Synthesis and characterization of a novel indoline based nonlinear optical chromophore with excellent electro-optic activity and high thermal stability by modifying the π-conjugated bridges

Article abstract of DOI:10.1039/c7tc00735c

Two novel second order nonlinear optical (NLO) chromophores based on indoline donors and tricyanofuran (TCF) acceptors linked together via modified polyene π-conjugation bridges have been synthesized in good overall yields and systematically characterized. Thermal stability, optical property and electro-optic property were measured to investigate the effects of the introduced rigid benzene derivative steric hindrance group on the bridge. Besides, density functional theory (DFT) was used to calculate the HOMO-LUMO energy gaps and first-order hyperpolarizability (β) of these chromophores. After introducing the benzene derivative steric hindrance group into the bridge, chromophore CLH-2 showed very good thermal stability with a decomposition temperature of 250 °C, which was 83 °C higher than chromophore CLH-1 without the isolation group on the bridge. In electro-optic activity, the introduction of rigid steric hindrance groups can effectively reduce dipole-dipole interactions to translate the relatively small β values into bulk high EO activities. By doping chromophores CLH-1 and CLH-2 with a high loading of 45 wt% in APC, EO coefficients (r₃₃) of up to 63 and 102 pm V^-1 at 1310 nm can be achieved, respectively. The r₃₃ value of the new chromophore CLH-2 was about 1.6 times that of chromophore CLH-1. The high r₃₃ value, good thermal stability and high yield suggest the promising applications of the new chromophore in nonlinear optical areas.

Full text of DOI:10.1039/c7tc00735c

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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
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DOI: 10.1039/C7TC00735C
Journal of Materials Chemistry C
ARTICLE
Synthesis and characterization of a novel indoline based nonlinear
optical chromophore with excellent electro-optic activity and high
thermal stability by modifying π-conjugated bridge
Received 00th January 20xx,
Accepted 00th January 20xx
ab
a*
a
a
a
a*
Chaolei Hu, Zhuo Chen, Hongyan Xiao, Zhen Zhen, Xinhou Liu and Shuhui Bo
DOI: 10.1039/x0xx00000x
Two novel second order nonlinear optical (NLO) chromophores based on indoline donors and tricyanofuran (TCF) acceptors
linked together via modified polyene π-conjugation bridges have been synthesized in good overall yields and systematically
characterized. Thermal stability, optical property and Electro-Optic property were measured to investigate the effects of the
introduced rigid benzene derivative steric hindrance group on the bridge. Besides, density functional theory (DFT) was used
to calculate the HOMO–LUMO energy gaps and first-order hyperpolarizability (β) of these chromophores. After introducting
benzene derivative steric hindrance group into the bridge, chromophore CLH-2 had very good thermal stability with
decomposition temperature of 250 °C, which was 83°C higher than chromophore CLH-1 without isolation group on the
bridge. In electro-optic activity, the introduction of rigid steric hindrance groups can effectively reduce dipole–dipole
interactions to translate the relatively small β values into bulk high EO activities. By doping chromophores CLH-1 and CLH-2
with a high loading of 45 wt % in APC, EO coefficients (r33) of up to 63 and 102 pm V-1 at 1310 nm can be achieved,
respectively. The r33 value of the new chromophore CLH-2 was about 1.6 times of chromophore CLH-1. The high r33 value,
good thermal stability and high yield suggest the promising applications of the new chromophore in nonlinear optical area.
www.rsc.org/
efficient NLO chromophores, optimization of the π-conjugated
Introduction
Second-order nonlinear optical (NLO) materials have been used in
commercial applications for computing, tele-communications, and
sensing such as electronic/photonics integrated circuits, phase array
radar, terahertz spectroscopy, etc . Compared with inorganic
materials, organic electro-optic (EO) materials have many
advantages of large EO coefficients, fast intrinsic response time, ease
of processing, lower cost and so on . A common electro-optic
device is the Mach-Zehnder modulator, which is very important
commercially for translating ultrafast electrical signals into optical
bridge, electron-donor and electron-acceptor characteristics of the
substituents are needed . Many studies on NLO chromophores have
mainly focused on the design of electron bridges and electron
1
9
2
0-22
acceptors
.
The electron donors, which are important
8,
components of NLO chromophores, have received little attention.
Traditional alkyl and aryl amines were considered to be the ideal
electron donors and were often used.
1
-3
23
1
1, 24, 25
However, the r33 values
of traditional amines FTC chromophores only achieved 39 pm/V at
4
-8
11, 24-26
2
5 wt.%
. So looking for a better donor is a huge challenge.
Indoline-based group has been reported an impressive electron
donor due to the powerful electron-donating capability of the
9
-11
signals for fiber-optic telecommunications . To meet the stringent
requirements for the using of devices, one of the most critical
challenges is to develop NLO chromophores with large EO activity,
excellent thermal and chemical stability as well as good
27-29
indoline unit.
That’s because the p-electrons on the nitrogen
atom can be directly transferred to the conjuagated system, so
chromophores using indoline as electron donor will show very big β
values. Besides, the indoline displayed good thermal stability and
1
2-14
transparency
. Furthermore, the microscopic hyperpolarizability
28
photochemical stability, due to the rigid structure. These properties
(
β) must be translated into macroscopic EO activity efficiently by
show that donor group’s efficacy in indoline chromophore was
1
5, 16
reducing the molecular electrostatic interaction in the polymer
In general, the dipolar second-order NLO chromophore consists of
a π-conjugated bridge end-capped with strong electron donor and
acceptor substituents (D–π–A)
.
30
higher than that of structurally similar amine-based chromophore.
In most of the organic nonlinear optical materials, the NLO
chromophores have the structure of a donor–π–acceptor which
1
7, 18
. In order to search for highly
usually possesses
a
rod-like structure leading to strong
intermolecular dipole-dipole interactions in the polymeric matrix and
makes the poling-induced noncentrosymmetric alignment of the
chromophores a daunting task . For this reason, many efforts have
been carried out to design and synthesize novel NLO chromophores,
seeking to engineer NLO molecules both microscopically (β) and
macroscopically (r33). On the one hand, it has been well established
a Key Laboratory of Photochemical Conversion and Optoelectronic Materials,
Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing
31
1
00190, PR China. *E-mail: boshuhui@mail.ipc.ac.cn; chenzhuo@mail.ipc.ac.cn
Fax: +86-01-82543530; Tel: +86-01-82543529
b University of Chinese Academy of Sciences, Beijing 100049, PR China
DOI: 10.1039/x0xx00000x
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that large β values of the chromophores can be achieved by careful by Wittig condensation, compounds 3 and 4 were prepared with a
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DOI: 10.1039/C7TC00735C
3
modification of the strength of donor and acceptor moieties, as well high yield. Treatment of compounds 4 with POCl and DMF gave
as the nature of π-conjugated spacer. On the other hand, introducing aldehyde 5. And the final condensations with the TCF acceptor give
the suitable isolation groups was proven to be an efficient approach chromophores CLH-1 and CLH-2 as green solids. During the synthesis
for minimizing intermolecular dipole-dipole interaction and process, Witting salt c was got from 4-(diethylamino) salicylaldehyde
enhancing the poling efficiency, which can increase the EO activities after substitution, reduction and salt formation. All the
32, 33
1
effectively.
So modifying the chromophore system and chromophores were completely characterized by H NMR, MS, UV-
surrounding environment may be the reasonable way to achieve Vis spectroscopic analysis and the data obtained were in full
excellent and better performance.
agreement with the proposed formulations.
In this work, the indoline units were selected to be the electron
donating groups due to unique electronic properties and strong
electron donating ability. We have designed and synthesized two
new chromophores CLH-1 and CLH-2 based on the indoline donors
and powerful tricyanovinyldihydrofuran (TCF) acceptor and the
polyene bridge (Chart 1). In the CLH-2, the benzene derivative steric
hindrance group (isolation group) with a long chain was introduced
into the π-electron bridge. The rigid structure can act as a good
isolating group, at the same time the long chain can be used to
increase the solubility of chromophores. The UV-Vis, solvatochromic,
density functional theory (DFT) quantum mechanical calculations,
thermal stabilities and EO activities of these chromophores were
systematically studied to prove the benefits of the suitable isolation
groups in the application of nonlinear optical chromophore design
and synthesis.
Scheme 1 Chemical structures and synthetic routes for
chromophores CLH-1 and CLH-2.
Thermal stability
NLO chromophores must be thermally stable enough to withstand
high temperatures (>200°C) in electric field poling and subsequent
processing of chromophore/polymer materials. The thermal stability
of the two chromophores was investigated using thermogravimetric
analysis (TGA) as shown in Fig. 1 and Table 1. Chromophore CLH-2
Chart 1 Chemical structure for chromophores CLH-1 and CLH-2.
has the higher decomposition temperature (T
d
=250 °C) than CLH-1
Results and discussion
d
(T =167 °C) with no steric hindrance on the π-electron bridge. The
Synthesis and characterization of chromophores
enhanced thermal stability of chromophore CLH-2 over
chromophore CLH-1 is due to the introduction of benzene derivative
steric hindrance groups into π-electron bridges. The excellent
thermal stability of chromophore CLH-2 makes it suitable for
practical device fabrication and EO device preparation.
Chromophores CLH-1 and CLH-2 were synthesized following the
general route laid out in Scheme 1. Starting from 1,3,3-trimethyl-2-
methyleneindoline, chromophores CLH-1 and CLH-2 were
synthesized in good overall yields (40%~50%) through simple three
or four step reactions: The compound 2 was obtained by treatment
3
of compound 1 with POCl and DMF. After introduction of the bridge
Table 1 Summary of thermal and optical properties and EO coefficients of chromophores CLH-1 and CLH-2.
r33 (pm V-1)
e
a
b
c
d
Chromophores
CLH-1
T
d
(℃
)
λ
max (nm)
λ
max (nm)
Δλ (nm)
63
167
250
696
703
668
679
28
24
1
02
CLH-2
a
-1 b
d
T was determined by an onset point and measured by TGA under nitrogen at a heating rate of 10 °C min . λmax was
c
d
b
b e
measured in chloroform. λmax was measured in dioxane. Δλ=λmax - λmax . r33 values were measured at the wavelength
of 1310 nm.
2
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DOI: 10.1039/C7TC00735C
Fig. 1 TGA curves of chromophores CLH-1 and CLH-2 with a heating
-1
rate of 10°C min in a nitrogen atmosphere
Optical properties
In order to explore the different charge-transfer (CT) absorption
properties of each chromophore and reveal the effect of steric
hindrance group on the intramolecular charge-transfer (ICT) of
dipolar chromophores, UV-Vis absorption spectra of the two
-5
-1
chromophores (c = 1×10 mol L ) were measured in a series solvents
with different dielectric constants as shown in Fig. 2. The spectral
data are summarized in Table 1. Depending on different structures,
the synthesized NLO chromophores exhibited a similar π→π*
intramolecular charge-transfer (ICT) absorption band in the visible
region. As shown in Fig. 2, chromophore CLH-1 and CLH-2 exhibited
the maximum absorption (λmax) from 696 nm to 703 nm in
chloroform. Compared to chromophore CLH-1, chromophore CLH-2
was red shifted by 7 nm. The reason is that the introduced isolation
group has a certain degree of electron-donating ability, and plays the
role of auxiliary electron donor.
Fig. 2 UV-Vis absorption spectra of chromophores CLH-1 and CLH-2
in five kinds of aprotic solvents with varying dielectric constants (ε)
chromophore CLH-1 was a little larger than chromophore CLH-2.
This may be explained by that conjugate structure was somehow
wrecked by the lateral group. These results correspond to the UV-Vis
results.
Besides, the solvatochromic behavior was also explored to
investigate the polarity of chromophores. When increasing the
solvent dielectric constant, both of the two chromophores showed
solvatochromic red-shifts. Chromophores CLH-1 and CLH-2 showed
bathochromic shifts of 28 nm and 24 nm when solvent was changed
from dioxane to chloroform, respectively. However, chromophore
CLH-2 exhibited weaker bathochromic shifts in comparison to CLH-1.
It indicated that chromophore CLH-1 is more polarizable than
chromophore CLH-2.
Table 2 DFT calculated properties of chromophores CLH-1 and CLH-2
Chromophores HOMO/eV LUMO/eV Ege/eV μ/D β/(10-30esu)
CLH-1
CLH-2
-5.36
-5.24
-2.98
-2.87
2.38 21.69 268.89
2.37 21.57 234.95
The frontier molecular orbitals are often used to characterize the
chemical reactivity and kinetic stability of a molecule and to obtain
qualitative information about the optical and electrical properties of
molecules. Besides, the HOMO–LUMO energy gap is also used to
Theoretical calculations
In order to model the ground state molecular geometries, the
HOMO–LUMO energy gaps and β values of these chromophores
were calculated. The DFT calculations were carried out at the hybrid
understand the charge transfer interaction occurring in
a
chromophore molecule. In the case of these chromophores, Fig. 3
represents the frontier molecular orbitals of chromophores CLH-1
and CLH-2. According to Fig. 3, it is clear that, the electron density is
concentrated on the donor moiety when at the HOMO state, while
on the π-bridge and acceptor moiety when at the LUMO state.
Furthermore, the theoretical microscopic Zero-frequency (static)
molecular first hyperpolarizability (β) was calculated using Gaussian
34
B3LYP level by employing the split valence 6-31G*basis set . The
data obtained from DFT calculations are summarized in Table 2.
The HOMO and LUMO energies were calculated by DFT
calculations as shown in Table 2. The energy gaps between the
HOMO and LUMO energies for chromophores CLH-1 and CLH-2 were
2.38 eV and 2.37 eV respectively. The HOMO–LUMO gap of
34
0
9 . As a reference reported earlier, β has been calculated at the 6-
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3
5
3
1+G* level under vacuum . From this, the scalar quantity of β can Kelvin poling temperature. When the intermolecular electrostatic
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DOI: 10.1039/C7TC00735C
be computed from the x, y, and z components according to the interactions are neglected, the electro-optic coefficient (r33) should
3
6
following equation :
increase linearly with chromophore density, dipole moment, first
(1) hyperpolarizability and the strength of the electric poling field. If
chromophore–chromophore dipolar interactions are treated in the
point dipole approximation, the order parameter for non-interacting
1
/2
2
x
2
y
2
z




 
 

Where
1
3
i   
(     ),i, j(x, y, z)
(2)
iii

ijj
jij
jji
2
chromophores is modified by an attenuation factor [1- L (W/kT)].
i j
Then,
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
energy and kT is the thermal energy. At this time, chromophores
Fig. 3 The frontier molecular orbitals of chromophores CLH-1 and with large dipole moments generate an intermolecular static electric
3
2

cos  

E
f (0) / 5kT

1 L

W / kT


(5)
p


12, 37
.
where L is the Langevin function, W is the dipole–dipole interaction
42
CLH-2
field dipole-dipole interaction, which leads to the unfavorable
antiparallel packing of chromophores. So the number of truly
oriented chromophores (N) is small. Therefore, introducing a huge
steric hindrance group to isolate chromophores is the most popular
and easy way to attenuate the dipole-dipole interactions of
chromophores in molecular optimization.
Table 3 Summary of EO coefficients of chromophores CLH-1 and CLH-
2
at different densities
a
33 (pm v-1)
r
CLH-1
18
Wt.%
5
15
25
35
CLH-2
15
32
64
88
As reported earlier, the β value has a close relationship with the
substituents, steric hindrance, and intramolecular charge-transfer,
39
56
63
38, 39
π-conjugation length and so on.
The β values of chromophore
4
5
—
102
CLH-2 was little smaller than that of chromophore CLH-1. This may
be explained by that chromophore CLH-2 possessed a less coplanar
geometry due to the steric hindrance of the lateral group.
A series of films were prepared by formulating these
chromophores into APC using dibromomethane as the solvent.
Firstly, the solution was filtered through a 0.2 μm PTFE filter and spin-
coated onto indium tin oxide (ITO) glass substrates. Films of doped
polymers were baked in a vacuum oven at 80 °C overnight to remove
the residual solvent. After the progress, films were prepared doped
with chromophores. All these films were loaded 5-45wt.% weight
percentage of chromophore. Chromophore CLH-2 showed obvious
better solubility than that of chromophre CLH-1 which may attribute
to the fact that a huge steric hindrance group with the long chain was
introduced to the π-electron bridge. The corana poling process was
Electro-Optic performance
In order to evaluate the poling efficiency and EO activity of these
chromophores, amorphous polycarbonate (APC) guest–host polymer
films incorporating these chromophores were prepared, corona
poled, and analysed via simple reflection method (Teng-Man) at
40
1
310 nm , using the corrected formula. In order to minimize the
contribution from multiple reflections, a carefully selected thin ITO
4
0
electrode with low reflectivity and good transparency was used .
The measured r33 values depend on the chromophore number
density (N), hyperpolarizability (β), and poling efficiency, described
g
carried out 10 °C above the glass transition temperature (T ) of the
films. The r33 values of films CLH-1/APC and CLH-2/APC were
measured in different loading densities, as shown in Table 3 and Fig.
3
41
by the <cos θ> order parameter, as indicated by
3
4
r  2Nf ()  cos   /n
(3)
3
3
4
. For chromophore CLH-1, the r33 values were gradually improved
where N is chromophore number density (molecules/cc), the f(ω)
term describes electric-field (Debye-Onsager) factors and n is the
refractive index of the film. Β is the molecular first hyperpolarizability
-1
-1
from 18 pm V (5 wt %) to 63 pm V (35 wt %). However, the film
CLH-1/APC with 45wt% loading density presented an obvious phase
separation. For chromophore CLH-2, the r33 values were improved
from 15 pm V (5 wt %) to 102 pm V (45 wt %). When the
concentration of the chromophore in APC is low, film CLH-1/APC
displayed a larger r33 value than that of films CLH-2/APC. As the
chromophore loading increased, this trend is reversed. This can be
explained by that, when in a low-density range, the intermolecular
dipolar interactions are relatively weak. Accompanied by the
increased concentration of NLO chromophore moieties in the
(
which depends on dielectric permittivity (ε) and upon optical
-1
-1
3
frequency (ω)). The term <cos θ> is the acentric order parameter
which depends on poling conditions and intermolecular electrostatic
interactions.
The acentric order parameter for non-interacting chromophores in
p
an electric poling field, E , is given by
42
3

cos   E f (0)/5kT
(4)
p
where μ is the chromophore dipole moment, E
p
f(0) is the poling field polymer, the intermolecular dipole-dipole interactions would
felt by the chromophore, k is the Boltzmann constant, and T is the become stronger and stronger, which would finally lead to a
4
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decreased NLO coefficient. The introduction of steric hindrance chromophore CLH-1 due to the isolation of benzene derivative steric
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DOI: 10.1039/C7TC00735C
groups attached to the conjugated π-system can make inter- hindrance groups on the π-electron. Moreover, the large r33 values
-1 24
chromophore electrostatic interactions less favourable.
(3 times of FTC，39 pm V ) of chromophore CLH-2 suggest brilliant
broad prospects in advanced material devices.
Experimental
Materials and instrument
All chemicals are commercially available and are used without
further purification unless otherwise stated. N, N-
dimethylformamide (DMF), Phosphorus oxychloride (POCl ),
3
tetrahydrofuran (THF) and ether were distilled over calcium hydride
and stored over molecular sieves (pore size 3Å). 2-
Dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran(TCF)
45
acceptor was prepared according to the literature . 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).
Fig.4 EO coefficients of NLO thin films as a function of chromophore
loading densities
Measurements and instrumentation
1H NMR 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
The long-term stability of the NLO property at high temperature
is very important for the practical use of NLO polymer. To investigate
the long-term NLO stability of the poled polymers, dipole
reorientation of the poled polymer films was observed by measuring
the EO coefficient (r33(t)/r33(0)) as a function of time at 85 °C (the
device processing temperature) in Fig.5. The poled films of 25%CLH-
-1
(
TA co) with a heating rate of 10 °C min under the protection of
1
/APC and 25%CLH-2/APC all displayed well long-term alignment
stability. After annealing at 85 °C for 200 h, the poled films of
5%CLH-1/APC and 25%CLH-2/APC could retain 85% and 89% (200
nitrogen. The DFT calculations using Gaussian 09 were carried out at
the hybrid B3LYP level by employing the split valence 6-31G* basis
set.
2
h) of the initial values at 85 °C respectively. This percentage was
considerably high enough. The fast decay of the EO coefficient at the
beginning of thermal treatment may result from recovery of bond
Syntheses and characterization
Compound 2
43, 44
angle and bond length of the oriented chromophores.
A solution of 10 ml DMF was cooled to 0 °C and was maintained at
this temperature during the dropwise addition of phosphorus
oxychloride (4.25 ml, 30 mmol). The solution was kept for 2 h of
stirring at 0 °C and the temperature was kept during the dropwise
addition of compound 1 in 30 ml DMF (3.45 g, 20 mmol). The solution
was gradually warmed to room temperature and stirred for 2 h of
stirring at 60 °C before being poured into 200 ml solution of sodium
carbonate (10%) for quench. The reaction mixture was extracted by
4
ethyl acetate, washed with brine, dried over MgSO . After removal
of the solvent under reduced pressure, the residue was purified by
column chromatography (hexane /acetone, 10/1, v/v) to give an
oyster white solid 2 (3.08 g, 15.3 mmol) in 76.4% yield.
+
MS (MALDI-TOF): m/z (M , C12
H
15N): calcd: 201.12; found: 201.116.
1
3
H NMR (400 MHz, CDCl ) δ 9.93 (d, J = 9.1 Hz, 1H), 7.32 – 7.23 (m,
Fig.5 Temporal stabilities of the EO coefficient for poled films CLH-
2
1
H), 7.08 (t, J = 7.4 Hz, 1H), 6.87 (d, J = 7.9 Hz, 1H), 5.45 (d, J = 9.1 Hz,
H), 3.28 (s, 3H), 1.65 (s, 6H).
1
/APC and CLH-2/APC at 85 °C for 200 h
Through the outcome above, we can obviously see that
Compound 3
chromophore CLH-2 containing benzene derivative steric hindrance
group on the π-electron bridge has about 2 times higher r33 value
than chromophore CLH-1 without steric hindrance group on the π-
electron bridge. It illustrates that chromophore CLH-2 can translate
its relatively low β value into bulk EO activity more effectively than
To a solution of 2 (0.30 g, 1.5 mmol) and tributyl(1,3-dioxolan-2-
ylmethyl)phosphonium bromide (d) (1.2 g, 3.3 mmol) in anhydrous
THF was added a sodium hydride (0.36g, 15 mmol), 18-crown-6 as
the catalyst. After the mixture was stirred at room temperature for
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+
2
0 h, HCl/THF (v/v) solution was added to quenching the reaction and MS(MALDI-TOF): m/z (M ,C17
H
28ClNO
2
): calcd: 313.18; found:
View Article Online
DOI: 10.1039/C7TC00735C
kept to stir for another 1 h. Then, the organic layers were extracted 313.166.
with ethyl acetate (3 × 50 ml). The combined organic extracts were 2) To a solution of the compound (3.10g, about 10mmol) got in last
dried over MgSO . After the removal of the solvent, the residue was step in dry CHCl (40 mL) was added triphenylphosphine
purified by column chromatography (hexane /acetone, 8/1, v/v) to hydrobromide (3.09 g, 9mmol). The mixture was refluxed for 3 h.
4
3
give a claybank solid 3 (0.21 g, 0.92 mmol) in 61.3% yield.
The solvent was evaporated under reduced pressure. The product
+
MS(MALDI-TOF): m/z (M ,C15
H
17NO) ： calcd:227.13 ； found: was collected and washed with anhydrous ethyl ether without
further purification. The product (compound c) was a white solid
2
1
27.129.
3
H NMR (400 MHz, CDCl ) δ 9.42 (d, J = 7.5 Hz, 1H), 7.74 (t, J = 13.3 (6.12 g, yield: 96%).
+
Hz, 1H), 7.25 – 7.14 (m, 2H), 6.99 (t, J = 7.4 Hz, 1H), 6.78 (d, J = 7.8 Hz, MS(MALDI-TOF): m/z (M ,C35H42ClNOP): calcd: 558.27; found:
1
3
H), 5.98 (dd, J = 13.9, 8.5 Hz, 1H), 5.57 (d, J = 12.5 Hz, 1H), 3.27 (s, 558.259.
H), 1.62 (s, 6H).
Compound 4
Under a N atmosphere, to a solution of 2 (3.01g, 10mmol) and c
Chromophore CLH-1
2
A solution of 3 (0.11 g, 0.5 mmol) and TCF (0.12 g, 0.6 mmol) in 50 ml (7.03 g, 11 mmol) in dry THF (40 mL) was added NaH (2.40 g,
ethanol was refluxed under microwaves for 2 h, then cooled to room 100mmol). The solution was allowed to stir for 24 h at room
temperature. After the removal of the solvent, the residue was temperature and then poured into ice water. The organic phase was
purified by column chromatography (hexane / AcOEt, 2/1, v/v) to extracted using ethyl acetate, washed with brine and dried over
4
give a black green solid chromophore CLH-1 (0.13 g, 0.35 mmol) in MgSO . After removal of the solvent under reduced pressure, the
7
0.8% yield.
residue was purified by column chromatography (hexane /acetone,
O) ： calcd:408.20 ； found: 20/1, v/v) to give a yellowish solid 4 (3.69 g, 7.67 mmol) in 76.7%
+
MS(MALDI-TOF): m/z (M ,C26
H N
24 4
4
08.196.
yield.
1
+
H NMR (400 MHz, CDCl
3
) δ 7.69 (d, J = 13.2 Hz, 1H), 7.54 (t, J = 13.3 MS(MALDI-TOF): m/z (M ,C30
H
2
41ClN O): calcd:480.29; found:
Hz, 1H), 7.35 – 7.28 (m, 2H), 7.12 (t, J = 7.3 Hz, 1H), 6.92 (d, J = 7.8 Hz, 480.287.
H), 6.28 (t, J = 12.6 Hz, 1H), 6.01 (d, J = 14.1 Hz, 1H), 5.76 (d, J = 13.0 1H NMR (400 MHz, Acetone) δ 7.19 – 7.08 (m, 2H), 7.01 (d, J = 7.3 Hz,
Hz, 1H), 3.40 (s, 3H), 1.64 (s, 11H), 1.25 (s, 6H), 0.98 (t, J = 6.3 Hz, 8H). 1H), 6.95 (dd, J = 11.1, 4.3 Hz, 1H), 6.58 (t, J = 7.4 Hz, 1H), 6.49 (d, J =
.8 Hz, 1H), 6.31 (d, J = 15.3 Hz, 1H), 6.15 (dd, J = 6.4, 2.4 Hz, 2H), 5.30
(d, J = 11.6 Hz, 1H), 3.91 (t, J = 6.4 Hz, 2H), 3.50 (dd, J = 8.8, 4.6 Hz,
1
7
Compound b
2
2
H), 3.25 (q, J = 7.0 Hz, 4H), 2.97 (s, 3H), 1.76 (dd, J = 13.7, 6.9 Hz,
H), 1.72 – 1.67 (m, 2H), 1.47 (d, J = 4.1 Hz, 6H), 1.43 (dd, J = 9.9, 6.3
A two-phase mixture of 4-(diethylamino)salicylaldehyde (3.87g, 20
mmol), 1,6-dichlorohexane (30 mL), tetrabutyl ammonium bromide
Hz, 4H), 1.01 (t, J = 7.0 Hz, 6H).
(
0.3 g, 1 mmol), and 1M NaOH (30mL) was heated to reflux for 6 h.
The mixture was diluted with ether (50 mL) and washed with HCl (1
M, 15 mL) and water (2 ×25 mL). The combined organic extracts were
Compound 5b
dried over MgSO
pressure, the residue was purified by column chromatography this temperature during the dropwise addition of phosphorus
hexane /acetone, 15/1, v/v) to give a yellowish oils liquid b (5.83g, oxychloride (0.92 g, 6 mmol). The solution was kept for 2 h of stirring
4
. After removal of the solvent under reduced A solution of 10 ml DMF was cooled to 0 °C and was maintained at
(
1
8.7mmol) in 93.4% yield.
at 0 °C and the temperature was kept during the dropwise addition
): calcd: 311.17; found: of compound 4 in 30 ml DMF (1.92 g, 4 mmol). The solution was
gradually warmed to room temperature and stirred for 2 h of stirring
+
MS(MALDI-TOF): m/z (M ,C17H26ClNO
2
3
11.162.
1
3
H NMR (400 MHz, CDCl ) δ 10.07 (s, 1H), 7.62 – 7.57 (m, 1H), 6.16 at 60ºC before being poured into 200 ml solution of sodium
(
3
dd, J = 9.0, 1.9 Hz, 1H), 5.93 (d, J = 2.0 Hz, 1H), 3.94 (t, J = 6.3 Hz, 2H), carbonate (10%) for quench. The reaction mixture was extracted by
.43 (t, J = 6.7 Hz, 2H), 3.31 (q, J = 7.1 Hz, 4H), 1.75 (dd, J = 13.2, 6.6 ethyl acetate, washed with brine, dried over MgSO . After removal
Hz, 2H), 1.69 (dd, J = 13.5, 6.7 Hz, 2H), 1.46 – 1.38 (m, 4H), 1.11 (t, J of the solvent under reduced pressure, the residue was purified by
4
=
7.1 Hz, 6H).
column chromatography (hexane /acetone, 10/1, v/v) to give an
orange solid 5 (1.81 g, 3.56 mmol) in 89% yield.
+
Compound c
) To a solution of compound b (3.11 g, 10 mmol) in methanol (30
mL) was added NaBH (0.57 g, 15 mmol) in batches at 0 °C in an ice
bath. After the temperature warmed up to room temperature and
the solution became clear, diluted hydrochloric acid was added to
neutralize the reaction and then kept stirring for 2 h. The organic
phase was extracted using ethyl acetate, washed with brine and
MS(MALDI-TOF): m/z (M ,C31
H
2
41ClN O
2
): calcd:508.29; found:
5
1
08.288.
1
H NMR (400 MHz, Acetone) δ 9.40 (s, 1H), 7.63 (d, J = 12.7 Hz, 1H),
.18 (d, J = 7.3 Hz, 1H), 7.07 (t, J = 7.6 Hz, 1H), 6.82 – 6.76 (m, 2H),
.72 (d, J = 7.9 Hz, 1H), 6.21 (dt, J = 8.4, 2.3 Hz, 2H), 5.40 (d, J = 12.7
Hz, 1H), 3.82 (t, J = 6.2 Hz, 2H), 3.37 (t, J = 6.7 Hz, 2H), 3.29 (q, J = 7.0
Hz, 4H), 2.97 (s, 3H), 1.56 (s, 6H), 1.55 – 1.47 (m, 4H), 1.27 (dt, J = 6.5,
.0 Hz, 4H), 1.05 (t, J = 7.0 Hz, 6H).
4
7
6
3
4
dried over MgSO . After removal of the solvent, the residue was
directly dried in the vacuum oven for the next step without flash
chromatography. The product was a colorless transparent liquid
Chromophore CLH-2
(
3.10 g, yield: 98%).
6
| J. Name., 2012, 00, 1-3
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J Po lue r an sael od fo Mn aot et rai ad l js u Cs ht emm ai rs gt ri yn sC
Journal Name
ARTICLE
The procedure for chromophore CLH-1 was followed to prepare performed on the cluster of Key Laboratory of Theoretical and
View Article Online
DOI: 10.1039/C7TC00735C
chromophore CLH-2 from 5 as a green solid in 61.8% yield (0.21 g, Computational Photochemistry, Ministry of Education, China.
0
.31 mmol).
+
MS(MALDI-TOF): m/z (M ,C42
H
5 2
48ClN O ): calcd:689.35; found:
Notes and references
6
89.326.
1
H NMR (400 MHz, Acetone) δ 8.00 (d, J = 13.5 Hz, 1H), 7.92 (d, J =
1
2
3
4
5
.
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3.6 Hz, 1H), 7.34 (d, J = 7.3 Hz, 1H), 7.21 (t, J = 7.7 Hz, 1H), 7.03 (dt,
8
J = 9.8, 7.5 Hz, 2H), 6.82 (d, J = 8.3 Hz, 1H), 6.37 – 6.27 (m, 2H), 5.83
(
d, J = 14.4 Hz, 1H), 5.66 (d, J = 13.3 Hz, 1H), 3.91 (d, J = 5.3 Hz, 2H),
3
6
1
.38 (t, J = 6.7 Hz, 2H), 3.33 (q, J = 7.0 Hz, 4H), 3.21 (s, 3H), 1.59 (s,
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.08 (t, J = 7.0 Hz, 6H).
Conclusions
In this article, two NLO chromophores CLH-1 and CLH-2 based on 6.
,3,3-Trimethyl-2-methyleneindoline donors and powerful
1
7.
tricyanovinyldihydrofuran (TCF) acceptors linked together via
modified polyene π-conjugation with rigid benzene derivative steric
hindrance group (chromophore CLH-2) or unmodified polyene π-
conjugation (chromophores CLH-1) moieties as the bridges had been
synthesized in good overall yields (40%~50%) and systematically
characterized by NMR, MS and UV-Vis absorption spectroscopy. In
order to investigate the effects of the introduced rigid benzene
derivative steric hindrance group on the structure and properties of
2
013, 54, 5655-5664.
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2
010, 110, 25-55.
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-1
afforded the largest r33 values of 102 pm V . However, polymers with
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16.
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These consequences indicated that chromophores with benzene
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efficiently reduce dipole–dipole interactions so as to translate the
relatively small β values into bulk EO performance more effectively.
The novel chromophore CLH-2 accompanied with advantages of
high-yield synthesis, excellent thermal stability and considerably high
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We are grateful to the National Natural Science Foundation of China
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Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C7TC00735C
Electro-optic activity and thermal stability are increased a lot after modifying π-conjugated bridge
via introducing suitable isolation groups.