A new donor-acceptor crosslinkable l-shape chromophore for NLO applications

Accepted Manuscript A new donor-acceptor crosslinkable l-Shape chromophore for NLO applications

Barbara Panunzi, Rosita Diana, Angela Tuzi, Antonio Carella, Ugo Caruso PII:

S0022-2860(19)30405-3

DOI:

10.1016/j.molstruc.2019.04.016

Reference:

MOLSTR 26388

To appear in:

Journal of Molecular Structure

Received Date:

21 February 2019

Accepted Date:

02 April 2019

Please cite this article as: Barbara Panunzi, Rosita Diana, Angela Tuzi, Antonio Carella, Ugo Caruso, A new donor-acceptor crosslinkable l-Shape chromophore for NLO applications, Journal of Molecular Structure (2019), doi: 10.1016/j.molstruc.2019.04.016

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ACCEPTED MANUSCRIPT A NEW DONOR-ACCEPTOR CROSSLINKABLE L-SHAPE CHROMOPHORE FOR NLO APPLICATIONS

Barbara Panunzi 1, Rosita Diana 1* Angela Tuzi 2, Antonio Carella 2, Ugo Caruso 2* 1 2

Department of Agriculture, University of Napoli Federico II, Portici NA, Italy Department of Chemical Sciences, University of Napoli Federico II, Napoli, Italy

* Correspondence: [email protected]; [email protected]; Tel.: +39 081 674366

Keywords: L-Shape, crosslinkable, NLO Chromophore

Abstract A new nonlinear-optical (NLO) chromophore containing L-Shape 2-benzofuranyldiazene in πelectron bridge has been synthetized and its chemical and thermal properties examined. Evaluation of the second order NLO properties was performed by EFISH measurements of μβ on chloroform solution and by SHG measurements on amorphous spin-coated thin films obtained from a blend of polymer and chromophores crosslinked “in situ”. The value of 830∙10-48 esu for  measured on the dye and of 10 pm/V for the d33 for the poled network are in medium range for similar systems, confirming the proper employ of the molecule to build NLO active networks. The crystal structures dye and its precursor examined by single-crystal analysis show a planar geometry and bond lengths pattern confirm the push pull L-shape nature of the D-π-A systems.

1. Introduction Organic Donor-Acceptor push–pull -conjugated systems (D--A) represent a fascinating class of materials in which the formation of a new molecular orbital due to the direct interaction of D and A group through the -system generates an intramolecular charge transfer (ICT). The ICT produces a dipolar character in D--A molecules which in turn causes a relevant activity in the optical properties. Historically most of organic D--A were chromophores used as synthetic dyestuffs [1, 2] and more recently [3] as media for nonlinear optics (NLO).

ACCEPTED MANUSCRIPT To date, due to their unique optical properties, organic D--A molecules have been utilized in dyesensitized solar cells (DSSCs)[4-8], bulk-heterojunction solar cells (BHJSCs) [9-12], organic lightemitting diodes (OLEDs)[13], two-photon absorbers (2PAs) [14, 15], near-infrared absorbing dyes[16, 17] and biological activities[18]. At the same time, new molecules that possess interesting nonlinear optical properties have been a major point of interest in the recent years [19-21]. Therefore, the overall interest toward D--A systems led to more elaborated architectures. In addition to the ordinary linear push-pull systems new advanced quadrupolar and tripodal arrangements chromophores have been adopted [22]. New extraordinary -conjugated structures of remarkable visual impact inspired by letters of the alphabet appeared quite recently in the literature [23]. The theoretical investigation of the conjugation pattern and consequently the different electronic arrangements can allow to predict dipole moment and optical properties of compounds. As for NLO behaviour, the charge transfer (CT) resulting in the molecule and first hyperpolarizabilities (β) can result enormously affected and even improved by the different geometry. At present one of the major problems encountered in optimizing organic NLO materials is the efficient translation of the large microscopic nonlinearity β into high macroscopic electrooptic coefficient d33 of the polymeric material. In fact, the strong intermolecular electrostatic dipole– dipole interactions of the dyes make the electric field poling-induced noncentro-symmetric alignment of chromophore moieties [24-26] a challenging task. In recent years, researchers reported novel NLO systems realized by adding different shaped NLO chromophores to the classical D--A linear groups which can decrease the electrostatic interactions and achieve bigger electrooptic coefficients. Due to the contribution of the normal tensorial components L-shape chromophores show different electronic trade-off compared to classical onedimensional dipolar chromophores, and different ICT [27]. Based on this site-isolation principle, various structures of chromophores. This effect in some case promotes NLO activity owing to the lower excited energy and stronger oscillator strength for the main excited state [28]. In order to realize a L-shape CT chromophore a central heterocyclic moiety can be conveniently used as -linker to achieve the proper orientation of D/A groups. In particular, a five-membered conjugated heterocycle within π-conjugated moieties can improve several characteristics such as liquid crystal [29], luminescence [30-32] and NLO activity [31, 33, 34]. This leads to the employ of this kind of chromophores in the application area of photoactive devices, in particular for non-linear optics [35-37]. By employing the appropriate synthetic pattern, it can be obtained a twodimensional NLO dye which can be used in combination with other conventional NLO chromophores [31] to break the dipolar coupling in the final material.

ACCEPTED MANUSCRIPT

Scheme 1. Synthetic route to the target compound L-BZO (L-shape is red highlighted)

In the present work, a new chromophore L-BZO was obtained by diazotation of a substituted 2aminobenzofurane with a substituted aniline (see Scheme 1). Depending on the orientation of the N,N-diethanolamino donor and nitrophenyl acceptor on the furan moiety, the push-pull pattern of L-BZO was tailored in L-shape. The molecule has an “half-cruciform” D-π-A pattern and has three

ACCEPTED MANUSCRIPT alcoholic functions suitable for cross-linking. First hyperpolarizability of the chromophore was determined and the effect of the L-shape dye co-crosslinked with a known NLO active thiophenebased trifunctional molecule (CTriox) on the EFISH response was studied on the final poled network L-NET. Single-crystal X-ray analysis of L-BZO dye and its precursor L’-BZO clarified structural and mechanistic aspects.

ACCEPTED MANUSCRIPT Scheme 2. Preparation of L-NET

2. Experimental All

starting

products

were

commercially

available.

Butyl

2-amino-5-hydroxy-4-(4-

nitrophenyl)benzofuran-3-carboxylate was obtained as described in literature [38]. Polyglicidyl methacrylate (PGMA) was obtained by a typical radical polyaddition in DMF at 70 °C with AIBN as initiator [39]. Optical observations were performed by using a Zeiss Axioscope polarizing microscope equipped with a FP90 Mettler heating stage. Phase transition temperatures and enthalpies were measured using a DSC scanning calorimeter Perkin Elmer Pyris 1 at a scanning rate of 10 °C/min, under nitrogen flow. The decomposition temperature (Td), assumed as the temperature where is recorded the 5wt. % weight loss, was determined by thermogravimetric analysis under nitrogen flow, using a Perkin Elmer TGA 4000. 1H NMR spectra were recorded with Bruker 200MHz apparatus. UVVisible spectra were recorded with JASCO spectrometer Jasco F-530 (scan rate 200 nm min-1).

2.1. Synthesis of precursor L’-BZO To a solution of butyl 2-amino-5-hydroxy-4-(4-nitrophenyl)benzofuran-3-carboxylate (1.00 g, 2.70 mmol) in 40 mL of ethanol an aqueous solution of HCl (32ml at 6%) was added dropwise at 0°C. After 10 min, 0.44 g of sodium nitrite (5.20 mmol) dissolved in 10 mL of water was added under stirring and the mixture kept at 0°C for 30 min. Another solution was prepared by dissolving 4.89 g (2.70 mmol) of 2,2'-(phenylazanediyl)bis(ethan-1-ol) in 40 mL of ethanol and 2 mL of 37% HCl solution and cooled at -4°C. By addition in portions of the first suspension to the second solution the colour turned from brown to brick red and finally to violet red. After 1.5 h at 0°C under stirring the solution was poured into 800 mL of water containing about 5 g of sodium acetate, the precipitation of a dark violet solid ensuing. The solid was recovered by filtration, washed twice with water and purified on a silica gel column employing chloroform/acetone (8:2) as eluent. The violet red solid obtained collecting the last fractions from column and removing the solvent was recrystallized in acetone/heptane in dark red needle-shape crystals. Yield 45%. Mp: 171°C, Tdec=340°C. 1H NMR (Acetone; 200 MHz) : 0.86 (t, 3H, J=7.2), 1.40 (m, 4H), 2.06 (m, 2H), 3.80 (m, 8H), 4.21 (t, 2H), 6.94 (d, 2H, J=9.2), 7.20 (d, 1H, J=9.4), 7.53 (d, 1 H, J=8.8), 7.72 (d, 2H,

ACCEPTED MANUSCRIPT J=8.8), 7.80 (d, 2H, J=9.4), 8.33 (d, 2H, J=8.8), 8.60 (s, 1H). Anal Calc for C29H30N4O8: N, 7.54; C, 58.24; H, 5.70. Found: N, 7.46; C,58.28; H,5.45%

2.2. Synthesis of L-BZO In a two necks flask 1.0 g (1.79 mmol) of L’-BZO was dissolved in 20 mL of THF and 15 g of potassium carbonate was added and finally 1.25 mL (18 mmol) of bromo ethanol. The mixture was kept at reflux under stirring for 8 h, after this time other 1.25 mL of bromo ethanol were added from the side neck and the reaction proceed for still other 16 h. The suspension was hence cooled and filtered in vacuo. From the solution reduced to about a quarter of volume and poured into water/ice, a dark purple solid was precipitated. The solid was then purified on a silica gel column employing chloroform/acetone (8:2) as eluent. The central fractions were collected and the solvent was removed by evaporation. The dark violet solid obtained was recrystallized from a chloroform/heptane solution in brick red needle-shape crystals. Yield 60%. Mp: 177°C, Tdec=330°C. 1H NMR (Acetone; 400 MHz) d: 0.86 (t, 3H, J=7.2), 1.35 (m, 4H), 2.06 (m, 2H), 3.80 (m, 10H), 4.21 (m, 4H), 6.95 (d, 2H, J=9.6), 7.370 (d, 1H, J=9.0), 7.64 (d, 1 H, J=9.0), 7.74 (d, 2H, J=8.8), 7.81 (d, 2H, J=9.2), 8.31 (d, 2H, J=8.8). Anal Calc for C31H34N4O9: N, 9.24; C, 61.38; H, 5.65. Found: N, 9.66; C,61.12; H,5.47%

2.3. Preparation and poling of L-NET According to Scheme 2, a solution of PGMA (0.073 g, 0.513 mmol glycidyl groups), CTriox (0.020 g, 0.039mmol) and L-BZO (0.080 g, 0.132 mmol) in THF (2 mL) was filtered on a 0.2 m PTFE filter and spin-coated on glass substrate. The film was corona poled by applying a voltage of 7 kV while temperature was raised from 25 to 140 °C. After 4 h the sample was cooled to room temperature and the electric field removed.

2.4. X-ray Crystallography Single crystals of L-BZO and its precursor L’-BZO suitable for X-ray crystal structure analysis were obtained from slow evaporation of chloroform/heptane (2:1) solutions at room temperature. One selected crystal of each compounds was mounted in flowing N2 at 173 K on a Bruker-Nonius KappaCCD diffractometer equipped with Oxford Cryostream apparatus (graphite monochromated MoK radiation,  = 0.71073 Å, CCD rotation images, thick slices, 

and  scans to fill

ACCEPTED MANUSCRIPT asymmetric unit). Semiempirical absorption corrections (SADABS) were applied. Both the two structures were solved by direct methods (SIR97 program [40]) and anisotropically refined by the full matrix least-squares method on F2 against all independent measured reflections using SHELXL-2018/3 [41] and WinGX software [42]. In both the two structures the hydroxy H atoms were located in difference Fourier maps and freely refined with Uiso(H) equal to 1.2Ueq of the carrier atom. All the other hydrogen atoms were introduced in calculated positions and refined according to the riding model with C–H distances in the range 0.95–0.99 Å and with Uiso(H) equal to 1.2Ueq or 1.5Ueq(Cmethyl) of the carrier atom. Both in the two structures the butyl group at O7 (LBZO) and O5 (L’-BZO) is disordered in two positions with refined occupancy factors 0.827(5)/0.173(5) for L-BZO and 0.635(6)/ 0.365(6) for L’-BZO. Some constraints were introduced in the last stage of the refinement to model the disorder using SAME and SIMU commands of SHELXL program. Crystal data and structure refinement details are reported in Table 1. The figures were generated using ORTEP-3 [43] and Mercury CSD 4.0 [44] programs. All crystal data were deposited at Cambridge Crystallographic Data Centre with assigned number CCDC 1898446 (L-BZO) and 1998447 (L’-BZO). These data can be obtained free of charge from www.ccdc.cam.ac.uk/data_request/cif. Table 1. Crystal data and structure refinement details for L’-BZO and L-BZO L-BZO

L’-BZO

CCDC number

CCDC 1898446

CCDC 1998447

Empirical formula

C31 H34 N4 O9

C28 H34 N4 O8

Formula weight

606.62

562.57

T (K)

173(2)

173(2)

 (Å)

0.71073

0.71073

Crystal system

Monoclinic

Monoclinic

Space group

P21/c

P21/c

a (Å)

18.474(3)

5.300(2)

b (Å)

7.511(2)

31.109(5)

c (Å)

22.784(4)

16.135(3)

a (°)

90

90

 (°)

110.88(3)

95.14(2)

 (°)

90

90

V (Å3)

2953.8(12)

2649.6(12)

Z

4

4

ACCEPTED MANUSCRIPT Dcalc

(Mg/m3)

1.364

1.410

 (mm-1)

0.101

0.104

F(000)

1280

1184

 range (°)

3.24 - 27.50

3.21- 25.02

Reflections collected / unique [R(int)]

21142 / 6480 [R(int) = 0.0794]

12859 / 4617 [R(int) = 0.0762]

Data / restraints / parameters

6480 / 39 / 427

4617 / 71 / 409

Goodness-of-fit on F2

0.916

1.009

FinalR, wR indices [I>2s(I)]

0.0564, 0.1092

0.0586, 0.0930

Final R, wR indices (all data)

0.1542, 0.1391

0.1721, 0.1212

Largest diff. peak / hole (eA-3)

0.209/-0.243

0.222/-0.247

Table 2. Selected bond lengths (Å) and angles (°) for L-BZO and L’-BZO with e.s.d.’s in parentheses Bond

L-BZO

L’-BZO

N1–C22

1.469(3)

1.462(4)

N2–N3

1.279(3)

1.286(3)

N4–C12

1.383(3)

1.368(4)

C6–C7

1.442(3)

1.445(4)

C7–C8

1.365(3)

1.362(4)

C12–N4–C15

120.0(2)

120.7(3)

C12–N4–C17

120.8(2)

121.5(3)

C15–N4–C17

118.4(2)

117.4(3)

N2–N3–C9–C10

4.0(3)

12.4(4)

O1–C8–N2–N3

1.3(3)

1.1(4)

-56.6(3)

-57.9(4)

C6–C5–C19–C20

ACCEPTED MANUSCRIPT Table 3. Hydrogen Bonding Geometry for L-BZO and L’-BZO (e.s.d.’s in parentheses) D–H (Å)

H···A (Å)

D⋯A (Å)

D–H⋯A (°)

O3–H⋯O8a

0.72(3)

1.97(3)

2.686(3)

173(3)

O8–H⋯O9

0.82(3)

1.88(3)

2.691(3)

175(3)

O9–H⋯O3b

0.77(3)

1.91(3)

2.671(3)

172(3)

O2–H⋯O8c

0.83(3)

1.92(3)

2.671(3)

150(3)

O7–H⋯N3d

0.86(3)

2.26(3)

3.102(4)

169(3)

O7–H⋯O1d

0.86(3)

2.42(3)

2.990(3)

124(3)

O8–H⋯O7

0.90(3)

1.87(3)

2.737(3)

163(3)

D–H⋯A L-BZO

L’-BZO

Symmetry code: a x-1,y-1,z; b -x+2,-y,-z+1; c 5 x+1,y,z-1; d x,-y+1/2,z+1/2

2.5. EFISH measurements Measurement of  nonlinearity of the chromophore L-BZO was obtained by the EFISH technique. The set-up allows the determination of the scalar  product where  is the ground state dipole moment and  the vector part of the quadratic hyperpolarizability tensor. The light source was a Q:switched Nd:Yag laser whose emission at 1.06 m was shifted to 1.907 m by stimulated Raman scattering. Measurements were calibrated relative to a quartz wedge: the experimental value of d11 = 1.2 ∙10-9 esu at 1.06 m was extrapolated to 1.1 ∙10-9 esu at 1.907 m. The projection  of the vector part of tensor ijk along the direction of the dipole moment was finally determined, neglecting the purely electronic contribution compared to the orientational part and allowing Kleinman symmetry. Measurements were made in molar chloroform solution at 5 kV. The  value for L-BZO at k = 1.907 m, is 830 ∙10-48 esu.

2.6. SHG measurements

ACCEPTED MANUSCRIPT SHG experimental data relative to p-p experiments (incident p-polarised wave detected p-polarised SH signal) were recorded as the incidence function at 1500 nm wavelength (SH = 750 nm) and fitted according to Hermannand Hayden SH power equation [45]. The calibration of the experimental setup was performed through SHG measurements on a sample with known second order NLO susceptibility. A 1 mm thick X-cut quartz plate was used (d11 = 0.30 pm/V [46]). The conditions d15 = d31 (Kleinmann symmetry [47]) and d31 = 1/3d33 [48] were assumed for the polymeric poled film and hence used in the expression of deff [46]. Measurements of nonlinear coefficient d33 were performed by means of the Maker fringes technique. The laser beam at fundamental frequency was provided by an optical parametric oscillator (OPO) whose wavelength could be tuned in the near-infrared range (800–1600 nm). The OPO was pumped by a Q-switched Nd:YAG laser having 10 ns pulse duration and 10 Hz repetition rate. The laser beam impinged on a variable attenuator made by a halfwave retardation plate and a polarizing beam splitter cube, allowing continuous variation of optical power impinging on the sample. The fundamental beam reflected by polarizing beam splitter cube was directed on a potassium dideuterophosphate (KDP) crystal, whose second harmonic signal, detected by a photodiode, was employed as a reference signal in order to take into account of the power fluctuations of the fundamental laser beam. A double Fresnel rhomb selected the proper polarization direction of the fundamental beam impinging on the sample, which was placed on a goniometric stage to allow variation of the incidence angle. A coloured filter absorbed the unwanted fundamental wavelength signal transmitted through the sample, while the second harmonic signal was detected by a high sensitivity amplified photodiode. Both the electric signals coming from photodiodes were acquired by a computer interfaced Tektronix TDS540 500 MHz bandwidth digitizing oscilloscope.

3. Results and discussion Compounds L-BZO and L’-BZO were obtained as summarized in Scheme 1. The synthetic route to obtain the precursor which was employed to prepare the L’-BZO by diazotation has been previously reported [38]. A subsequent alkylation of the phenolic group produces the final dye. We followed a synthetic strategy that takes advantage of the position of the nitrophenyl substituent on the benzofuran moiety in order to obtain the desired “half-cruciform” D-π-A pattern. The identification and the evaluation of the purity degree were carried out by and 1H-NMR. Phase behaviour was examined by optical observation, DSC and TGA analysis. L-BZO shows a large range of stability after melting (177°C) and no decomposition is detected till about 330°C in air, making it a good candidate for NLO applications. Photophysical measurements were performed in solution. The maximum absorption peaks were recorded at 477 nm for the chromophore in a

ACCEPTED MANUSCRIPT chloroform solution and at 489 nm in DMF solution showing a moderate red-shift effect depending on solvent polarity (solvatochromic shift). This is consistent with the existence of a polar excited state, which is stabilized in a polar environment and has an increased probability of decaying to the ground state by non-radiative paths. The thermal and photophysical properties are summarised in Table 4 for both the dye and its precursor. Table 4. Thermal behaviour and absorbance maxima for L-BZO and L’-BZO

Compound

Tm(°C)a

Td(°C)b

abs (nm)c

L’-BZO

171

340

470

L-BZO

177

330

477

[a] Melting point; [b] Decomposition temperature, calculated as the 5% weight loss temperature in N2; [c] Wavelength of UV-Visible absorbance maxima in chloroform solution.

3.1. X-ray Crystallography Single crystals of L-BZO and its precursor L’-BZO suitable for X-ray crystal structure analysis were obtained from slow evaporation of chloroform/heptane solutions at room temperature. Both the two compounds crystallize in the monoclinic P21/c space group with one molecule contained in the independent unit. Crystal data and structural details are reported in Table 1. All bond distances and angles are in the expected range, a selection of them is reported in Table 2. Both in L-BZO and L’-BZO the molecule is characterized by one intramolecular OH···O hydrogen bond that drives a local approximate mirror symmetry of the hydroxyethyl groups attached at N amine atom.

ACCEPTED MANUSCRIPT

Figure 1. Ortep view of L-BZO with thermal ellipsoids drawn at 50% probability level. Only major part of the disordered alkyl chain at O7 is reported for clarity. In L-BZO (Figure 1) the most energetically favoured trans configuration at N1-N2 double bond is found. The molecule assumes a quite planar shape with nitrobenzene mean plane 54.3° tilted with respect to benzofurane mean plane, probably due to a steric hindrance with the pendant group at C7. The observed planar geometry at the amine N3 atom agrees with sp2 hybridization that favour donation towards the adjacent phenyl ring. The overall planar geometry of the molecule and the bond lengths pattern are consistent with push-pull systems [49] and suggest a long path of conjugation in the molecule that displays the peculiar form of a D-π-A L-shape system. In the crystal packing all the hydroxy groups in the molecule are involved in strong intra- and intermolecular OH⋯O hydrogen bonds (Table 3) in a mono-dimensional H-bonding pattern. Chains of head-to-tail H-bonded molecules are formed across inversion centres with a π-π stacking of benzofurane groups at about 3.4 Å (Figure 2).

Figure 2. H-bonding pattern in L-BZO with benzofurane π stacking.

ACCEPTED MANUSCRIPT The molecular structure of the precursor L’-BZO is reported in Figure 3. As expected no relevant differences in the pattern of bond lengths and angles is found with respect to L-BZO (Table 2) and the two molecules can be quite perfectly superimposed, thus indicating that phenol alkylation have no relevant effects on the push-pull D-π-A system.

Figure 3. Ortep view of L’-BZO with thermal ellipsoids drawn at 50% probability level. Only major part of the disordered alkyl chain at O5 is reported for clarity. In L’-BZO crystal packing a mono-dimensional H-bonding pattern (Tab.3) is found with chains of molecules running in the (a-c) direction through head-to-tail OH···O and lateral bifurcated OH···N and OH···O hydrogen bonds (Figure 4).

ACCEPTED MANUSCRIPT Figure 4. H-bonding pattern of L’-BZO molecules with rows of head-to-tail H-bonded molecules joined by bifurcated H-bonds.

3.2. NLO measurements Unlike other passive co-crosslinkers, we built L-BZO as a dye with a D-π-A L-shape pattern, able to exhibit NLO properties itself. EFISH measurements were affected on compound L-BZO and the  value measured by EFISH technique in chloroform solution at k = 1.907 m, is 830 ∙10-48 esu, is quite in the average for organic L-shape dyes [50]. The most common strategy used to produce NLO active materials with efficient and lasting polar order involves the production of a network by crosslink of appropriate polyfunctionalised monomers/oligomers and/or polymers under poling conditions [27, 31, 49, 51]. According to this approach, we tested the potential of the chromophore in a crosslinked poled film. L-NET was prepared at 20% by weight of chromophore CTriox and 80% of L-BZO (see Scheme 2). The total alcoholic functions amount was stoichiometrically balanced by the total amount of epoxy functions of PGMA. We achieved the epoxy ring-opening of PGMA by reaction with the alcoholic functions of the two chromophores to obtain the final network in absence of initiator. The hydroxylic functions ensure both good crosslinking aptitude and good reaction-rate control under poling conditions, due to their moderate reactivity with epoxydic functions. Moreover, this procedure not involves radicals in order to avoid damage to the system and to preserve reproducibility. The d33 coefficient reaches a value of 10 pm/V for the poled network. This value was measured unaltered after 3 months on the same film. The SHG signal recorded on L-NET is in the average range for organic polymeric materials[52] . A very similar value (11 pm/V) has been measured for CTriox/2,2’-(Naphthalene-2,7-diylbis(oxy))diethanol/PMGA poled film [31], where a passive colinker was added at 70% by weight, proving that the level of the NLO properties displayed by the crosslinked film L-NET are in medium range for similar polymeric systems and that L-BZO dye can be proper employed to build NLO active networks.

Conclusions

A novel trifunctional benzofurane-based NLO dye suited for crosslinking was synthesised. The Lshape D-π-A chromophore L-BZO was examined by single-crystal structure analysis. Planar

ACCEPTED MANUSCRIPT geometry and bond lengths pattern in the molecule confirm the D-π-A push-pull L-shape nature of the system. Moreover, the NLO properties were studied, determining the  value of 830∙10-48 esu of L-BZO, which results in the average for organic L-shape dyes. The presence of three hydroxyl functional groups in the dye allowed to incorporate it as a dipolar coupling-breaker into a crosslinked material, in combination with a conventional NLO thiophene-based chromophore. The synthetic approach for the attainment of the poled material is simple and well-manageable using the alcoholic functions and PMGA in absence of initiator. The value of the d33 SHG coefficient was 10 pm/V for the poled network, in medium range for similar polymeric systems, proving L-BZO might be a good candidate for practical applications.

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ACCEPTED MANUSCRIPT

Highlights • A new NLO L-shape D-π-A chromophore was synthesized and characterized.

For the chromophore it has been determined a  value of 830∙10-48 esu. The poled network shows d33 SHG coefficient was 10 pm/V. Chromophore shows a good thermal stability for practical applications as NLO dye.