Preparation of polymer films containing multi-branched chromophores for enhanced nonlinear optical activity

Article abstract of DOI:10.1016/j.dyepig.2016.09.040

Two new multi-branched chromophores were synthesized via esterification from monochromophores to achieve ideal macroscopic nonlinear optical activities. Molecular chemical structures of chromophores were confirmed by ¹H NMR, FT-IR spectroscopy,

Full text of DOI:10.1016/j.dyepig.2016.09.040

Dyes and Pigments 136 (2017) 791e797
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Preparation of polymer films containing multi-branched
chromophores for enhanced nonlinear optical activity
Wenxin Lin, Yuanjing Cui*, Jiancan Yu, Yu Yang, Guodong Qian**
State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new multi-branched chromophores were synthesized via esterification from monochromophores to
achieve ideal macroscopic nonlinear optical activities. Molecular chemical structures of chromophores
were confirmed by 1H NMR, FT-IR spectroscopy, elemental analysis, mass spectrometry and UVevisible
absorption spectra. Monochromophore N1 and bichromophore DN were doped into poly (4-vinylphenol)
to fabricate guest-host polymer films Film-N1 and Film-DN with high molecular loading density (up to
30 wt%). And the maximum second harmonic generation coefficients (d33) of polymer films Film-N1 and
Film-DN reached to 25 pm Vꢀ1 and 39 pm Vꢀ1, respectively. In contrast, six-branched dendritic chro-
mophore SN was utilized directly to prepare thin film Film-SN without any polymer matrix due to its
large molecular weight (about 3183 Da) and the d33 value of Film-SN was up to 208 pm Vꢀ1. Compared
with Film-N1, films containing multi-branched chromophores Film-DN and Film-SN exhibited about
1.6-fold and 8.3-fold enhancement in the d33 value indicating the multi-branched chromophore could
significantly promote the macroscopic optical nonlinearity through the site-isolation effect.
© 2016 Elsevier Ltd. All rights reserved.
Received 18 August 2016
Received in revised form
15 September 2016
Accepted 15 September 2016
Available online 16 September 2016
Keywords:
Multi-branched chromophore
Nonlinear optical activity
Film
Second harmonic generation coefficient
Esterification
Site-isolation effect
1. Introduction
induced head-to-tail interactions, and the noncentrosymmetric
arrangement is hard to be gained in NLO material efficiently.
Nonlinear optical (NLO) materials are widely investigated by
researchers after the mid 1980s [1e5]. Compared with inorganic
materials, organic ones are paid more attention for their large
nonlinear optical coefficients, low dielectric constants, and excel-
lent of processing [6,7]. The organic second-order nonlinear optical
materials could be used as optical switching, optical information
processing, and electro-optic modulation based on these advan-
tages [8e10].
Therefore, the macroscopic nonlinear optical activities do not come
up to the expectation [15e17].
Multi-chromophoric dendritic chromophores, such as bichro-
mophore, trichromophore bundles, three-armed multi-chromo-
phoric dendrimers, and star-shaped dipolar chromophores, have
been reported to resolve the issue these years [18e24]. The den-
dritic structures could reduce the inter-chromophore electrostatic
interactions through the site-isolation effect and obtain large EO
coefficients and favorable stability in multiple-dendron-modified
NLO chromophores [25e28]. Multichromophores are prepared by
monochromophores with tether groups or tether cores, and they
show larger EO coefficients and more stable than mono-
chromophores [18,21,22,26,28e34].
In this paper we report a handy and efficient method for the
preparation of multi-branched chromophores which show
enhanced nonlinear activities due to their tree-like morphology.
The bichromophore DN and six-branched chromophore SN are
synthesized from monochromophore N1 via esterification [18,35].
(Fig. 1). To gain macroscopic optical nonlinearity, hyperpolarisable
bichromophore DN is doped as a gust in a polymeric host matrix
poly (vinyl phenol) (PVPh) and six-branched chromophores SN are
prepared as films directly, following by poled via an electrical field
A
number of organic chromophores with high hyper-
polarizabilities (( )) values have been synthesized up to now
[11e14]. However, a problem emerged in achieving ideal nonline-
arity is converting the large values of organic chromophores to
b
b
the macroscopic nonlinearity of NLO materials in effect. The
electro-optic (EO) coefficient often decreases with the increase of
chromophore number density due to the strong inter-chromophore
electrostatic interactions. Generally, the strong dipole-dipole in-
teractions between readily hyperpolarisable chromophores
* Corresponding author.
** Corresponding author.
E-mail addresses: cuiyj@zju.edu.cn (Y. Cui), gdqian@zju.edu.cn (G. Qian).
http://dx.doi.org/10.1016/j.dyepig.2016.09.040
0143-7208/© 2016 Elsevier Ltd. All rights reserved.

792
W. Lin et al. / Dyes and Pigments 136 (2017) 791e797
Fig. 1. Structure of compound N1, DN and SN.
[25,36,37]. The linear properties of chromophores and nonlinear
2.3. Synthesis of compound 1
optical properties of films are discussed in detail.
Compound 1 was gained according to the literature [44]. Yield:
90%. 1H NMR (500 MHz, CDCl3,
(t,12H, Si(CH3)2), 0.99 (s, 9H, C(CH3)3),1.04 (s,18H, C(CH3)3), 7.71 (d,
2H, ArH), 8.28 (s, 1H, ArH).
d ppm): 0.23 (s, 6H, Si(CH3)2), 0.38
2. Experimental
2.1. Materials and measurements
2.4. Synthesis of compound 2
All chemical reagents were gained from Aldrich and Alfa Aesar,
and used without further purification. Dichloromethane (CH2Cl2)
and tetrahydrofuran (THF) were refluxed and distilled before use,
while N, N-dimethylformamide (DMF) was dried by rotary evapo-
ration before reaction. Other solvents, of analytical-grade quality,
were used as received.
Compound 2 was synthesized on the basis of the literature [44].
Yield: 72%. 1H NMR (500 MHz, DMSO-d6,
d ppm): 0.27 (s, 6H,
Si(CH3)2), 1.01 (s, 9H, C(CH3)3), 7.61 (d, 2H, ArH), 8.15 (t, 1H, ArH),
13.37 (s, 2H, COOH). Elemental analysis calcd (%) for C14H20O5Si: C,
56.73; H, 6.80. Found: C, 56.72; H, 6.89.
1H NMR spectra were recorded on a Bruker Avance DMX500
spectrometer (500 MHZ) using tetramethylsilane (TMS) as an in-
ternal standard. Fourier-transform infrared (FT-IR) spectra were
obtained via Thermo Scientific Nicolet iS10. A Bruker Daltonics
esquire 3000plus mass spectrometer and a Bruker Dalton Microflex
MALDI-TOF mass spectrometer were used for mass spectrometry
and MALDI-TOF analysis, respectively. Element analysis was carried
out on a Thermo Finnigan Flash EA 1112 element analyzer. Differ-
ential scanning calorimetry (DSC) and Thermalgravimetric analysis
(TGA) were studied on a Netzsch Instruments 200 F3 and a TA In-
struments SDT Q600 under nitrogen atmosphere. UVevisible ab-
sorption spectra were performed by a Hitachi spectrometer U-4100.
The second harmonic generation coefficients (d33) of the films were
investigated according to the Maker fringe technique [38,39]. The
films were measured by SHG measurement with a Q-switched
2.5. Synthesis of bichromophore DN
Compound N1 (1.08 g, 3 mmol) and 2 (0.45 g, 1.5 mmol) were
dissolved in CH2Cl2 (180 mL). EDCꢁHCl (0.68 g, 3.6 mmol) and 4-
dimethylaminopyridine (DMAP; 0.42 g, 3.6 mmol) were added
and stirring was continued at room temperature for 24 h. The
resulting solution was diluted with CH2Cl2 (200 mL) and washed
with brine and water. After the organic phase was dried over
Na2SO4 and concentrated by rotary evaporation, the residue was
purified via flash chromatography on silica gel using a mixture of
CH2Cl2/ethyl acetate (v:v ¼ 20:1) as the eluent to yield solid
products. Yield: 45%. 1H NMR (500 MHz, CDCl3,
d ppm): 0.20 (s, 6H,
Si(CH3)2), 1.0 (s, 9H, C(CH3)3), 1.75 (s, 12H, C(CH3)2), 3.20 (s, 6H,
N(CH3)), 3.88e3.90 (t, 4H, NCH2), 4.55e4.57 (t, 4H, NCH2CH2),
6.75e6.78 (d, 2H, CH]CH), 6.82e6.84 (d, 4H, ArH), 7.55e7.60 (m,
8H, ArH, CH]CH), 8.14 (s, 1H, ArH). FT-IR (KBr, cmꢀ1): 2934 (w),
2227 (s), 1730 (s), 1521 (m), 1445 (w), 1380 (s), 1276 (m), 1167 (m),
1113 (m), 997 (w), 966 (w), 819 (w). Elemental analysis calcd (%) for
Nd:YAG laser at 1064 nm, which
a Y-cut quartz crystal
(d11 ¼ 0.5 pm Vꢀ1) was used as reference [40e43].
2.2. Synthesis of N1
C
56H56N8O7Si: C, 68.55; H, 5.75; N, 11.42. Found: C, 68.32; H, 5.98;
Chromophore N1 was synthesized via a direct Knoevenagel
N, 11.40. MS (ESI): exact mass calcd for C56H56N8O7Si [MþH]þ,
condensation on the basis of the literature [18]. Yield: 74%. 1H NMR
981.40. Found: 981.5.
(500 MHz, DMSO-d6,
d ppm): 1.75 (s, 6H, C(CH3)2), 3.12 (s, 3H,
N(CH3)), 3.58e3.59 (d, 4H, NCH2CH2), 4.78 (s, 1H, OH), 6.85e6.87
(d, 3H, ArH, CH]CH), 7.75e7.77 (d, 2H, ArH), 7.90e7.94 (d,1H, CH]
CH). FT-IR (KBr, cmꢀ1): 3473 (s), 2874 (w), 2227 (s), 1525 (s), 1463
(m), 1373 (s), 1278 (s), 1161 (s), 1108 (w), 1048 (s), 959 (m), 871 (w),
832 (m), 750 (m), 658 (m), 560 (m), 486 (m). Elemental analysis
calcd (%) for C21H20N4O2: C, 69.98; H, 5.59; N, 15.55. Found: C,
69.94; H, 5.60; N, 15.28.
2.6. Synthesis of compound DH
Compound
4,40,400-(ethane-1,1,1-triyl)triphenol
(3.00
g,
10 mmol) was dissolved in ethanol (6 mL). A solution of NaOH
(1.50 g, 37.5 mmol) in water (5 mL) was added and the ensuing
mixture was refluxed for 30 min with stirring. A solution of 3-

W. Lin et al. / Dyes and Pigments 136 (2017) 791e797
793
chloropropane-1,2-diol (3.96 g, 36 mmol) in ethanol (5 mL) was
added and the resulting blend was stirred and heated at reflux for
4 h before cooled to room temperature. Then the resulting solution
was poured into water (100 mL) and was extracted with ethyl ac-
etate, the organic layers were dried over MgSO4. After the solvent
was evaporated under reduced pressure, the residue was purified
by silica column chromatography using a mixture of ethanol/ethyl
acetate (v: v ¼ 1: 5) as the eluent to give white solid DH. Yield: 81%.
1H NMR (500 MHz, DMSO-d6, d (ppm)): 2.03 (s, 3H, CH3), 3.43 (d,
6H, OCH2), 3.80 (m, 6H, OH), 3.95 (m, 3H, CH), 4.67 (d, 3H, higher
field branch of AB quartet, CH2OH), 4.95 (d, 3H, lower field branch
of AB quartet, CH2OH), 6.82 (d, 6H, ArH), 6.91 (d, 6H, ArH). 13C NMR
(125 MHz, DMSO-d6, d (ppm)): 157.2, 141.8, 129.7, 114.1, 70.5, 69.9,
63.2, 50.6, 30.9. Elemental analysis calcd (%) for C29H36O9: C, 65.89;
H, 6.86; Found: C, 65.52, H, 7.06. MS (ESI): exact mass calcd for
the polymeric host matrix PVPh, and then the solid mixtures were
dissolved into cyclopentanone (8% of total solid weight). Mean-
while, six-branched chromophore SN was dissolved into cyclo-
pentanone directly at same ratio without polymeric host matrix for
large molecular weight of SN. The mixed solutions were stirred for
1 h and filtered by 0.22 mm Teflon membrane filters. After that, the
resulting solutions were spin-coated on the indium-tin oxide (ITO)
glass substrates to fabricate Film-N1, Film-DN and Film-SN.
3. Results and discussion
3.1. Synthesis and characterization
For the strong inter-chromophore dipole-dipole interactions,
high hyperpolarisability (b) is hard to convert to large macroscopic
C
29H36O9 [MþH]þ, 527.20. Found: 527.90.
optical nonlinearity. To reduce the inter-chromophore dipole-
dipole electrostatic interactions through the site-isolation effect
from dendritic structures, bichromophore DN and six-branched
chromophore SN are synthesized from monochromophore N1.
The detailed synthetic routes to bichromophore DN and six-
branched chromophore SN are shown in Scheme 1.
2.7. Synthesis of compound 3
The chromophore N1 (0.36 g, 1 mmol), succinic anhydride
(0.15 g, 1.5 mmol), 4-dimethylaminopyridine (DMAP) (0.13 g,
1 mmol) and pyridine (2 mL) were dissolved in anhydrous CH2Cl2
and stirring was continued at room temperature overnight. Then
the resulting solution was washed with brine and deionized water.
The organic layer was extracted by CH2Cl2 and dried over MgSO4.
After the solvent was evaporated under reduced pressure, the
residue was purified by column chromatography on silica gel using
a mixture of CH2Cl2/ethyl acetate (v: v ¼ 10: 1) as the eluent and
compound 3 was gained. Yield: 74%. 1H NMR (500 MHz, DMSO-d6,
The Knoevenagel reaction between 4-((2-hydroxyethyl)
(methyl)amino)benzaldehyde and TCF acceptor 2-(3-cyano-4,5,5-
trimethylfuran-2 (5H)-ylidene)malononitrile afforded chromo-
phore N1. Besides, 5-hydroxyisophthalic acid and tert-butyl-
chlorodimethylsilane produced compound 1, then it was reacted
with AcOH to create compound 2 with a functional terminal group.
Under EDCꢁHCl coupling conditions, bichromophore DN was pre-
pared by chromophore N1 attaching to the compound 2 via ester-
ification reaction in which 4-(dimethylamino)-pyridine (DMAP)
acted as a catalyst. As for six-branched chromophore SN, the tether
core DH was produced by Williamson ester reaction of 4,40,400-
(ethane-1,1,1-triyl)triphenol and 3-chloropropane-1,2-diol. Then,
carboxylic acid functionalized chromophore 3, which synthesized
from monochromophore and succinic anhydride, attached to tether
core DH through esterification to obtain six-branched chromo-
phore SN. The structures of N1, DN and SN were confirmed by 1H
NMR, FT-IR spectroscopy, elemental analysis and mass spectrom-
etry. The details of the synthesis and characterizations were
described in the Experimental Section.
Thermal properties of chromophore N1, DN and SN were studied
by differential scanning calorimetry (DSC) and thermalgravimetric
analysis (TGA). The melting point (Tm) of chromophore N1 was
276 ꢂC, while bichromophore DN and six-branched SN showed
glass transition temperatures (Tg) at about 115 ꢂC and 129 ꢂC
without melting point. Compared with DN, SN exhibited higher Tg
for its larger molecular weight and more rigid structure resulting in
bigger limitation of movement. The decomposition temperatures
(Td) of chromophore N1 and DN were 281 ꢂC and 313 ꢂC respec-
tively (Fig. 2) indicating connecting two chromophores could
improve thermal stability. However, the Td of SN dropped to 265 ꢂC
due to the star-shaped structure and two adjacent ester groups
which connected monochromophores and DH to form SN. The star-
shaped structure was influenced greatly by temperature and the
bonds of two adjacent ester groups were destroyed easily resulting
in low Td of SN.
d
ppm): 1.76 (s, 6H, C(CH3)2), 2.34 (d, 2H, COCH2), 2.41 (m, 2H,
CH2COOH), 3.10 (m, 3H, NCH3), 3.77 (d, 2H, NCH2), 4.23 (d, 2H,
CH2O), 6.87e6.91 (d, 3H, ArH, CH]CH), 7.78 (d, 2H, ArH), 7.91 (d,
1H, CH]CH, J ¼ 15.8 Hz). MS (ESI): exact mass calcd for C25H24N4O5
[MꢀH]ꢀ: 459.1. Found: 459.1.
2.8. Synthesis of six-branched chromophore SN
Compound 3 (0.49 g, 1.05 mmol) and DH (0.079 g, 0.15 mmol)
were dissolved in mixed solution THF/CH2Cl2 (25 mL/75 mL). The
mixture was stirred at room temperature for 48 h after the addition
of EDCꢁHCl (0.30 g, 1.58 mmol) and 4-dimethylaminopyridine
(DMAP; 0.037 g, 0.3 mmol). The reacting solution was evaporated
and the residue was dissolved in CH2Cl2 (150 mL). Then the organic
phase was washed with brine and water. After the resulting solu-
tion was dried over MgSO4 and concentrated, the products were
obtained via flash chromatography on silica gel using a mixture of
CH2Cl2/THF (v:v ¼ 25:1) as the eluent. Yield: 82%. 1H NMR
(500 MHz, CDCl3, d ppm): 1.74 (s, 36H, C(CH3)2), 2.04 (d, 3H, CCH3),
2.59 (m, 24H, COCH2), 3.13 (s, 18H, NCH3), 3.74 (t, 12H, NCH2), 4.05
(d, 6H, CCH2O), 4.30 (s, 15H, OCH2; higher field branch of AB
quartet, ArOCH2), 4.41 (d, 3H, lower field branch of AB quartet, Ar-
O-CH2), 5.37 (s, 3H, CHCH2), 6.76 (m, 24H, ArH; CH]CH, J ¼ 16 Hz),
6.93 (d, 6H, ArH), 7.55 (d, 12H, ArH), 7.61 (d, 6H, CH]CH, J ¼ 16 Hz).
13C NMR (125 MHz, CDCl3,
d ppm): 176.5, 174.7, 172.3, 156.5, 153.2,
148.6, 142.5, 132.5, 129.9, 122.6, 114.0, 112.9, 112.7, 112.2, 111.7, 109.5,
97.3, 94.9, 70.3, 66.2, 62.9, 61.7, 54.9, 50.9, 39.2, 30.6, 29.1, 28.9, 26.9.
FT-IR (KBr, cmꢀ1): 2223 (s), 1734 (s), 1521 (m), 1377 (s), 1279 (m),
1167 (m), 962 (w), 816 (w), 730 (w), 653 (w). Elemental analysis
calcd (%) for C179H168N24O33 (%): C, 67.54; H, 5.32; N, 10.56. Found:
C, 67.41; H, 5.92; N, 9.78. MS (ESI): exact mass calcd for
3.2. Linear and nonlinear optical properties
The linear optical properties of N1, DN and SN were performed
by UVevisible absorption spectra. The maximum absorption
wavelengths (lmax) of chromophore N1, DN and SN were 586 nm,
574 nm and 568 nm in DMF, indicating the absorption of chro-
mophore shifted bluely with the increase of chromophoric branch
(Fig. 3). Compared with chromophore N1, multichromophore
C
179H168N24O33 [M]:3183.39. Found: 3182.93.
2.9. Preparation of films
Monochromophore N1 and bichromophore DN were doped into

794
W. Lin et al. / Dyes and Pigments 136 (2017) 791e797
Synthesis of monochromophore N1
Synthesis of bichromophore DN
Synthesis of six-branched chromophore SN
Scheme 1. Synthesis of chromophore N1, DN and SN.
showed blue shifts in lmax due to the
p
-
p
* electronic transition.
resulted from spatial interactions between monochromophores in
multichromophore. Besides, no significant absorption broadening
in multichromophores compared with monochromophore N1,
reveal there was no influence in charge-transfer band after chro-
mophores were connected to form multi-branched chromophores.
NLO polymer films (Film-N1 and Film-DN) were fabricated by
doping the chromophores into polymer matrix PVPh and the
Take DN for an example, the variation of the DN structure, a new
chemical group (eCOOe) was synthesized from N1 via esterifica-
tion, induced the reduction of electron-release behavior of the
donor resulting in the lmax of bichromophore DN blue shifts
[45e47]. The same phenomena occurred in SN. As for the small
blue-shift of 6 nm for SN, comparing with biochromophore DN,

W. Lin et al. / Dyes and Pigments 136 (2017) 791e797
795
The d33 values of polymer films, which were poled by a 5.5 kV dc
voltage, were displayed in Fig. 4. The d33 values of gust-host films
improved with the increase of chromophore loading density and
reached to the highest values (Film-DN was 39 pm Vꢀ1 and Film-
N1 was 25 pm Vꢀ1) when the loading concentration was 30 wt%.
Compared with Film-N1, the Film-DN was about 1.6 times in the
second harmonic coefficient, indicating that the bichromophore
could promote the macroscopic optical nonlinearities because of
the site-isolation effect from their tree-like structures. For large
molecular weight of SN, Film-SN was prepared directly without any
polymer matrix. The active chromophore density of Film-SN
reached to 68 wt% and the d33 value up to 208 pm Vꢀ1 which was
8.3 times in that of Film-N1, revealing six-branched chromophore
could further improve nonlinear optical properties and loading
content simultaneously (Fig. 5). Introducing dendritic multi-
chromophores into films could decrease the inter-chromophore
electrostatic interactions and improve the macroscopic optical
nonlinearity effectively.
Fig. 2. TGA traces for chromophore N1, DN and SN.
3.3. Stability of nonlinear activity
N1 in DMF
DN in DMF
SN in DMF
1.0
0.8
0.6
0.4
0.2
0.0
Besides, temperature-dependent decay of d33 was used to
evaluate the long-time stability of molecular orientation in films.
The temperature-dependent decays of Film-N1, Film-DN and Film-
SN were illustrated in Fig. 6. The d33 of Film-DN decayed obviously
after 100 ꢂC, and remained 50% of original d33 at 119 ꢂC. Meanwhile,
400
500
600
700
Wavelength (nm)
Fig. 3. UVevisible absorption spectra of compound N1, DN and SN in DMF.
molecule loading densities were up to 30 wt% without phase sep-
aration. Six-branched chromophore SN was adopted to fabricate
film Film-SN directly. The second-order NLO properties of the films
were investigated by SHG measurement.
Fig. 5. Illustration of maximum d33 values of polymer films and pure film.
Fig. 4. d33 values of polymer films as a function of molecule loading densities of
compound N1 and DN: black, Film-N1; red, Film-DN. (For interpretation of the ref-
erences to colour in this figure legend, the reader is referred to the web version of this
article.)
Fig. 6. Temperature-dependence decays of NLO coefficients for Film-N1, Film-DN and
Film-SN.

796
W. Lin et al. / Dyes and Pigments 136 (2017) 791e797
138e47.
the second harmonic coefficient of Film-N1 decayed rapidly after
80 ꢂC and maintained half of the original signals at 111 ꢂC. These
phenomena revealed that the site-isolation effect from the tree-like
architectures could improve the stability of polymer films mark-
edly. However, the d33 of Film-SN maintained half of the original
signals at 92 ꢂC showing less stable than polymer films. It could be
attributed to the absence of polymer matrix and the flexibility of
tether core.
[14] Zhang YY, Shi Y, Li YZ. Photoexcitation mechanisms of new D-p-A coumarin
derivatives in linear and nonlinear optical processes. J Mater Sci Mater Elec-
tron 2016;27:7132e40.
[15] Dalton LR, Harper AW, Robinson BH. The role of London forces in defining
noncentrosymmetric order of high dipole moment high hyperpolarizability
chromophores in electrically poled polymeric thin films. Proc Natl Acad Sci U.
S. A 1997;94:4842e7.
[16] Harper AW, Sun S, Dalton LR, Garner SM, Chen A, Kalluri S, et al. Translating
microscopic optical nonlinearity into macroscopic optical nonlinearity: the
role of chromophore-chromophore electrostatic interactions. J Opt Soc Am B
Opt Phys 1998;15:329e37.
[17] Robinson BH, Dalton LR. Monte Carlo statistical mechanical simulations of the
competition of intermolecular electrostatic and poling-field interactions in
defining macroscopic electro-optic activity for organic chromophore/polymer
materials. J Phys Chem A 2000;104:4785e95.
[18] Gao JK, Cui YJ, Yu JC, Lin WX, Wang ZY, Qian GD. A 3-phenoxypropane-1,2-
diol based bichromophore for enhanced nonlinear optical properties. Dyes
Pigment 2010;87:204e8.
[19] Gopalan P, Katz HE, McGee DJ, Erben C, Zielinski T, Bousquet D, et al. Star-
shaped azo-based dipolar chromophores: design, synthesis, matrix compati-
bility, and electro-optic activity. J Am Chem Soc 2004;126:1741e7.
[20] Luo JD, Zhou XH, Jen AKY. Rational molecular design and supramolecular
assembly of highly efficient organic electro-optic materials. J Mater Chem
2009;19:7410e24.
4. Conclusions
New multi-chromophores DN and SN were synthesized from
monochromophore N1 via esterification. The d33 values of Film-DN
enhanced with the increase of loading densities, and the highest
value reached to 39 pm Vꢀ1 when the chromophore concentration
was 30 wt%. Furthermore, the second harmonic coefficient of Film-
SN was up to 208 pm Vꢀ1 and the active chromophore density was
68 wt%. Compared with Film-N1, the films containing multi-
branched chromophores Film-DN and Film-SN were about 1.6-
fold and 8.3-fold enhancement in the d33 values, indicating the
dendritic architecture could reduced dipole-dipole interactions
between chromophores significantly and improved the macro-
scopic nonlinear optical activities markedly. The easy and practi-
cable strategy of the preparation of multi-branched chromophores
provided broader potential application in design and synthesis of
multichromophore dendrimers with excellent nonlinear activity.
[21] Ma H, Chen BQ, Sassa T, Dalton LR, Jen AKY. Highly efficient and thermally
stable nonlinear optical dendrimer for electrooptics.
J Am Chem Soc
2001;123:986e7.
[22] Ma H, Liu S, Luo JD, Suresh S, Liu L, Kang SH, et al. Highly efficient and
thermally stable electro-optical dendrimers for photonics. Adv Funct Mater
2002;12:565e74.
[23] Ma H, Wu JY, Herguth P, Chen BQ, Jen AKY. A novel class of high-performance
perfluorocyclobutane-containing polymers for second-order nonlinear optics.
Chem Mater 2000;12:1187e9.
[24] Yokoyama S, Nakahama T, Otomo A, Mashiko S. Intermolecular coupling
enhancement of the molecular hyperpolarizability in multichromophoric
dipolar dendrons. J Am Chem Soc 2000;122:3174e81.
Acknowledgements
[25] Cho MJ, Lee SK, Jin JI, Choi DH, Dalton LR. Electro-optic property of
chromophore-terminated trifunctional dendrimer in
Thin Solid Films 2006;515:2303e9.
a guest-host system.
The authors gratefully acknowledge financial support from Na-
tional Natural Science Foundation of China (Nos. 51272229,
51472217 and 51432001), Zhejiang Provincial Natural Science
Foundation of China (No. LR13E020001 and LZ15E020001), and
Fundamental Research Funds for the Central Universities (Nos.
2015QNA4009 and 2016FZA4007).
[26] Kim TD, Kang JW, Luo JD, Jang SH, Ka JW, Tucker N, et al. Ultralarge and
thermally stable electro-optic activities from supramolecular self-assembled
molecular glasses. J Am Chem Soc 2007;129:488e9.
[27] Zhou XH, Luo JD, Huang S, Kim TD, Shi ZW, Cheng YJ, et al. Supramolecular
self-assembled dendritic nonlinear optical chromophores: fine-tuning of
arene-perfluoroarene interactions for ultralarge electro-optic activity and
enhanced thermal stability. Adv Mater 2009;21:1976e81.
[28] Shi ZW, Luo JD, Huang S, Zhou XH, Kim TD, Cheng YJ, et al. Reinforced site
isolation leading to remarkable thermal stability and high electrooptic ac-
tivities in cross-linked nonlinear optical dendrimers. Chem Mater 2008;20:
6372e7.
[29] Gao JK, Cui YJ, Yu JC, Lin WX, Wang ZY, Qian GD. Enhancement of nonlinear
optical activity in new six-branched dendritic dipolar chromophore. J Mater
Chem 2011;21:3197e203.
[30] Lin WX, Cui YJ, Gao JK, Yu JC, Liang T, Qian GD. Six-branched chromophores
with isolation groups: synthesis and enhanced optical nonlinearity. J Mater
Chem 2012;22:9202e8.
References
[1] Burland DM, Miller RD, Walsh CA. Second-order nonlinearity in poled-
polymer systems. Chem Rev 1994;94:31e75.
[2] Kanis DR, Ratner MA, Marks TJ. Design and construction of molecular as-
semblies with large second-order optical nonlinearities-quantum-chemical
aspects. Chem Rev 1994;94:195e242.
[3] Ghebremichael F, Kuzyk MG, Lackritz HS. Nonlinear optics and polymer
physics. Prog Polym Sci 1997;22:1147e201.
[31] Wu WB, Xu Z, Xiang WD, Li Z. Using an orthogonal approach and one-pot
method to simplify the synthesis of nonlinear optical (NLO) dendrimers.
Polym Chem 2014;5:6667e70.
[4] Zeng SM, Ouyang XH, Zeng HP, Ji W, Ge ZY. Synthesis, tunable two and three-
photon absorption properties of triazine derivatives by branches. Dyes
Pigment 2012;94:290e5.
[32] Wu WB, Wang ZP, Xiao R, Xu Z, Li Z. Main chain dendronized hyperbranched
polymers: convenient synthesis and good second-order nonlinear optical
performance. Polym Chem 2015;6:4396e403.
[33] Xu HJ, Fu MK, Bo SH, Liu XH. Synthesis of asymmetric dendrimers with
controllable chromophore concentration and improved electro-optical per-
formance. RSC Adv 2016;6:25023e7.
[34] Yang HT, Tang R, Wu WB, Liu W, Guo Q, Liu YL, et al. A series of dendronized
hyperbranched polymers with dendritic chromophore moieties in the pe-
riphery: convenient synthesis and large nonlinear optical effects. Polym Chem
2016;7:4016e24.
[35] Chen LJ, Jin XF, Cui YJ, Qian GD, Wang MQ. Effect of triphenylamine agents as
screening moieties for electrostatic interaction in the nonlinear optical
response of hybrid organic-inorganic films. Thin Solid Films 2008;516:
4153e8.
[36] Firestone KA, Reid P, Lawson R, Jang SH, Dalton LR. Advances in organic
electro-optic materials and processing. Inorg Chim Acta 2004;357:3957e66.
[37] Dalton LR. Organic electro-optic materials. Pure Appl Chem 2004;76:
1421e33.
[38] Maker PD, Savage CM, Terhune RW, Nisenoff M. Effects of dispersion and
focusing on production of optical harmonics. Phys Rev Lett 1962;8:21e3.
[39] Jerphagn J, Kurtz SK. Maker fringes e a detailed comparison of theory and
experiment for isotropic and uniaxial crystals. J Appl Phys 1970;41:1667e81.
[40] Cui YJ, Qian GD, Gao JK, Chen LJ, Wang ZY, Wang MQ. Preparation and
nonlinear optical properties of inorganic-organic hybrid films with various
substituents on chromophores. J Phys Chem B 2005;109:23295e9.
[5] Zhang XY, Xu Z, Ge ZY, Ouyang XH, Ji W. Tunable molecular configuration for
significant enhancement of two-photon absorption based on novel octupolar
benzoimidazole derivatives. J Photochem Photobio A 2014;290:22e30.
[6] Facchetti A, Abbotto A, Beverina L, van der Boom ME, Dutta P, Evmenenko G,
et al. Layer-by-layer self-assembled pyrrole-based donor-acceptor chromo-
phores as electro-optic materials. Chem Mater 2003;15:1064e72.
[7] Lee M, Katz HE, Erben C, Gill DM, Gopalan P, Heber JD, et al. Broadband
modulation of light by using an electro-optic polymer. Science 2002;298:
1401e3.
[8] Asselberghs I, Zhao Y, Clays K, Persoons A, Comito A, Rubin Y. Reversible
switching of molecular second-order nonlinear optical polarizability through
proton-transfer. Chem Phys Lett 2002;364:279e83.
[9] Dalton LR, Lao D, Olbricht BC, Benight S, Bale DH, Davies JA, et al. Theory-
inspired development of new nonlinear optical materials and their integration
into silicon photonic circuits and devices. Opt Mater 2010;32:658e68.
[10] Dalton LR, Sullivan PA, Bale DH. Electric field poled organic electro-optic
materials: state of the art and future prospects. Chem Rev 2010;110:25e55.
[11] Dalton LR. Rational design of organic electro-optic materials. J Phys Condens
Matter 2003;15:897e934.
[12] Liu S, Haller MA, Ma H, Dalton LR, Jang SH, Jen AKY. Focused microwave-
assisted synthesis of 2,5-dihydrofuran derivatives as electron acceptors for
highly efficient nonlinear optical chromophores. Adv Mater 2003;15:603e7.
[13] Liu FG, Xiao HY, Yang YH, Wang HR, Zhang H, Liu JL, et al. The design of
nonlinear optical chromophores exhibiting large electro-optic activity and
high thermal stability: the role of donor groups. Dyes Pigment 2016;130:

W. Lin et al. / Dyes and Pigments 136 (2017) 791e797
797
[41] Cui YJ, Wang MQ, Chen LJ, Qian GD. Synthesis and characterization of an
alkoxysilane dye for nonlinear optical applications. Dyes Pigment 2005;65:
61e6.
[42] Yu JC, Cui YJ, Gao JK, Wang ZY, Qian GD. Enhanced optical nonlinearity and
improved transparency of inorganic-organic hybrid materials containing
benzimidazole chromophores. J Phys Chem B 2009;113:14877e83.
[43] Cui YJ, Wang MQ, Chen LJ, Qian GD. Synthesis and spectroscopic character-
ization of an alkoxysilane dye containing C. I. Disperse Red 1. Dyes Pigment
2004;62:43e7.
bichromophores for nonlinear optical applications in polymer films. React
Funct Polym 2011;71:496e501.
[45] McRae EG. Theory of solvent effects on molecular electronic spectra-
frequency shifts. J Phys Chem 1957;61:562e72.
[46] Paley MS, Harris JM, Looser H, Baumert JC, Bjorklund GC, Jundt D, et al.
A solvatochromic method for determining second-order polarizabilities of
organic-molecules. J Org Chem 1989;54:3774e8.
[47] Liao Y, Firestone KA, Bhattacharjee S, Luo JD, Haller M, Hau S, et al. Linear and
nonlinear optical properties of a macrocyclic trichromophore bundle with
parallel-aligned dipole moments. J Phys Chem B 2006;110:5434e8.
[44] Gao JK, Cui YJ, Yu JC, Lin WX, Wang ZY, Qian GD. Design and synthesis of