Synthesis and optical nonlinear property of Y-type chromophores based on double-donor structures with excellent electro-optic activity

Article abstract of DOI:10.1039/c4tc00508b

New Y-type chromophores FTC-yh1 and FTC-yh2 containing bis(N,N-diethyl) aniline as a novel electron-donor, thiophene as a π-conjugated bridge and tricyanofuran (TCF) as an acceptor have been synthesized and systematically investigated in this paper. Density functional theory (DFT) was used to calculate the HOMO-LUMO energy gaps and first-order hyperpolarizability (β) of these chromophores. These chromophores showed better thermal stability with their decomposition temperatures all above 240 °C. Most importantly, the high molecular hyperpolarizability of these chromophores can be effectively translated into large electro-optic (EO) coefficients (r₃₃) in poled polymers. The doped film-A containing 25 wt% chromophore FTC-yh1 displayed a value of 149 pm V^-1 at 1310 nm, and the doped film-B containing FTC-yh2 showed a value of 143 pm V^-1 at the concentration of 25 wt%. These values are almost four times higher than the EO activity of usually reported traditional single (N,N-diethyl)aniline nonlinear optical (NLO) chromophores FTC. High r₃₃ values indicated that the double donors of the bis(N,N-diethyl)aniline unit can efficiently improve the electron-donating ability and reduce intermolecular electrostatic interactions, thus enhancing the macroscopic EO activity. These properties, together with the good solubility, suggest the potential use of the new chromophores as advanced material devices.

Full text of DOI:10.1039/c4tc00508b

Journal of
Materials Chemistry C
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PAPER
Synthesis and optical nonlinear property of Y-type
chromophores based on double-donor structures
with excellent electro-optic activity
Cite this: J. Mater. Chem. C, 2014, 2,
5124
Yuhui Yang,ab Huajun Xu,ab Fenggang Liu,ab Haoran Wang,ab Guowei Deng,ab
a
Peng Si,ab Heyan Huang,ab Shuhui Bo, Jialei Liu,a Ling Qiu,a Zhen Zhena
*
a
*
and Xinhou Liu
New Y-type chromophores FTC-yh1 and FTC-yh2 containing bis(N,N-diethyl)aniline as a novel electron-
donor, thiophene as a p-conjugated bridge and tricyanofuran (TCF) as an acceptor have been
synthesized and systematically investigated in this paper. Density functional theory (DFT) was used to
calculate the HOMO–LUMO energy gaps and first-order hyperpolarizability (b) of these chromophores.
These chromophores showed better thermal stability with their decomposition temperatures all above
240 ꢀC. Most importantly, the high molecular hyperpolarizability of these chromophores can be
effectively translated into large electro-optic (EO) coefficients (r33) in poled polymers. The doped film-A
containing 25 wt% chromophore FTC-yh1 displayed a value of 149 pm Vꢁ1 at 1310 nm, and the doped
film-B containing FTC-yh2 showed a value of 143 pm Vꢁ1 at the concentration of 25 wt%. These values
are almost four times higher than the EO activity of usually reported traditional single (N,N-diethyl)aniline
nonlinear optical (NLO) chromophores FTC. High r33 values indicated that the double donors of the
bis(N,N-diethyl)aniline unit can efficiently improve the electron-donating ability and reduce
intermolecular electrostatic interactions, thus enhancing the macroscopic EO activity. These properties,
together with the good solubility, suggest the potential use of the new chromophores as advanced
material devices.
Received 14th March 2014
Accepted 15th April 2014
DOI: 10.1039/c4tc00508b
www.rsc.org/MaterialsC
Generally, the NLO chromophores have the structures of a
donor–p–acceptor which usually possess a rod-like structure. So
1. Introduction
the strong intermolecular dipole–dipole interactions will
develop in the polymeric system and further make the poling-
induced noncentrosymmetric alignment of chromophores a
daunting task.11 Furthermore, accompanying with the increased
concentration of chromophore moieties in the materials, these
intermolecular dipole–dipole interactions would become
stronger, which would nally lead to a decreased EO activity.12
Thus, how to decrease these interactions, and efficiently
translate the large b values of the organic chromophores into a
high macroscopic EO activity of polymers, has become one of
the major problems in optimizing organic NLO materials.13–15
To achieve higher EO activity and suppress the dipole interac-
tion among chromophores, rational molecular designs of
dipole chromophores have been made from the conjugated
push–pull molecules. Many efforts have been carried out to
design and synthesize novel NLO chromophores, seeking to
engineer NLO molecules both microscopically (b) and macro-
scopically (r33).13,16,17 However, it should be noted that the
majority of these works were focused on the conjugated bridge
and acceptor structures.18–25 The electron donors, which are
important components of NLO chromophores, have received
little attention. Among all the materials studied, the dipolar
Organic electro-optic (EO) materials have attracted considerable
attention over the past two decades because of their potential
applications in optical communication and optical data pro-
cessing technologies.1–4 As an important branch, organic EO
polymers have excellent characteristics with large EO coeffi-
cients, ultrafast response times, and easy processing,3,5–8 so they
have shown great promise for applications in recent years, such
as high speed EO modulators, switches, directional couplers
and so on. However, for practical applications, one of the
challenges in preparing excellent EO materials is to develop
nonlinear optical (NLO) chromophores with large hyper-
polarizability (b) and to reduce adverse strong inter-molecular
electrostatic interactions among the chromophore mole-
cules.9,10 Thus, chromophores with large b and weak inter-
molecular electrostatic interaction, as the decisive factor, must
be designed and prepared.
aKey Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical
Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, PR
China. E-mail: boshuhui@mail.ipc.ac.cn; xhliu@mail.ipc.ac.cn; xinhouliu@foxmail.
com; Fax: +86-01-62554670; Tel: +86-01-82543528
bUniversity of Chinese Academy of Sciences, Beijing 100043, PR China
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Chart 1 The structure of the chromophore of FTC, FTC-yh1 and
FTC-yh2.
chromophores bearing N,N-dimethyl aniline as a donating
group have been widely studied due to their large molecular
nonlinearity with signicantly enhanced thermo- and
photostabilities.8,20,25–27
Scheme 1 Chemical structure and synthetic scheme for chromo-
phore FTC-yh1.
In this paper, we choose the bis(N,N-diethylaniline) unit as a
new donating moiety. Due to its high electron-density and low
cost,28 the bis(N,N-diethylaniline) unit has been widely studied
in the dye-sensitized solar cells (DSCs).4,28,29 On the one hand,
the new donor with two N,N-diethylaniline units may improve
the electron-donating ability and thus may enhance the optical
nonlinearity. One of the N,N-diethylaniline unit can act as both
the additional donor and the isolated group (IG). Applying the
site isolation principle, the introduction of some IGs into the
chromophore moieties is an effective approach to suppress
the dipole interactions among chromophores and improve the
poling efficiency, thus achieving much larger macroscopic NLO
effects.15,30 On the other hand, as reported, controlling the
shape of the chromophore was proven to be an efficient
approach for minimizing this interaction and enhancing the
poling efficiency.31 These new chromophores having the double
benzene rings with an appropriate angle make the special
Y-type structure which is different from the general NLO chro-
mophores showing the rod-like structure. So it may efficiently
reduce the intermolecular electrostatic interactions and thus
may enhance the macroscopic EO activity. To the best of our
knowledge, the novel double donor units rarely appeared in the
NLO chromophore before.
Chromophores FTC-yh1 and FTC-yh2 were prepared according
to different strategies. FTC-yh1 was obtained in ve steps
starting from the commercially available Michler's ketone
(Scheme 1). Alcohol 2a was obtained in moderate yield by
reduction of the Michler's ketone with sodium borohydride in
boiling THF and was then directly converted to phosphonate 3a
using a procedure described in the literature.32 Phosphonate 3a
was condensed with 2-thenaldehyde by Horner–Emmons reac-
tion in which the proper base plays a key role in determining the
yield. We found that replacing the commonly used potassium
tert-butoxide with sodium hydride produced 4a with a much
improved yield (60%). Treatment of compound 4a with n-BuLi
and DMF gave an aldehyde 5a. The target chromophore FTC-yh1
was obtained via the Wittig reaction of aldehyde 5a with
acceptor TCF in the presence of a catalytic amount of
piperidine.
FTC-yh2 was obtained in ve steps in a different way (Scheme
2). The crucial reaction involves the creation of an additional
double bond and a functional group on the donor of Michlers
Ethylketone for later conversion to aldehyde. The reaction of 1b
Considering the abovementioned advantages, we choose the
bis(N,N-diethylaniline) unit as a new donating moiety. Two new
chromophores (in Chart 1) with the bis(N,N-diethylaniline) unit
as a donor were designed and prepared by a facile route from
Michler's ketone. They showed great solubility in common
organic solvents, good compatibility with polymers, and large
EO activity in the poled lms.1H-NMR and 13C-NMR analyses
were carried out to demonstrate the preparation of these chro-
mophores. Thermal stability, photophysical properties, DFT
calculations and EO activities of these chromophores were
systematically studied and were compared with the single-
aniline chromophore FTC (Chart 1).
2. Results and discussion
2.1. Synthesis and characterization of chromophores
The synthesis of FTC-yh1, FTC-yh2 and traditional FTC chro-
Scheme 2 Chemical structure and synthetic scheme for chromo-
mophores is depicted in Schemes 1–3, respectively. phore FTC-yh2.
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materials. Thermal properties of the two chromophores were
measured by Thermogravimetric Analysis (TGA). Both FTC-yh1
and FTC-yh2 showed excellent stability. The decomposition
temperatures (Td) of chromophores FTC-yh1 and FTC-yh2 were
249 ꢀC and 247 ꢀC, respectively, while, the traditional single
donor FTC showed a Td of 242 ꢀC. Therefore, the double donor
chromophores have a better thermo-stability than the tradi-
tional FTC chromophore. Therefore, the Td of the two chro-
mophores was high enough for the application in EO device
preparation.
Scheme 3 Chemical structure and synthetic scheme for chromo-
phore FTC.
with diisopropyl (cyanomethyl)-phosphonate using sodium
hydride as a base resulted in 2b with 65% yield. The reduction
with DIBAL-H followed by acid hydrolysis converts the nitrile
group on 2b into the corresponding aldehyde 3b with 83% yield.
Aldehyde 3b was condensed with 2-thienyltriphenyl-
phosphonate bromide by Wittig condensation to gain 4b. As
expected, aer introduction of the thiophene bridge by Wittig
condensation, treatment of compound 4b with n-BuLi and DMF
gave an aldehyde 5b. The target chromophore FTC-yh2 was
obtained via the Knoevenagel condensation reaction of alde-
hyde 5b with acceptor TCF in the presence of a catalytic amount
of piperidine.
2.3. Optical properties
In order to reveal the effect of double donors on the intra-
molecular charge transfer (ICT) of dipolar chromophores,
UV-Vis absorption spectra of three chromophores (c ¼ 1 ꢂ
10ꢁ5 mol Lꢁ1) were measured in a series of aprotic solvents with
different polarity so that the solvatochromic behavior of these
chromophores could be investigated to explore the polarity of
chromophores in a wide range of dielectric environments (Fig. 1
and 2). The spectrum data are summarized in Table 1. The
synthesised chromophores exhibited a similar p / p* intra-
molecular charge-transfer (ICT) absorption band in the visible
region. FTC-yh1 and FTC-yh2 showed the maximum absorption
(lmax) of 725 nm and 750 nm in CHCl3 respectively. With
extending a double bond into the chromophore FTC-yh1, the
lmax of FTC-yh2 chromophore red shied by 25 nm to 750 nm.
These values are exceptionally large compared to the traditional
FTC (lmax of 676 nm in CHCl3) with single aniline donor and the
same p-conjugated bridge and acceptor. The double donors
shied the ICT absorption band of the chromophore to the
lower energy. As shown in Fig. 1 and 2, the peak wavelength of
FTC-yh1 and FTC-yh2 showed a bathochromic shi of 71 nm
from dioxane to chloroform, displaying the larger sol-
vatochromism compared with the single donor FTC chromo-
phore (55 nm in Table 1). The resulting spectrum data
conrmed that the chromophores with double donors were
more easily polarizable than the single donor FTC. These
analyses implied that the double donors of bis(N,N-diethyl)-
aniline improved the electron-donating capability and
increased the polarizability of FTC-yh1 and FTC-yh2.
The traditional FTC chromophore was obtained in three
steps starting from the commercially available aldehyde 1c
(Scheme 3). The aldehyde 1c was condensed with 2-thienyl-
triphenylphosphonate bromide by Wittig condensation to gain
2c. As expected, aer introduction of the thiophene bridge by
Wittig condensation, treatment of compound 2c with n-BuLi
and DMF gave an aldehyde 3c. The target chromophore FTC was
obtained via the Knoevenagel condensation reaction of alde-
hyde 3c with acceptor TCF in the presence of a catalytic amount
of piperidine.
1
All the chromophores were fully characterized by H-NMR,
13C-NMR, and mass spectroscopy. These chromophores possess
good solubility in common organic solvents, such as dichloro-
methane, chloromethane and acetone.
2.2. Thermal analysis
NLO chromophores must be thermally stable enough to with-
stand encountered high temperatures (>200 ꢀC) in electric eld
poling and subsequent processing of chromophore/polymer
Fig. 1 UV-Vis absorption spectra in different solvents of chromophore Fig. 2 UV-Vis absorption spectra in different solvents of chromophore
FTC-yh1 (c ¼ 1 ꢂ 10ꢁ5 mol Lꢁ1).
FTC-yh2 (c ¼ 1 ꢂ 10ꢁ5 mol Lꢁ1).
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Table 1 Summary of thermal optical properties and EO coefficients of
chromophores FTC, FTC-yh1 and FTC-yh2
obtain qualitative information about the optical and electrical
properties of molecules.36–38 Besides, the HOMO–LUMO energy
gap is also used to understand the charge transfer interaction
occurring in a chromophore molecule.38–40 In the case of these
chromophores, Fig. 4 represents the frontier molecular orbitals
of chromophores FTC, FTC-yh1 and FTC-yh2. According to
Fig. 4, it is clear that the electronic distribution of the HOMO is
delocalized over the thiophene linkage and benzene ring,
whereas the LUMO is mainly constituted by the acceptor
moieties.38
Td (ꢀC) lmaxb(nm) lmaxc(nm) Dld (nm) r33 (pm Vꢁ1
)
a
e
FTC
FTC-yh1 249
FTC-yh2 247
242
676
725
750
621
654
679
55
71
71
39
149
143
a
Td was determined by an onset point, and measured by TGA under a
nitrogen atmosphere at a heating rate of 10 ꢀC minꢁ1
.
lmax was
b
c
d
b
measured in CHCl3. lmax was measured in dioxane. Dl ¼ lmax
ꢁ
c
e
lmax
. r33 values were measured at the wavelength of 1310 nm.
The HOMO and LUMO energy were calculated by DFT
calculations as shown in Table 2. For double donor chromo-
phores FTC-yh1 and FTC-yh2, the effect of double donor
structures narrows the energy gap between the HOMO and
LUMO energy with DE values of 1.963 eV and 1.766 eV respec-
tively. By contrast, the DE value of FTC is 2.032 eV. It can be
concluded that the LUMO energy of chromophore FTC is
0.021 eV larger than that of FTC-yh1 (ꢁ3.192 eV vs. ꢁ3.123 eV),
while the HOMO energy of FTC is 0.048 eV smaller than that of
FTC-yh1 (ꢁ5.224 eV vs. ꢁ5.176 eV). The same trend can be
observed in chromophore FTC-yh2. This may result from the
fact that the double donor structure inuences the HOMO
energy to a greater extent than the LUMO energy. The HOMO–
LUMO gaps of FTC-yh1 (1.963 eV) and FTC-yh2 (1.766 eV) are
lower than FTC (2.032 eV), and this indicates that FTC-yh1 and
FTC-yh2 should exhibit better ICT and NLO property than FTC.
This is well supported by the facts that the lower is the optical
gap, the greater possibility will be the ICT and higher
nonlinearity.38
The HOMO–LUMO gap was also investigated by cyclic vol-
tammetry (CV). It showed an energy gap (DE) value of 1.353 eV
for FTC-yh1 and 1.212 eV for FTC-yh2, while the chromophore
FTC exhibited a DE value of 1.529 eV.8 This comparison
demonstrated that the double donors narrowed the energy gap
indicating the excellent ICT of the double donor chromophores.
This result corresponded with the conclusion of UV-Vis spectra
analysis and the DFT results.
As reported,33 the observed blueshis (H type) or redshis
(J type) of dyes in optical absorption spectra are due to the
interplay of optical selection rules modied through intermo-
lecular interactions. However, we nd that there is no dipole–
dipole interaction in the solvents at this low concentration of
our chromophores (10ꢁ5 mol Lꢁ1). By testing the different
concentrations of these three chromophores in CHCl3, we have
proved that there was no shi in the shape of the absorption
peaks shown in Fig. 3. In our work, the absorption peak shis in
the different solvent were measured for solvatochromism which
was related to the polarization and nonlinearity of the
chromophores.
2.4. Theoretical calculations
In order to model the ground state molecular geometries, the
HOMO–LUMO energy gaps and b values of these chromophores
were calculated. The DFT calculations were carried out at the
hybrid B3LYP level by employing the split valence 6-31 g (d, p)
basis set.34–36 The data obtained from DFT calculations are
summarized in Table 2.
The frontier molecular orbitals are oen used to characterize
the chemical reactivity and kinetic stability of a molecule and to
Further, the theoretical microscopic b was calculated by
Gaussian 03. The b value is related to the substituent, molecular
conguration, and intramolecular charge-transfer.41 As the
reference reported earlier, the b has been calculated at the 6-
31 g (d, p) level.42 From this, the scalar quantity of b can be
computed from the x, y, and z components according to the
following equation:
Fig. 3 UV-Vis absorption spectra of different concentrations of three
chromophores in CHCl3.
Table 2 Data from DFT calculationsa
d
bmax
Chromophores EHOMO/eV ELUMO/eV DEb/eV DEc/eV 10ꢁ30 esu
/
FTC
FTC-yh1
FTC-yh2
ꢁ5.224
ꢁ5.176
ꢁ5.038
ꢁ3.192
ꢁ3.213
ꢁ3.272
2.032
1.963
1.766
1.529.
1.353
1.212
883
713
995
a
b
DE ¼ ELUMO ꢁ EHOMO
.
Results were calculated by DFT. c Results were
d
from the cyclic voltammetry experiment. b values were calculated
using Gaussian03 at the B3LYP/6-31 g(d) level and the direction of the
maximum value is directed along the charge transfer axis of the
chromophores.
Fig. 4 The frontier molecular orbitals of chromophores FTC, FTC-yh1
and FTC-yh2.
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2
2
2 1/2
the removal of the residual solvent. The corona poling process
was carried out at a temperature of 10 C above the glass tran-
b ¼ (bx + by + bz )
(1)
ꢀ
X
1
3
sition temperature (Tg) of the polymer. The r33 values were
measured using the Teng-Man simple reection technique at
the wavelength of 1310 nm using a carefully selected thin ITO
electrode with low reectivity and good transparency in order to
minimize the contribution from multiple reections.43
where bi ¼ biii
þ
ðbijj þ bjij þ bjjiÞ;i, j ˛ (x, y, z)
isj
Due to the double donors with the stronger electron-
donating ability and better conjugated system, chromophore
FTC-yh2 showed a larger b value than the other two chromo-
phores, while chromophore FTC-yh1 exhibited the smallest b
value (713 ꢂ 10ꢁ30 esu). It may be revealed by the optimized
congurations (Fig. 5) that chromophore FTC-yh1 possessed a
less coplanar geometry compared to the FTC chromophore, due
to the double benzene ring with an angle in FTC-yh1. As for
FTC-yh2, on the one hand, with extending a double bond from
FTC-yh1, the steric hindrance between the aromatic groups
indeed decreases with the lengthening of the ethylenic spacer.4
On the other hand, FTC-yh2 has a better conjugation effect
which can be veried in the UV-Vis data. Due to the above-
mentioned features, FTC-yh2 with the largest b value is not hard
to understand.
Chromophore FTC-yh1 possessed a little smaller b value, but
it showed a larger r33 value in the next section. Many factors can
affect the r33 value. One important factor may be the less elec-
trostatic interaction for FTC-yh1 between the chromophore
molecules. Besides, due to the improved coplanar geometry, the
electrostatic interaction between the chromophore molecules
was enhanced which led to FTC-yh2 a little smaller r33 than FTC-
yh1.
The r33 values of lms containing chromophores FTC-yh1
(lm-A), FTC-yh2 (lm-B) and FTC (lm-C) were measured in
different loading densities, as shown in Fig. 6. Traditional
chromophore FTC with the single N,N-diethylaniline donor
gained the r33 value from 12 pm Vꢁ1 (10 wt%) to 39 pm Vꢁ1
(25 wt%), while the r33 values of chromophore FTC-yh1 were
gradually improved from 30 pm Vꢁ1 (10 wt%) to 149 pm Vꢁ1
(25 wt%). The similar trend of enhancement was also observed
for chromophore FTC-yh2, whose r33 values increased from
50 pm Vꢁ1 (10 wt%) to 143 pm V (25 wt%). When the chromo-
phore loading density was up to 25 wt%, the r33 value of lm B
was 143 pm Vꢁ1. However, as the loading density increases from
25 wt% to 30 wt%, the lm-B displayed a downward trend. To
our regret, the lm-A with the 30 wt% loading density of FTC-
yh1 presents an obvious phase separation.
Through the outcome above, we can obviously see that the
chromophores with the bis(N,N-diethylaniline) unit as a donor
have nearly 4 times higher r33 value than the chromophore FTC,
illustrating that the double donors of the chromophores
signicantly increase their macroscopic EO activity. This may be
explained by the fact that one of the donors could be also acted
as the isolation group. As reported earlier,44 the introduction of
some isolation groups into the chromophore moieties to further
control the shape of the chromophore could be an efficient
approach to minimize interactions between the chromophores.
So the double donor chromophores have an obvious advantage
in translating b into r33 and thus increased the macroscopic EO
activity.
As above stated, we have not come to an exact ascertainment
that our double donors of Y-type chromophore based bis(N,N-
diethyl)aniline unit are different from the general NLO chro-
mophores. These new chromophores have an obvious advan-
tage in transferring the microscopic b to macroscopic electro-
optic effect.
2.5. Electric eld poling and EO property measurements
As shown in Fig. 6, when the concentration of chromophores
in APC is low, lm B displayed a larger r33 value than lm A. As
the chromophore loading density increases, this trend is
For studying EO property derived from these chromophores, a
series of guest–host polymers were generated by formulating
the chromophores into amorphous polycarbonate (APC) using
dibromomethane as a solvent. The resulting solutions were
ltered through a 0.2 mm PTFE lter and spin-coated onto
indium tin oxide (ITO) glass substrates. Films of doped poly-
mers were baked in a vacuum oven at 80 ꢀC overnight to ensure
Fig. 5 The optimized structure of chromophores FTC, FTC-yh1 and Fig. 6 EO coefficients of NLO thin films as a function of chromophore
FTC-yh2.
loading densities.
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presence of 1 mM n-tetrabutylammoniumperchlorate as the
supporting electrolyte. All chemicals, commercially available,
are used without further purication unless otherwise stated.
The DMF and THF were freshly distilled prior to their use. The
2-dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran (TCF)
acceptor was prepared according to the literature.45
3.2. Synthesis
Fig. 7 UV-Vis absorption spectra of E–O polymers before and after
poling.
3.2.1 Synthesis of compound 3a. Alcohol 2a was obtained
in moderate yield by reduction of the Michler's ketone with
sodium borohydride in boiling THF and was then directly
converted to phosphonate 3a using a procedure described in the
literature.32
inversed. This can be explained, when, at a low-density range,
the intermolecular dipolar interactions are relatively weak. FTC-
yh2 had a larger b and was easily poled which displayed a larger
r33 value. As the chromophore loading density increases, FTC-
yh2 with a better coplanar geometry presented a stronger
negative effect of inter-chromophore dipole–dipole interactions
which displayed a smaller r33 value.
1H-NMR (400 MHz, acetone-d6): d ¼ 7.34 (dd, JHH ¼ 8.5 Hz,
JHP ¼ 1.5 Hz, 4H, Ar–H), 6.62 (d, J ¼ 8.6 Hz, 4H, Ar–H), 4.21 (d, J
¼ 25.0 Hz, 1H, CH), 3.75–4.08 (m, 4H, CH2O), 3.34 (m, 8H,
CH2N), 1.33 (t, J ¼ 7.0 Hz, 6H, 2 Me), 1.20 (t, J ¼ 7.0 Hz, 6H, 2
Me), 1.12 (t, J ¼ 7.0 Hz, 6H, 2 Me).
MALDI-TOF: m/z calcd for C25H38N2O3P: 446.26 [M]+; found:
446.27.
In order to verify the effect of chromophore structure on the
NLO activity, the order parameter (F) was calculated by
measuring UV-Vis absorption spectra (see Fig. 7). Aer the
corona poling, the dipole chromophores in the polymer were
aligned, and the absorption curve decreased due to birefrin-
gence. From the absorption changes, the order parameter (F)
for lms can be calculated from the absorption changes
according to the following equation: F ¼ 1 ꢁ A1/A0, in which A1
and A0 are the respective absorptions of the polymer lms aer
and before corona poling. The order parameter (F) of poled
lms at a loading density of 10 wt% was calculated. The F value
of lm-A (FTC-yh1/APC) is 17%, while that of lm-B (FTC-yh2/
APC) is 28% (Fig. 7). The difference in the order parameter
indicates that lm-B containing chromophore FTC-yh2 has
weaker interchromophore electrostatic interactions and is more
easily poled than lm-A. At the same time, with an extended
double bond into FTC-yh1, FTC-yh2 has an advantage of
molecular rotation and thus makes it move more easily under
the electric eld. This result corresponded with the conclusion
of UV-Vis spectra analysis.
3.2.2 Synthesis of compound 4a. To a suspension of diethyl
bis(4-(dimethylamino)phenyl) methylphosphonate 3a (1.5 g,
3.36 mmol), and thiophene-2-carbaldehyde (336 mg, 3 mmol) in
20 mL dry THF and NaH (0.14 g, 5.6 mmol) were added and the
mixture turned yellow. The mixture was stirred at room
temperature for 24 h. Saturated NH4Cl was added and the
resulting mixture was extracted with EtOAc (20 ꢂ 3 mL). The
combined extracts were washed with water and dried over
MgSO4. Aer ltration and removal of the solvent under
vacuum, the crude product was puried by column chroma-
tography to give a yellow liquid (0.73 g, 60%).
1H-NMR (400 MHz, acetone-d6): d ¼ 7.18 (d, J ¼ 9.0 Hz, 2H,
Ar–H), 7.14 (s, 1H, CH), 7.06 (d, J ¼ 5.0 Hz, 1H, CH), 6.99 (d, J ¼
8.7 Hz, 2H, Ar–H), 6.93 (d, J ¼ 3.6 Hz, 1H, CH), 6.85 (dd, J ¼ 5.0,
3.6 Hz, 1H, CH), 6.80 (d, J ¼ 8.7 Hz, 2H, Ar–H), 6.64 (d, J ¼ 9.0
Hz, 2H, Ar–H), 3.43 (m, 8H, CH2N), 1.22 (t, J ¼ 7.0 Hz, 6H, 2 Me),
1.15 (t, J ¼ 7.0 Hz, 6H, 2 Me).
13C-NMR (100 MHz, acetone-d6): d ¼ 148.56, 148.09, 143.84,
141.69, 132.06, 129.05, 128.85, 127.97, 127.14, 126.61, 125.46,
117.00, 113.07, 112.13, 44.90, 12.99, 12.94.
MALDI-TOF: m/z calcd for C26H32N2S: 404.23 [M]+; found:
404.22.
3. Experimental
3.1. Materials and instrumentation
3.2.3 Synthesis of compound 5a. To a solution of 4a (1.0 g,
1H NMR spectra were recorded by an Advance Bruker 2.47 mmol) in dry THF (20 mL) was added a 2.4 M solution of n-
400(400 MHZ) NMR spectrometer (tetramethylsilane as an BuLi in hexane (1.5 mL, 3.7 mmol) dropwise at ꢁ78 ꢀC under a N2
internal reference). The MS spectra were obtained on MALDI- atmosphere. Aer this the mixture was stirred at this temperature
TOF-(Matrix Assisted Laser Desorption/Ionization Time of for 1 h, and the dry DMF (0.23 mL, 3.0 mmol) was introduced.
Flight) on a BIFLEXIII(Broker Inc.) spectrometer. The UV-Vis The resulting solution was stirred for another 1 h at ꢁ78 ꢀC and
spectra were recorded on a Cary 5000 photo spectrometer. The then allowed to warm up to room temperature. The reaction was
TGA was determined by a TA5000-2950TGA (TA Co) with a quenched by water. THF was removed by evaporation. The
ꢁ1
ꢀ
heating rate of 10 C min under the protection of nitrogen. residue was extracted with CH2Cl2 (3 ꢂ 30 mL). The organic layer
Cyclic voltammetry (CV) experiments were performed on a was dried by MgSO4 and concentrated in vacuo. The residue was
CHI660D electrochemical workstation by a cyclic voltammetry puried by column chromatography on a silica gel (hexane–
(CV) technique in CH3CN solution, using two platinum wires as acetone, v/v, 10/1) to obtain a red solid (0.87 g, 82%).
the working and counter electrodes, respectively, and a satu-
rated calomel electrode as the reference electrode in the (d, J ¼ 4.0 Hz, 1H, CH), 7.25–7.22 (overlap, 3H, Ar–H, CH), 7.09
1H-NMR (400 MHz, acetone-d6): d ¼ 9.74 (s, 1H, CHO), 7.67
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(d, J ¼ 4.0 Hz, 1H, CH), 7.02–6.98 (m, 2H, Ar–H), 6.87–6.81 quench the reaction. The mixture was stirred for 1 h to complete
(m, 2H, Ar–H), 6.67 (m, 2H, Ar–H), 3.44 (m, 8H, CH2N), 1.22 the hydrolysis. The organic solvent was collected and removed
(t, J ¼ 7.0 Hz, 6H, 2 Me), 1.15 (t, J ¼ 7.0 Hz, 6H, 2 Me).
in vacuo. The residue was puried by column chromatography
13C-NMR (100 MHz, acetone-d6): d ¼ 183.06, 153.68, 148.94, on a silica gel (hexane–acetone, v/v, 10/1) to yield a red solid
147.41, 142.10, 137.35, 131.75, 129.49, 129.01, 115.86, 113.07, (2.9 g, 83%).
111.76, 44.90, 12.93.
1H-NMR (400 MHz, CDCl3): d ¼ 9.47 (d, J ¼ 8.2 Hz, 1H, CHO),
MALDI-TOF: m/z calcd for C27H32N2OS: 432.24 [M]+; found: 7.31 (d, J ¼ 8.8 Hz, 2H, Ar–H), 7.19 (d, J ¼ 8.7 Hz, 2H, Ar–H), 6.65
432.22.
(d, J ¼ 8.7 Hz, 2H, Ar–H), 6.62 (d, J ¼ 8.8 Hz, 2H, Ar–H), 6.39 (d, J
3.2.4 Synthesis of chromophore FTC-yh1. A mixture of ¼ 8.2 Hz, 1H, CH), 3.40 (dd, J ¼ 13.5, 6.6 Hz, 8H, CH2N), 1.20 (dt,
aldehydic bridge 5a (0.85 g, 1.97 mmol) and acceptor 6 (0.43 g, J ¼ 8.9, 6.7 Hz, 12H, 4 Me).
2.16 mmol) in ethanol (30 mL) was stirred at 75 ꢀC for 4 h in the
13C-NMR (100 MHz, CDCl3): d ¼ 194.86, 164.90, 150.42,
presence of a catalytic amount of piperidine. Aer removal of 149.76, 134.04, 132.05, 127.59, 124.79, 123.11, 111.72, 111.40,
the solvent, the residue was puried by column chromatog- 45.36, 45.29, 13.52.
raphy on a silica gel (hexane–ethyl acetate, v/v, 4 : 1). A dark
solid was obtained (0.45 g, 37%).
MALDI-TOF: m/z calcd for C23H30N2O: 350.24 [M]+; found:
350.24.
3.2.7 Synthesis of compound 4b. Under a N2 atmosphere, a
1H-NMR (400 MHz, acetone-d6): d ¼ 7.98 (d, J ¼ 15.7 Hz, 1H,
CH), 7.54 (d, J ¼ 4.2 Hz, 1H, CH), 7.33–7.26 (overlap, 3H, Ar–H, mixture of 3b (2.0 g, 5.7 mmol) and 2-thienyl triphenyl-
CH), 7.14 (d, J ¼ 4.2 Hz, 1H, CH), 7.01 (d, J ¼ 8.7 Hz, 2H, Ar–H), phosphonate bromide (3.01 g, 6.86 mmol) in dry THF (20 mL) at
6.88 (d, J ¼ 8.7 Hz, 2H, Ar–H), 6.69 (d, J ¼ 9.0 Hz, 2H, Ar–H), 6.46 room temperature, and NaH (0.82 g, 34.2 mmol) was added. The
(d, J ¼ 15.7 Hz, 1H, CH), 3.55–3.39 (m, 8H, CH2N), 1.79 (s, 6H, 2 mixture turned yellow and was stirred at room temperature for
Me), 1.25 (t, J ¼ 7.0 Hz, 6H, 2 Me), 1.17 (t, J ¼ 7.0 Hz, 6H, 2 Me). 24 h. Saturated NH4Cl was added and the resulting mixture was
13C-NMR (100 MHz, acetone-d6): d ¼ 177.45, 174.88, 154.58, extracted with EtOAc (20 ꢂ 3 mL). The combined extracts were
154.55, 149.48, 149.27, 149.23, 148.92, 141.19, 139.71, 137.54, washed with water and dried over MgSO4. Aer ltration and
131.81, 131.06, 130.01, 129.11, 125.35, 116.24, 113.47, 113.25, removal of the solvent under vacuum, the crude product was
112.80, 112.06, 111.84, 111.65, 98.62, 97.03, 45.10, 44.96, 26.39, puried by column chromatography on a silica gel (hexane–
12.95.
MALDI-TOF: m/z calcd for C38H39N5OS: 613.29 [M]+; found:
acetone, v/v, 50/1) to obtain a yellow solid (1.47 g, 60%).
1H-NMR (400 MHz, CDCl3): d ¼ 7.27 (d, J ¼ 8.8 Hz, 2H, Ar–H),
7.21 (d, J ¼ 10.6 Hz, 1H, CH), 7.14 (d, J ¼ 8.7 Hz, 2H, Ar–H), 7.05
613.22.
HRMS (ESI) (M+, C38H39N5OS): calcd: 614.29481; found: (d, J ¼ 3.9 Hz, 1H, CH), 7.02–6.98 (m, 1H, CH), 6.94–6.83 (m, 1H,
614.29509.
CH), 6.68–6.60 (m, overlap, 5H, Ar–H, CH), 6.42–6.28 (m, 1H,
3.2.5 Synthesis of compound 2b. A 250 mL three-necked CH), 3.41–3.34 (m, 8H, CH2N), 1.22–1.14 (m, 12H, 4Me).
ask was charged with NaH (1.5 g, 62.5 mmol) in dry THF
13C-NMR (100 MHz, acetone-d6): d ¼ 147.77, 147.53, 147.05,
(30 mL) under a N2 atmosphere. Diisopropyl (cyanomethyl)- 146.94, 131.88, 131.78, 129.79, 129.00, 128.83, 127.67, 127.05,
phosphonate (8.05 g, 0.050 mol) was introduced into the 126.88, 126.32, 125.39, 124.92, 123.50, 123.23, 122.44, 119.58,
mixture dropwise by a syringe at 0 ꢀC with an ice bath. Aer the 119.01, 111.31, 111.28, 111.09, 110.96, 78.56, 44.10, 44.07,
solution became clear, compound 1b (8.0 g, 0.025 mol) in THF 13.30, 12.21.
(20 mL) was added. The mixture was reuxed for 24 h. The
resulting solution was poured into 100 mL ice water and was 430.07.
MALDI-TOF: m/z calcd for C28H34N2S: 430.24 [M]+; found:
extracted with CH2Cl2 (3 ꢂ 30 mL). The organic layer was dried
3.2.8 Synthesis of compound 5b. In a similar manner as
(MgSO4) and concentrated in vacuo, and the residue was puri- described above, 5b was synthesized from 4b as a red solid
ed by column chromatography on a silica gel (hexane–acetone, (82%).
v/v, 50/1) to obtain a yellow solid (5.57 g, 65%).
1H-NMR (400 MHz, CDCl3): d ¼ 9.75 (1H, s, CHO), 7.56 (1H,
1H-NMR (400 MHz, acetone-d6): d ¼ 7.33–7.26 (m, 2H, Ar–H), d, J ¼ 4.0 Hz, CH), 7.23 (2H, d, J ¼ 8.8 Hz, Ar–H), 7.12 (2H, d, J ¼
7.26–7.17 (m, 2H, Ar–H), 6.78–6.73 (m, 2H, Ar–H), 6.72–6.67 8.7 Hz, Ar–H), 7.08 (1H, d, J ¼ 11.5 Hz, CH), 6.94 (1H, d, J ¼ 4.0
(m, 2H, Ar–H), 5.48 (s, 1H, CH), 3.46 (m, 8H, CH2N), 1.18 (dt, J ¼ Hz, CH), 6.72–6.66 (3H, overlap, Ar–H, CH), 6.63–6.57 (3H,
10.4, 7.0 Hz, 12H, 4 Me).
overlap, Ar–H, CH), 3.39 (8H, m, CH2N), 1.20 (12H, m, 4 Me).
13C-NMR (100 MHz, CDCl3): d ¼ 206.35, 147.38, 147.10,
13C-NMR (100 MHz, acetone-d6): d ¼ 163.64, 150.23, 149.81,
132.25, 131.17, 126.73, 124.84, 120.52, 111.76, 111.40, 86.95, 146.48, 141.73, 132.07, 131.97, 129.51, 129.01, 127.45, 127.01,
44.93, 44.88, 12.94, 12.88.
126.85, 124.82, 119.58, 119.41, 111.00, 110.78, 44.32, 12.70.
MALDI-TOF: m/z calcd for C29H34N2OS: 458.24 [M]+; found:
458.28.
MALDI-TOF: m/z calcd for C23H29N3: 347.29 [M]+; found:
347.23.
3.2.6 Synthesis of compound 3b. To a solution of 2b (3.47 g,
3.2.9 Synthesis of chromophore FTC-yh2. In a similar
10 mmol) in dry toluene (30 mL) was added a 1 M solution of manner as described above, FTC-yh2 was synthesized from 5b
diisobutylaluminum hydride in hexane (20 mL, 20 mmol) by a as a dark solid (38%).
syringe at ꢁ78 ꢀC with a dry ice/acetone bath. The reaction
1H-NMR (400 MHz, acetone-d6): d ¼ 8.12 (d, J ¼ 15.8 Hz, 1H,
mixture was stirred at ꢁ78 ꢀC for 2 h. Aer the mixture was CH), 7.64 (d, J ¼ 4.0 Hz, 1H, CH), 7.22 (d, J ¼ 8.9 Hz, 2H, Ar–H),
warmed to room temperature, NH4Cl solution was added to 7.11–7.13 (overlap, 3H, Ar–H, CH), 7.07 (d, J ¼ 11.0 Hz, 1H, CH),
5130 | J. Mater. Chem. C, 2014, 2, 5124–5132
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6.92 (d, J ¼ 15.8 Hz, 1H, CH), 6.84–6.77 (overlap, 3H, Ar–H, CH), maximum r33 value of 149 pm Vꢁ1 at the doping concentration
6.73 (d, J ¼ 11.0 Hz, 1H, CH), 6.68 (d, J ¼ 8.9 Hz, 2H, Ar–H), 3.40 of 25 wt%, while lm-B containing chromophore FTC-yh2
(m, 8H, CH2N), 1.86 (s, 6H, 2 Me), 1.20 (m, 12H, 4 Me).
showed a maximum r33 value of 143 pm Vꢁ1 at 25 wt%. Those
13C-NMR (100 MHz, acetone-d6): d ¼ 177.48, 175.02, 154.32, consequences indicate that these chromophores with double
149.81, 148.99, 148.77, 140.47, 139.05, 138.83, 134.96, 133.00, N,N-diethylaniline donors could efficiently reduce the inter-
132.86, 130.53, 130.26, 129.93, 128.49, 126.87, 123.03, 122.83, chromophore electrostatic interactions and enhance the
113.37, 113.15, 112.67, 112.00, 111.82, 98.98, 97.61, 45.02, macroscopic optical nonlinearity. This novel donor chromo-
44.79, 26.21, 12.88.
phore showed promising applications in NLO chromophore
MALDI-TOF: m/z calcd for C40H41N5OS: 639.30 [M]+; found: synthesis. We believe that these novel Y-type chromophores can
639.26.
be used in exploring high-performance organic EO and photo-
HRMS (ESI) (M+, C40H41N5OS): calcd: 640.31046; found: refractive materials where both thermal stability and optical
640.30990.
nonlinearity are of equal importance.
3.2.10 Synthesis of compound 2c. In a similar manner as
described above, 2c was synthesized from 1c as a yellow solid
(68%).
Acknowledgements
1H-NMR (400 MHz, CDCl3): d ¼ 7.33 (d, J ¼ 8.9 Hz, 2H, Ar–H),
7.11–7.07 (m, 1H, CH), 7.01 (d, J ¼ 16.1 Hz, 1H, CH), 6.96 (d, J ¼
3.4 Hz, 1H, CH), 6.85 (d, J ¼ 16.1 Hz, 1H, CH), 6.64 (d, J ¼ 8.9 Hz,
2H, Ar–H), 6.47 (d, J ¼ 3.4 Hz, 1H, CH), 3.41–3.31 (m, 4H, CH2N),
1.17 (t, J ¼ 7.1 Hz, 6H, 2 Me).
We are grateful to the National Nature Science Foundation of
China (no. 61101054) for nancial support.
Notes and references
13C-NMR (100 MHz, CDCl3): d ¼ 148.10, 144.72, 130.66,
129.48, 128.22, 127.95, 127.03, 125.05, 124.67, 123.34, 117.69,
112.45, 112.06, 44.88, 13.21.
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