Facile structure and property tuning through alteration of ring structures in conformationally locked phenyltetraene nonlinear optical chromophores

Article abstract of DOI:10.1039/c0jm02855j

A series of phenyltetraene-based nonlinear optical (NLO) chromophores 1a-c with the same donor and acceptor groups, but different tetraene bridges that are partly connected by various sizes of aliphatic rings, have been synthesized and systematically inve

Full text of DOI:10.1039/c0jm02855j

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PAPER
Facile structure and property tuning through alteration of ring structures in
conformationally locked phenyltetraene nonlinear optical chromophores†
Xing-Hua Zhou,a Joshua Davies,a Su Huang,a Jingdong Luo,a Zhengwei Shi,a Brent Polishak,a Yen-Ju Cheng,a
a
Tae-Dong Kim, Lewis Johnson and Alex Jen
b
ab
*
Received 29th August 2010, Accepted 21st December 2010
DOI: 10.1039/c0jm02855j
A series of phenyltetraene-based nonlinear optical (NLO) chromophores 1a–c with the same donor and
acceptor groups, but different tetraene bridges that are partly connected by various sizes of aliphatic
rings, have been synthesized and systematically investigated. The interposed conjugated tetraene
segments in three chromophores studied are based on isophorone, (1S)-(ꢀ)-verbenone, and 3,4,4-
trimethyl-2-cyclopentenone, respectively. This kind of structural alteration has significant effect on the
intrinsic electronic structures and physical properties of these highly polarizable chromophores as
revealed by a variety of characterization techniques. The introduction of the verbenone- and
trimethylcyclopentenone-based tetraene bridges could significantly improve the glass-forming ability of
chromophores 1b and 1c in comparison with the highly crystalline characteristics of isophorone-based
chromophores 1a. More importantly, chromophores 1a–c exhibited distinct optical features in
absorption band shape, solvatochromic behavior, as well as energy band gap from the UV-vis-NIR
absorption measurements. Quantum mechanical calculations using density functional theory (DFT)
were also used to evaluate second-order NLO properties of these chromophores. The electro-optic (EO)
coefficients of 1a–c in poled polymers with the 10 wt% chromophore content showed an apparent
decrease from 78 pm Vꢀ1 for 1a to 42 pm Vꢀ1 for 1c. This decrease is attributed to the gradual decrease
of the molecular hyperpolarizability (b) of the chromophores which is associated with the progressive
cyanine-like electronic structure from the isophorone-based 1a to the cyclopentenone-based 1c
chromophore.
effectively translate these large b values into bulk EO activities
Introduction
together with improvement of other auxiliary properties through
proper molecular engineering of these dipolar chromophores.6–10
Among numerous chromophore systems studied, the combina-
tion of dialkylaminophenyl donors and strong CF3–TCF
acceptors, linked by isophorone-derived tetraene (CLD) bridges,
represents one of the most effective frameworks that yield large
b values and good processibility.11 This class of D–p–A struc-
tures has served as the core p-conjugated building blocks for
many of the newly developed EO materials.12 Therefore, it has
stimulated interest in further improving the properties of these
materials and the synthetic methodologies of making them.
Using two-level model and bond-length-alternation (BLA)
theory to calculate the optimal combination of donor and
acceptor strength for a given bridge in NLO chromophores have
been commonly used for achieving balanced electronic asym-
metry and electron polarization.13,14 Another structural param-
eter is the modification of polymethine conjugation path by
incorporating part of the methine skeletons into single or fused
aliphatic rings. Although this approach has been widely used to
improve the thermal and photochemical stability of polyenic
chromophores, its effect on tuning the ground-state polarization
Organic and polymeric EO materials have been intensively
studied for the past two decades due to their potential applica-
tions for high-speed and broadband information technologies.1
However, the dynamic development has been hampered by the
fact that several critical material properties need to be simulta-
neously optimized. Recently, there is a resurgence of interest in
organic EO materials due to the demonstration of several inno-
vative devices using cleverly engineered processing methodolo-
gies.2–5 To meet the stringent requirements of these devices,
several series of organic EO materials have been developed
through rational design of nonlinear optical (NLO) chromo-
phores to optimize their molecular hyperpolarizability (b), and
aDepartment of Materials Science and Engineering, University of
Washington, Seattle, Washington, 98195, USA. E-mail: ajen@u.
washington.edu
bDepartment of Chemistry, University of Washington, Seattle,
Washington, 98195, USA
† Electronic supplementary information (ESI) available: 1H and 13C
NMR spectra for the compounds discussed, and details for quantum
mechanical calculations. See DOI: 10.1039/c0jm02855j
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of dipolar polyene chromophores is not obvious.15 This is
partially due to the fact that some of these earlier generations of
NLO chromophores only contain relatively weak electron
acceptors thus possess relatively large BLA. Recent studies
indicated that the intramolecular charge transfer (ICT) of
highly efficient dipolar polyene chromophores can be tuned to
a certain extent by different substituents along the conjugating
bridge.11a,b,16 However, it remains to be proved if the ICT of these
highly polarized NLO chromophores can be modulated by
structural modification of bridges.
accomplished in good overall yields by condensing the TBDMS-
protected dienones with diethyl(cyanomethyl)phosphonate using
the Wittig–Horner reaction, followed by reducing the resultant
trienenitriles with DIBAL-H and subsequent hydrolysis. Finally,
a strong CF3–TCF-type acceptor17 was condensed with the cor-
responding trienals to afford the desired phenyltetraene-based
chromophores 1a–c. As suggested by their 1H-NMR spectra,
chromophores 1a and 1b contain a mixture of inseparable E/Z-
isomers with a ratio of about 82 : 18 and 70 : 30%, respectively;
while 1c has almost all-trans double-bond configuration.
In this study, we report the significant role of aliphatic rings
(connected with part of the tetraene bridge), in tuning the ICT
and NLO properties of chromophores 1a–c. These chromo-
phores contain the same dialkylaminophenyl donor and strong
CF3–TCF acceptor. Three different ring-locked tetraene bridges
were derived from isophorone, verbenone, and trimethylcyclo-
pentenone, respectively. The thermal, electrochemical, linear and
nonlinear optical properties of all three chromophores were
thoroughly investigated. Density functional theory (DFT),
quantum mechanical calculations and electric-field poling
study were also used to evaluate the changes in both micro-
scopic and macroscopic nonlinearity to be expected with bridge
modification.
Thermal properties of chromophores 1a–c were evaluated by
differential scanning calorimetry (DSC) and results are shown in
Fig. 1. The isophorone-derived chromophore 1 exhibited a highly
crystalline characteristic with a melting point at 188 ꢁC.
However, 1b and 1c which contain the verbenone- and trime-
thylcyclopentenone-based ring structures showed thermody-
namically stable amorphous states and did not undergo
crystallization or any other phase transition upon further heating
beyond the glass transition temperature (Tg). Compared with the
crystalline compound 1a, the significantly improved glass-form-
ing ability of 1b and 1c was mainly attributed to the increased
steric hindrance caused by the three-dimensional ring structures
around the planar tetraene chain, which can prevent close
packing of molecules and hence crystallization. The Tgs of 1b and
1c, as measured by DSC, were at 100 ꢁC and 75 ꢁC, respectively.
Considering few shape modifications performed in 1b and 1c, it is
very attractive that they could act as a new class of molecular
glass chromophores.11c
Results and discussion
Scheme 1 shows the chemical structures and synthetic approach
for this series of ring-locked tetraene chromophores 1a–c.11a
The Knoevenagel condensation between N-ethyl-N-(2-hydroxy-
ethyl)aminobenzaldehyde and three different b-methyl-
cycloenone derivatives, including isophorone, (1S)-(ꢀ)-verbenone,
and 3,4,4-trimethyl-2-cyclopentenone, furnished the correspond-
ing aminophenyldienone derivatives, of which the free hydroxyl
group on the donor-end was then protected with tert-butyldime-
thylsilyl (TBDMS) group to improve the solubility and compati-
bility with polymer matrix. The extension of the conjugated p-
bridge to yield the key aminophenyltrienal intermediates was
To determine the electrochemical properties of chromophores
1a–c, cyclic voltammetry (CV) experiments were conducted in
degassed anhydrous dichloromethane solutions containing 0.1 M
tetrabutylammonium hexafluorophosphate (TBAPF) as the
supporting electrolyte. As shown in Fig. 2, chromophores 1a–c
all exhibited one reversible oxidation wave with an onset
potential versus ferrocene/ferrocenium at about 0.20, 0.20 and
0.23 V, respectively. A slight but reliable increase of the onset
oxidation potential of 1c by around 30 mV with respect to those
of 1a and 1b indicates the lowered electron density of the dia-
lkylamino donor of 1c, which probably originates from better
charge transfer between the donor and acceptor groups through
the conformationally locked tetraene bridge using the cyclo-
pentene-based ring structure instead of the cyclohexene-based
Scheme 1 Chemical structures and synthetic scheme for the ring-locked
tetraene chromophores 1a–c.
Fig. 1 DSC curves of chromophores 1a–c with a heating rate of 10 ꢁC
minꢀ1 in nitrogen.
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a series of aprotic solvents with different polarity so that the
solvatochromic behavior of each chromophore could be inves-
tigated in a wide range of dielectric environments (Fig. 4). With
the solvents varying from the slightly polar dioxane to the
moderately polar dichloromethane, a continuous shift of the
absorption maxima to longer wavelength was observed for all
three chromophores together with the significant alteration of
the spectral shape. Such spectral behaviors were most obviously
noticed from 1b and 1c in going from toluene to chloroform. The
extinction coefficients of 1a–c also gradually increased with
increasing the solvent polarity. More dramatic effects were
observed while investigating the absorption spectra of 1a–c in
highly polar solvents, such as acetone and acetonitrile. In
comparison with a rather broad absorption band recorded for
1a, chromophore 1c showed a sharp and intense cyanine-type
absorption band with a dramatically narrowed bandwidth.
Chromophore 1b fell in between the other two dyes in terms of its
spectral features. Furthermore, a saturation behavior was found
for 1c in the more polar solvents, such as dichloromethane,
acetone, and acetonitrile. The absorption peak of 1c in these
solvents exhibited almost no shift with increase of solvent
polarity; however, the dominant low-energy peak of 1b was still
red-shifted progressively in going from dichloromethane to
acetonitrile, which is consistent with the positive solvatochromic
behavior observed in the less polar solvents. Additionally for all
Fig. 2 Cyclic voltammograms of chromophores 1a–c recorded in
CH2Cl2 solutions containing 0.1 M Bu4NPF6 supporting electrolyte at
a scan rate of 100 mV sꢀ1
.
ones as in the case of 1a and 1b. This explanation is supported by
the photophysical properties of 1a–c using UV-vis spectroscopy.
The UV-vis-NIR absorption spectra of chromophores 1a–c in
dilute chloroform solution (10ꢀ5 M) are shown in Fig. 3. This
series of dipolar tetraene chromophores exhibited quite different
spectral patterns of the characteristic p–p* charge-transfer
absorption. Chromophore 1a showed a maximum absorption
(lmax) at 788 nm together with a broad, low-energy shoulder. In
contrast, a slightly red-shifted absorption spectrum with an
apparently increased long-wavelength absorption was recorded
for 1b. Two absorption peaks with comparable intensity were
found at 793 and 867 nm, respectively. As for 1c, the absorption
spectrum with a slightly smaller fwhm (full width at half-
maximum) showed a dominant absorption peak at 867 nm and
a shoulder at 786 nm. It is noteworthy that the onset wavelength
of the absorption of 1c at the long-wavelength range was obvi-
ously blue-shifted by around 40 nm in comparison with those of
1a and 1b. The interesting evolution of the absorption spectra of
1a–c showed that the low-energy absorption (at 867 nm for both
1b and 1c) was intensified steadily while the higher energy
component (at ca. 790 nm for all of them) remained almost
unchanged from the measurement of the extinction coefficients.
In order to understand the dependence of the electronic
absorption properties of 1a–c on their structures, the UV-vis-
NIR absorption spectra were also measured quantitatively in
Fig. 4 Solvatochromic behaviors of chromophores 1a–c recorded in
different solvents (10ꢀ5 M) of varying dielectric constants (1,4-dioxane:
2.25; toluene: 2.38; chloroform: 4.81; dichloromethane: 8.93; acetone:
20.7; acetonitrile: 37.5) at room temperature.
Fig. 3 UV-vis-NIR absorption spectra of chromophores 1a–c in chlo-
roform solutions (10ꢀ5 M) at room temperature.
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Table 1 Summary of experimental and theoretical data of chromophores 1a–c
Absorption in CHCl3
DFT calculation in CH2Cl2
Tg/ꢁC
lmax/nm
E/Mꢀ1 cmꢀ1
lonset/nm
m/D
bzzz(0)/10ꢀ30 esu
r33/pm Vꢀ1 @ 100 V mmꢀ1
ꢀ
BLA/A
Compd
1a
1b
1c
188 (mp)
100
75
788
867 (793)
867 (796)
65 100
68 100 (66 900)
77 300 (64 600)
978
966
931
0.0170
0.0171
0.0155
41.1
41.4
42.7
1849
1732
1664
78
63
42
of the more polar solvents, a significant blue shift of the long-
wavelength absorption tail of 1c was found with respect to those
of 1a and 1b.
critical figure-of-merit, [bzzz(0)], for all three chromophores,
showed a progressive decrease from chromophores 1a to 1c,
owing to their gradually increased cyanine-like electronic struc-
ture as suggested by the experimental UV-vis spectral results
presented in the previous section.
For a given donor–acceptor-substituted polymethine mole-
cule, such as chromophores 1a–c, the ground-state structure
could be viewed as a combination of neutral and charge-sepa-
rated canonical resonance forms. The relative contribution of
these two resonance forms to the ground state can be controlled
by the polarity of the solvent in which the chromophore is dis-
solved. The positive solvatochromism observed for chromo-
phores 1a–c in most of the solvents used for the study indicated
their neutral polyene-like electronic structures; however, in the
most polar solvents of acetone and acetonitrile, an electron
distribution near the so-called cyanine limit (with equal contri-
butions from neutral and charge-separated resonance forms) was
realized for 1c, as dictated by a very sharp cyanine-type
absorption band and vanished solvatochromism in the highly
polar solvents. The more pronounced polarization effect exerted
on 1c by polar solvents suggests that the cyclopentene-based
tetraene bridge employed in 1c might provide the most effective
pathway to achieve charge redistribution between the donor and
acceptor groups due to its more straight and coplanar molecular
structure in comparison with the cyclohexene-based ones utilized
in 1a and 1b.18 Such structural difference is also responsible for
the apparent narrowing of the spectral band and the significant
blue shift of the low-energy absorption tail observed for 1c.
Notably, similar solvent-dependent changes of UV/vis spectra
were also found for some merocyanine dyes19 or even the tetraene
chromophores containing the much stronger heteroaryl-amino
donors.20
To evaluate their EO activity, 10 wt% of the chromophores 1a–
c were doped into a commonly used polymer matrix, poly(methyl
methacrylate) (PMMA), as guestꢀhost polymers. By avoiding
severe intermolecular electrostatic interactions at such low
chromophore loading level, the performance of the materials was
more related to the intrinsic molecular properties. Therefore, this
could help shed some light for deeper understanding of the
structure–property relationships within this series of chromo-
phores. The EO activities (r33 values) of poled films were
measured by the Teng–Man method at a wavelength of 1.31 mm
using carefully selected thin ITO electrode with low reflectivity
and good transparency in order to minimize the contribution
from multiple reflections.28 For this series of tetraene chromo-
phores, the obtained r33 values showed a gradual decrease from
78 pm Vꢀ1 for 1a to 63 pm Vꢀ1 for 1b, and further to 42 pm Vꢀ1
for 1c. In order to elucidate the origins of the significant variation
of the EO activities of 1a–c, we also measured the order
parameters of the poled films of EO polymers based on linear
optical dichroism of intramolecular charge transfer bands.29 The
axial orientation of the poled samples was described as the order
parameter F ¼ 1 ꢀ A/A0, where A0 and A are the integral
absorbance for the unpoled and poled samples at normal inci-
dence, instead of the absorbance maximum, due to the change of
the spectral shape after poling (particularly for 1b and 1c). The
decreased absorbance and changed band shape of the poled films
could nearly recover after being annealed at poling temperatures
for 10 min, indicating that very litter chemical degradation
occurred during poling. The order parameters of 1a–c in the
formulated polymer composites were 0.11, 0.13, and 0.16,
respectively, showing a progressive enhancement. Since the
chromophore number density was also pretty similar for all the
EO polymers, the considerable decrease in the EO activity from
1a to 1c should be mainly attributed to the decrease in the first
hyperpolarizability (b) of the chromophores doped in the polar
polymer matrix. This corresponded well with the results of sol-
vatochromism study and DFT calculations on these molecules.
The relevant physical properties of chromophores 1a–c are
summarized in Table 1.
In order to obtain further understanding of the bridge
dependent ground-state polarization of this intriguing series of
EO chromophores, DFT21,22 calculations using Gaussian 0923
were carried out on chromophores 1a–c at the hybrid B3LYP24,25
level employing the split valence 6-31G*26 basis set (detailed in
the ESI†). When used carefully and consistently, this method of
DFT has been shown to give relatively consistent descriptions
of first-order hyperpolarizabilities for a number of similar
chromophores.8a,27 All molecules were assumed to be in trans-
configurations and their geometries were optimized in di-
chloromethane using default PCM parameters. The relevant
theoretically calculated parameters of 1a–c, including bond-length
alternation (BLA), dipole moment (m), and zero-frequency
molecular first hyperpolarizability [bzzz(0)], are displayed in
Table 1. It was found that there was a decrease of BLA in going
from cyclohexene (1a and 1b) to cyclopentene (1c) containing
chromophores. This result corroborates the hypothesis that the
chromophores show a trend in increasing ground-state polari-
zation going from chromophores 1a to 1c. The calculation of the
Conclusions
A series of highly polarizable phenyltetraene-based chromo-
phores 1a–c has been synthesized by fusing different aliphatic
rings into the tetraene chain. In addition to the widely used
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isophorone-based tetraene (CLD) bridge, two new tetraene
structures, derived from verbenone and trimethylcyclopente-
none, were introduced as efficient p-bridges to construct the new
phenyltetraene chromophores. The effects of the different ring-
locked tetraene bridges on the comprehensive properties of the
resultant chromophores were systematically investigated.
Our results demonstrated that apart from the variation of the
donor and acceptor groups, the intrinsic electronic structure and
the ultimate optical properties for these phenyltetraene-based
NLO chromophores could also be effectively tuned through
conformationally locked aliphatic ring structures. By varying the
ring structures from cyclohexene to cyclopentene, the molecular
polarization of the tetraene chromophores could be significantly
enhanced. Therefore, the ground-state electronic character of
chromophore 1c could be readily tuned from polyene to cyanine
type by increasing the solvent polarity as suggested from the
band shape and solvatochromism of its UV-vis spectra. This
provides a deeper understanding of the structure–property rela-
tionships of polyene chromophores, which is beneficial for
further optimization of their molecular properties for improving
bulk EO material performance.
Compound 2b. To a solution of 4-[N-(2-hydroxyethyl)-N-ethy-
lamino]benzaldehyde (1.06 g, 5.49 mmol) and (1S)-(ꢀ)-verbenone
(1.00 g, 6.65 mmol) in anhydrous ethanol was added a freshly
prepared solution of sodium ethoxide (7.00 mmol) by syringe. The
reaction mixture was stirred at 70 ꢁC for 24 h and then was poured
into a saturated solution of ammonium chloride and extracted
with ethyl acetate; the combined organic extracts were washed
with brine and dried over Na2SO4. After removal of the solvent,
the residue was purified by column chromatography using hexane/
ethyl acetate as eluent to give the product as orange-red solids
(1.36 g, yield: 76%). 1H NMR (CDCl3, 300 MHz, ppm): 7.38 (2H,
d, J ¼ 9.0 Hz, Ar-H), 6.86 (1H, d, J ¼ 16.2 Hz, CH), 6.75 (1H, d,
J ¼ 16.2 Hz, CH), 6.72 (2H, d, J ¼ 9.0 Hz, Ar-H), 5.84 (1H, s,
CH), 3.83 (2H, t, J ¼ 6.0 Hz, CH2OH), 3.54–3.44 (4H, m,
NCH2), 3.12 (1H, td, J ¼ 6.0 and 1.5 Hz, CH), 2.89 (1H, dt, J ¼
9.0 and 5.7 Hz, CH2), 2.70 (1H, td, J ¼ 6.0 and 1.8 Hz, CH), 2.11
(1H, d, J ¼ 9.0 Hz, CH2), 1.57 (3H, s, CH3), 1.21 (3H, t, J ¼
6.3 Hz, CH3), 1.01 (3H, s, CH3). 13C NMR (CDCl3, 125 MHz,
ppm): 204.91, 165.94, 149.16, 135.90, 129.31, 123.99, 122.59,
120.18, 112.18, 60.17, 58.22, 52.95, 52.43, 45.66, 43.94, 40.20,
26.94, 22.30, 12.16. HRMS (ESI) (M+, C21H27NO2): calcd:
325.2042; found: 325.2035%.
Compound 2c. The procedure for compound 2b was followed
Experimental
to
prepare
2c
from
4-[N-(2-hydroxyethyl)-N-ethyl-
Materials and measurements
amino]benzaldehyde and 3,4,4-trimethyl-2-cyclopentenone as
orange-red solids (yield: 54%). 1H NMR (CDCl3, 300 MHz,
ppm): 7.41 (2H, d, J ¼ 9.0 Hz, Ar-H), 7.20 (2H, d, J ¼ 16.2 Hz,
CH), 6.74 (2H, d, J ¼ 9.0 Hz, Ar-H), 6.59 (1H, d, J ¼ 16.2 Hz,
CH), 6.15 (1H, s, CH), 3.87–3.81 (2H, m, CH2OH), 3.54 (2H, t,
J ¼ 5.7 Hz, NCH2), 3.49 (2H, t, J ¼ 6.9 Hz, NCH2), 2.38 (2H, s,
CH2), 1.33 (6H, s, CH3), 1.20 (3H, t, J ¼ 6.9 Hz, CH3). 13C NMR
(CDCl3, 125 MHz, ppm): 207.54, 181.79, 149.24, 139.51, 129.26,
123.60, 122.66, 114.68, 112.01, 60.13, 52.25, 52.22, 45.51, 42.03,
27.59, 11.94. HRMS (ESI) (M+, C19H25NO2): calcd: 299.1885;
found: 299.1880%.
All chemicals were purchased from Aldrich and used as received.
3,4,4-Trimethyl-2-cyclopentenone and chromophore 1a were
prepared according to the literature procedures, respectively.11a,30
1H and 13C NMR spectra were recorded on a Bruker AV300 and
AV500 spectrometer using CDCl3 as solvent in all cases. High-
resolution mass spectrometry (HRMS) was performed on
a Bruker APEX III 47e Fourier transform mass spectrometer.
Thermal transitions were analyzed with a TA Instruments
differential scanning calorimeter (DSC) Q20 under nitrogen at
a heating rate of 10 ꢁC minꢀ1. Cyclic voltammetric data were
measured on a BAS CV-50W voltammetric analyzer using
a conventional three-electrode cell with a Pt metal as the working
electrode, a Pt gauze as the counter-electrode, and an Ag/AgNO3
as the reference electrode at a scan rate of 100 mV sꢀ1. The 0.1 M
tetrabutylammonium hexafluorophosphate (TBAPF) in CH2Cl2
is the electrolyte. UV-vis-NIR spectra were recorded on a Perkin-
Elmer spectrophotometer (Lambda 9 UV/vis/NIR).
Compound 3b. tert-Butyldimethylsilyl chloride (0.483 g, 3.20
mmol) was added in portions to the mixture of compound 2b
(0.862 g, 2.65 mmol) and imidazole (0.236 g, 3.47 mmol) in
anhydrous dimethylformamide. After stirring at room tempera-
ture for 4 h, the reaction mixture was poured into water and
extracted with ethyl acetate. The combined organic extracts were
washed with brine and dried over Na2SO4. After removal of the
solvent, the residue was purified by column chromatography
using hexane/ethyl acetate as eluent to give the product as
orange-red oil (0.920 g, yield: 79%). 1H NMR (CDCl3, 300 MHz,
ppm): 7.36 (2H, d, J ¼ 9.0 Hz, Ar-H), 6.86 (1H, d, J ¼ 15.9 Hz,
CH), 6.74 (1H, d, J ¼ 15.9 Hz, CH), 6.65 (2H, d, J ¼ 9.0 Hz, Ar-
H), 5.83 (1H, s, CH), 3.77 (2H, t, J ¼ 6.3 Hz, OCH2), 3.49–3.41
(4H, m, NCH2), 3.12 (1H, td, J ¼ 6.0 and 1.2 Hz, CH), 2.89 (1H,
dt, J ¼ 9.0 and 5.7 Hz, CH2), 2.69 (1H, td, J ¼ 6.0 and 1.8 Hz,
CH), 2.11 (1H, d, J ¼ 9.3 Hz, CH2), 1.57 (3H, s, CH3), 1.17 (3H,
t, J ¼ 6.9 Hz, CH3), 1.01 (3H, s, CH3), 0.89 (9H, s, CH3), 0.03
(6H, s, CH3). 13C NMR (CDCl3, 125 MHz, ppm): 204.66, 165.76,
148.96, 135.88, 129.33, 123.59, 122.42, 120.23, 111.75, 60.77,
58.31, 52.84, 52.58, 45.76, 43.98, 40.17, 27.00, 26.09, 25.89, 22.36,
18.50, 12.36, ꢀ5.18. HRMS (ESI) (M+, C27H41NO2Si): calcd:
439.2907; found: 439.2901%.
Poling and r33 measurements
For studying the EO property derived from the chromophores,
guest–host polymers were generated by formulating chromo-
phores 1a–c (10 wt%) into poly(methyl methacrylate) (PMMA)
using 1,1,2-trichloroethane (TCE) as the solvent. The resulting
solutions (with the solid content of 10 wt%) were filtered through
a 0.2 mM PTFE filter and spincoated onto thin-film device (TFD)
indium tin oxide (ITO) glass substrates. Films of doped polymers
ꢁ
were baked in a vacuum oven at 60 C overnight to ensure the
removal of the residual solvent. Then, a thin layer of gold was
sputtered onto the films as a top electrode for contact poling. The
r33 values were measured using the Teng–Man simple reflection
technique at the wavelength of 1.31 mm.
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Compound 3c. The procedure for compound 3b was followed to
prepare 3c from compound 2c as orange-red oil (yield: 76%). 1H
NMR (CDCl3, 300 MHz, ppm): 7.39 (2H, d, J ¼ 9.0 Hz, Ar-H),
7.20 (2H, d, J ¼ 16.2 Hz, CH), 6.67 (2H, d, J ¼ 9.0 Hz, Ar-H), 6.58
(1H, d, J ¼ 16.2 Hz, CH), 6.15 (1H, s, CH), 3.78 (2H, t, J ¼ 6.3 Hz,
OCH2), 3.50–3.42 (4H, m, NCH2), 2.38 (2H, s, CH2), 1.33 (6H, s,
CH3), 1.18 (3H, t, J ¼ 6.9 Hz, CH3), 0.89 (9H, s, CH3), 0.04 (6H, s,
CH3). 13C NMR (CDCl3, 125 MHz, ppm): 207.35, 181.71, 149.02,
139.59, 129.26, 123.05, 122.57, 114.33, 111.50, 60.52, 52.37, 52.27,
45.57, 42.02, 27.64, 25.86, 18.25, 12.12, ꢀ5.40. HRMS (ESI) (M+,
C25H39NO2Si): calcd: 413.2750; found: 413.2745%.
DIBAL in hexane (1.0 M, 2.6 mL, 2.6 mmol) was added dropwise
by syringe. After being kept at ꢀ78 ꢁC for 2 h, wet silica gel was
added to quench the reaction and the mixture was stirred at 0 ꢁC
for 2 h. The product mixture was filtered off, and the resulting
precipitates were washed with ethyl acetate. Evaporation of the
solvent and purification by column chromatography using
hexane/ethyl acetate as eluent gave the product as dark red oil
(0.580 g, yield: 83%). The ratio of the Z : E isomers is 25 : 75%
1
calculated by the integration of respective protons. H NMR
(CDCl3, 300 MHz, ppm): 10.14 (0.25H, d, J ¼ 8.1 Hz, CHO),
9.89 (0.75H, d, J ¼ 8.1 Hz, CHO), 7.35–7.31 (2H, m, Ar-H), 6.93
(0.25H, s, CH), 6.74–6.70 (2H, m, CH), 6.64 (2H, d, J ¼ 9.0 Hz,
Ar-H), 6.10 (0.75H, s, CH), 5.84 (0.75H, d, J ¼ 8.4 Hz, CH), 5.63
(0.25H, d, J ¼ 8.4 Hz, CH), 3.76 (2H, t, J ¼ 6.0 Hz, OCH2), 3.70
(1H, t, J ¼ 5.4 Hz, CH), 3.48–3.40 (4H, m, NCH2), 3.04 (1H, t, J
¼ 5.4 Hz, CH), 2.81–2.70 (1H, m, CH2), 1.76 (1H, d, J ¼ 9.0 Hz,
CH2), 1.56 (2.2H, s, CH3), 1.51 (0.8H, s, CH3), 1.17 (3H, t, J ¼
7.2 Hz, CH3), 0.89 (12H, s, CH3), 0.03 (6H, s, CH3). 13C NMR
(CDCl3, 125 MHz, ppm): 190.02, 189.84, 164.83, 164.36, 157.87,
157.63, 148.48, 133.02, 132.92, 128.79, 124.17, 123.87, 123.57,
123.33, 123.00, 120.18, 117.01, 111.78, 60.78, 53.67, 52.57, 47.81,
45.71, 45.51, 43.62, 43.49, 37.56, 37.51, 26.91, 26.71, 26.07, 22.04,
21.92, 18.44, 12.36, ꢀ5.20. HRMS (ESI) (M+, C29H43NO2Si):
calcd: 465.3062; found: 465.3055%.
Compound 4b. Under N2 atmosphere to the mixture of NaH
(0.093 g, 3.87 mmol) in dry THF was added diethyl cyano-
ꢁ
phosphonate (0.685 g, 3.87 mmol) dropwise by syringe at 0 C
with an ice bath. After the solution became clear, compound 3b
(0.848 g, 1.93 mmol) in dry THF was added. The mixture was
refluxed for 3 h and then poured into a saturated solution of
ammonium chloride and extracted with ethyl acetate; the
combined organic extracts were washed with brine and dried
over Na2SO4. After removal of the solvent, the residue was
purified by column chromatography using hexane/ethyl acetate
as eluent to give the product as orange-red oil (0.758 g, yield:
85%). The ratio of the Z : E isomers is 50 : 50% calculated by the
1
integration of respective protons. H NMR (CDCl3, 300 MHz,
ppm): 7.34–7.29 (2H, m, Ar-H), 6.72–6.62 (4H, m, Ar-H and
CH), 6.47 (0.5H, s, CH), 6.05 (0.5H, s, CH), 4.92 (0.5H, s, CH),
4.79 (0.5H, s, CH), 3.79–3.74 (2H, m, OCH2), 3.48–3.40 (4H, m,
NCH2), 3.27 (0.5H, td, J ¼ 5.7 and 1.5 Hz, CH), 3.02–2.96 (1H,
m, CH2), 2.79–2.68 (1.5H, m, CH), 1.69–1.63 (1H, m, CH2), 1.54
(1.5H, s, CH3), 1.49 (1.5H, s, CH3), 1.20–1.14 (3H, m, CH3), 0.89
(9H, s, CH3), 0.84 (3H, s, CH3), 0.03 (6H, s, CH3). 13C NMR
(CDCl3, 125 MHz, ppm): 165.30, 165.06, 156.54, 156.24, 148.45,
132.86, 132.70, 128.78, 124.19, 123.37, 123.10, 121.07, 119.17,
118.35, 111.80, 87.26, 86.00, 60.82, 52.60, 52.29, 49.58, 47.72,
47.56, 45.74, 43.22, 43.07, 37.41, 37.27, 26.60, 26.10, 25.90, 21.92,
18.48, 12.40, ꢀ5.16. HRMS (ESI) (M+, C29H42N2OSi): calcd:
462.3066; found: 462.3061%.
Compound 5c. The procedure for compound 5b was followed
to prepare 5c from compound 4c as orange-red oil (yield: 77%).
The ratio of the Z : E isomers is 28 : 72% calculated by the
1
integration of respective protons. H NMR (CDCl3, 300 MHz,
ppm): 9.98 (0.28H, d, J ¼ 8.1 Hz, CHO), 9.77 (0.72H, d, J ¼ 8.1
Hz, CHO), 7.38–7.33 (2H, m, Ar-H), 7.17–7.09 (1.28H, m, CH),
6.66 (2H, d, J ¼ 9.0 Hz, Ar-H), 6.58–5.50 (1H, m, CH), 6.41
(0.72H, s, CH), 5.94 (0.72H, td, J ¼ 1.8, 8.1 Hz, CH), 5.76–5.73
(0.28H, td, J ¼ 1.8, 8.1 Hz, CH), 3.77 (2H, t, J ¼ 6.3 Hz, CH2),
3.49–3.42 (4H, m, CH2), 2.98 (1.44H, d, J ¼ 1.8 Hz, CH2), 2.71
(0.56H, d, J ¼ 1.8 Hz, CH2), 1.31 (4.32H, s, CH3), 1.29 (1.68H, s,
CH3), 1.18 (3H, t, J ¼ 6.9 Hz, CH3), 0.89 (9H, s, CH3), 0.04 (6H,
s, CH3). 13C NMR (CDCl3, 125 MHz, ppm): 190.79, 189.85,
168.96, 168.64, 168.51, 167.54, 148.57, 148.54, 136.64, 136.34,
128.71, 128.70, 125.91, 123.70, 123.69, 120.11, 118.03, 117.33,
115.90, 115.67, 111.53, 60.53, 52.38, 49.89, 46.09, 45.54, 45.50,
44.11, 28.02, 27.83, 25.86, 18.24, 12.13, ꢀ5.40. HRMS (ESI) (M+,
C27H41NO2Si): calcd: 439.2907; found: 439.2902%.
Compound 4c. The procedure for compound 4b was followed
to prepare 4c from compound 3c as orange-red oil (yield: 83%).
The ratio of the Z : E isomers is 45 : 55% calculated by the
1
integration of respective protons. H NMR (CDCl3, 300 MHz,
ppm): 7.37–7.32 (2H, m, Ar-H), 7.12 (0.45H, d, J ¼ 16.2 Hz,
CH), 7.04 (0.55H, d, J ¼ 16.2 Hz, CH), 6.67–6.63 (2.45H, m, Ar-
H and CH), 6.47 (1H, d, J ¼ 16.2 Hz, CH), 6.31 (0.55H, s, CH),
5.00 (0.55H, t, J ¼ 2.1 Hz, CH), 4.79 (0.45H, t, J ¼ 2.1 Hz, CH),
3.79–3.75 (2H, m, OCH2), 3.49–3.41 (4H, m, NCH2), 2.77 (1.1H,
d, J ¼ 2.1 Hz, CH2), 2.60 (0.9H, d, J ¼ 2.1 Hz, CH2), 1.28 (3.3H,
s, CH3), 1.26 (2.7H, s, CH3), 1.20–1.15 (3H, m, CH3), 0.89 (9H, s,
CH3), 0.04 (6H, s, CH3). 13C NMR (CDCl3, 125 MHz, ppm):
168.33, 148.48, 136.34, 135.86, 128.67, 128.58, 123.71, 123.64,
122.42, 119.59, 119.04, 115.63, 115.37, 111.53, 83.04, 81.91,
60.55, 52.40, 48.19, 47.70, 45.97, 45.80, 45.55, 27.93, 27.84, 25.88,
18.27, 12.15, ꢀ5.38. HRMS (ESI) (M+, C27H40N2OSi): calcd:
436.2910; found: 436.2905%.
Compound 1b. Compound 5b (0.158 g, 0.34 mmol) and
acceptor 6 (0.097 g, 0.38 mmol) were dissolved in the mixture
solvent of anhydrous ethaꢁnol and CH2Cl2. The reaction mixture
was allowed to stir at 60 C for 1–3 h and monitored by TLC.
After removal of the solvents, the residue was purified by column
chromatography eluting with hexane/ethyl acetate. Further
purification of the product by reprecipitation from methanol/
dichloromethane afforded the desired chromophore as dark
solids (0.150 g, yield: 58%). The ratio of the Z : E isomers is
1
30 : 70% calculated by the integration of respective protons. H
NMR (CDCl3, 300 MHz, ppm): 8.54 (0.30H, t, J ¼ 12.6 Hz,
CH), 8.16 (0.40H, t, J ¼ 12.6 Hz, CH), 7.91 (0.30H, b, CH), 7.51–
7.49 (5H, m, Ar-H), 7.42–7.36 (2H, m, Ar-H), 6.95–6.88 (1H, m,
CH), 6.82–6.73 (1H, m, CH), 6.67 (2H, d, J ¼ 9.0 Hz, Ar-H), 6.56
(0.30H, s, CH), 6.32–6.13 (2.40H, m, CH), 6.02 (0.30H, d,
Compound 5b. The solution of compound 4b (0.694 g, 1.50
ꢁ
mmol) in dry toluene was cooled to ꢀ78 C and the solution of
4442 | J. Mater. Chem., 2011, 21, 4437–4444
This journal is ª The Royal Society of Chemistry 2011

View Article Online
2 (a) C. V. McLaughlin, L. M. Hayden, B. Polishak, S. Huang, J. Luo,
T.-D. Kim and A. K.-Y. Jen, Appl. Phys. Lett., 2008, 92, 151107; (b)
X. Zheng, A. Sinyukov and L. M. Hayden, Appl. Phys. Lett., 2005, 87,
081115; (c) F. D. J. Brunner, O.-P. Kwon, S.-J. Kwon, M. Jazbinsek,
J ¼ 12.6 Hz, CH), 3.78 (2H, m, CH2), 3.52–3.44 (4H, m, CH2),
3.16–3.04 (2H, m, CH), 2.83–2.73 (1H, m, CH2), 1.76 (1H, d, J ¼
9.0 Hz, CH2), 1.59–1.52 (4H, m, CH3), 1.19 (3H, t, J ¼ 6.9 Hz,
CH3), 0.88 (9H, s, CH3), 0.82 (1H, s, CH3), 0.74 (1H, s, CH3),
0.03 (6H, s, CH3). 13C NMR (CDCl3, 125 MHz, ppm): 176.41,
168.60, 164.51, 161.73, 149.90, 146.65, 146.46, 145.89, 138.06,
137.94, 137.59, 131.22, 130.36, 130.33, 129.65, 126.96, 126.73,
126.04 125.49, 125.39, 124.05, 123.04, 119.10, 114.85, 112.09,
111.67, 60.79, 52.60, 51.12, 47.00, 45.92, 44.89, 39.28, 27.15,
26.96, 26.04, 21.96, 21.88, 21.79, 18.42, 12.38, ꢀ5.23. HRMS
(ESI) (M+, C45H49F3N4O2Si): calcd: 762.3577; found:
762.3571%.
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N. Peyghambarian, Nat. Photonics, 2007, 1, 183; (b) Y. Enami,
D. Mathine, C. T. DeRose, R. A. Norwood, J. Luo, A. K.-Y. Jen
and N. Peyghambarian, Appl. Phys. Lett., 2007, 91, 093505.
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W. Yuan, B. Bortnik, H. R. Fetterman, C. Wang, W. H. Steier and
C. Zhang, Appl. Phys. Lett., 2005, 87, 061112.
Compound 1c. The procedure for chromophore 1b was fol-
lowed to prepare 1c from compound 5c and acceptor 6 as dark
solids (yield: 45%). Almost only E-isomer was obtained. 1H
NMR (CDCl3, 300 MHz, ppm): 8.01 (1H, b, CH), 7.50 (5H, s,
Ar-H), 7.42 (2H, d, J ¼ 9.0 Hz, Ar-H), 7.33 (1H, d, J ¼ 16.2 Hz,
CH), 6.69 (2H, d, J ¼ 9.0 Hz, Ar-H), 6.62 (1H, d, J ¼ 16.2 Hz,
CH), 6.57 (1H, s, CH), 6.37 (1H, d, J ¼ 12.9 Hz, CH), 6.16 (1H,
d, J ¼ 14.4 Hz, CH), 3.79 (2H, t, J ¼ 6.0 Hz, CH2), 3.54–3.46
(4H, m, CH2), 2.80–2.75 (2H, m, CH2), 1.30 (6H, s, CH3), 1.21
6 (a) P. A. Sullivan and L. R. Dalton, Acc. Chem. Res., 2010, 43, 10; (b)
J. Luo, X.-H. Zhou and A. K.-Y. Jen, J. Mater. Chem., 2009, 19,
7410; (c) R. U. A. Khan, O.-P. Kwon, A. Tapponnier,
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A. N. Rashid and P. Gunter, Adv. Funct. Mater., 2006, 16, 180; (d)
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H. Jang, L. R. Dalton and A. K.-Y. Jen, J. Phys. Chem. B, 2004,
108, 8523.
(3H, t, J ¼ 6.9 Hz, CH3), 0.89 (9H, s, CH3), 0.03 (6H, s, CH3). 13
C
7 (a) D. Frattarelli, M. Schiavo, A. Facchetti, M. A. Ratner and
T. J. Marks, J. Am. Chem. Soc., 2009, 131, 12595; (b) H. Kang,
A. Facchetti, H. Jiang, E. Cariati, S. Righetto, R. Ugo,
C. Zuccaccia, A. Macchioni, C. L. Stern, Z. Liu, S.-T. Ho,
E. C. Brown, M. A. Ratner and T. J. Marks, J. Am. Chem. Soc.,
2007, 129, 3267; (c) A. Facchetti, E. Annoni, L. Beverina,
M. Morone, P. Zhu, T. Marks and G. Pagani, Nat. Mater., 2004, 3,
910.
NMR (CDCl3, 125 MHz, ppm): 176.62, 173.15, 150.75, 148.74,
145.3, 142.94, 131.10, 130.95, 129.57, 127.73, 126.79, 123.53,
121.54, 121.30, 115.92, 113.12, 112.67, 112.20, 112.13, 60.77,
52.65, 46.04, 28.27, 26.03, 25.82, 18.41, 12.36, ꢀ5.23. HRMS
(ESI) (M+, C43H47F3N4O2Si): calcd: 736.3420; found:
736.3415%.
8 (a) J. A. Davies, A. Elangovan, P. A. Sullivan, B. C. Olbricht,
D. H. Bale, T. R. Ewy, C. M. Isborn, B. E. Eichinger,
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Soc., 2008, 130, 10565; (b) P. A. Sullivan, H. Rommel, Y. Liao,
B. C. Olbricht, A. J. P. Akelaitis, K. A. Firestone, J.-W. Kang,
J. Luo, J. A. Davies, D. H. Choi, B. E. Eichinger, P. J. Reid,
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Chem. Soc., 2007, 129, 7523.
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W. Kang, J. Luo, S.-H. Jang, J.-W. Ka, N. Tucker, J. B. Benedict,
L. R. Dalton, T. Gray, R. M. Overney, D. H. Park, W. N. Herman
and A. K.-Y. Jen, J. Am. Chem. Soc., 2007, 129, 488; (c) T.-
D. Kim, J. Luo, J.-W. Ka, S. Hau, Y. Tian, Z. Shi, N. M. Tucker,
S.-H. Jang, J.-W. Kang and A. K.-Y. Jen, Adv. Mater., 2006, 18, 3038.
10 (a) A. M. R. Beaudin, N. Song, Y. Bai, L. Men, J. P. Gao,
Z. Y. Wang, M. Szablewski, G. Cross, W. Wenseleers, J. Campo
and E. Goovaerts, Chem. Mater., 2006, 18, 1079; (b) Y. Bai,
N. Song, J. P. Gao, X. Sun, X. Wang, G. Yu and Z. Y. Wang, J.
Am. Chem. Soc., 2005, 127, 2060.
11 (a) Y.-J. Cheng, J. Luo, S. Huang, X. H. Zhou, Z. Shi, T.-D. Kim,
D. H. Bale, S. Takahashi, A. Yick, B. M. Polishak, S.-H. Jang,
L. R. Dalton, P. J. Reid, W. H. Steier and A. K.-Y. Jen, Chem.
Mater., 2008, 20, 5047; (b) J. Luo, S. Huang, Y.-J. Cheng, T.-
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4471; (c) Y.-J. Cheng, J. Luo, S. Hau, D. H. Bale, T.-D. Kim,
Z. Shi, D. B. Lao, N. M. Tucker, Y. Tian, P. J. Ried, L. R. Dalton
and A. K.-Y. Jen, Chem. Mater., 2007, 19, 1154.
12 (a) X.-H. Zhou, J. Luo, S. Huang, T.-D. Kim, Z. Shi, Y.-J. Cheng, S.-
H. Jang, D. B. Knorr, R. M. Overney and A. K.-Y. Jen, Adv. Mater.,
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Acknowledgements
This work was supported by the National Science Foundation
(NSFSTC program under Agreement Number DMR-0120967),
the Defense Advanced Research Projects Agency (DARPA)
MORPH program, the Office of Naval Research (ONR), and the
World Class University (WCU) program through the National
Research Foundation of Korea under the Ministry of Education,
Science and Technology (R31-10035). Alex K.-Y. Jen thanks the
Boeing-Johnson Foundation for its support. Additionally the
authors thank B. H. Robinson, and B. E. Eichinger as well as
their relevant funding agencies [Air Force Office of Scientific
Research (AFOSR) and NSF (DMR-0092380)] for providing the
guidance and framework necessary to perform calculations.
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4444 | J. Mater. Chem., 2011, 21, 4437–4444
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