Monolithic NLO chromophores with different pendant groups and matrix-assisted-poling effect: Synthesis and chractorization

Article abstract of DOI:10.1016/j.dyepig.2018.04.061

Realization of the large electro-optic (EO) activity for organic nonlinear optical (NLO) chromopores with high first order hyperpolarizability requires simultaneous optimization for molecular structure. In this work, we investigated the influences of diff

Full text of DOI:10.1016/j.dyepig.2018.04.061

Accepted Manuscript
Monolithic NLO chromophores with different pendant groups and matrix-assisted-
poling effect: Synthesis and chractorization
Huajun Xu, Nan Wang, Xiaoling Zhang, Zhonghui Li, Guowei Deng
PII:
S0143-7208(18)30738-1
10.1016/j.dyepig.2018.04.061
DYPI 6722
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 2 April 2018
Revised Date: 28 April 2018
Accepted Date: 28 April 2018
Please cite this article as: Xu H, Wang N, Zhang X, Li Z, Deng G, Monolithic NLO chromophores with
different pendant groups and matrix-assisted-poling effect: Synthesis and chractorization, Dyes and
Pigments (2018), doi: 10.1016/j.dyepig.2018.04.061.
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ACCEPTED MANUSCRIPT
Monolithic NLO chromophores with different pendant groups
and matrix-assisted-poling effect: synthesis and chractorization
Huajun Xub, Nan Wanga, Xiaoling Zhanga, Zhonghui Lia, Guowei Denga*
a College of Chemistry and Life Science, Institute of Functional Molecules, Chengdu Normal University, Chengdu
611130, China.
b Department of Chemistry, University of Washington, Seattle, WA, USA 98195.
* Corresponding author. Tel.: +86-28-66775260.
Email: guoweideng86@163.com
Abstracts
Realization of the large electro-optic (EO) activity for organic nonlinear optical (NLO) chromopores with high first
order hyperpolarizability requires simultaneous optimization for molecular structure. In this work, we investigated
the influences of different pendant groups in chromophore’s side chains on the performance of EO materials. A
series of NLO chromophores F1-F3 based on the same conjugated structure but with different pendant groups have
been synthesized and systematically investigated. Due to the disperse-red type pendant groups, chromophore F3
shows excellent film-forming ability and relatively high glass transition temperature without blending with
optically inactive polymer matrix. The Variable Angle Spectroscopic Ellipsometry (VASE) measurement proves
the neat F3 film displays a higher index of refraction value and weak absorption at 1310 nm and 1550 nm, which
is beneficial for reducing the operation voltage and optical loss of modulator. Due to the effective isolating ability
of pendant groups, the best EO coefficient of the poled F3 film reaches to 81pm/V, which is two times larger than
the value of the same type chromophore in guest-host material. This result, together with high index of refraction
and low optical loss, will shed light on a new perspective for the design of new monolithic organic EO materials.
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Keywords: nonlinear optic; chromophore; pendant group; matrix-assisted; poled polymer
1. Introduction
Organic electro-optic (EO) materials have drawn much attention due to their attractive commercial applications in
computing, telecommunications, and sensing such as phased array radar, electronic/photonic integrated circuits,
terahertz spectroscopy, etc.[1-8] Compared with traditional inorganic and semiconductor materials, the organic EO
materials have faster intrinsic response times and lower dielectric constants than lithium niobate leading to higher
modulation bandwidth and efficiency.[9-13] The EO coefficient (r33) of organic material mainly depends on three
critical parameters: EO chromophore’s first molecular hyperpolarizability, βzzz, number density, N, and the acentric
order parameter, <cos3 θ>. The r33 value were calculated by the following equation:
(1)
Where n is the material’s index of refraction and the ratio λmax2/λ2 refers to the wavelength at maximum
2
2
absorbance to the wavelength of the incident light field. The local field correction FL = ((η0 (ηω +3))/(
2
2
2
ηω +2η0 ))(( ηω +2)/3)2 is the product of Lorentz and Onsager field factors for the static- and
frequency-dependent refractive indices of the material.[14]
In the past decade, many researches have mainly focused on the design of chromophore with improving high
βzzz.[3, 7, 15-26] Generally, the improvement of βzzz will be accompanied with the increase of molecular dipole
moment. Extensive experimental and theoretical studies have shown that the chromophore’s aggregation, which
was mainly caused by the strong intermolecular electrostatic interaction among chromophores with high dipole
moment, hinders chromophore getting acentric order under poling electric field.[25-28] The chromophores should
be systematically modified to reduce dipole-dipole aggregation. Recently, the nonlinear optical (NLO)
chromophore’s design methodology with enhanced N and <cos3 θ> has been turned into a hot research spot in the
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area of organic EO materials.[29-38] Several successful monolithic EO materials have been reported in which the
pendant groups are incorporated into chromophore’s side-chain to promote intermolecular cooperativity over
nanometer length scales. Jen et al. have introduced arene-perfluoroarene interaction which is known as a strong
face-to-face interaction into NLO chromophore design to create tightly packed molecular assemblies leading to a
new class of supramolecular materials. [12, 39-41] Dalton et al. have systematically researched the chromophore
self-assembly from coumarin-coumarin intermolecular interactions. [29, 42-46] Due to the large steric hindrance
of pendant groups, the chromophore will be well isolated with other neighbor chromophores to avoid detrimental
anti-parallel aggregation.[22, 47-50] This kind of side-chain chromophores generally exhibit excellent
film-forming ability and moderate glass transition temperature (Tg), which mean they can be used to fabricated EO
device without polymer host. For the Mach−Zehnder EO modulator, the voltage required to produce a π-phase
shift of light, Vπ, is a key parameter for energy consumption and thermal management, which is given by
푑
2 3ꢀ33퐿Г
푉
휋
(2)
Where λ is the optical wavelength, n is the index of refraction, d is the electrode gap, L is the electrode length
(interaction length of the electrical and optical fields), and Γ is the electrical/optical overlap integral. The
monolithic materials display higher index of refraction compared with chromophore/polymer system, which is
useful for Vπ decrease. Pendant groups interactions covalently linked to chromophores with large dipole moments
effectively prevent phase separation which is common in guest-host materials with high chromophore
concentration. What’s more, monolithic EO materials exhibit some other important properties, such as better
solubility, lower optical loss, etc.[8]
In this work, we design and synthesize three “FTC” (thiophene bridge) type chromphores with different pendant
groups in side chains. The hydroxyl group, bulky tert-butyl-diphenyl-silyl group (TBDPS) and disperse-red 1
(DR1) are chosen as pendant functional parts. DR1 is a common dye widely used in textile industry and NLO
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materials, which has large steric hindrance and weak dipole-dipole interaction with each other. Meanwhile, the
weak intermolecular interaction between DR1s would be helpful for improving the film-forming ability and Tgs of
monolithic materials. The abilities of assisting chromophore-poling are compared. Apart from chromophore F1,
the other two chromophores (F2 and F3) were spin-coated into thin films without polymer matrix. The
structural-directing side chains act as the matrix which can effectively improve the chromophore concentration and
index of refraction, and reduce the optical loss. For reasonable comparison, previously reported chromophores
EZ-FTC was used as bench chromophores.[18, 51] Four chromphores’ structures were presented in Figure 1.
These NLO chromophores all choose 2-dicyanomethylene-3-cyano-4,5,5-dimethyl-2,5-dihydrofuran (TCF) as
1
electron acceptors. H and 13C NMR and MALDI-TOF were carried out to demonstrate the preparation of these
chromophores. The Variable Angle Spectroscopic Ellipsometry (VASE) is used to measure the optical constants of
films. Thermal properties, photophysical properties, density functional theory (DFT) calculations and EO
performances of these chromophores were systematically studied and compared to illustrate the influences of
different side-chain groups on rational monolithic EO material design.
--------------------------------------Figure 1----------------------------------------------
2. Experimental section
2.1 Materials and instruments
All chemicals are commercially available and are used without further purification unless otherwise stated.
N, N-dimethyl formamide (DMF) was distilled over calcium hydride and stored over molecular sieves (pore size
3Å). Acetone was dried with anhydrous MgSO4, then distilled and stored over molecular sieves (pore size 3Å).
The 2-dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran(TCF) acceptor was prepared according to the
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1
literature.[52] H and 13C NMR spectra were determined by Advance Bruker NMR spectrometer (400 MHZ). The
MS spectra were obtained on MALDI-TOF (Matrix Assisted Laser Desorption/Ionization of Flight) on BIFLEXIII
(Broker Inc.) spectrometer. Electric field poling and Teng-Man ellipsometry were carried out on a home built
instrument. The UV-Vis experiments were performed on Cary 5000 photo spectrometer. Cyclic-Voltammetry(CV)
was carried out at 10-3 M in acetonitrile versus Ag/AgCl, glassy carbon working electrode, Pt counter electrode,
20 ℃, 0.1 M Bu4NPF6, 100 mV s-1 scan rate, ferrocene internal reference E1/2 = +0.43 V. The thermogravimetric
analysis (TGA) was determined by TA5000-2950TGA (TA co) with a heating rate of 10 oC min-1 under the
protection of nitrogen. The film thickness was measured by Ambios Technology XP-1. The VASE analysis was
performed using J. A. Woollam M-2000 instrument. Data were acquired at 55°, 65° and 75°; and fitting was done
using Woollam CompleteEASE software.
--------------------------------------Figure 2---------------------------------------------
2.2 Synthesis
Chromophore F1
A screw cap vial was charged with 5 (0.317 g, 1.00 mmol) and ethanol (20 mL, 200 proof). After 5 were
completely dissolved, TCF (0.24 g, 1.20 mmol) was added at once. Then , the vial was capped and the reaction
mixture were stirred at 60 °C for 6 h. The reaction was monitored by TLC. Finally, the solution was cooled to
room temperature and solvent was removed under reduced pressure. The crude product was purified using silica
gel chromatography eluting with dichloromethane/ethyl acetate (v/v: 95/5) to remove unwanted materials.
Changing the eluent system to 5% methanol in DCM, 0.38 g product was obtained as dark blue solid. Yield: 76%.
Yield: 76%. 1H NMR (400 MHz, DMSO-d6) δ (ppm) 8.17 (d, J = 15.6 Hz, 1H), 7.47 (d, J = 8.7 Hz, 2H), 7.25 (d, J
= 15.9 Hz, 2H), 7.23 (s, 1H), 7.18 (d, J = 15.9 Hz, 1H), 6.72 (d, J = 8.7 Hz, 2H), 6.57 (d, J = 15.6 Hz, 1H), 4.70 (t,
J = 5.4 Hz, 2H), 3.56 (t, J = 5.4 Hz, 2H), 3.46 (t, J = 5.4 Hz, 2H), 3.00 (s, 3H), 1.76 (s, 6H). 13C NMR (100 MHz,
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DMSO) δ (ppm) 177.43, 174.85, 154.30, 152.63, 150.45, 138.57, 135.13, 132.68, 129.41, 128.86, 123.57, 116.10,
113.47, 112.25, 111.43, 98.63, 95.49, 58.64, 58.22, 26.07. HRMS (ESI) (M+, C28H26N4O3S): calcd: 498.17256;
found: 498.17252.
Chromophore F2
In a 25 mL round bottom flask were combined F1 (0.125 g, 0.25 mmol), imidazole (0.068 g, 1.00 mmol), and dry
DMF (10 mL). After completely dissolved, TBDPS-Cl (1.37 g, 1.00 mL) was added, the solution was stirred for
another 3h at room temperature. The mixture was then diluted with ethyl acetate, washed with DI water, dried over
MgSO4. Solvent was removed under reduced pressure. The crude material was purified using silica gel
chromatography eluting with hexanes/ethyl acetate (v/v: 5/1) to afford 0.20 g of dark blue solid. Yield: 85%.1H
NMR (400 MHz, CDCl3) δ (ppm) 7.77 (d, J = 15.5 Hz, 1H), 7.64 (m, 4H), 7.62 (d, J = 9.0 Hz, 2H), 7.48 – 7.27 (m,
16H), 7.04 (d, J = 15.8 Hz, 1H), 6.92 (d, J = 15.8 Hz, 1H), 6.86 (s, 1H), 6.57 (d, J = 8.9 Hz, 2H), 6.51 (d, J = 15.5
Hz, 1H), 4.79 (s, 2H), 3.83 (t, J = 5.9 Hz, 2H), 3.55 (t, J = 5.9 Hz, 2H), 3.01 (s, 3H), 1.61 (s, 6H), 1.07 (s, 9H),
1.04 (s, 9H). 13C NMR (100 MHz, CHCl3) δ (ppm) 176.05, 174.23, 173.32, 162.61, 153.10, 151.16, 150.25,
135.57, 133.27, 132.72, 127.90, 123.63, 112.65, 112.14, 96.95, 36.50, 31.43, 19.08. HRMS (ESI) (M+,
C62H62N4O3S): calcd: 942.45426; found: 942.45421.
Chromophore F3
An oven dried 100mL flask was charged with F1 (0.125 g, 0.25 mmol), 1,3-dicyclohexylcarbodiimide (0.25 g,
0.60 mmol), DPTS (0.69 g, 0.044 mmol). This mixture was dissolved in a mixture of freshly distilled DCM (20
mL). The reaction was stirred overnight, washed with NaCl (sat'd) and then DI water. The organic phase was
separated and dried over MgSO4 and concentrated in vacuo. The dark blue crude residue was then purified by silica
1
gel column chromatography (5% THF/DCM) to yield 0.22g of dark blue solid. Yield: 68%. H NMR (400 MHz,
CDCl3) δ(ppm) 8.24 (d, J = 1.4 Hz, 2H), 8.21 (d, J = 1.4 Hz, 2H), 7.94 (d, J = 15.6 Hz, 1H), 7.85 – 7.77 (m, 8H),
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7.27 (d, J = 8.9 Hz, 2H), 7.11 (s, 1H), 6.92 (d, 1H), 6.87 (d, 1H), 6.73 (d, J = 3.5 Hz, 2H), 6.69 (d, J = 3.5 Hz, 2H),
6.60 (d, J = 8.9 Hz, 2H), 6.48 (d, J = 15.6 Hz, 1H), 5.10 (d, 4H), 4.28 – 4.17 (m, 4H), 4.05 (m, 2H) 3.64 – 3.52 (m,
4H), 3.44 (m, 4H), 2.95 (s, 3H), 2.58 (dd, 3H), 1.68 (s, 6H), 1.55 (m, 4H), 1.22 – 1.13 (m, 6H). 13C NMR (100
MHz, CDCl3) δ (ppm) 182.82, 173.16, 172.18, 171.19, 162.35, 156.71, 152.19, 151.24, 147.45, 143.86, 135.09,
130.91, 128.92, 126.27, 124.69, 122.67, 112.10, 111.49, 99.00, 61.65, 60.42, 48.70, 45.67, 38.75, 28.87, 26.52,
21.07, 14.22, 12.31. HRMS (ESI) (M+, C68H66N12O13S): calcd: 1290.45930; found: 1290.45928.
3. Results and discussion
3.1. Synthesis and characterization
Synthetic approaches for the chromophores F1-F3 were showed in Figure 2. All reactions were performed under
nitrogen protection. TCF acceptor was prepared according to the literature. The synthesis of compounds 1 and 5
have been reported previously.[14, 22, 53] The compound 1 was introduced to the core through esterification in the
presence of DCC (N,N′-dicyclohexylcarbodiimide) and DPTS (4-(dimethylamino) pyridinium 4-tosylate), which
yield the functionalized side-chain chromophore F3. The resulting material was then purified by silica gel column
chromatography. All the chromophores were completely characterized by 1H-NMR, 13C-NMR, MS, UV-Vis
spectroscopic analysis and the data obtained were in full agreement with the proposed formulations.
--------------------------------------Figure 3----------------------------------------------
--------------------------------------Table 1----------------------------------------------
3.2 Optical and Cyclic Voltammetry analysis
The nature of the intramolecular charge transfer (ICT) absorption and solvatochromic behavior of F1-F3 were
investigated using UV-Vis absorption measurements in aprotic solvents with different polarities. The Figure 3
displays the spectra of F1-F3 in three solvents and films with different dielectric constants. The spectra data are
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summarized in Table 1. The shape and position of the ICT band of this type of chromophore mainly depends on
the dielectric properties of the solvents and the side chains of chromophores. Different from the other two
chromophores, F3 shows two apparent ICT absorption peaks (469 nm and 644nm in chloroform) in UV-Vis
spectra. The one in low wavelength represented the absorption of two disperse-red units in side chains and the one
in high wavelength belongs to FTC conjugated structure. Three chromophores show similar solvatochromic
behaviour in solvents with different dipole moment. When the solvents changing from acetone to chloroform, the
λmax of F1 shifted from 632 nm to 645 nm, which is the smallest red-shift compared with others. UV-Vis spectra in
thin films (Figure 3) were also measured. The characteristic absorption band of the film will be broader than
solutions because of material inhomogeneity and chromophore interactions in film.[12, 35, 54, 55] In the neat
films, the pendant groups are acted as the matrix where chromophores are dispersed in. The change of the matrix
dielectric constant will also result in red- or blue-shifts of absorption peak for a chromophore. DR1 group
possesses a higher dielectric constant compared with bulky TBDPS group, which results in the largest red-shift of
absorption peak of F3 when the surrounding environment changing from chloroform solution to neat films. The
electrochemical properties of three chromophores were studied by cyclic voltammetry (CV). As shown in Figure 4,
all three chromophores exhibited the similar oxidation potential, reduction potential and a lower energy gap, which
was attributed to the same conjugating structures. The results also indicated that the modification of the pendant
groups has little influence on the chromophores’ ICT ability, which could affect the βzzz value and further materials’
macroscopic EO activities.
--------------------------------------Figure 4----------------------------------------------
3.3 VASE analysis
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To investigate the optical absorption behavior of EO films, VASE analysis was performed to measure the optical
constants (real index of refraction, n, and absorption coefficient, к) of chromophore films ( as shown in Figure 5).
At two of the important wavelengths for telecom (1310 nm, 1550 nm), F3 film shows the largest n value (n1310
=
1.79, n1550 = 1.77) compared with F2 and F1 at 25 wt% in PMMA host polymer (n1310 ≈ n1550 = 1.56). According to
the equation 2, the operation voltage (Vπ) is inversely proportional to value of n3r33, so increasing n can
significantly decrease the power requirements and solve the thermal management problems of the device.
Meanwhile, the films show extremely weak absorption at the wavelengths 1310 nm and 1550 nm, which is
significant for reducing the optical loss of device.
--------------------------------------Figure 5----------------------------------------------
3.4 Thermalphysical analysis
The thermal stability of chromophores were investigated by TGA. The decomposition temperatures (Td,
temperature at which 5% mass loss occurs during heating) are summarized in Table 2. Chromophores F1-F3 show
higher Td values (above 200 ℃) which is similar with the chromophore EZ-FTC (Figure 6). The Tds of three
chromophores are high enough to meet the requirement of device fabrication.
--------------------------------------Figure 6---------------------------------------------
--------------------------------------Figure 7----------------------------------------------
The Tgs were measured by DSC and showed in Figure 7. Although F1 shows the highest Tg, the lack of flexible
groups leads to poor film-forming ability by spin-coating method which can’t afford the flat films for electric-field
poling. F3 exhibits the moderate higher Tg value (83.5 ℃) compared with F2 which has Tg values of 62.0 ℃. The
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weak dipole-dipole interactions between DR1 groups in side chains are the reason of material’s Tg improvement.
Nearly neutral TBDPS groups can only act as bulky groups to isolate chromophores.
3.5 EO performance
In order to evaluate their EO activities, the monolithic EO chromophores were spin-coated into thin films on
indium-tin oxide (ITO) glass substrates from 1,1,2-trichloroethane solution and poled by electric field. F2 and F3
exhibited excellent film-forming abilities and get neat films with high quality. However, F1 failed to get
satisfactory films due to the strong molecular rigidity and lack of flexible groups. Therefore, F1 was doped into
PMMA with 25 wt% for film preparation. The EO films were poled by contact-poling apparatus and measured by
Teng-Man simple reflection method[56, 57] The r33 values were calculated by the following equation:
(3)
휋 2
Where Ic is the output beam intensity, Im is the amplitude of the modulation, Vm is the modulating voltage.
The poling electric-field is 180 V/μm. The poling data are also summarized in Table 2. Figure 8 shows the Im, Ic,
temperature, and the current (real-time) monitored by Teng-Man. Im is a signal intensity related to the change in
index of refraction on poling and proportional to r33 - r13.[46] As shown in Figure 8, F2 and F3 showed the similar
behaviour in poling process. Figure 8 also shows the curves of current and Im/Ic with time and temperature. When
film was heated to Tg under a poling field, there is a sudden rise in Im/Ic, which indicates the start of poling. At the
same time, the current increases quickly. It is common for the increase of current or current spiked upon poling
process and severe in neat chromophore systems. Due to the relatively large electric resistance, lower poling
current increase was observed in F1/PMMA films. According to equation 2, the r33 is proportional to the value of
Im/Ic because others are constants that only have relationships with apparatus and the original refractive indices of
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the materials. The results also indicated that the rise of Im/Ic value occurs in reaching F3’s Tg, which shows similar
law with Im/Ic and current.
--------------------------------------Table 2----------------------------------------------
--------------------------------------Figure 8---------------------------------------------
Due to low blending concentration and the lack of bulky groups to inhibit anti-parallel aggregation, F1/PMMA
exhibits the lowest r33 value (23 pm/V) though the F1 has the same conjugate structure with other three
chromophores. In contrast to F2 and F3, F1’s D-π-A stucture is exposed to others due to the poor performance of
hydroxyl groups to isolate the chromophores with each other. The geometric optimization was carried out on three
chromophores using B3LYP method at 6-311G* level, and was shown in Figure 9. F1 shows a bare D-π-A
structure with perfect planarity which lead to unfavourable anti-parallel aggregations. As to F2 and F3, there are
large bulky groups in donor and bridge parts to change the planar D-π-A conjugating system into 3D structures.
Anti-parallel aggregation would be hard to occur in neat EO films. After contact poling, the F3 film shows large
improvement in EO activity (81 pm/V at 1310 nm) compared with EZ-FTC (39 pm/V), F2 (56 pm/V). Meanwhile,
according to previous report, the r33 value of DR1/PMMA system is only about 3.7 pm/V, which is not the
root-cause of r33 value change.[58] Combination with the higher index of refraction, the n3r33 value of poled F3
reached to 464 pm/V, five times larger than the value of F1/PMMA (89 pm/V).
--------------------------------------Figure 9---------------------------------------------
4. Conclusion.
Three organic NLO chromophores modified by different pendant groups in side chains have been synthesized
and systematically characterized by NMR, MS, UV-Vis spectra and EO activities test. Thermogravimetric analysis
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showed good thermal and thermoxidative stabilities of the three chromophores. F2 and F3 showed good solubility
and comparability with polymer which were crucial to make high quality EO films. The effects of solvatochromic
behavior on the UV-Vis absorption were also investigated to comparative discuss the influences of different
pendant groups on the ICT absorption of the conjugated structure. Meanwhile, VASE measurement was carried
out to analyze the index of refraction and the absorption coefficients at 1310 nm and 1550 nm. The chromophore
F3, functionalized with DR1 as pendant groups, exhibits relatively high Tg and the index of refraction (n1310 = 1.79,
n1550 = 1.77). The poled monolithic chromophore thin film of F3 displays large r33 value which is two times larger
than EZFTC in traditional guest-host system. Together with higher index of refraction, the n3r33 value of poled F3
is about 464 pm/V, much larger than the poled F1/PMMA film. These results are useful for designing new
monolithic EO materials with high EO activity and index of refraction to improve the performance of device.
Acknowledgments
We are grateful to the the Key Project of of Sichuan Provincial Education Department (18ZA0078), Scientific
Research Innovation Team of Sichuan Provincial Education Department (17TD0005), and Applied Basic Research
Project (No. 2016JY0186, 18YYJC1026) of Sichuan Province, China for the financial support.
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Figure captions：
Figure 1. The structures of chromophores.
Figure 2. The synthesis routes of chromophores.
Figure 3. The UV-Vis spectra of chromophores.
Figure 4. The Cyclic-Voltammetry curves of chromophores.
Figure 5. Optical constants of chromophores in films.
Figure 6. TGA curves of chromophores.
Figure 7. DSC traces of chromophores.
Figure 8. The poling curves of EO films on ITO.
Figure 9. Optimized chromophores structures..
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Table 1. Optical constants, UV-Vis and CV data
λmax/nma
λmax/nmb
λmax/nmc
λmax/nmd
643
Eox/Ve
0.430
0.372
0.435
Ered/Ve
-0.663
-0.737
-0.656
ΔE/eVe
1.093
nf
ng
632
632
645
1.57
1.74
1.79
1.56
1.74
1.77
F1
F2
F3
640
636
671
661
1.109
624
620
644
687
1.091
d
e
a measured in toluene. b measured in acetone. c measured in chloroform. measured in film. 10-3 M in acetonitrile
versus Ag/AgCl, glassy carbon working electrode, Pt counter electrode, 20 ℃, 0.1 M Bu4NPF6, 100 mV s-1 scan
rate, ferrocene internal reference E1/2 = +0.43 V. f is the index of refraction at 1310 nm. g is the index of refraction at
1550 nm.
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Table 2. Thermalphysical properties and poling data of chromophores
b
Density(wt%)a
Tg/℃
111.9
62.0
Td/℃
256
233
224
Tp /℃
r33 /(pm/V)c
25%
105
63
23
56
81
F1
F2
F3
49%
36%
83.5
83
a is the weight percent of the active part of the NLO chromophore (D-π-A conjugated part) in films. b are the poling
temperatures. c are measured by Teng-Man ellipsometry (Home made instrument).
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Highlights
1. Three novel chromophores with different pendant groups were synthesized.
2. The effects of different pendant groups on the performance were investigated.
3. The highest electro-optic activity of poled films reached to 81 pm/V.