Comparative studies on structure-nonlinearity relationships in a series of novel second-order nonlinear optical chromophores with different aromatic amine donors

Article abstract of DOI:10.1016/j.dyepig.2015.05.003

A series of second-order nonlinear optical chromophores containing an identical π-bridge and electron acceptor but different, aromatic amine electron-donating groups have been synthesized and systematically investigated. The donors studied here include traditional donors carbazole, triphenylamine and N,N-diethylaniline and novel donor phenothiazine, phenoxazine and N-(4-methoxyphenyl)phenoxazine. The ultraviolet absorption, solvatochromic, redox properties, density functional theory calculations, thermal stabilities and electro-optic activities of these chromophores were systematically studied to compare the strength of the donors and illustrate the structure-performance relationships within six chromophores. The results show that the new donors have stronger electron-donating ability than traditional donors. Moreover, they show reduced energy gap, much larger molecular quadratic hyperpolarizability (μβ) and r₃₃ value. Exemplified by the N-(4-methoxyphenyl)phenoxazine chromophore, it showed nearly three times higher μβ and more than four times higher r₃₃ value than that of the N-hexylcarbazole containing chromophore.

Full text of DOI:10.1016/j.dyepig.2015.05.003

Accepted Manuscript
Comparative studies on structure-nonlinearity relationships in a series of novel
second-order nonlinear optical chromophores with different aromatic amine donors
Fenggang Liu, Yuhui Yang, Haoran Wang, Jialei Liu, Chaolei Hu, Fuyang Huo,
Shuhui Bo, Zhen Zhen, Xinhou Liu, Ling Qiu
PII:
S0143-7208(15)00174-6
10.1016/j.dyepig.2015.05.003
DYPI 4766
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 13 March 2015
Revised Date: 24 April 2015
Accepted Date: 1 May 2015
Please cite this article as: Liu F, Yang Y, Wang H, Liu J, Hu C, Huo F, Bo S, Zhen Z, Liu X, Qiu L,
Comparative studies on structure-nonlinearity relationships in a series of novel second-order nonlinear
optical chromophores with different aromatic amine donors, Dyes and Pigments (2015), doi: 10.1016/
j.dyepig.2015.05.003.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Comparative studies on structure-nonlinearity relationships in a
series of novel second-order nonlinear optical chromophores
with different aromatic amine donors
a
Fenggang Liu ab, Yuhui Yang ab, Haoran Wang ab, Jialei Liu , Chaolei Hu ab, Fuyang
Huo ab, Shuhui Bo a, Zhen Zhen a, Xinhou Liu a, and Ling Qiu a*
a Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and
Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China
b University of Chinese Academy of Sciences, Beijing 100043, PR China
* Corresponding authors. Tel.: +86-01-82543529; Fax: +86-01-2543529
E-mail address: qiuling@mail.ipc.ac.cn; tipcqiuling@163.com
Abstract
A series of second-order nonlinear optical chromophores containing an identical π-bridge and electron acceptor but
different, aromatic amine electron-donating groups have been synthesized and systematically investigated. The
donors studied here include traditional donors carbazole, triphenylamine and N,N-diethylaniline and novel donor
phenothiazine, phenoxazine and N-(4-methoxyphenyl)phenoxazine. The ultraviolet absorption, solvatochromic,
redox properties, density functional theory calculations, thermal stabilities and electro-optic activities of these
chromophores were systematically studied to compare the strength of the donors and illustrate the
structure-performance relationships within six chromophores. The results show that the new donors have stronger
electron-donating ability than traditional donors. Moreover, they show reduced energy gap, much larger molecular
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quadratic hyperpolarizability (µβ) and r33 value. Exemplified by the N-(4-methoxyphenyl)phenoxazine
chromophore, it showed nearly three times higher µβ and more than four times higher r33 value than that of the
N-hexylcarbazole containing chromophore.
Keywords: Nonlinear optical materials; Chromophore; Second-order; Electro-optic; Donor; Heteroatom;
1. Introduction
Organic electro-optic (OEO) materials have attracted great attention in recent years due to their potential
applications in optical switches, optical sensors, information processors, and telecommunications [1-3]. The OEO
materials have many advantages over inorganic materials including lower cost, ease of processing, larger EO
coefficients and so on [4-6]. The second-order nonlinear optical (NLO) chromophores are the key construction
blocks for OEO materials [7]. One of the most critical challenges in developing these materials is to design and
synthesize chromophores with a large molecular quadratic hyperpolarizability (µβ), excellent thermal and chemical
stabilities, good transparency as well as easy syntheses [8-10]. In addition, organic NLO chromophores, especially
those demonstrating high µβ values, typically have large ground state dipole moments. The strong inter
chromophore dipole-dipole interactions may lead to unfavorable antiparallel packing of the chromophores, thus
reducing the optical nonlinearities [11], so, weak molecular electrostatic interaction in the polymer matrix is
needed to effectively translate these large µβ values into bulk EO activities [12, 13].
In general, these chromophores have been constructed with a typical electron donor–π bridge–electron acceptor
(D–π–A) configuration [14, 15]. When considering the design of second-order nonlinear optical materials,
optimization of π-conjugated bridge, electron-donor and electron-acceptor characteristics of the substituents are
needed to obtain maximum nonlinearity at the molecular level [16]. Many studies on NLO chromophores have
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mainly focused on the design of electron bridges and electron acceptors [17-19]. The electron donors, who also
play a crucial role in determining the performance of NLO chromophores, have received relatively little attention
[16]. Donors derived from 4-(dialkylamino)phenyl groups or triphenylamine were used in most cases [20-22].
Many different amine-based donors have been used in organic materials chemistry such as second-order
NLO,[23] third-order NLO [24], two-photon absorption [25] and hole-transport materials [26]. Previously, Marder
et al. have systematically compared the strength of electron donors in a series of aminoaryl systems (mainly the
aminophenyl ones) using density functional theory (DFT) calculations which provides a valuable guideline for the
design of NLO chromophores [27]. However, apart from a few works, very little experimental or theoretical
research has been focused on the comparison of different aromatic amine electron-donating groups in the
performance of NLO chromophores [16, 28].
Chart 1
Fig. 1
So, in this study we would like to compare the structure–property relationship between the second-order
chromophores with six different donors. The donors are traditional carbazole (CBZ) [29], triphenylamine (TPA)
[20] and N,N-diethylaniline (FTC) [30] which is often used in second-order chromophore and phenothiazine (PTZ),
phenoxazine (POZ) and and N-(4-methoxcyphenyl)phenoxazine (PPZ) which is often employed in dye-sensitized
solar cells (DSSCs) [31, 32]. The r33 values of traditional aryl amine chromophore are much lower than those
obtained from their alkyl D-π-A analogues [33]. Recent studies showed that introducing additional heteroatoms
into the benzene ring moiety of donor could provide abundant opportunities for further modifications of
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chromophores thus influence nonlinear optical properties of chromophores [34-36]. So, aryl donors PTZ, POZ and
PPZ units were introduced to the second-order NLO chromophores due to its additional electron-rich sulfur or
oxygen heteroatom.
The electronic and spatial structures of the donors are quite different. The CBZ and TPA is both typical aryl
donor with one electron-rich nitrogen heteroatom, the geometry of CBZ is totally planar, while the three phenyl
rings of TPA are symmetrically twisted from the central plane. The PTZ, POZ and PPZ units have strong
electron-donating ability with its additional electron-rich nitrogen and sulfur or oxygen heteroatoms. The geometry
of PTZ and POZ are not totally planar but are rather slightly bent in the middle to give a butterfly shape [37]. As
for PPZ, the two benzene rings exhibited almost planar structures, the N-(4-methoxyphenyl) substituent located on
the nitrogen atom almost perpendicular with average plane (Figure 1).
In this study, we have designed and synthesized six chromophores containing an identical thiophene bridge and
tricyanovinyldihydrofuran (TCF) acceptor but different aromatic amine electron-donating groups (Chart 1). The
synthesis, UV-Vis, solvatochromic behaviour, redox properties, DFT quantum mechanical calculations, thermal
stabilities and EO activities of these chromophores were systematically studied and compared to illustrate the
influence of electron-donating groups on rational NLO chromophore designs.
2. Experimental
2.1 Materials and instrument
All chemicals are commercially available and are used without further purification unless otherwise stated. N,
N-dimethylformamide (DMF), Phosphorusoxychloride (POCl3), tetrahydrofuran (THF) and ether were distilled
over calcium hydride and stored over molecular sieves (pore size 3Å).10-Hexyl-10H-phenoxazine (2b) and
10-Hexyl-10H-phenoxazine-3-carbaldehyde (3b) were synthesized according to literature [38].
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10-Hexyl-10H-phenothiazine (2c) and 10-Hexyl-10H-phenothiazine-3-carbaldehyde (3c) were synthesized
according
to
previous
publication
[12].
10-(4-Methoxyphenyl)-10H-phenoxazine
(2d)
and
10-(4-methoxyphenyl)-10H-phenoxazine-3-carbaldehyde (3d) were synthesized according to literature [39].
2-Dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran(TCF) acceptor was prepared according to the literature
[40]. Triphenylamine based chromophore TPA was synthesized according to literature [20]. N,N-diethylaniline
based chromophore FTC was synthesized according to literature [30]. TLC analyses were carried out on 0.25 mm
thick precoated silica plates and spots were visualized under UV light. Chromatography on silica gel was carried
out on Kieselgel (200-300 mesh).
1HNMR spectra were determined on an Advance Bruker 400M (400 MHz) NMR spectrometer
(tetramethylsilane as internalreference). The MS spectra were obtained on MALDI-TOF (Matrix Assisted Laser
Desorption/Ionization of Flight) on BIFLEXIII (Broker Inc.,) spectrometer. The UV-Vis spectra were performed
on Cary 5000 photo spectrometer. The TGA was determined by TA5000-2950TGA (TA co) with a heating rate of
10 °C min-1 under the protection of nitrogen. Cyclic voltammetric data were measured on a BAS CV-50W
voltammetric analyzer using a conventional three-electrode cell with Pt metal as the working electrode, Pt gauze as
the counter-electrode, and Ag/AgNO3 as the reference electrode at a scan rate of 100 mV s-1. The 0.1 M
tetrabutylammonium hexa-fluorophosphate (TBAPF) in acetonitrile is the electrolyte. The elemental analyses were
measured on Flash EA 1112 Elemental Analyzer. The melt points were obtained by TA DSC Q10 under N2 at a
heating rate of 10 °C min-1.
2.2 Syntheses
2.2.1 Synthesis of 9-hexyl-9H-carbazole (Compound 2a)
Under a N2 atmosphere, potassium tert-butylate (5.07 g, 45 mmol) was added to a solution of compound 1a
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（5.02 g，30.0mmol）and n-hexylbromide（9.06g, 60.0mmol）in THF (60ml).The mixture was stirred at 48 ºC for
12 h and then poured into water. The organic phase was extracted by CH2Cl2, washed with brine and dried over
MgSO4. After removal of the solvent under reduced pressure, the crude product was purified by silica
chromatography, eluting with (Acetone: Hexane=1:10) to give compound 2a as a yellow oil in 93.4% yield (7.04 g,
28.02 mmol). MS, m/z: 251.17. (M+). 1H NMR (400 MHz, CDCl3) δ 8.09 (d, J = 7.6 Hz,2H), 7.44 (d, J = 7.7 Hz,
2H), 7.38 (d, J = 7.9 Hz, 2H), 7.20 (d, J = 5.7 Hz, 2H), 4.26 (t, J = 7.1 Hz, 2H), 1.88 – 1.75 (m, 2H), 1.33 (m, 6H),
0.85 (t, J=8.6Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 140.41, 125.58, 122.85, 120.23, 118.58, 108.62, 43.05, 31.57,
28.79, 26.96, 22.45, 13.99. Anal. Calcd (%) for C18H21N: C, 86.01; H, 8.42; N, 5.57; found: C, 86.13; H, 8.47; N,
5.53;
2.2.2 Synthesis of 9-hexyl-9H-carbazole-3-carbaldehyde (Compound 3a)
DMF (1.64 g, 22.50 mmol) was added to freshly distilled POCl3 (2.30 g, 15.00 mmol) under an atmosphere of
N2 nitrogen at 0 °C, and the resultant solution was stirred until its complete conversion into a glassy solid. After the
addition of 2a (2.51 g, 10.00 mmol) in 1,2-dichloroethane (60 mL) dropwise, the mixture was stirred at room
temperature overnight, then poured into a saturation aqueous solution of sodiumacetate (300 mL). After 2 hour
stirring at room temperature, the mixture extracted with chloroform (5 × 30 mL), and the organic fractions were
collected and dried over anhydrous MgSO4. The crude product was purified through a silica gel chromatography
eluting with (Acetone: Hexane = 1:5) to afford a yellow oil 3a in 75.6% yield (2.11 g, 7.56mmol). MS, m/z: 279.16.
(M+). 1H NMR (400 MHz, CDCl3) δ 9.85 (s, 1H), 8.30 (s, 1H), 7.88 (d, J = 7.8 Hz, 1H), 7.75 (d, J = 8.5 Hz, 1H),
7.32 (m, 1H,ArH), 7.19 (d, J = 8.2 Hz, 1H), 7.15 (d, J = 8.5 Hz, 1H), 7.10 (m, 1H), 3.97 (t, J = 7.2 Hz, 2H), 1.68 –
1.47 (m, 2H), 1.20 – 0.95 (m, 6H), 0.68 (t, J = 5.9 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 191.18, 143.71, 140.91,
128.33, 126.73, 126.42, 123.47, 122.78, 122.73, 120.39, 119.98, 109.12, 108.59, 42.51, 31.21, 28.57, 26.17, 21.89,
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13.51. Anal. Calcd (%) for C19H21NO: C, 81.68; H, 7.58; N, 5.01; found: C, 81.73; H, 7.52; N, 5.12;
2.2.3 Synthesis of (E)-9-hexyl-3-(2-(thiophen-2-yl) vinyl)-9H-carbazole (Compound 4a)
NaH (0.59 g, 25.00 mmol) was added to a stirred solution of compound 3a (1.26 g, 5.00 mmol) and 3e (3.47 g,
6.00 mmol) in ether (100 mL) under nitrogen. The solution was stirred for 24 h and then poured into water. The
organic phase was extracted by AcOEt, washed with brine and dried over MgSO4. After removal of the solvent
under reduced pressure, the crude product was purified by silica chromatography, eluting with (Acetone: Hexane =
1:20) to give compound 4a as yellow solid in 84.3% yield (1.51 g, 4.21 mmol). m.p. : 104.6 ºC. MS, m/z: 359.17
(M+). 1H NMR (400 MHz, CDCl3) δ 8.07 (s, 1H), 7.91 (d, J = 7.6 Hz, 1H), 7.38 (d, J = 8.3 Hz, 1H), 7.35 – 7.28 (m,
1H), 7.17 (dd, J = 14.0, 8.4 Hz, 2H), 7.13 – 7.07 (m, 1H), 6.91 (m, 1H), 6.83 (d, J = 4.5 Hz, 1H), 6.76 – 6.70 (m,
1H), 6.65 (d, J = 11.9 Hz, 1H), 6.58 (d, J = 11.8 Hz, 1H), 3.97 (t, J = 6.8 Hz, 2H), 1.63 (m, 2H), 1.13 (m, 6H), 0.76
(t, J=6.8 Hz,3H). 13C NMR (100 MHz, CDCl3) δ 140.58, 140.28, 139.84, 129.88, 127.62, 127.54 , 126.56, 126.15,
125.52 , 124.73, 122.84, 122.80, 121.92, 120.68, 120.25, 118.79, 108.61, 108.50, 42.80, 31.17 , 28.71 , 26.54 ,
22.36, 13.85. Anal. Calcd (%) for C24H25NS: C, 80.18; H, 7.01; N, 3.90; found: C, 80.23; H, 7.09; N, 3.85;
2.2.4 Synthesis of (E)-10-hexyl-3-(2-(thiophen-2-yl) vinyl)-10H-phenothiazine (Compound 4b)
The procedure for compound 4a was followed to prepare 4b from 3b and 3e as orange oil in 85.7% yield (0.34 g,
0.86 mmol). MS, m/z: 391.14 (M+). 1H NMR (400 MHz, CDCl3) δ 7.36 (s，1H), 7.17 (m, 2H), 7.13 (d, J = 7.8 Hz,
2H), 7.02 (d, J = 3.4 Hz, 1H), 6.92 (dd, J = 8.2, 4.6 Hz, 2H), 6.87 (d, J = 8.1 Hz, 1H), 6.81 (d, J = 8.2 Hz, 1H), 6.63
(d, J = 11.9 Hz, 1H), 6.44 (d, J = 11.9 Hz, 1H), 3.95 – 3.81 (m, 2H), 1.84 (m, 2H), 1.54 – 1.41 (m, 2H), 1.34 (m,
4H), 0.91 (t, J = 6.7 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 143.88, 143.51, 142.12, 138.79, 132.80, 132.56,
130.17, 127.06, 126.45, 126.13, 125.47, 124.35, 123.51, 121.66, 121.17, 114.15, 46.50, 30.44, 25.77, 25.49, 21.56,
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12.98. Anal. Calcd (%) for C24H25NS2: C, 73.61; H, 6.43; N, 3.58; found: C, 73.71; H, 6.48; N, 3.63;
2.2.5 Synthesis of (E)-10-hexyl-3-(2-(thiophen-2-yl)vinyl)-10H-phenoxazine (Compound 4c)
The procedure for compound 4a was followed to prepare 4c from 3c and 3e as orange oil with 87.3% yield (0.33
g, 0.87 mmol). MS, m/z: 375.27 (M+). 1H NMR (400 MHz, CDCl3) δ 7.15 (d, J = 4.8 Hz, 1H), 7.02 (m, ArH, 2H),
6.98 (d, J = 3.8 Hz, 1H), 6.85 (d, J = 8.4 Hz, 1H), 6.81 (m, 2H), 6.74 (d, J = 16.0 Hz, 1H), 6.65 (m, 2H), 6.48 (d, J
= 7.9 Hz, 1H), 6.41 (d, J = 8.2 Hz, 1H), 3.51 – 3.45 (m, 2H), 1.67 (m, 2H), 1.43 (m, 6H), 0.94 (t, J = 5.8 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 145.1, 144.69, 143.28 , 132.82 , 132.54, 129.96, 127.48 , 125.29 , 123.54 , 122.77,
120.78, 119.35 , 115.40 , 112.00, 111.36 , 111.11 , 44.06 , 31.64 , 26.59 , 24.99, 22.67 , 14.02. Anal. Calcd (%) for
C24H25NOS: C, 76.76; H, 6.71; N, 3.73; found: C, 76.83; H, 6.82; N, 3.67;
2.2.6 Synthesis of (E)-10-(4-methoxyphenyl)-3-(2-(thiophen-2-yl)vinyl)-10H-phenoxazine (Compound 4d)
The procedure for compound 4a was followed to prepare 4d from 3d and 3e as yellow solid with 82.1% yield
1
(1.63 g, 4.10 mmol). m.p. : 146.8 ºC. MS, m/z: 397.11 (M+). H NMR (400 MHz, CDCl3) δ 7.23 (d, J = 8.8 Hz,
2H), 7.11 (d, J = 5.0 Hz, 1H), 7.07 (d, J = 8.8 Hz, 2H), 6.99 (d, J = 3.4 Hz, 1H), 6.89 (d, J = 4.6 Hz, 1H), 6.71 (s,
1H), 6.62 (d, J = 9.6 Hz, 2H), 6.58 (d, J = 7.6 Hz, 2H), 6.52 (d, J = 11.9 Hz, 1H), 6.30 (d, J = 11.9 Hz, 1H), 5.92 (d,
J = 7.6 Hz, 1H), 5.87 (d, J = 8.2 Hz, 1H), 3.85 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 159.16, 143.67, 143.53,
139.61, 134.18, 133.82, 131.24, 129.82, 128.09, 127.58, 126.33, 125.00, 123.87, 123.04, 121.78, 121.07, 115.99,
115.43, 115.15, 113.0, 112.72, 55.00. Anal. Calcd (%) for C25H19NO2S: C, 75.54; H, 4.82; N, 3.52; found: C, 75.61;
H, 4.93; N, 3.49;
2.2.7 Synthesis of (E)-5-(2-(9-hexyl-9H-carbazol-3-yl) vinyl) thiophene-2-carbaldehyde (Compound 5a)
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Under a N2 atmosphere, 4a (0.72 g, 2.00 mmol) was dissolved in 150 mL freshly distilled THF and cooled to
-78 °C. Approximately 2 equivalents of BuLi in hexanes (16 mL, 4 mmol) was added drop wise over 20 min.
Reaction continued at -78 °C for 1 h at which time DMF (0.29 g, 4.00 mmol) was added over 1 min. The reaction
was allowed to reach RT while the solution stirred for 1h. The organic phase was extracted by AcOEt, washed with
brine and dried over MgSO4. After removal of the solvent under reduced pressure, the crude product was purified
by silica chromatography, eluting with (Acetone: Hexane = 1:5) to give compound 6c as an orange solid with 76.7%
yield (0.59 g, 1.53 mmol). m.p. : 115.8 ºC. MS, m/z: 387.17 (M+). 1H NMR (400 MHz, CDCl3) δ 9.78 (s, 1H), 8.12
(s, 1H), 8.06 (d, J = 7.7 Hz, 1H), 7.56 (d, J = 3.9 Hz, 1H), 7.54 – 7.41 (m, 2H), 7.35 (d, J = 8.2 Hz, 1H), 7.29 –
7.25 (m, 2H), 7.22 (d, J = 8.9 Hz, 1H), 7.14 (d, J = 16.0 Hz, 1H), 7.03 (d, J = 3.9 Hz, 1H), 4.18 (t, J = 7.3 Hz, 2H),
1.76-1.83(m,2H), 1.38 – 1.29 (m, 2H), 1.26-1.28 (m, 4H), 0.84 (t, J = 7.0 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ
182.33, 153.53, 140.75, 140.40, 137.44, 134.06, 126.73, 125.96, 125.36, 124.58, 123.14, 122.60, 120.29, 119.38,
119.22, 117.76, 108.81, 43.04, 31.43, 28.81, 26.81, 22.43, 13.92. Anal. Calcd (%) for C25H25NOS: C, 77.48; H,
6.50; N, 3.61; found: C, 77.52; H, 6.46; N, 3.65;
2.2.8 Synthesis of (E)-5-(2-(10-hexyl-10H-phenothiazin-3-yl)vinyl)thiophene-2-carbaldehyde (Compound 5b)
The procedure for compound 5a was followed to prepare 5b from 4b as a red solid in 73.2% yield (0.26 g, 0.63
1
mmol). m.p. : 126.48 °C. MS, m/z: 419.64 (M+). H NMR (400 MHz, CDCl3) δ 9.81 (s, 1H), 7.59 (d, J = 3.8 Hz,
1H), 7.20 (d, J = 8.0 Hz, 2H), 7.13 (m, 2H), 7.05 (d, J = 3.9 Hz, 1H), 6.99 (d, J = 5.5 Hz, 2H), 6.92 (t, J = 7.5 Hz,
1H), 6.84 (d, J = 8.2 Hz, 1H), 6.77 (d, J = 8.2 Hz, 1H), 3.81 (t, J = 7.2 Hz, 2H), 1.83 – 1.70 (m, 2H), 1.46 – 1.35 (m,
2H), 1.33 – 1.23 (m, 4H), 0.88 (t, J = 6.6 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 182.31, 152.72, 145.52 , 144.32 ,
140.96, 137.23 , 131.66, 130.07 , 127.29 , 127.25 , 126.51, 125.96 , 125.03 , 124.96, 123.80, 122.56 , 118.79 ,
115.35, 115.14 , 47.52 , 31.32, 26.67 , 26.47 , 22.48 , 13.89. Anal. Calcd (%) for C25H25NOS2: C, 71.56; H, 6.01; N,
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3.34; found: C, 71.63; H, 6.11; N, 3.27;
2.2.9 Synthesis of (E)-5-(2-(10-hexyl-10H-phenothiazin-3-yl)vinyl)thiophene-2-carbaldehyde (Compound 5c)
The procedure for compound 5a was followed to prepare 5c from 4c as as a red solid with 75.6% yield (0.27 g,
0.66 mmol). m.p. : 126.90 °C. MS, m/z: 403.56 (M+). 1H NMR (400 MHz, CDCl3) δ 9.81 (s, 1H), 7.61 (d, J = 3.9
Hz, 1H), 7.05 (d, J = 3.9 Hz, 1H), 6.93 (d, J = 3.4 Hz, 2H), 6.86 (dd, J = 8.3, 1.5 Hz, 1H), 6.82 – 6.76 (m, 2H),
6.69 – 6.59 (m, 2H), 6.47 (d, J = 8.3 Hz, 1H), 6.40 (d, J = 8.3 Hz, 1H), 3.49 – 3.43 (m, 2H), 1.65 (m, 2H), 1.38 (m,
6H), 0.92 (t, J = 6.7 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ 182.23, 153.17 , 145.22 , 144.74 , 140.95 , 137.14 ,
134.22 , 132.46 , 132.15, 128.81 , 125.66 , 124.05 , 123.69, 121.31, 118.09, 115.45 , 112.31, 111.57 , 111.11, 44.20,
31.53 , 26.56 , 25.10, 22.60, 13.94. Anal. Calcd (%) for C25H25NO2S: C, 74.41; H, 6.24; N, 3.47; found: C, 74.49;
H, 6.19; N, 3.53;
2.2.10 Synthesis of (E)-5-(2-(10-(4-methoxyphenyl)-10H-phenoxazin-3-yl)vinyl) thiophene-2-carbaldehyde
(Compound 5d)
The procedure for compound 5a was followed to prepare 5d from 4d as yellow solid with 73.1% yield (0.62 g,
1
1.46 mmol). m.p. : 158.5 ºC. MS, m/z: 425.11 (M+). H NMR (400 MHz, CDCl3) δ 9.78 (s, 1H), 7.59 (d, J = 3.9
Hz, 1H), 7.24 – 7.19 (m, 2H), 7.12 – 7.07 (m, 2H), 7.04 (d, J = 3.9 Hz, 1H), 6.93 (d, J = 16.0 Hz, 1H), 6.87 (d, J =
16.0 Hz, 1H), 6.83 (d, J = 1.9 Hz, 1H), 6.69 – 6.66 (m, 2H), 6.65 (s, 1H), 6.64 – 6.54 (m, 1H), 5.97 – 5.91 (m, 1H),
5.88 (d, J = 8.3 Hz, 1H), 3.88 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 182.29, 159.41, 153.02, 144.06, 143.59,
140.71, 137.34, 135.31, 133.74, 132.01, 131.38, 130.42, 129.08, 125.74, 123.50, 123.29, 121.46, 118.04, 116.18,
115.31, 113.39, 112.98, 112.31, 55.44. Anal. Calcd (%) for C26H19NO3S: C, 73.39; H, 4.50; N, 3.29; found: C,
73.42; H, 4.53; N, 3.26;
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2.2.11 Synthesis of 2-(3-cyano-4-((E)-2-(5-((E)-2-(9-hexyl-9H-carbazol-3-yl) vinyl) thiophen-2-yl)
vinyl)-5,5-dimethylfuran-2(5H)-ylidene)malononitrile (Chromophore CBZ)
To a solution of 5a (0.19 g, 0.50mmol) and the 2-dicyanomethylene-3-cyano-4,5,5-dimethyl-2,5-dihydrofuran
(TCF) acceptor (0.12 g, 0.60 mmol) in MeOH (60 mL) was added several drops of triethylamine. The reaction was
stirred at 78 ºC for 5 h. The reaction mixture was cooled. After removal of the solvent under reduced pressure, the
crude product was purified by silica chromatography, eluting with (AcOEt: Hexane = 1:5) to give chromophore A
as a purple solid in 61.9% yield (0.18 g, 0.31mmol). m.p. : 197.7 ºC. MS, m/z: 568.23 (M+). 1H NMR (400 MHz,
d6-acetone) δ 8.45 (s, 1H), 8.16 (d, J = 15.9 Hz, 2H), 7.80 (dd, J = 8.6, 1.5 Hz, 1H), 7.70 (d, J = 4.0 Hz, 1H), 7.64
– 7.57 (m, 2H), 7.51 (d, J = 6.1 Hz, 2H), 7.48 (dd, J = 8.2, 0.9 Hz, 1H), 7.31 (d, J = 4.0 Hz, 1H), 7.27 – 7.22 (m,
1H), 6.87 (d, J = 15.9 Hz, 1H), 4.44 (t, J = 7.2 Hz, 2H), 1.70 (s, 6H), 1.43 – 1.36 (m, 2H), 1.33 – 1.25 (m, 6H),
0.86(t, J=8.5Hz,3H). 13C NMR (100 MHz, d6-acetone) δ 186.12, 178.19, 153.92, 142.51, 141.35, 139.82, 139.06,
135.99, 129.65, 128.97, 127.77, 126.65, 124.76, 124.17, 122.09, 121.28, 120.87, 119.94, 113.11, 112.50, 110.96,
105.84, 102.34, 99.76, 57.49, 44.40, 32.98, 28.05, 26.84, 24.63, 23.67, 15.08 14.86. Anal. Calcd (%) for
C36H32N4OS : C, 76.03; H, 5.67; N, 9.85; found: C, 76.13; H, 5.69; N, 9.79;
2.2.12
Synthesis
of
2-(3-cyano-4-((E)-2-(5-((E)-2-(10-hexyl-10H-phenothiazin-3-yl)
vinyl)thiophen-2-yl)vinyl)-5,5-dimethylfuran-2(5H)-ylidene)malononitrile (Chromophore PTZ)
The procedure for chromophore CBZ was followed to prepare chromophore PTZ from 5b as a purple solid in
63.2% yield (0.19 g, 0.32 mmol). m.p. : 200.23 °C. MS, m/z: 600.20 (M+). 1H NMR (400 MHz, d6-acetone) δ 8.15
(d, J = 15.9 Hz, 1H), 7.68 (d, J = 3.9 Hz, 1H), 7.44 (dd, J = 11.7, 4.4 Hz, 3H), 7.29 (d, J = 3.9 Hz, 1H), 7.21 (d, J =
4.4 Hz, 1H), 7.18 (d, J = 3.2 Hz, 1H), 7.15 (d, J = 7.5 Hz, 1H), 7.05 (d, J = 8.4 Hz, 2H), 6.96 (t, J = 7.5 Hz, 1H),
11

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6.88 (d, J = 15.9 Hz, 1H), 3.98 (t, J = 6.9 Hz, 2H), 1.89 (s, 6H), 1.52 – 1.39 (m, 2H), 1.27 (m, 6H), 0.86 (t, J = 6.6
Hz, 3H). 13C NMR (100 MHz, d6-acetone) δ 177.22, 174.73, 152.18, 146.43, 145.17, 140.44 , 139.71 , 138.06,
132.40, 131.53 , 129.13 , 128.31 , 127.92, 127.76, 125.76 , 125.76 , 124.56 , 123.52 , 120.22 , 116.71 , 116.52,
113.84, 113.04, 112.41 , 111.42 , 99.06, 47.79 , 32.02 , 27.43 , 26.88, 26.05, 22.89, 14.10. Anal. Calcd (%) for
C36H32N4OS2 : C, 71.97; H, 5.37; N, 9.33; found: C, 72.04; H, 5.39; N, 9.29;
2.2.13
Synthesis
of
2-(3-cyano-4-((E)-2-(5-((E)-2-(10-hexyl-10H-phenoxazin-3-yl)
vinyl)thiophen-2-yl)vinyl)-5,5-dimethylfuran-2(5H)-ylidene)malononitrile (Chromophore POZ)
The procedure for chromophore CBZ was followed to prepare chromophore POZ from 5c as a green solid in in
65.3% yield (0.19 g, 0.33 mmol). m.p. : 201.13 °C. MS, m/z: 585.02 (M+). 1H NMR (400 MHz, d6-acetone) δ 8.13
(d, J = 15.9 Hz, 1H), 7.66 (d, J = 3.9 Hz, 1H), 7.29 (d, J = 16.1 Hz, 1H), 7.25 (d, J = 3.9 Hz, 1H), 7.09 (d, J = 15.8
Hz, 2H), 6.96 (s, 1H), 6.84 (dd, J = 11.7, 4.2 Hz, 2H), 6.76 – 6.62 (m, 4H), 3.66 (t, J=7.6Hz, 2H), 1.89 (s, 6H),
1.74 – 1.64 (m, 2H), 1.49 (m, 2H), 1.43 – 1.34 (m, 4H), 0.91 (t, J = 6.8 Hz, 3H). 13C NMR (100 MHz, d6-acetone)
δ 177.23 , 175.04, 152.61, 145.76, 145.31 , 140.47 , 139.43, 138.24, 134.93, 133.08, 132.93 , 130.04 , 128.93,
125.51, 124.81, 122.14, 119.33 , 115.92 , 113.65, 113.08, 112.96, 112.91, 112.57, 112.42, 111.52 , 99.01, 44.05,
32.15, 26.83, 26.11, 25.50 , 23.21 , 14.01 . Anal. Calcd (%) for C36H32N4O2S : C, 73.95; H, 5.52; N, 9.58; found: C,
74.03; H, 5.58; N, 9.55;
2.2.14 Synthesis of 2-(3-cyano-4-((E)-2-(5-((E)-2-(10-(4-methoxyphenyl)-10H-phenoxazin-3-yl) vinyl)
thiophen-2-yl)vinyl)-5,5-dimethylfuran-2(5H)-ylidene)malononitrile (Chromophore PPZ)
The procedure for chromophore CBZ was followed to prepare chromophore PPZ from 5d as a green solid in
60.8% yield (0.18 g, 0.30 mmol). m.p. : 203.8 ºC. MS, m/z: 606.17 (M+). 1H NMR (400 MHz, d6-acetone) δ 8.13
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(d, J = 15.9 Hz, 1H), 7.66 (d, J = 4.0 Hz, 1H), 7.33 (m, 3H), 7.25 (d, J = 4.0 Hz, 1H), 7.22 (d, J = 8.9 Hz, 2H),
7.09 (d, J = 16.0 Hz, 1H), 7.03 (s, 1H), 6.92 (d, J = 9.9 Hz, 1H), 6.84 (d, J = 15.9 Hz, 1H), 6.67 (m, 3H), 5.93 (t, J
= 7.9 Hz, 2H), 3.90 (s, 3H), 1.88 (s, 6H). 13C NMR (100 MHz, CDCl3) δ 181.98, 159.75, 152.81, 144.34, 143.82,
139.20, 138.10, 136.84, 136.02, 133.78, 132.99, 131.44, 130.67, 129.29, 127.52, 124.09, 123.39, 121.85, 118.01,
116.40, 115.48, 113.64, 113.27, 112.34, 110.96, 110.18, 108.81, 105.03, 99.33, 96.92, 55.57, 29.66 , 26.47, 24.26.
Anal. Calcd (%) for C37H26N4O3S : C, 73.25; H, 4.32; N, 9.23; found: C, 73.36; H, 4.38; N, 9.17;
Scheme 1
3. Results and discussion
3.1 Synthesis and characterization
Scheme 1 shows the synthetic approach to the chromophores CBZ, PTZ, POZ and PPZ. Starting from the amine
donor intermediates compound 1a-c, chromophores CBZ, PTZ, POZ and PPZ were synthesized in good overall
yields through simple five step reactions: The free N-H group on the donors was protected by the alkyl or aryl
group to improve either the solubility or stability. Treatment of compound 2a-d with POCl3 and DMF gave an
aldehydes 3a-d. After introduction of the thiophene bridge by a Wittig condensation, compounds 4a-d were
prepared with a high yield. Treatment of compound 4a-d with n-BuLi and DMF gave aldehyde 5a-d, the final
condensations with the TCF acceptor give chromophores CBZ, PTZ as purple solids and chromophores POZ, PPZ
as green solids. All of the chromophores were fully characterized by 1H-NMR and 13C-NMR spectroscopy,
elemental analysis and mass spectrometry. These chromophores possess good solubility in common organic
solvents, such as dichloromethane, chloromethane and acetone.
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Fig. 2
3.2 Thermal stability
The thermal stability of the chromophores was investigated using thermogravimetric analysis (TGA) as shown
in Figure 2 and Table 1. All the chromophores exhibited good thermal stabilities with the decomposition
temperatures (Td) higher than 210 °C (216 °C-298 °C). Chromophore TPA has the highest decomposition
temperature (298 °C) [41], followed by PPZ (252 °C), FTC (242 °C) [30] , PTZ (232 °C), POZ (223 °C) and CBZ
(216 °C). The enhanced thermal stability of the chromophores TPA and PPZ over PTZ, POZ, CBZ and FTC is due
to the replacement of alkyl chain to benzene ring on the donor nitrogen. All the thermal stabilities of five
chromophores were high enough for the application in EO device preparation [36].
Fig. 3
Table 1
3.3 Optical properties
In order to reveal the effect of different electron donors on the charge-transfer (CT) absorption properties of the
six chromophores, UV-Vis absorption spectra of the six chromophores were measured in a series solvent with
different dielectric constants as shown in Figure 3 and 4. The spectral data are summarized in Table 1. The
absorption maxima (λmax) of chromophores CBZ, TPA, PTZ, POZ, PPZ and FTC are 606, 620, 610, 665, 660 and
675 nm, respectively. The five aryl chromophores CBZ, TPA, PTZ, POZ and PPZ were blue-shifted in their
absorption spectra, compared to the alkyl chromophore FTC, probably due to delocalization of the nitrogen lone
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pair into the other phenyl rings of the donor. Although chromophore POZ showed a slight 10 nm blue-shift, its
charge-transfer band is slightly broader than that of chromophore FTC (Figure 3), which extends to about 900 nm.
This could indicate that the CT state is populated over a wide range of energy levels, suggesting energy gaps ∆E
(optical) of chromophore POZ is still smaller than that of chromophore FTC. Chromophores POZ and PPZ were
red-shifted in their absorption spectra, compared to the other three aryl chromophores CBZ, TPA and PTZ, due to
the gradually increased π-donor strength which induced by additional electron donor O atom. The S atom is quite a
weak electron donor, so the λmax of chromophore PTZ is similar to chromophores CBZ and TPA. Although
chromophore PTZ showed a slight blue-shift, its charge-transfer band is slightly broader than that of chromophore
TPA. This could also indicate that ∆E (optical) of chromophore PTZ is still smaller than that of chromophore TPA.
Chromophore PPZ including the N-(4-methoxyphenyl) substituent showed a slight blue-shift in its absorption
spectrum, compared to chromophore POZ including the N-butylchain. This may be ascribed to the
N-(4-methoxyphenyl) substituent, which is particular to the average plane of the chromophore, gave inefficient
conjugation as showed by the following theoretical calculations (section 3.4).
The solvatochromic behavior was also an important aspect to investigate the polarity of chromophores. It was
found that chromophores POZ, PPZ and FTC showed very large bathochromic shifts of 49 nm, 50 nm and 54nm,
respectively, on moving from dioxane to chloroform. Chromophores CBZ, TPA and PTZ showed slightly smaller
bathochromic shift of 40 nm, 43 nm and 36 nm respectively, from dioxane to chloroform. This confirms that
chromophores POZ, PPZ and FTC are more easily polarizable than chromophores CBZ, TPA and PTZ [42, 43].
Fig. 4
Table 2
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3.4 Redox properties and Theoretical calculations
In order to determine the electrochemical properties of the six chromophores, cyclicvoltammetry (CV)
measurements were conducted in degassed anhydrous acetonitrile solutions containing 0.1mol/L
tetrabutylammonium hexafluorophosphate (TBAPF) as the supporting electrolyte. The relative data of 1×10-4
mol/L chromophore were recorded, as shown in Table 2 and Fig. 6. The HOMO and LUMO levels of the six
chromophores can be calculated from their corresponding oxidation and reduction potentials [47]. The difference
between these two values provides the HOMO-LUMO energy difference ∆E (CV). The calculation results are
summarized in Table 2. The energy gaps between the HOMO and LUMO energy for chromophores CBZ, TPA,
PTZ, POZ, PPZ and FTC were 1.83 eV, 1.72 eV, 1.52 eV, 1.40 eV, 1.48eV and 1.43eV, respectively.
From the calculated values reported in Table 2, it can be concluded that the LUMO energy levels are
approximately the same for all the compounds. Conversely, chromophores CBZ, TPA, PTZ, POZ, PPZ and FTC
showed oxidation potential versus ferrocene/ferrocenium at 0.65 V, 0.59 V, 0.41 V, 0.30 V, 0.37 V and 0.32 V,
respectively. The gradual decrease of the oxidation potentials were dictated by the progressively increased strength
of the donor group. The HOMO energy levels are systematically lowered with an increase in the donor strength
which influences the HOMO to a greater extent than the LUMO level. From the λmax, the cutoff wavelength (λ
cut-off) and the energy gap between the HOMO and LUMO energy of the six chromophores, we could assign the
order of electron donor strength under the same accepting strength from TCF as follows: CBZ < TPA < TPZ < PPZ
< FTC < POZ.
The DFT calculations were carried out at the hybrid B3LYP level by employing the split valence 6-311g (d, p)
basis set [44, 45] to understand the ground-state polarization of the chromophores with different configurations.
All molecules were assumed to be in trans-configurations. The geometrically optimized structures of the
molecules were investigated by calculating the dihedral angles of the donor moieties as shown in Fig. 5. The
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geometries of the six chromophores are totally different. The geometry of chromophore CBZ is planar, reveals the
aromatic character of the central CBZ heterocycle, which facilitates the delocalization of the nitrogen lone pair into
the other phenyl rings. So, the CBZ based chromophore exhibits reduced µβ. The three benzene rings of the TPA
are not in the same plane, the dihedral angle between the other two benzene rings on the N atom of the TPA moiety
and the average plane of the average plane of the chromophores was ca. 66.40° and 67.39°, respectively, as shown
in picture 1 and 5. The twisted structure may somehow attenuate the delocalization of the nitrogen lone pair into
two phenyl rings.
The geometry of PTZ and POZ moieties are not totally planar but are rather slightly bent in the middle to give a
butterfly shape. In the optimized structures, the angle between the non-planar phenyl ring of the PTZ/ POZ moiety
and the average plane of the chromophores was ca. 9.32 ° and 25.98 °, respectively. As for chromophore PPZ, the
two benzene rings exhibited almost planar structures with small torsion angles (1.34°), the N-(4-methoxyphenyl)
substituent located on the nitrogen atom made a large dihedral angle of about 90° with average plane of the
chromophore. This large dihedral angle caused large steric hindrance that suppressed aggregations among
molecules.
Fig. 5
Fig. 6
The frontier molecular orbitals are often used to obtain information about the optical and electrical properties of
molecules [46]. Fig. 5 depicts the electron density distribution of the HOMO and LUMO structures which
indicated the density of the ground and excited state electron is asymmetrical along the dipolar axis of the
chromophores.
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The molecular quadratic hyperpolarizability (µβ) of the chromophores obtained from DFT calculations are
calculated as shown in Table 2. When used carefully and consistently, this method of DFT has been shown to give
relatively consistent descriptions of first-order hyperpolarizability for a number of similar chromophores [8, 45,
47].
The µβ value of chromophore CBZ and TPA was smaller than that of chromophore FTC, due to delocalization
of the nitrogen lone pair into the other phenyl rings. The geometry of chromophore CBZ is planar, reveals the
aromatic character of the central CBZ heterocycle, which facilitate the delocalization of the nitrogen lone pair into
the other phenyl rings. So, the CBZ based chromophore exhibit reduced µβ compared to chromophore FTC
although they both contain one donor N atom donor. The delocalization of the nitrogen lone pair into the other two
phenyl rings of chromophore TPA could also result in smaller µβ than that of chromophore FTC. The µβ value of
chromophore TPA was larger than that of chromophore CBZ due to a narrower energy gap between HOMO and
LUMO. With additional electron-rich sulfur heteroatoms into the benzene ring moiety of donor, the PTZ show a
little stronger donor strength than TPA. The POZ unit with electron-rich nitrogen and oxygen heteroatoms has
stronger electron-donating ability than PTZ because O atom is a much stronger donor than S atom in this case thus
results in larger µβ. With two additional oxygen heteroatoms into the benzene ring moiety of donor, the
chromophore PPZ showed an even larger µβ. This indicates that by introducing additional heteroatoms into the
donor could provide abundant opportunities for further modifications of chromophores thus influence nonlinear
optical properties of chromophores
3.5 Electro-Optic performance
In order to investigate the translation of the microscopic hyperpolarizability into a macroscopic EO response,
the polymer films doped with 25wt% chromophores into amorphous polycarbonate (APC) were prepared using
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dibromomethane as solvent. The resulting solutions were filtered through a 0.2-ꢀm PTFE filter and spin-coated
onto indium tin oxide (ITO) glass substrates. Films of doped polymers were baked at 80 °C in a vacuum oven
overnight. The corona poling process was carried out at a temperature of 10 °C above the glass transition
temperature (Tg) of the polymer. The r33 values of poled films were measured by Teng–Man simple reflection
method at a wavelength of 1310 nm using a carefully selected thin ITO electrode with low reflectivity and good
transparency in order to minimize the contribution from multiple reflections [48, 49].
The r33 values were calculated by the following equation [50]:
3/2
3
λ
Ι
m
(n2 − sin2 θ
)
1
r33 =
4
π
V
m
I
n2 (n2 − 2sin2 θ ) sin2 θ
c
Where r33 is the EO coefficient of the poled polymer, λ is the optical wavelength, h is the incidence angle, Ic is
the output beam intensity, Im is the amplitude of the modulation, Vm is the modulating voltage, and n is the
refractive indices of the polymer films.
The poled films of CBZ/APC, TPA/APC, PTZ/APC, POZ/APC, PPZ/APC and FTC/APC afforded r33 values of
13, 19, 23, 49, 61 and 39 pmV-1 at 1310 nm, respectively. In these chromophores, the r33 values were gradually
improved from 13 pm/V to 61 pm/V, illustrating that the increases donor strength of the chromophores
significantly increase their macroscopic EO activities. The additional donor oxygen or sulfur heteroatom may
strengthen the electron-donating power of the donor. The stronger the electron-donating power of the donor leads
to higher λmax, µβ, and r33values [51]. Besides, solvatochromic behaviour indicated that chromophores POZ, PPZ
and FTC are more easily polarizable than chromophores CBZ, TPA and PTZ. Therefore, in corona poling,
chromophores POZ, PPZ and FTC may obtain orientation more easily in contrast with chromophore CBZ, TPA
and PTZ. Except for larger µβ, the much larger r33 value of films POZ/APC and PPZ/APC over film FTC/APC
may also be explained by favourable poling efficiency which related to chromophore property, chromophore-host
compatibility and so on. The long alkyl chain in chromophores POZ can provides effective site isolation to
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decrease the strong electrostatic interactions among chromophores. As for chromophores PPZ, the
N-(4-methoxyphenyl) substituent located on the nitrogen atom at the donor which almost perpendicular to the
average plane of the chromophore was intended to prevent the strong electrostatic interactions between
chromophores. The undesired antiparallel packing between chromophores is expected to decrease during the
poling process [51]. Although the µβ value of chromophore PPZ is only 19% larger than that of chromophore POZ,
the r33value is almost 25% larger due to a better isolation effect. Moreover, the chromophore PPZ showed nearly
three times higher µβ and more than four times higher r33 value than that of chromophore CBZ. Besides, the
r33values of this new aryl chromophore can even be higher than those obtained from their alkyl D-π-A analogue
chromophore FTC. So the chromophore PPZ has not only a larger µβ but also advantages in translating µβ into the
macroscopic EO activity due to additional donor oxygen heteroatom and isolation effect of N-(4-methoxyphenyl)
substituent.
4. Conclusion
Six second-order nonlinear optical chromophores containing an identical π-bridge and electron acceptors but
different, aromatic amine electron-donating groups have been synthesized and systematically characterized. To
further study the effect of different electron donating groups of second-order nonlinear optical chromophores on
nonlinearity performance, three chromophores based on novel donors (PTZ, POZ, and PPZ) were synthesized to
compare with chromophores based on traditional donors (CBZ, TPA and FTC). Theoretical and experimental
investigations suggest that donor group's efficacy in PTZ, POZ, and PPZ chromophore was higher than that of
structurally similar CBZ and TPA chromophore. Cyclicvoltammetry (CV) measurements and DFT calculations
show that chromophores PTZ, POZ, and PPZ have reduced energy gap, much larger molecular quadratic
hyperpolarizability (µβ) than that of chromophores CBZ and TPA. The high molecular hyperpolarizability of these
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chromophores can be effectively translated into electro-optic (EO) coefficients (r33) in poled polymers. The r33
value of chromophores PTZ and POZ were even higher than their alkyl D-π-A analogue chromophores FTC. These
two chromophores showed excellent thermal stability with an onset decomposition temperatures higher than
220 °C. High r33values, high thermal stability, together with good solubility, showed that the novel donors which
contain nitrogen and oxygen heteroatoms show promising applications in nonlinear optical (NLO) chromophore
devices.
Acknowledgments
We are grateful to the National Natural Science Foundation of China (No. 11104284 and No. 61101054) for the
financial support.
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Table 1 Thermal and optical properties data of the chromophores.
Cmpd
CBZ
TPA
PTZ
POZ
PPZ
FTC
Td (
216
298
232
223
252
242
℃
)
λmaxa (nm) λmaxb (nm) ꢀλc (nm)
606
620
610
665
660
675
566
577
574
615
611
40
43
36
50
49
54
621
b
a
b
a λmax was measured in chloroform. λmax was measured in dioxane. c ꢀλ was the difference between λmax and
λmax.
Table 2 Summary of DFT, electro-chemical data and EO coefficients of chromophores
Cmpd
CBZ
TPA
PTZ
POZ
PPZ
△
E(CV)a(eV)
E ox b(V)
0.653
0.590
0.408
0.304
0.372
0.321
E red c(V)
-1.185
-1.136
-1.115
-1.099
-1.113
-1.109
µβ d(10-48esu)
3805.75
r33(pm/V)
1.83
1.72
1.52
1.40
1.48
1.43
13
19
23
49
61
39
6776.72
7075.97
8523.60
10167.05
7737.78
FTC
b
△E(CV)a was calculated from their corresponding oxidation and reduction potentials.
Referenced to ferrocene
standard. c Referenced to ferrocene standard. µβ d is calculated from DFT quantum mechanical methods.