in the lowest-energy absorption band, the Re(I) complexes 1, 4, 5 and 9 as thin films deposited on glass were not emissive. In the case of compound 3, 6 and 7 a weak emission with the em at 621, 616 and 573 nm, respectively, was observed (cf. Table 3). Table 3. Summary of photoluminescent properties of complexes 1–9. Maximum of excitation wavelength (ex) [nm]

Emission [nm]

Stokes shift [cm-1]

τ[ns]

χ2

φ [%]

MeCN

370, 273

672

12140

1.087

0.5

CHCl3 solid

393, 315, 258

660

10290

1.152

0.1

457

600

5215

0.977

1.4

392

nd

––

1.99 (82.86 %) 4.67 (17.14%) 3.08 23.92 (33.42%) 93.97 (66.58%) ––

––

––

Compound

1 O

O H3C

CH3

N N

Cl

N Re

OC

CO CO

film

Journal Pre-proof 2 O

O

H3C

CH3

S

378, 331, 297 394, 297 416

735 730 630

12850 12610 8165

4.44 6.29 362.08

0.881 1.049 1.128

0.9 0.4 3.8

MeCN CHCl3 solid film

385, 285 425, 316 503, 406 412

743 744 667 621

12515 10090 4890 ––

3.63 4.99 63.70 ––

0.989 0.916 1.080 ––

0.3 0.4 1.8 ––

MeCN CHCl3 solid

369, 285 393, 317 462, 380, 265

666 657 580

12085 10225 4400

1.098 1.082 1.013

1.1 1.3 16.3

392

nd

––

2.14 3.86 67.87 (4.28%) 466.79 (95.72%) ––

––

––

MeCN CHCl3 solid film

398, 335, 303 401, 345, 257 495 416

703 702 620 nd

10900 10690 4070 ––

4.79 6.28 208.12 ––

1.062 1.057 1.060 ––

0.4 0.3 9.5 ––

MeCN CHCl3 solid

394, 295 418, 296 480, 371

725 719 666

11590 10015 5820

0.908 1.095 1.013

0.7 0.8 1.6

616

––

3.66 5.12 13.88 (18.94%) 119.95 (81.06%) ––

––

––

1.037

0.7

1.164

0.6

1.060

0.6

–– 1.083 1.037 1.128

–– 1.0 1.3 8.2

S

N Cl

N

MeCN CHCl3 solid

N Re

OC

CO CO

3 O

O H3C

CH3

N

N

N

N Cl

N Re

OC

CO

4 H3C

O O

O H3C

CH3

N N

Cl

film

N Re

OC

CO

H3C

O

O

O

H3C

CH3

S

S

N Cl

N

N Re CO

re

OC

H3C O O

O H3C

CH3

N

N

N

N Cl

film

N Re

CH3

O

O

CH3

MeCN

387, 303, 239

656

10595

CHCl3

399, 302, 260

654

10415

477, 326

633

5165

406 397, 369, 297 419, 328, 248 481

573 722 717 612

–– 11335 9920 4450

2.88 (48.14%) 7.13 (51.86%) 4.14 (89.72%) 30.36 (10.28%) 39.66 (48.33%) 137.77(51.67%) –– 4.79 6.99 216.54

413, 334, 292, 245 431, 337, 295 539, 388 432

734

10590

3.93

1.022

0.9

739 686 nd

9670 3975 ––

5.66 158.14 ––

1.032 1.233 ––

0.6 0.8 ––

solid

N N Cl

N Re

OC

CO CO

8 O

CH3

O

Cl

film MeCN CHCl3 solid

S

N N

CH3

na

7

S

410

CO CO

Jo ur

OC

lP

CO

6

-p

5

ro

CO

of

CO

N Re

OC

CO CO

MeCN

9 O

CH3

O

N

N N Cl

N N

Re OC

CO CO

CH3

CHCl3 solid film

The underlined wavelengths were taken to register the emission spectrum; nd- emission was not detected

The emission of 1–9 is dependent on the imine acceptor core demonstrating red-shift in the order dppy  dtpy  terpy for all three series 1–3, 4–6 and 7–9 (Table 3).

Journal Pre-proof Exemplarily, in the solid state, the emission maxima of 1, 2 and 3 appeared at 600, 630 and 667 nm, respectively. Solid-state emission of terpyridyl Re(I) complexes is also clearly modulated by the substitution pattern of methoxy groups and π conjugation of aryl group attached to the central pyridine. The red-shift follows the order 3,4,5-trimethoxy-1-phenyl (4, em=580 nm ) < 3,5-dimethoxy-1-phenyl (1, em=600 nm) < 4,7-dimethoxy-1-naphthyl (7, em=633 nm). Conversely, in solution, the emission maxima of terpyridyl Re(I) complexes (1, 4 and 7) appear in rather narrow range 654–672 nm, demonstrating little impact of substitution pattern of methoxy groups and π conjugation of the aryl group. Stronger substituent influence was

of

observed for Re(I) bearing dtpy- and dppy-based ligands. As shown in Table 3, the

occurs

in

higher

energy

region

in

ro

emission of Re(I) with dtpy/dppy substituted with 3,4,5-trimethoxy-1-phenyl (5 and 6) relation

to

those

with

attached

-p

3,5-dimethoxy-1-phenyl (2 and 3) and 4,7-dimethoxy-1-naphthyl (8 and 9). A hypsochromic shift of the emission after introduction of methoxy group at the para

re

position of the phenyl ring may imply MLCT character of the excited states for Re(I)

lP

complexes bearing triimine ligands with phenyl-based substituents (1–6). The electron-donating groups are expected to destabilize MLCT excited states, which is manifested in blue-shift of the emission band [86]. A red-shift reported for 8 and 9 with

na

4,7-dimethoxy-1-naphthyl can be attributed to the effect of extended π conjugation of

process.

Jo ur

naphthyl substituent and contribution of ILCT excited states in the deactivation

In solution, the Re(I) carbonyls are weakly emissive, with quantum yields below 1.3%. The photoluminescence lifetimes of 1–9 fall in the nanosecond time regime, which is characteristic of vast majority of rhenium(I) carbonyls with terpy-like ligands [74-79]. Larger values of

 have been reported for rhenium(I) carbonyls with

2,2′:6′,2″-terpyridine functionalized with carbazole and diphenylamine substituents [70]. In the powdered solid-state form, the quantum yield for 1–9 was found to be strongly structure-dependent, varying from 0.6% to 16.3 %. Particularly significant enhancement of the quantum yield was found for 4 (16.3 %) and 5 (9.5 %) in comparison to that of 1 (1.4 %) and 2 (3.8 %), while the solid state emission quantum yield of Re(I) bearing dppy-derivatives was only slightly affected by ligand modification (0.8-1.8 %). The data clearly indicate beneficial influence of the electron-donating methoxy group at the para position of the phenyl ring attached to the

Journal Pre-proof central pyridine ring of terpy and dtpy. Referring to the previously examined [ReCl(CO)3(4-R-terpy-κ2N)] (30.55 %) and [ReCl(CO)3(4-R-dtpy-κ2N)] (5.87 %) with 4-methoxy-1-phenyl substituent, however, different trends are observed for 4 and 5 complexes. While the emission quantum yield of terpyridyl Re(I) complex (4) decreases, the compound 5 shows an enhancement of photoluminescence, demonstrating that the substituent effect depends on the triimine core. A remarkably improved emission efficiency in solid state was also found for 8. Its emission quantum yield (8.2 %) was significantly higher in relation to [ReCl(CO)3(4-R-dtpy-κ2N)] with 4-methoxy-1-naphthyl (3.43 %) [78].

of

Additionally, the possibility of light emission induced by external voltage of

thin

films

were

applied

as

active

ro

prepared Re(I) complexes was tested. Compounds 3, 6 and 7, which exhibited PL as layers

in

a

diode

structure

-p

ITO/PEDOT:PSS/complex/Al. However, only device with 7 emitted light with maximum emission band (EL) located at 666 nm (cf. Fig. 5). In the next step, diodes

re

with guest-host configuration were fabricated. As matrix, a mixture of (PVK)

(50

wt

%)

and

lP

poly(9-vinylcarbazole)

(2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole) (PBD) (50 wt %) was utilized. Re(I) complexes 1, 3, 4–7 and 9 as luminophore with concentration of 2 wt% in the matrix

na

were dispersed. All diodes were emissive and emitted light with EL in the range of 594–630 nm. It was found that the devices with complexes bearing terpyridine skeleton

Jo ur

(1, 4 and 7) emitted light with EL bathochromically shifted compared to the others (cf. Table 4). The effect of substituent on the EL ability can be seen in the series of diodes with 1, 4 and 7. The highest EL intensity was found for the device with compound containing 3,5- dimetoxy-1-phenyl unit (1). However, the lowest turn-on voltage ws measured

for

the

diode

based

on

triimine

skeleton

substituted

with

3,4,5-trimethoxy-1-phenyl unit (4). Additionally, diodes with lower luminophore (6 and 7) content, that is, 1 wt % in the matrix, were prepared. It can be seen that together with reduction of compound content, significant increase of the EL intensity was observed (cf. Table 4)

Journal Pre-proof

200

16V

17V

18V

14V

150 640 nm

100

50

0 400

500

600

ITO/PEDOT:PSS/PVK:PBD:7 (2wt%)/Al

19V

Intensity [counts]

Intensity [counts]

900

ITO/PEDOT:PSS/7/Al

700

800

600

500

6000

700

800

900

ITO/PEDOT:PSS/PVK:PBD:7(1wt%)/Al

of

Intensity [counts]

5000

23V

4000

ro

590 nm

2000

500

600

700

800

Wavelength [nm]

900

3000 2000

-p

4000

re

Intensity [counts]

23V

0 400

600

Wavelength [nm]

ITO/PEDOT:PSS/PVK:PBD:7(1wt%)/Al

6000

18V

300

Wavelength [nm]

8000

17V

594 nm

0 400

900

15V

1000 0

0

10

20

30

40

Voltage [V]

lP

Figure 5. Electroluminescence spectra of the diodes based on Re(I) complex 7.

na

Table 4. Position of maximum of electroluminescence band (EL) obtained under external voltage (V) and its maximal reached EL intensity.

Jo ur

Code ITO/PEDOT:PSS/complex/Al

λEL [nm] (V)

Intensity [a.u]

–– –– 1 nd nd 3 –– –– 4 –– –– 5 nd nd 6 640 (19V) 150 7 –– –– 9 ––: not measured; nd: EL not detected

ITO/PEDOT:PSS/PVK:PBD:complex/Al content of complex in the matrix 2 wt% 1 wt% λEL [nm] (V) Intensity λEL [nm] Intensity [a.u] (V) [a.u] –– –– 605 (26V) 9055 –– –– 625 (10V) 1068 –– –– 594 (6V) 614 –– –– 630 (16V) 1505 625 (25V) 1913 615 (20V) 5233 594 (15V) 504 591 (23V) 5032 –– –– 630 (26V) 111

Electrochemistry To investigate the redox behavior and estimate HOMO/LUMO energy levels and band gap energy (Eg) of 1–9, cyclic voltammetry (CV) and differential pulse voltammetry

Journal Pre-proof (DPV) on a glassy carbon working electrode in CH2Cl2 with 0.1 M n-Bu4NPF6 as the supporting electrolyte were used. The potentials were referenced to the ferrocene/ferrocenium redox couple, and onsets of the first oxidation and reduction waves were used to estimate the values of IP and EA, which can be regarded as closely related to the HOMO and LUMO levels, respectively [87]. The electrochemical data are gathered in Table 5, while the CVs and DPVs are shown in Figure S30.

Table 5. Relevant electrochemical data.

-1.70 -1.49 -1.37 -1.88 -1.60 -1.39 -1.71 -1.60 -1.34

0.71 0.90 1.06 0.58 0.82 1.02 0.82 0.87 1.08

0.62 0.78 0.86 0.50 0.73 0.79 0.69 0.73 0.89

IP [eV]

Eg [eV]

of

-1.80 -1.60 -1.50 -1.99 -1.69 -1.48 -1.82 -1.70 -1.46

EA [eV]

-5.72 -5.88 -5.96 -5.60 -5.83 -5.89 -5.79 -5.83 -5.99

2.32 2.27 2.23 2.38 2.33 2.18 2.40 2.33 2.35

-3.40 -3.61 -3.73 -3.22 -3.50 -3.71 -3.39 -3.50 -3.64

ro

1 2 3 4 5 6 7 8 9

Ered1(onset) Eox1(onset) E ox1 [V] [V] [V]

-p

Ered1 [V]

re

Code

lP

IP = -5,1 - Eox1(onset), EA = -5,1 - Ered1(onset), Eg = Eutl(onset) - Ered(onset). Solution: CH2Cl2, concentration: 10-3 mol/L, electrolyte: 0.1M Bu4NPF6. GC as working electrode.

na

Consistent with the theoretical studies, the LUMO of these systems is predominately localized on the triimine core, thus the first wave, reversible (2) or quasi-reversible (1,

Jo ur

3-9), can be assigned to triimine-centered reduction process. Introduction of an additional N- or S-donor atom into the -deficient trisheterocyclic unit of dtpy and dppy leads to increase of -acceptor properties of dtpy and dppy ligands and stabilization of the LUMO orbital Re(I) complexes bearing 2,6-di(thiazol-2-yl)pyridine and 2,6-di(pyrazin-2-yl)pyridine derivatives, relative to those with 2,2′:6′,2′′-terpyridines, which is reflected in occurring the first reduction peak at less negative potentials in the order terpy  dtpy  dppy. The first oxidation potentials of 1–9, assigned to the ReI/ReII couple, were slightly sensitive to the type of the triimine skeleton. For all three series 1–3, 4–6 and 7–9, the easiest to oxidize were the Re(I) complexes with the 2,2′:6′,2′′-terpyridine ligands, while those bearing with 2,6-di(pyrazin-2-yl)pyridines showed the highest values of Eox1. A small variation of the oxidation potential can be also correlated with the substitution pattern of phenyl ring. Introduction of the methoxy group into the para

Journal Pre-proof position resulted in slightly decreased first oxidation potential of 4–6 relative to corresponding 1–3.

Conclusions Concluding the results obtained in the context of impact of both the chemical structure of the triimine skeleton and the substituent: 

all synthesized complexes showed high enough values of Tm, which is necessary for applications in optoelectronic devices;



Re(I) complexes of 2,2′:6′,2′′-terpyridines (terpy) functionalized with

of

2,6-di(pyrazin-2-yl)pyridine

substituted

with

ro

carbonyl

of

3,5-dimethoxy-1-phenyl (1) and 4,7-dimethoxy-1-naphthyl (7) units and Re(I)

3,5-dimethoxy-1-phenyl group (3) formed amorphous material with high Tg; replacement of terpy core by dtpy and dppy resulted in bathochromic shift of the

-p



series 1–3, 4–6 and 7–9;

methoxy substituent pattern had weaker impact on the location of the

lP



re

low-energy absorption bands and emission maxima in solution for all three

longest-wavelength absorption and emission in solution than π conjugation of the attached aryl group;

in film, upon excitation into the lowest-energy absorption band, only the Re(I) complexes

of

na



2,6-di(pyrazin-2-yl)pyridines

(dppy)

substituted

with

Jo ur

3,5-dimethoxy-1-phenyl (3) and 3,4,5-trimethoxy-1-phenyl (6) and the Re(I) carbonyl of 2,2′:6′,2′′-terpyridine with 4,7-dimethoxy-1-naphthyl (7) were emissive and emitted light with the em in the range of 573–621 nm. Among them only 7 was applied as an active layer in a diode, and exhibited weak electroluminescence. On the other hand, all the devices with Re(I) complexes dispersed molecularly in a matrix emitted light under external voltage.

Experimental section Materials Re(CO)5Cl and poly(9-vinylcarbazole) PVK (Mn= 25000–50000) were commercially available (Sigma Aldrich) and they were used without further purification. Poly(3,4-(ethylenedioxy)thiophene): poly-(styrenesulfonate) (PEDOT:PSS) (0.1–1.0 S/cm) and substrates with pixilated ITO anodes were supplied by Ossila. All solvents

Journal Pre-proof for synthesis were of reagent grade, while HPLC grade solvents were used for spectroscopy studies. The ligands L1–L9 were synthesized following the methodology based on condensation of 2-acetylpyridine (L1, L4, L7), 2-acetylthiazole (L2, L5, L8) and 2-acetylpyrazine (L3, L6, L9) with 3,5-dimethoxybenzaldehyde (L1-L3), 3,4,5-trimethoxy-1-naphthaldehyde (L4-L6) and 4,8-dimethoxy-2-naphthaldehyde (L7-L9) [75, 78, 79]. Preparations of [ReCl(CO)3(Ln-κ2N)] complexes (1–9) The precursor [Re(CO)5Cl (0.10 g, 0.27 mmol) and molar equivalent of the corresponding Ln ligand (0.27 mmol) were dissolved in argon-saturated acetonitrile (1,

of

2, 4, 5, 6, 7, 9) or toluene (3, 8) (50 mL) and heated under reflux for 8h. The resulting

ro

yellow (1, 4, 5, 7), red (3) or orange (2, 6, 9, 8) solid was collected by filtration, washed with diethyl ether and dried.

-p

[ReCl(CO)3(L1)] (1): Yield: 65 %. IR (KBr, cm-1): 2021(vs), 1914(vs) and 1890(vs) ν(C≡O); 1606 (m), 1541 (m) ν(C=N) and ν(C=C). 1H NMR (400 MHz, DMSO) δ 9.11

re

(d, J = 8.2 Hz, 1H, HC4), 9.07 (d, J = 5.2 Hz, 1H, HC1), 9.04 (s, 1H, HB4), 8.81 (d, J = 4.3 Hz, 1H, HA1), 8.39 (t, J = 7.8 Hz, 1H, HC3), 8.22 (s, 1H, HB2), 8.07 (t, J = 7.1 Hz, 1H,

lP

HA3), 7.91 (d, J = 7.7 Hz, 1H, HA4), 7.81 – 7.76 (m, 1H, HC2), 7.66 – 7.61 (m, 1H, HA2), 7.31 (d, J = 2.1 Hz, 2H, HD2), 6.74 (t, J = 2.0 Hz, 1H, HD4), 3.89 (s, 6H, HD5).13C NMR

na

(100 MHz, DMSO) δ 197.81 (CCO), 194.41 (CCO), 190.94 (CCO), 161.40 (CB1), 161.23 (CD3), 157.84 (CA5), 157.03 (CB5), 156.22 (CC5), 152.69 (CC1), 150.74 (CD1), 149.21

Jo ur

(CA1), 139.93 (CC3), 136.98 (CB3), 136.93 (CA3), 127.49 (CC2), 125.60 (CA4), 125.20 (CC4), 124.94 (CA2), 124.73 (CB2), 120.98 (CB4), 105.94 (CD2), 102.79 (CD4), 55.68 (CD5). HR-MS (ESI): calcd. for C26H19N3O5Re [M-Cl]+ 640.0884, found 640.0878. Anal. Calcd. for C26H19O5N3ClRe (675.11 g/mol): C, 46.26; H, 2.84; N, 6.22 %; found: C, 46.38; H, 2.98; N, 6.31 %. DSC: I heating scan: Tm=297 C, II heating scan Tg=173 C, Tc=266 C, Tm= 290 C. [ReCl(CO)3(L2)] (2): Yield: 60%. IR (KBr, cm-1): 2019 (vs), 1907(vs) ν(C≡O); 1606 (m), 1537 (m) ν(C=N) and ν(C=C). 1H NMR (400 MHz, Acetone) δ 8.79 (s, 1H), 8.36 (d, J = 2.8 Hz, 1H), 8.29 – 8.23 (m, 2H), 8.13 (d, J = 2.6 Hz, 1H), 8.07 (d, J = 2.5 Hz, 1H), 7.25 (s, 2H), 6.72 (s, 1H), 3.90 (s, 6H). 13C NMR not recorded due to insufficient complex solubility. HR-MS (ESI): calcd. for C22H15ClN3NaO5ReS2 [M+Na]+ 709.9580, found 709.9583. Anal. Calcd. for C22H15O5N3ClReS2 (687.15 g/mol): C, 38.4; H, 2.20; N 6.12%; found C, 38.52; H, 2.55; N, 6.06 %.

Journal Pre-proof [ReCl(CO)3(L3)] ∙ C6H5CH3, (3∙ C6H5CH3): Yield: 70%. IR (KBr, cm-1): 2029(vs), 1933(vs) and 1909(vs) ν(C≡O); 1603 (m), 1594 (m) ν(C=N) and ν(C=C). 1H NMR (400 MHz, DMSO) δ 10.37 (d, J = 0.9 Hz, 1H), 9.28 (d, J = 1.8 Hz, 1H), 9.15 (d, J = 1.2 Hz, 1H), 9.14 (dd, J = 3.1, 1.1 Hz, 1H), 8.99 (d, J = 3.1 Hz, 1H), 8.94 – 8.92 (m, 2H), 8.46 (d, J = 1.8 Hz, 1H), 7.37 (d, J = 2.2 Hz, 2H), 6.75 (t, J = 2.1 Hz, 1H), 3.89 (s, 6H). 13

C NMR (100 MHz, DMSO) δ 196.55, 194.55, 189.49, 161.27, 158.70, 155.41,

153.51, 150.95, 150.91, 147.93, 147.20, 145.85, 145.79, 145.33, 144.07, 136.43, 125.80, 121.95, 106.05, 103.10, 55.70. HR-MS (ESI): calcd. for C24H17ClN5NaO5Re [M+Na]+ 700.0360, found 700.0363. Anal. Calcd. for C25H18O5N5ClRe (690.11

ro

heating scan: Tm=258 C, II heating scan Tg=164 C.

of

g/mol): C, 43.51; H, 2.63; N, 10.15 %; found: C, 43.43; H, 2.81; N, 10.18 %. DSC: I [ReCl(CO)3(L4)] (4): Yield: 70%.IR (KBr, cm-1): 2023(vs), 1944(vs) and 1864 (vs)

-p

ν(C≡O); 1611 (m), 1587 (m) ν(C=N) and ν(C=C). 1H NMR (400 MHz, DMSO) δ 9.09 – 9.03 (m, 2H, HC1+C4), 9.00 (s, 1H, HB4), 8.80 (d, J = 4.2 Hz, 1H, HA1), 8.40 (t, J = 7.6

re

Hz, 1H, HC3), 8.23 (s, 1H, HB2), 8.06 (t, J = 6.3 Hz, 1H, HA3), 7.88 (d, J = 7.4 Hz, 1H, HA4), 7.79 (t, J = 6.4 Hz, 1H, HC2), 7.66 – 7.61 (m, 1H, HA2), 7.40 (s, 2H, HD2), 3.95 (s, 13

C NMR (100 MHz, DMSO) δ 197.82 (CCO), 194.41

lP

6H, HD5), 3.76 (s, 3H, HD6).

(CCO), 190.98 (CCO), 161.31 (CB1), 157.97 (CA5), 156.84 (CB5), 156.27 (CC5), 153.58

na

(CD3), 152.71 (CC1), 150.89 (CD1), 149.23 (CA1), 139.90 (CC3), 136.94 (CA3), 130.47 (CB3), 127.47 (CC2), 125.51 (CC4), 125.19 (CA4), 124.92 (CA2), 124.51 (CB2), 120.89

Jo ur

(CB4), 105.70 (CD2), 60.21 (CD6), 56.44 (CD5). HRMS (ESI): calcd. for C27H22N3O6Re [M+H]+ 706.0741; found: 706.0742. Anal. Calcd. for C27H21O6N3ClRe (705.14 g/mol): C, 45.99; H, 3.00; N, 5.96 %; found: C, 46.07; H, 3.16; N, 6.07 %. DSC: I heating scan: Tm=322 C with degradation.

[ReCl(CO)3(L5)] (5): Yield: 60%. IR (KBr, cm-1): 2019(vs), 1920(vs) and 1910(vs) ν(C≡O); 1612 (m), 1589 (m) ν(C=N) and ν(C=C). 1H NMR (400 MHz, DMSO) δ 9.23 (s, 1H), 8.80 (d, J=3.1 Hz 1H), 8.72 (s, 1H), 8.69 (d, J = 3.0 Hz, 1H), 8.58 (d, J = 2.7 Hz, 1H), 8.51 (d, J = 3.0 Hz, 1H), 7.90 (s, 2H), 4.41 (s, 6H), 4.28 (s, 3H). 13C NMR not recorded due to insufficient complex solubility. HR-MS (ESI): calcd. for C23H17ClN3NaO6ReS2 [M+Na]+ 739.9686, found 739.9699. Anal. Calcd. for C23H17O6N3ClReS2 (717.18 g/mol): C, 38.52; H, 2.39; N, 5.86 %; found: C, 38.39; H, 2.72; N, 5.88. DSC: I heating scan: Tm=325 C with degradation.

Journal Pre-proof [ReCl(CO)3(L6)].H2O (6.H2O): Yield: 70%. IR (KBr, cm-1): 2026(vs), 1956(vs) and 1898(vs) ν(C≡O); 1608 (m), 1585 (m) ν(C=N) and ν(C=C). 1H NMR (400 MHz, DMSO) δ 10.34 (s, 1H), 9.23 (d, J = 0.7 Hz, 1H), 9.15 – 9.13 (m, 2H), 8.99 (d, J = 3.0 Hz, 1H), 8.94 – 8.92 (m, 2H), 8.45 (d, J = 1.7 Hz, 1H), 7.46 (s, 2H), 3.95 (s, 6H), 3.77 (s, 3H).

13

C NMR (100 MHz, DMSO) δ 196.58, 194.58, 189.56, 158.61, 155.26,

153.63, 151.10, 150.98, 147.93, 147.13, 145.91, 145.82, 145.34, 144.14, 140.21, 129.89, 125.54, 121.77, 105.82, 60.25, 56.49. HR-MS (ESI): calcd. for C25H19ClN5NaO6Re [M+Na]+ 730.0465, found 730.0466. Anal. Calcd. for C25H21O7N5ClRe (725.13 g/mol): C, 42.46; H, 2.71; N, 9.90 %; found: C, 41.41; H,

of

2.92; N, 9.66 %. DSC: I heating scan: Tm=281 C with degradation. [ReCl(CO)3(L7)] (7.CH3CN.H2O): Yield: 70%. IR (KBr, cm-1): 2020(vs), 1919(vs)

ro

and 1880(vs) ν(C≡O); 1622(m), 1606 (m), 1582 (m) ν(C=N) and ν(C=C). 1H NMR

-p

(400 MHz, DMSO) δ 9.08 (d, J = 5.2 Hz, 1H, HC1), 9.00 (s, 1H, HB4), 8.97 (d, J = 8.2 Hz, 1H, HC4), 8.78 (d, J = 4.6 Hz, 1H, HA1), 8.35 – 8.30 (m, 1H, HC3), 8.23 (d, J = 9.1

re

Hz, 1H, HD6), 8.05 (dt, J = 7.7, 0.7 Hz, 1H, HA3), 7.98 (s, 1H, HB2), 7.93 (d, J = 7.8 Hz, 1H, HA4), 7.79 – 7.73 (m, 2H, HC2+D2), 7.63 – 7.59 (m, 1H, HA2), 7.31 – 7.26 (m, 2H,

lP

HD7+D9), 7.04 (d, J = 8.2 Hz, 1H, HD3), 4.04 (s, 3H, HD11), 3.76 (s, 3H, HD12). 13C NMR (100 MHz, DMSO) δ 197.73 (CCO), 194.51 (CCO), 191.06 (CCO), 161.12 (CB1), 158.61

na

(CD8), 157.72 (CA5), 156.74 (CB5), 156.59 (CD4), 156.39 (CC5), 152.72 (CD1), 151.94 (CC1), 149.28 (CA1), 140.02 (CC3), 136.87 (CA3), 132.30 (CD10), 129.93 (CD2), 127.84

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(CB2), 127.37 (CC2), 125.75 (CC4), 125.31 (CA4), 125.13 (CA2), 124.91 (CB3), 124.27 (CD6), 124.11 (CB4), 120.07 (CD5), 117.42 (CD7), 103.66 (CD9), 102.57 (CD3), 55.92 (CD11), 55.08 (CD12). HR-MS (ESI): calcd. for C30H22ClN3O5Re [M+H]+ 726.0792, found 726.0799. Anal. Calcd. for C32H26O6N4ClRe (784.23 g/mol): C, 49.01; H, 3.34; N, 7.14 %; found: C, 49.34; H, 3.48; N, 7.12 %. DSC: I heating scan: Tm= 198 C, II heating scan Tg=158 C. [ReCl(CO)3(L8)]∙½ C6H5CH3 (8∙½C6H5CH3): Yield: 70%. IR (KBr, cm-1): 2023(vs), 1924(vs) and 1898(vs) ν(C≡O); 1618 (m), 1609 (m), 1584 (m) ν(C=N) and ν(C=C) 1H NMR (400 MHz, Acetone) δ 8.73 (s, 1H), 8.38 (d, J = 3.3 Hz, 1H), 8.29 (d, J = 9.2 Hz, 1H), 8.25 (d, J = 3.3 Hz, 1H), 8.15 – 8.11 (m, 2H), 8.06 (d, J = 3.2 Hz, 1H), 7.77 (d, J = 8.1 Hz, 1H), 7.44 (d, J = 2.4 Hz, 1H), 7.26 – 7.25 (m, 1H), 7.04 (d, J = 8.1 Hz, 1H), 4.10 (s, 3H), 3.83 (s, 3H).

13

C NMR not recorded due to insufficient complex solubility.

HR-MS (ESI): calcd. for C26H17ClN3NaO5ReS2 [M+Na]+ 759.9737, found 759.9741.

Journal Pre-proof Anal. Calcd. for C26H19O5N3ClRe (675.11 g/mol): C, 46.26; H, 2.84; N, 6.22 %; found: C, 46.38; H, 2.98; N, 6.31 %. [ReCl(CO)3(L9)].CHCl3 (9): Yield: 65%. IR (KBr, cm-1): 2023(vs), 1920(vs) and 1893(vs) ν(C≡O); 1622 (m), 1608 (m), 1574 (m) ν(C=N) and ν(C=C). 1H NMR (400 MHz, DMSO) δ 10.24 (s, 1H), 9.28 (d, J = 1.2 Hz, 1H), 9.16 (s, 1H), 9.15 (d, J = 2.9 Hz, 1H), 8.97 (d, J = 3.0 Hz, 1H), 8.90 (s, 2H), 8.26-8.21 (m, 2H), 7.80 (d, J = 8.1 Hz, 1H), 7.36 (d, J = 2.3 Hz, 1H), 7.29 (dd, J = 9.2, 2.4 Hz, 1H), 7.07 (d, J = 8.2 Hz, 1H), 4.05 (s, 3H), 3.78 (s, 3H).

13

C NMR (100 MHz, DMSO) δ 196.50, 194.59, 189.63,158.76,

158.48, 156.85, 155.15, 153.45, 152.36, 151.16, 147.83, 146.99, 145.88, 145.78,

of

145.36, 144.13, 132.27, 130.44, 128.96, 125.37,125.28, 124.13, 120.06, 117.56,

ro

103.72, 102.66, 55.99, 55.16. HR-MS (ESI): calcd. for C28H19ClN5NaO5Re [M+Na]+ 750.0516, found 750.0508. Anal. Calcd. for C29H20O5N5Cl4Re (846.52 g/mol) calcd.

-p

41.15; H, 2.38; N, 8.27 %; found: C, 41.87; H, 2.62; N, 8.50 %. DSC: I heating scan:

re

Tm=233 C, Tc=244 C, Tm= 287 C with degradation. Crystal structure determination and refinement

lP

X-ray quality crystals of 5, 7 and 9 were obtained by recrystallization from mixture of acetonitrile/chloroform. The X-ray intensity data of 5, 7 and 9 were collected on a

na

Gemini A Ultra diffractometer equipped with Atlas CCD detector and graphite monochromated MoKα radiation (λ= 0.71073 Å) at room temperature. The unit cell

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determination and data integration were carried out using the CrysAlis package of Oxford Diffraction, and Lorentz polarization and empirical absorption correction were applied [88]. The structures were solved by the Patterson method using SHELXS-2014 and refined with SHELXL-2014 using full-matrix least-squares on F2 [89]. All the non-hydrogen atoms were refined anisotropically, and hydrogen atoms were placed in calculated positions refined using idealized geometries (riding model) and assigned fixed isotropic displacement parameters, d(C–H) = 0.93 Å, Uiso(H) = 1.2 Ueq(C) (for aromatic) and d(C–H) = 0.96 Å, Uiso(H) = 1.5 Ueq(C) (for methyl). The methyl groups were allowed to rotate about their local threefold axis. The crystallographic data of 5, 7 and 9 are summarized in Table S1 in ESI. CCDC- 1974623 (5), 1974625 (7) and 1974624 (9) contains the supplementary crystallographic data. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Journal Pre-proof Physical measurements The IR spectra were recorded with a Nicolet iS5 FTIR spectrophotometer in the spectral range 4000–400 cm–1 with the samples in the form of KBr pellets. The electronic spectra were measured using ThermoScientific Evolution 220 UV/Vis Spectrometer (in MeCN and CHCl3 solution) and Jasco V570

UV-V-NIR

Spectrometer (in solid state as film deposited on a glass substrate). The 1H NMR and 13

C NMR spectra were recorded (295 K) on Bruker Avance 400 NMR spectrometer at a

resonance frequency of 400 MHz for 1H NMR spectra and 100 MHz for

13

C NMR

spectra using DMSO-d6 or acetone-d6 as solvent. The HRMS measurements were

of

performed using Q-TOF MaXis Impact Bruker mass spectrometer equipped with an

ro

electrospray (ESI) ion source and q-TOF type mass analyzer. The recorded data were processed using Data Analylis 4.1 software package. The analyzed samples were

-p

dissolved in a mixture of MeCN CHCl3 (1/1). Elemental analysis was registered by Vario EL Cube (Elemental company) using acetanilide as a standard. Steady-state

re

luminescence spectra of solid state and solution samples were measured with FLS-980 fluorescence spectrophotometer equipped with a 450 W Xe lamp and high gain

lP

photomultiplier PMT+250nm (Hamamatsu, R928P) detector. The PL lifetime measurement was performed with a time correlated single photon counting (TCSPC) or

na

multi-channel scaling (MCS) method. Excitation wavelength (375 nm, 410 nm) for TCSPC was obtained using the TCSPC diode with various pulse periods as light

Jo ur

source. For MCS excitation wavelength was obtained using 60W microsecond Xe flash lamp. Differential Scanning Calorimetry (DSC) was performed with a TA-DSC 2010 apparatus, under nitrogen atmosphere using sealed aluminum pans with heating rate 20 °C/min. Electrochemical measurements were performed with Eco Chemie Autolab PGSTAT128n potentiostat device. The measurements were investigated in dichloromethane (Sigma-Aldrich, 99.8%) solution (c = 10-3 mol/L) using glassy carbon electrode (diam. 2.0 mm) as a working electrode with 0.1M Bu4NPF6 (Sigma-Aldrich, 99%) as a electrolyte. The platinum coil and silver wire as auxiliary and reference electrode were used. Cyclic voltammetry (CV) were recorded with moderate scan rate equal to 0.1 V/s and differential pulse voltammetry (DPV) with moderate scan rate equal to 0.01 V/s. The solution was purged with argon for about 10 min before every measurement. All potentials were referenced with respect to ferrocene couple (Fc/Fc+) which was used as the internal standard. The IP of Fc/Fc+

Journal Pre-proof was calculated to be equal to -5.1 eV as shown in literature data [86]. All measurements were performed at 25 ± 1 ˚C. Photoluminescence spectra in solid state as films deposited on a glass substrate and as blends with PVK:PBD were registered using Hitachi F-2500 spectrometer. In order to collect electroluminescence (EL) spectra the voltage was applied using a precise voltage supply (GwInstek PSP-405) and the sample was fixed to an XYZ stage. Light from the OLED device was collected through a 30 mm lens, focused on the entrance slit (50 μm) of a monochromator (Shamrock SR-303i) and detected using a CCD detector (Andor iDus 12305). Typical acquisition times were equal to 10 seconds. The

of

pre-alignment of the setup was done using a 405 nm laser.

ro

Computational details

-p

The calculations were performed using the GAUSSIAN-16 program package [90]. The geometries of the singlet ground state (S0) of 1–9 were fully optimized without any

re

symmetry restrictions at the DFT level with the PBE1PBE hybrid exchange-correlation functional [91-92]. The calculations were performed using def2-TZVPD basis set for

lP

rhenium and 6-31g* for carbon, 6-31g for hydrogen and 6-31g** basis set for other elements (Cl, N, O) [93-97]. The starting point for geometry optimization was taken

na

from the X-ray structure, and all the subsequent calculations were performed based on the optimized geometries. To verify that each of the geometries is a minimum on the

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potential energy surface, vibrational frequencies were calculated on the basis of the optimized geometry. Polarized continuum model (PCM) was employed to recreate media effects in acetonitrile and chloroform (MeCN and CHCl3) [98-100]. The predicted bond lengths and angles for the ground state are within the range of error expected for DFT calculations of rhenium(I) complexes, and the general trends observed in the experimental data are well reproduced in the calculations, providing confidence on the reliability of the chosen method to reproduce the geometry of studied complexes (Table S2).

Acknowledgments The research was co-financed by National Science Centre of Poland grants no. DEC2017/25/B/ST5/01611 and 2017/27/B/ST3/02457. Magdalena Małecka thanks to „PIK”- program for facilitating scientific self-development for PhD students,

Journal Pre-proof co-financed by the European Union. The calculations were carried out in Wroclaw Centre for Networking and Supercomputing (http://www.wcss.wroc.pl). Authors thank dr. Henryk Janeczek for DSC measurements.

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Author Contribution:

Magdalena Małecka recorded NMR and IR spectra, took part into the studies concerning electronic absorption and emission spectroscopy in solution and in solid as powder as well as participated in the discussion of the optical properties. She also carried out part of DFT computations and participated in the discussion of the correlation between computation results and optical properties.

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Anna Świtlicka carried out the synthesis of rhenium(I) complexes and performed the X-Ray measurements.

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Grażyna Szafraniec-Gorol - synthesized 2,2′:6′,2′′-terpyridine, 2,6-di(thiazol-2-yl)pyridines and 2,6-di(pyrazin-2-yl)pyridine ligands.

na

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Sonia Kotowicz - carried out the electrochemical measurements and discussed the electrochemical properties of the Re(I) carbonyl complexes, as well as she took part into the studies concerning electronic absorption and emission spectroscopy in solution and in solid as powder.

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Mariola Siwy prepared the film and blend from complexes, registered their UV-vis and PL spectra, as well as fabricated diodes for EL measurements and recorded EL spectra

Marcin Szalkowski and Sebastian Madkowski are responsible for electroluminescence studies.

Ewa Schab-Balcerzak designed as well as discussed the results from UV-Vis, PL and EL measurements of the synthesized ligands and complexes in solid state as film and blend.

Barbara Machura designed as well as discussed the results from X-Ray analysis and investigations of optical properties of solution and solid state.

Barbara Machura and Ewa Schab-Balcerzak co-produced the manuscript.

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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.

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☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Highlights

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Graphical abstract

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Series of Re(I) carbonyls complexes with terpy-like ligands were investigated. Their photophysical properties were explored by carrying out absorption and emission studies Impact of the triimine core and aryl substituent decorated with methoxy groups was discussed. The capacity of the obtained Re(I) complexes for electroluminescence was tested.