- Email: [email protected]
Enhanced electro-optic activity from the triarylaminophenyl-based chromophores by introducing different steric hindrance groups
Materials Letters 196 (2017) 230–233
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Enhanced electro-optic activity from the triarylaminophenyl-based chromophores by introducing different steric hindrance groups Lu Chen a,b, Yanling He a,b, Fenggang Liu a,b, Jialei Liu a, Hua Zhang a,b, Fuyang Huo a,b, Shuhui Bo a,⇑, Hongyan Xiao a, Zhen Zhen a,⇑ a b
Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China University of Chinese Academy of Sciences, Beijing 100043, PR China
a r t i c l e
i n f o
Article history: Received 7 March 2017 Received in revised form 9 March 2017 Accepted 11 March 2017 Available online 18 March 2017 Keywords: NLO Chromophore Isolation group Organic EO activity Thin films
a b s t r a c t Chromophores L1 and L2 based on modified triphenylamine donors with diverse steric hindrance groups, have been designed in order to achieve large macroscopic r33 value of NLO polymers comparing to traditional triarylaminophenyl chromophore T1. In electro-optic activities, the doped film L1-APC and L2-APC showed r33 value of 37 pm/V and 49 pm/V at the concentration of 25 wt%, which were more than two times higher than that of film T1/APC (16 pm/V). These properties, together with the good thermostability, suggest the potential use of the new chromophores as advanced material devices. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Organic second-order nonlinear optical (NLO) materials have been extensively studied for their potential applications in photonics due to their large NLO coefficients, ultrafast response time, and ease of integration [1–6]. The most representative NLO chromophores which exhibit the highest thermal stability have been reported with a triarylamine (TAA) donor and a thiophene-bridge [7,8]. However, these triarylamine (TAA) chromophores usually exhibit reduced EO activity in polymer due to molecular aggregation and low hyperpolarizability b value [9]. Fortunately, isolation groups are good modification way to improve the shape of chromophores and enhance EO activity of materials [10,11]. In this paper, we have synthesized two D-p-A chromophores (L1 and L2) which are modified by different steric hindrance of hexan-1-ol and tert-butyl(heptyloxy)diphenylsilane while chromophore T1 was chosen as a reference compound for comparison, as shown in Scheme 1. The UV–Vis, DFT calculations, thermal stabilities and EO activities of these chromophores were systematically studied and compared to illustrate the advantage of the new chromophores. Our results prove that the introduction
⇑ Corresponding authors. E-mail addresses: [email protected] (S. Bo), [email protected] (Z. Zhen). http://dx.doi.org/10.1016/j.matlet.2017.03.052 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
of above two isolation groups onto the benzene ring of the TAA donor can dramatically enhance the electron-donating capability and improve the hyperpolarization b value besides attenuating large dipole–dipole between chromophores.
2. Experimental section 2.1. Materials and instrumentation All chemicals are commercially available and used without further purification unless otherwise stated. Compound 1,compound 2, 2-Dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran (TCF) were synthesized according to literature [12,13]. 1H NMR spectra were determined using an Advance Bruker 400 M (400 MHz) NMR spectrometer (tetramethylsilane as internal reference). The MS spectra were obtained by MALDI-TOF (Matrix Assisted Laser Desorption/Ionization of Flight) on a BIFLEXIII (Broker Inc.) spectrometer.
2.2. Synthesis Detailed synthetic procedures, 1H NMR spectra data as well as MS spectra data of compound 3a, 4a, 5a and 6b are available in the Supporting information.
L. Chen et al. / Materials Letters 196 (2017) 230–233
231
Scheme 1. Chemical structures and synthetic routes for chromophores L1 and L2.
2.2.1. Synthesis of compound L1 A mixture of aldehydic bridge 2e (0.28 g, 0.56 mmol) and acceptor TCF (0.123 g, 0.62 mmol) in anhydrous ethanol (10 mL) was stirred at 75 °C for 6 h. After removal of the solvent, the residue was purified by chromatography to obtain a dark-blue solid (0.14 g, 37%). 1H NMR (400 MHz, CDCl3) d 7.74 (d, J = 15.9 Hz, 1H), 7.42 (d, J = 16.1 Hz, 1H), 7.36 (m, 2H), 7.31 (t, J = 7.6 Hz, 4H), 7.21 (d, J = 16.0 Hz, 1H), 7.14 (d, J = 7.6, Hz, 4H), 7.10 (t, J = 7.3 Hz, 2H), 7.05 (d, J = 4.0 Hz, 1H), 6.63 (d, J = 15.7 Hz, 1H), 6.59 (d, J = 8.5, 1H), 6.55 (s, 1H), 3.84 (t, J = 6.3 Hz, 2H), 3.67 (t, J = 6.5 Hz, 2H), 2.36 (s, 1H), 1.82 (m, 2H), 1.76 (s, 6H), 1.47 (m, 6H). 13C NMR (101 MHz, CDCl3) d 158.18, 154.55, 150.33, 147.10, 139.41, 137.89, 137.28, 130.94, 129.55, 128.95, 128.37, 127.33, 125.45, 124.07, 118.86, 114.96, 112.18, 111.37, 111.02, 106.04, 99.51, 97.03, 96.71, 68.48, 65.62, 62.84, 32.81, 29.10, 26.63, 26.14, 25.66. MS(MALDI-TOF): m/z (M+, C42H38N4O3S): calcd:678.8; found:678.3
2.2.2. Synthesis of compound L2 A mixture of aldehydic bridge 3e (0.28 g, 0.38 mmol) and acceptor TCF (0.083 g, 0.42 mmol) in anhydrous ethanol (10 mL) was stirred at 75 °C for 6 h. After removal of the solvent, the residue was purified by chromatography. A dark-blue solid was obtained (0.12 g, 33%). 1H NMR (400 MHz, CDCl3) d 7.77 (d, J = 15.6 Hz, 2H), 7.65 (d, J = 7.8, 4H), 7.41 (d, J = 15.8 Hz, 2H), 7.36 (d, J = 7.3 Hz, 4H), 7.34 (d, J = 3.6 Hz, 2H), 7.28 (m, 6H), 7.13 (d, J = 7.7 Hz, 4H), 7.08 (t, J = 7.3 Hz, 2H), 6.99 (d, J = 8.0 Hz, 1H), 6.59 (d, J = 8.0 Hz, 1H), 6.57 (s, 1H), 3.82 (t, J = 6.6 Hz, 2H), 3.66 (t, J = 6.4 Hz, 2H), 1.76 (m, 2H), 1.72 (s, 6H), 1.60 (m, 6H), 1.03 (s, 9H). 13C NMR (101 MHz, CDCl3) d 175.82, 173.02, 167.80, 158.31, 154.72, 150.35, 147.11, 139.56, 137.89, 137.42, 135.70, 134.31, 131.00, 130.03, 129.00, 127.74, 125.49, 124.11, 119.02, 118.82, 114.95, 112.03, 111.48, 111.13, 106.11, 96.79, 96.52, 68.51, 65.68, 63.85, 32.37, 29.65, 29.13 (s), 27.07, 26.65, 25.66, 19.36. MS (MALDI-TOF): m/z (M+, C58H56N4O3SSi): calcd: 917.2; found: 917.4
232
L. Chen et al. / Materials Letters 196 (2017) 230–233
3. Results and discussion
introducing end-capping tert-Butyldiphenylsilane which largely prevent the molecular aggregation [16].
3.1. Synthesis and characterization 3.3. Optical properties Scheme 1 showed the synthetic routes for the chromophores L1 and L2. Compound 4a was prepared by Wittig condensation of compound 3a. Then a formylation reaction was carried out to prepare compound 5a. Chromophore L1 and L2 was prepared by the Knoevenagel condensation. 3.2. Thermal properties NLO chromophores must be thermally stable enough to withstand high temperatures in electric field poling and subsequent processing of chromophore/polymer materials [14]. Thermal properties of chromophores L1 and L2 were evaluated by differential scanning calorimetry (DSC) measurements on a TA5000, 2910MDSC with a heating rate of 10 °C min1 under the protection of nitrogen. The results are shown in Fig. 1. Chromophores L1 appeared as highly crystalline compound with a melting point at 180 °C. While chromophore L2 was obtained as an amorphous solid with a glass transition temperature (Tg) at 128 °C. They are higher than many commonly used chromophores like TED1 and AJL34 [15]. The improved glass-forming ability of chromophore L2 was mainly attributed to the increased steric hindrance by
Fig. 1. DSC curves of chromophores L1 and L2.
UV–Vis absorption spectra of three chromophores (c = 1 105 mol/L) performed on a Cary 5000 photo spectrometer were measured in six organic solvents (Fig. 2). The spectrum data are summarized in Table 1. Comparing to the chromophore T1 whose kmax was only 621 nm in chloroform, the kmax of the chromophores L1 and L2 are 642 nm and 644 nm in chloroform, respectively, accompanying with red shift. Moreover, in the Fig. 2 and Table 1, it is noted that L1 and L2 own a bathochromic shift of 50 nm and 49 nm from acetone to chloroform, respectively, which are more than 44 nm of T1 by analyzing the solvatochromic behavior. Those results clearly show isolation groups modified L1 and L2 play the positive effect on improving the strength of donor, shifting the CT absorption band of chromophores to lower energy and enhancing polarity of chromophores [17]. 3.4. Theoretical calculations To understand the microscopic NLO properties of the designed chromophores, DFT calculations were performed to analyze the frontier molecular orbitals and b value of T1, L1 and L2. The geometries of chromophores were optimized at the B3LYP/6-31G⁄ level.
Fig. 2. UV-vis absorption spectra of chromophores L1 and L2 in six solvents.
233
L. Chen et al. / Materials Letters 196 (2017) 230–233 Table 1 Summary of UV-vis, DFT calculations and EO coefficients of chromophores T1, L1 and L2.
a b c
Cmpd
kmaxa (nm)
kmaxb (nm)
HOMO (eV)
LUMO (eV)
bc/(1030esu)
r33 (pm/V)
T1 L1 L2
577 591 595
621 641 644
5.25 5.05 5.16
3.26 3.16 3.20
685.89 723.36 692.50
16 37 49
kmax was measured in acetone. kmax was measured in CHCl3. b is the first-order hyperpolarizability, and was calculated based on DFT quantum mechanical methods.
First hyperpolarizabilities (b) were calculated at the CAM-B3LYP/631+G⁄ level. All the calculations were performed by the Gaussian 09 program package. According to the DFT calculations, the results are summarized in Table 1. The energy gap (DE) values of chromophores L1 and L2 are 1.89 eV and 1.96 eV, which are smaller than 1.99 eV of T1. In addition, the b of L1 and L2 are 723.36 1030 esu and 692.50 1030 esu, respectively, while the b of T1 is only 685.89 1030 esu. These indicate site-isolated triarylamine donors of chromophores L1 and L2 are beneficial to largely improve the donor ability. Also, those introduced isolation groups can effectively suppress chromophore dipole-dipole interaction and molecular aggregation to improve EO coefficient. 3.5. Electro-optic performance To testify the EO activities of L1 and L2, 25 wt% of chromophores were formulated into amorphous polycarbonate to prepare the guest-host L1/APC and L2/APC films. According to the previous reference, the r33 value of 25 wt% T1/APC was only 16 pm/V at 1310 nm [9]. However, the r33 value of 37 pm/V and 49 pm/V for 25 wt% L1/APC and 25 wt% L2/APC was achieved at 1310 nm, respectively. The result proves site-isolated group modified TAA donor can effectively improve the EO activities of materials and TBDPS-termination has the strongest steric hindrance to achieve the high efficiency of translating the microscopic nonlinearity into the macroscopic EO coefficients for chromophore L2. 4. Conclusion In conclusion, a series of NLO chromophores based on a modified TAA donor have been synthesized and systematically investigated by NMR, MS, UV–vis absorption spectroscopy, DFT calculations, electric field poling and EO property measurements, the results showed the better performance of chromophores L1 and L2 than chromophores T1 because of the modification of isolation groups. The EO coefficient of poled 25 wt% L1-APC and 25 wt% L2-APC films afford 37 pm/V and 49 pm/V at 1310 nm, respectively. While the poled film of 25 wt% T1-APC achieved 16 pm/V at 1310 nm. In addition, chromophores L1 and L2 showed good solubility and thermal stability. These above advantages of chromophores L1 and L2 prove that the two novel chromophores own brilliant broad application prospects in organic EO and photorefractive materials area. Acknowledgments We are grateful to the National Nature Science Foundation of China (No. 21504099 and No. 21473227), the National Key Research and Development Program of China (Grant No. 2016YFB0402004) and Youth Innovation Promotion Association
of Chinese Academy of Sciences (2017033) for the financial support. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.matlet.2017.03. 052. References [1] D.M. Burland, R.D. Miller, C.A. Walsh, Second-order nonlinearity in poledpolymer systems, Chem. Rev. 94 (1) (1994) 31–75. [2] I.V. Kityk, N. Alzayed, A.H. Reshak, K.J. Plucinski, J. Berdowski, I. Fuks-Janczarek, et al., Optically-operated elastooptical effects in polymer matrices with nanocrystallites, Funct. Mater. Lett. 04 (04) (2011) 357–359. [3] A. Danel, E. Gondek, I. Kityk, 1H-pyrazolo[3,4-b]quinoline and 1H-pyrazolo [3,4-b]quinoxaline derivatives as promising materials for optoelectronic applications, Opt. Mater. 32 (2) (2009) 267–273. [4] J. Hao, M.-J. Han, K. Guo, Y. Zhao, L. Qiu, Y. Shen, et al., A novel NLO azothiophene-based chromophore: synthesis, characterization, thermal stability and optical nonlinearity, Mater. Lett. 62 (6–7) (2008) 973–976. [5] H. Wang, M. Zhang, Y. Yang, F. Liu, C. Hu, H. Xiao, et al., Synthesis and characterization of one novel second-order nonlinear optical chromophore based on new benzoxazin donor, Mater. Lett. 164 (2016) 644–646. [6] J. Liu, G. Xu, F. Liu, I. Kityk, X. Liu, Z. Zhen, Recent advances in polymer electrooptic modulators, RSC Adv. 5 (21) (2015) 15784–15794. [7] P.A. Sullivan, H. Rommel, Y. Liao, B.C. Olbricht, A.J.P. Akelaitis, K.A. Firestone, et al., Theory-guided design and synthesis of multichromophore dendrimers: an analysis of the electro-optic effect, J. Am. Chem. Soc. 129 (24) (2007) 7523– 7530. [8] S. Suresh, H. Zengin, B.K. Spraul, T. Sassa, T. Wada, D.W. Smith Jr, Synthesis and hyperpolarizabilities of high temperature triarylamine-polyene chromophores, Tetrahedron Lett. 46 (22) (2005) 3913–3916. [9] Y. Yang, F. Liu, H. Wang, S. Bo, J. Liu, L. Qiu, et al., Enhanced electro-optic activity from the triarylaminophenyl-based chromophores by introducing heteroatoms to the donor, J. Mater. Chem. C 3 (20) (2015) 5297–5306. [10] S.R. Hammond, O. Clot, K.A. Firestone, D.H. Bale, D. Lao, M. Haller, et al., Siteisolated electro-optic chromophores based on substituted 2,20 -bis(3,4propylenedioxythiophene) p-conjugated bridges, Chem. Mater. 20 (10) (2008) 3425–3434. ˇ ermáková, J. Kulhánek, M. Ludwig, W. Kuznik, I.V. Kityk, et al., [11] F. Bureš, H. C Structure-property relationships and nonlinear optical effects in donorsubstituted dicyanopyrazine-derived push-pull chromophores with enlarged and varied p-linkers, Eur. J. Org. Chem. 2012 (3) (2012) 529–538. [12] Y.-J. Cheng, J. Luo, S. Hau, D.H. Bale, T.-D. Kim, Z. Shi, et al., Large electro-optic activity and enhanced thermal stability from diarylaminophenyl-containing high-b nonlinear optical chromophores, Chem. Mater. 19 (5) (2007) 1154– 1163. [13] P.S. Hariharan, N. Hari, S.P. Anthony, Triphenylamine based new Schiff base ligand: solvent dependent selective fluorescence sensing of Mg2+ and Fe3+ ions, Inorg. Chem. Commun. 48 (2014) 1–4. [14] H. Wang, Y. Yang, J. Liu, F. Liu, L. Qiu, X. Liu, et al., Great improvement of performance for NLO chromophore with cyclopentadithiophenone unit as pelectron bridge, Mater. Lett. 161 (2015) 674–677. [15] D.B. Knorr, X.-H. Zhou, Z. Shi, J. Luo, S.-H. Jang, A.K.Y. Jen, et al., Molecular mobility in self-assembled dendritic chromophore glasses, J. Phys. Chem. B 113 (43) (2009) 14180–14188. [16] J. Wu, S. Bo, J. Liu, T. Zhou, H. Xiao, L. Qiu, et al., Synthesis of novel nonlinear optical chromophore to achieve ultrahigh electro-optic activity, Chem. Commun. 48 (77) (2012) 9637–9639. [17] P.A. Sullivan, A.J.P. Akelaitis, S.K. Lee, G. McGrew, S.K. Lee, D.H. Choi, et al., Novel dendritic chromophores for electro-optics: influence of binding mode and attachment flexibility on electro-optic behavior, Chem. Mater. 18 (2) (2006) 344–351.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Enhanced electro-optic activity from the triarylaminophenyl-based chromophores by introducing different steric hindrance groups Lu Chen a,b, Yanling He a,b, Fenggang Liu a,b, Jialei Liu a, Hua Zhang a,b, Fuyang Huo a,b, Shuhui Bo a,⇑, Hongyan Xiao a, Zhen Zhen a,⇑ a b
Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China University of Chinese Academy of Sciences, Beijing 100043, PR China
a r t i c l e
i n f o
Article history: Received 7 March 2017 Received in revised form 9 March 2017 Accepted 11 March 2017 Available online 18 March 2017 Keywords: NLO Chromophore Isolation group Organic EO activity Thin films
a b s t r a c t Chromophores L1 and L2 based on modified triphenylamine donors with diverse steric hindrance groups, have been designed in order to achieve large macroscopic r33 value of NLO polymers comparing to traditional triarylaminophenyl chromophore T1. In electro-optic activities, the doped film L1-APC and L2-APC showed r33 value of 37 pm/V and 49 pm/V at the concentration of 25 wt%, which were more than two times higher than that of film T1/APC (16 pm/V). These properties, together with the good thermostability, suggest the potential use of the new chromophores as advanced material devices. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Organic second-order nonlinear optical (NLO) materials have been extensively studied for their potential applications in photonics due to their large NLO coefficients, ultrafast response time, and ease of integration [1–6]. The most representative NLO chromophores which exhibit the highest thermal stability have been reported with a triarylamine (TAA) donor and a thiophene-bridge [7,8]. However, these triarylamine (TAA) chromophores usually exhibit reduced EO activity in polymer due to molecular aggregation and low hyperpolarizability b value [9]. Fortunately, isolation groups are good modification way to improve the shape of chromophores and enhance EO activity of materials [10,11]. In this paper, we have synthesized two D-p-A chromophores (L1 and L2) which are modified by different steric hindrance of hexan-1-ol and tert-butyl(heptyloxy)diphenylsilane while chromophore T1 was chosen as a reference compound for comparison, as shown in Scheme 1. The UV–Vis, DFT calculations, thermal stabilities and EO activities of these chromophores were systematically studied and compared to illustrate the advantage of the new chromophores. Our results prove that the introduction
⇑ Corresponding authors. E-mail addresses: [email protected] (S. Bo), [email protected] (Z. Zhen). http://dx.doi.org/10.1016/j.matlet.2017.03.052 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
of above two isolation groups onto the benzene ring of the TAA donor can dramatically enhance the electron-donating capability and improve the hyperpolarization b value besides attenuating large dipole–dipole between chromophores.
2. Experimental section 2.1. Materials and instrumentation All chemicals are commercially available and used without further purification unless otherwise stated. Compound 1,compound 2, 2-Dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran (TCF) were synthesized according to literature [12,13]. 1H NMR spectra were determined using an Advance Bruker 400 M (400 MHz) NMR spectrometer (tetramethylsilane as internal reference). The MS spectra were obtained by MALDI-TOF (Matrix Assisted Laser Desorption/Ionization of Flight) on a BIFLEXIII (Broker Inc.) spectrometer.
2.2. Synthesis Detailed synthetic procedures, 1H NMR spectra data as well as MS spectra data of compound 3a, 4a, 5a and 6b are available in the Supporting information.
L. Chen et al. / Materials Letters 196 (2017) 230–233
231
Scheme 1. Chemical structures and synthetic routes for chromophores L1 and L2.
2.2.1. Synthesis of compound L1 A mixture of aldehydic bridge 2e (0.28 g, 0.56 mmol) and acceptor TCF (0.123 g, 0.62 mmol) in anhydrous ethanol (10 mL) was stirred at 75 °C for 6 h. After removal of the solvent, the residue was purified by chromatography to obtain a dark-blue solid (0.14 g, 37%). 1H NMR (400 MHz, CDCl3) d 7.74 (d, J = 15.9 Hz, 1H), 7.42 (d, J = 16.1 Hz, 1H), 7.36 (m, 2H), 7.31 (t, J = 7.6 Hz, 4H), 7.21 (d, J = 16.0 Hz, 1H), 7.14 (d, J = 7.6, Hz, 4H), 7.10 (t, J = 7.3 Hz, 2H), 7.05 (d, J = 4.0 Hz, 1H), 6.63 (d, J = 15.7 Hz, 1H), 6.59 (d, J = 8.5, 1H), 6.55 (s, 1H), 3.84 (t, J = 6.3 Hz, 2H), 3.67 (t, J = 6.5 Hz, 2H), 2.36 (s, 1H), 1.82 (m, 2H), 1.76 (s, 6H), 1.47 (m, 6H). 13C NMR (101 MHz, CDCl3) d 158.18, 154.55, 150.33, 147.10, 139.41, 137.89, 137.28, 130.94, 129.55, 128.95, 128.37, 127.33, 125.45, 124.07, 118.86, 114.96, 112.18, 111.37, 111.02, 106.04, 99.51, 97.03, 96.71, 68.48, 65.62, 62.84, 32.81, 29.10, 26.63, 26.14, 25.66. MS(MALDI-TOF): m/z (M+, C42H38N4O3S): calcd:678.8; found:678.3
2.2.2. Synthesis of compound L2 A mixture of aldehydic bridge 3e (0.28 g, 0.38 mmol) and acceptor TCF (0.083 g, 0.42 mmol) in anhydrous ethanol (10 mL) was stirred at 75 °C for 6 h. After removal of the solvent, the residue was purified by chromatography. A dark-blue solid was obtained (0.12 g, 33%). 1H NMR (400 MHz, CDCl3) d 7.77 (d, J = 15.6 Hz, 2H), 7.65 (d, J = 7.8, 4H), 7.41 (d, J = 15.8 Hz, 2H), 7.36 (d, J = 7.3 Hz, 4H), 7.34 (d, J = 3.6 Hz, 2H), 7.28 (m, 6H), 7.13 (d, J = 7.7 Hz, 4H), 7.08 (t, J = 7.3 Hz, 2H), 6.99 (d, J = 8.0 Hz, 1H), 6.59 (d, J = 8.0 Hz, 1H), 6.57 (s, 1H), 3.82 (t, J = 6.6 Hz, 2H), 3.66 (t, J = 6.4 Hz, 2H), 1.76 (m, 2H), 1.72 (s, 6H), 1.60 (m, 6H), 1.03 (s, 9H). 13C NMR (101 MHz, CDCl3) d 175.82, 173.02, 167.80, 158.31, 154.72, 150.35, 147.11, 139.56, 137.89, 137.42, 135.70, 134.31, 131.00, 130.03, 129.00, 127.74, 125.49, 124.11, 119.02, 118.82, 114.95, 112.03, 111.48, 111.13, 106.11, 96.79, 96.52, 68.51, 65.68, 63.85, 32.37, 29.65, 29.13 (s), 27.07, 26.65, 25.66, 19.36. MS (MALDI-TOF): m/z (M+, C58H56N4O3SSi): calcd: 917.2; found: 917.4
232
L. Chen et al. / Materials Letters 196 (2017) 230–233
3. Results and discussion
introducing end-capping tert-Butyldiphenylsilane which largely prevent the molecular aggregation [16].
3.1. Synthesis and characterization 3.3. Optical properties Scheme 1 showed the synthetic routes for the chromophores L1 and L2. Compound 4a was prepared by Wittig condensation of compound 3a. Then a formylation reaction was carried out to prepare compound 5a. Chromophore L1 and L2 was prepared by the Knoevenagel condensation. 3.2. Thermal properties NLO chromophores must be thermally stable enough to withstand high temperatures in electric field poling and subsequent processing of chromophore/polymer materials [14]. Thermal properties of chromophores L1 and L2 were evaluated by differential scanning calorimetry (DSC) measurements on a TA5000, 2910MDSC with a heating rate of 10 °C min1 under the protection of nitrogen. The results are shown in Fig. 1. Chromophores L1 appeared as highly crystalline compound with a melting point at 180 °C. While chromophore L2 was obtained as an amorphous solid with a glass transition temperature (Tg) at 128 °C. They are higher than many commonly used chromophores like TED1 and AJL34 [15]. The improved glass-forming ability of chromophore L2 was mainly attributed to the increased steric hindrance by
Fig. 1. DSC curves of chromophores L1 and L2.
UV–Vis absorption spectra of three chromophores (c = 1 105 mol/L) performed on a Cary 5000 photo spectrometer were measured in six organic solvents (Fig. 2). The spectrum data are summarized in Table 1. Comparing to the chromophore T1 whose kmax was only 621 nm in chloroform, the kmax of the chromophores L1 and L2 are 642 nm and 644 nm in chloroform, respectively, accompanying with red shift. Moreover, in the Fig. 2 and Table 1, it is noted that L1 and L2 own a bathochromic shift of 50 nm and 49 nm from acetone to chloroform, respectively, which are more than 44 nm of T1 by analyzing the solvatochromic behavior. Those results clearly show isolation groups modified L1 and L2 play the positive effect on improving the strength of donor, shifting the CT absorption band of chromophores to lower energy and enhancing polarity of chromophores [17]. 3.4. Theoretical calculations To understand the microscopic NLO properties of the designed chromophores, DFT calculations were performed to analyze the frontier molecular orbitals and b value of T1, L1 and L2. The geometries of chromophores were optimized at the B3LYP/6-31G⁄ level.
Fig. 2. UV-vis absorption spectra of chromophores L1 and L2 in six solvents.
233
L. Chen et al. / Materials Letters 196 (2017) 230–233 Table 1 Summary of UV-vis, DFT calculations and EO coefficients of chromophores T1, L1 and L2.
a b c
Cmpd
kmaxa (nm)
kmaxb (nm)
HOMO (eV)
LUMO (eV)
bc/(1030esu)
r33 (pm/V)
T1 L1 L2
577 591 595
621 641 644
5.25 5.05 5.16
3.26 3.16 3.20
685.89 723.36 692.50
16 37 49
kmax was measured in acetone. kmax was measured in CHCl3. b is the first-order hyperpolarizability, and was calculated based on DFT quantum mechanical methods.
First hyperpolarizabilities (b) were calculated at the CAM-B3LYP/631+G⁄ level. All the calculations were performed by the Gaussian 09 program package. According to the DFT calculations, the results are summarized in Table 1. The energy gap (DE) values of chromophores L1 and L2 are 1.89 eV and 1.96 eV, which are smaller than 1.99 eV of T1. In addition, the b of L1 and L2 are 723.36 1030 esu and 692.50 1030 esu, respectively, while the b of T1 is only 685.89 1030 esu. These indicate site-isolated triarylamine donors of chromophores L1 and L2 are beneficial to largely improve the donor ability. Also, those introduced isolation groups can effectively suppress chromophore dipole-dipole interaction and molecular aggregation to improve EO coefficient. 3.5. Electro-optic performance To testify the EO activities of L1 and L2, 25 wt% of chromophores were formulated into amorphous polycarbonate to prepare the guest-host L1/APC and L2/APC films. According to the previous reference, the r33 value of 25 wt% T1/APC was only 16 pm/V at 1310 nm [9]. However, the r33 value of 37 pm/V and 49 pm/V for 25 wt% L1/APC and 25 wt% L2/APC was achieved at 1310 nm, respectively. The result proves site-isolated group modified TAA donor can effectively improve the EO activities of materials and TBDPS-termination has the strongest steric hindrance to achieve the high efficiency of translating the microscopic nonlinearity into the macroscopic EO coefficients for chromophore L2. 4. Conclusion In conclusion, a series of NLO chromophores based on a modified TAA donor have been synthesized and systematically investigated by NMR, MS, UV–vis absorption spectroscopy, DFT calculations, electric field poling and EO property measurements, the results showed the better performance of chromophores L1 and L2 than chromophores T1 because of the modification of isolation groups. The EO coefficient of poled 25 wt% L1-APC and 25 wt% L2-APC films afford 37 pm/V and 49 pm/V at 1310 nm, respectively. While the poled film of 25 wt% T1-APC achieved 16 pm/V at 1310 nm. In addition, chromophores L1 and L2 showed good solubility and thermal stability. These above advantages of chromophores L1 and L2 prove that the two novel chromophores own brilliant broad application prospects in organic EO and photorefractive materials area. Acknowledgments We are grateful to the National Nature Science Foundation of China (No. 21504099 and No. 21473227), the National Key Research and Development Program of China (Grant No. 2016YFB0402004) and Youth Innovation Promotion Association
of Chinese Academy of Sciences (2017033) for the financial support. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.matlet.2017.03. 052. References [1] D.M. Burland, R.D. Miller, C.A. Walsh, Second-order nonlinearity in poledpolymer systems, Chem. Rev. 94 (1) (1994) 31–75. [2] I.V. Kityk, N. Alzayed, A.H. Reshak, K.J. Plucinski, J. Berdowski, I. Fuks-Janczarek, et al., Optically-operated elastooptical effects in polymer matrices with nanocrystallites, Funct. Mater. Lett. 04 (04) (2011) 357–359. [3] A. Danel, E. Gondek, I. Kityk, 1H-pyrazolo[3,4-b]quinoline and 1H-pyrazolo [3,4-b]quinoxaline derivatives as promising materials for optoelectronic applications, Opt. Mater. 32 (2) (2009) 267–273. [4] J. Hao, M.-J. Han, K. Guo, Y. Zhao, L. Qiu, Y. Shen, et al., A novel NLO azothiophene-based chromophore: synthesis, characterization, thermal stability and optical nonlinearity, Mater. Lett. 62 (6–7) (2008) 973–976. [5] H. Wang, M. Zhang, Y. Yang, F. Liu, C. Hu, H. Xiao, et al., Synthesis and characterization of one novel second-order nonlinear optical chromophore based on new benzoxazin donor, Mater. Lett. 164 (2016) 644–646. [6] J. Liu, G. Xu, F. Liu, I. Kityk, X. Liu, Z. Zhen, Recent advances in polymer electrooptic modulators, RSC Adv. 5 (21) (2015) 15784–15794. [7] P.A. Sullivan, H. Rommel, Y. Liao, B.C. Olbricht, A.J.P. Akelaitis, K.A. Firestone, et al., Theory-guided design and synthesis of multichromophore dendrimers: an analysis of the electro-optic effect, J. Am. Chem. Soc. 129 (24) (2007) 7523– 7530. [8] S. Suresh, H. Zengin, B.K. Spraul, T. Sassa, T. Wada, D.W. Smith Jr, Synthesis and hyperpolarizabilities of high temperature triarylamine-polyene chromophores, Tetrahedron Lett. 46 (22) (2005) 3913–3916. [9] Y. Yang, F. Liu, H. Wang, S. Bo, J. Liu, L. Qiu, et al., Enhanced electro-optic activity from the triarylaminophenyl-based chromophores by introducing heteroatoms to the donor, J. Mater. Chem. C 3 (20) (2015) 5297–5306. [10] S.R. Hammond, O. Clot, K.A. Firestone, D.H. Bale, D. Lao, M. Haller, et al., Siteisolated electro-optic chromophores based on substituted 2,20 -bis(3,4propylenedioxythiophene) p-conjugated bridges, Chem. Mater. 20 (10) (2008) 3425–3434. ˇ ermáková, J. Kulhánek, M. Ludwig, W. Kuznik, I.V. Kityk, et al., [11] F. Bureš, H. C Structure-property relationships and nonlinear optical effects in donorsubstituted dicyanopyrazine-derived push-pull chromophores with enlarged and varied p-linkers, Eur. J. Org. Chem. 2012 (3) (2012) 529–538. [12] Y.-J. Cheng, J. Luo, S. Hau, D.H. Bale, T.-D. Kim, Z. Shi, et al., Large electro-optic activity and enhanced thermal stability from diarylaminophenyl-containing high-b nonlinear optical chromophores, Chem. Mater. 19 (5) (2007) 1154– 1163. [13] P.S. Hariharan, N. Hari, S.P. Anthony, Triphenylamine based new Schiff base ligand: solvent dependent selective fluorescence sensing of Mg2+ and Fe3+ ions, Inorg. Chem. Commun. 48 (2014) 1–4. [14] H. Wang, Y. Yang, J. Liu, F. Liu, L. Qiu, X. Liu, et al., Great improvement of performance for NLO chromophore with cyclopentadithiophenone unit as pelectron bridge, Mater. Lett. 161 (2015) 674–677. [15] D.B. Knorr, X.-H. Zhou, Z. Shi, J. Luo, S.-H. Jang, A.K.Y. Jen, et al., Molecular mobility in self-assembled dendritic chromophore glasses, J. Phys. Chem. B 113 (43) (2009) 14180–14188. [16] J. Wu, S. Bo, J. Liu, T. Zhou, H. Xiao, L. Qiu, et al., Synthesis of novel nonlinear optical chromophore to achieve ultrahigh electro-optic activity, Chem. Commun. 48 (77) (2012) 9637–9639. [17] P.A. Sullivan, A.J.P. Akelaitis, S.K. Lee, G. McGrew, S.K. Lee, D.H. Choi, et al., Novel dendritic chromophores for electro-optics: influence of binding mode and attachment flexibility on electro-optic behavior, Chem. Mater. 18 (2) (2006) 344–351.