Synthesis and characterization of two novel second-order nonlinear optical chromophores based on julolidine donors with excellent electro-optic activity

Article abstract of DOI:10.1039/c6ra21814h

Julolidine and its derivatives are excellent electron-rich structures thus two novel second order nonlinear optical (NLO) chromophores based on julolidine donors and tricyanofuran (TCF) acceptors linked via isophorone bridge (zh-1) and modified isophorone bridge (zh-2) have been synthesized. Density functional theory (DFT) was used to optimize the geometrical structures, calculate the HOMO-LUMO energy gaps and first-order hyperpolarizability (β) of these chromophores. Besides, to determine the redox properties of these chromophores, cyclic voltammetry (CV) experiments were performed. The optimized structures suggest that chromophore zh-1 possesses better planarity which increases the ability of electron delocalization. These chromophores showed good thermal stability with their decomposition temperatures all above 210 °C. The electro-optic coefficients (r₃₃) of poled films containing 25 wt% of these chromophores doped in amorphous polycarbonate (APC) afforded values of 170 and 101 pm V^-1 at 1310 nm for chromophores zh-1 and zh-2, respectively. These properties show the potential use of the new chromophores as advanced material devices.

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Synthesis and characterization of two novel second-order
nonlinear optical chromophores based on julolidine donors with
excellent electro-optic activity
Received 00th January 20xx,
Accepted 00th January 20xx
Hua Zhang,ab Fuyang Huo,ab Fenggang Liu,ab Zhuo Chen,a Jialei Liu,a Shuhui Bo,a* Zhen Zhen a and
Ling Qiu a*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Julolidine and its derivatives are excellent electron-rich structures thus two novel second order nonlinear optical (NLO)
chromophores based on julolidine donors and tricyanofuran (TCF) accepters linked via isophorone bridge (zh-1) and
modified isophorone bridge (zh-2) have been synthesized. Density functional theory (DFT) was used to optimize the
geometrical structures, calculate the HOMO–LUMO energy gaps and first-order hyperpolarizability (β) of these
chromophores. Besides, to determine the redox properties of these chromophores, cyclic voltammetry (CV) experiments
were performed. The optimized structures suggest that chromophore zh-1 possesses better planarity which increases the
ability of electron delocalization. These chromophores showed good thermal stability with their decomposition
temperatures all above 210°C. The electro-optic coefficients (r33) of poled films containing 25 wt% of these chromophores
doped in amorphous polycarbonate (APC) afforded values of 170 and 101 pm V-1 at 1310 nm for chromophores zh-1 and
zh-2, respectively. These properties show the potential use of the new chromophores as advanced material devices.
while the πꢀconjugated bridge provides a pathway for the ultrafast
redistribution of electric charges under an applied external electric
field 15ꢀ17. The most widely studied system are guestꢀhost poled
polymers which achieve macroscopic EO response via
chromophores’ alignment in the same direction under poling electric
field 18. During this process, the chromophores with a rodꢀlike
structure and strong dipoleꢀdipole interactions are easily to form
unfavorable antiparallel distribution in the polymer matrix, which
makes difficulties during the conversion from the first
Introduction
In the past few decades, organic and polymeric electroꢀoptic (EO)
materials have attracted significant interests on account of their
potential applications in optical communication and information
technologies1ꢀ6
. Compared with the traditional inorganic and
semiconductor materials, the organic EO materials have many
significant advantages such as larger nonlinear optical coefficients,
simpler preparation and lower costs7ꢀ11. For further applications in
the above area, EO materials should exhibit additional properties
such as high thermal and chemical stabilities and good transparency.
The most common organic EO material as well as the highly
investigated field are poled guestꢀhost polymeric material in which
19,
hyperpolarizability (β) into macroscopic EO efficiency (r33 value)
20. So the efficient way to improve the r33 values of the guest–host
EO materials is the optimization of the structure of push–pull
chromophores.
the EO chromophores are directly dispersed in a polymer matrix 12
.
In order to suppress dipole interaction among chromophores,
many researches have been explored to design and synthesize novel
NLO chromophores, seeking to engineer NLO molecules with both
large microscopically (β) and macroscopically (r33)12, 21ꢀ23. For one
thing, structure–property relationships indicate that large β values of
the chromophores can be obtained by careful modification of the
strength of donor and acceptor groups, as well as the length of the πꢀ
bridge 24, 25. For another thing, by introducing isolation groups into
donor or bridge moieties could suppress the dipole interactions
among chromophores thus improve the macroscopic EO coefficients
(r33 value)26ꢀ30. In addition, the planarity of the whole molecule plays
an essential role on the pathway for the ultrafast redistribution of
An organic NLO chromophore is generally composed of push–
pull structure, which consists of an electronꢀdonating group (donor)
and an electronꢀwithdrawing group (acceptor) coupled through a πꢀ
conjugated bridge 13,14. In such molecules, the donor and acceptor
moieties provide the fundamental groundꢀstate charge asymmetry,
electric charges under an applied external electric field 15, 16
.
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In the previous work from our group 10, 21, 22, 31ꢀ34, we found that 8ꢀ 1, 1, 7, 7ꢀtetramethylꢀformyljulolidine group, but to have the
hydroxyꢀ1, 1, 7, 7ꢀtetramethylꢀformyljulolidine group possessed different isolation groups on the isophorone πꢀconjugation. Firstly
good electron donating ability and the alkyl chain on its side can act the long flexible chain with one halogen atom at the end was
well as the isolation group. Isophorone bridge also shows its good attached to the 8ꢀhydroxyꢀ1, 1, 7, 7ꢀtetramethylꢀformyljulolidine to
ability for electron transport over the whole molecule compared with prepare electron donor group using NaOH as the base. Then in the
thiophene bridges35. On the conditions of these fascinating presence of sodium ethoxide, isophorone 4 can be reacted directly
properties, we designed and synthesized two novel chromophores with 1 in oneꢀpot via the Knoevenagel condensation to obtain 5a
zhꢀ1 and zhꢀ2 (Chart 1) using the modified 8ꢀhydroxyꢀ1, 1, 7, 7ꢀ with a high overall yield of 80%.
tetramethylꢀformyljulolidine group as the donor and isophorone
group as the πꢀconjugated bridge. The two modulated chromophores
be easily deprotonated to form a nucleophilic thiolate which
with the different πꢀconjugated bridges (one was the isophorone
In the presence of sodium ethoxide as the base, 1ꢀbutanethiol can
underwent ringꢀopening reaction of epoxyisophorone 2 to selectively
bridge, and the other was the butylthio substituted isophorone
generate 2ꢀBuꢀSꢀsubstituted isophorone 3 in a nearly quantitative
bridge) had the same tricyanofuran acceptor (TCF) for comparison.
yield37. This intermediate can be reacted directly with 1 in oneꢀpot
The butylthio group on the bridge was expected to act as both the
via the Knoevenagel condensation to achieve 5b with a high overall
isolation group and the electron donating group. 1HꢀNMR, 13CꢀNMR
yield of 75%. Then 5a and 5b were reacted with diethyl
and MS analyses were carried out to demonstrate the structure of
(cyanomethyl) phosphonate to result in compound 6a and 6b
these chromophores. These chromophores showed great solubility in
respectively in a nearly 70% yield, and the following reaction
common organic solvents, good thermal stability (with their onset
converted the nitrile group on 6a and 6b into the corresponding
decomposition temperatures all above 210°C), and good
aldehyde 7a and 7b using DIBALꢀH as the reducing agent in 81%
compatibility with polymers. Thermal stability, photo physical
yield. The targeted chromophores zhꢀ1 and zhꢀ2 were successfully
properties and DFT calculations of these chromophores were
synthesized by condensing aldehydes 7a and 7b with acceptor (TCF)
systematically studied. In addition, the macroscopic EO activity (r33)
in absolute ethanol in the presence of a catalytic amount of
of these chromophores in amorphous polycarbonate was also
triethylamine.
discussed.
Chart 1 The structure of chromophores zhꢀ1 and zhꢀ2
Compared with previous researches containing similar thiolated
structure36, we choose 8ꢀhydroxyꢀ1, 1, 7, 7ꢀtetramethylꢀ
formyljulolidine group possessing much greater ability on donating
electrons than phenylamine in the above reference which also
showed significant thermal stabilities. Meanwhile we preferred the
slightly weaker and moderate tricyanofuran (TCF) as the accepter
due to its simpler synthetic method than the strong CF3ꢀPhꢀTCF
Scheme 1 Synthetic scheme for chromophores zhꢀ1 and zhꢀ2
whose synthetic route was to some extent dangerous and had a low
Thermal analysis
yield over the whole process. As considerable efforts we have made
previously by carefully optimizing donor and accepter strength, we
have now obtained chromophores with the maximum absorption
wavelength of 763 nm and 757 nm in CHCl3 and meanwhile, under
the load density of 25wt%, 170 and 101 pm/V of r33 values were
observed after the corona poling process.
Results and discussion
Synthesis and characterization of chromophores
The synthesis route of chromophores zhꢀ1 and zhꢀ2 is presented in
Scheme 1. These NLO chromophores were designed to have the
same strong electron acceptor (TCF) and electron donor 8ꢀhydroxyꢀ
Fig.1 TGA curves of chromophores zhꢀ1 and zhꢀ2 with a heating
rate of 10°C minꢀ1 in a nitrogen atmosphere
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NLO chromophores must be thermally stable enough to withstand
Compared with the unsubstituted analogue zhꢀ1, the sulfur atom
encountered high temperature (>200°C) in electric field poling and on the bridge in zhꢀ2 may make the molecule maintain poorer
subsequent processing of chromophore/polymer materials. Thermal planarity so that the electron delocalization ability becomes worse
properties of these chromophores were measured by and the maximum absorption λmax of chromophore zhꢀ2 achieves 6
thermogravimetric analysis (TGA) with a heating rate of 10°C minꢀ1 nm blueꢀshifts. The analysis corresponds well with the optimized
under nitrogen. Fig.1 showed the TGA curves of chromophore zhꢀ1 structure.
and zhꢀ2. In particular, the highest decomposition temperature (Td)
was observed for chromophore zhꢀ1 (256°C), which indicated that Theoretical calculations
the introduction of butylthio group on the isophorone ring resulted in
For further study on the groundꢀstate molecular geometries and
relatively poor thermal tolerance (216°C) for the zhꢀ2. Even so, we polarization, the HOMO–LUMO energy gaps and β values of these
could see that the decomposition temperature (Td) of all the chromophores were calculated. The DFT calculations were carried
chromophores was above 210°C as summarized in Table 1. The out at the hybrid B3LYP level by employing the split valence 6ꢀ
39ꢀ41
chromophore zhꢀ1, which showed better thermal stability than the 31G** (d, p) basis set
using Gaussian 09 program package. As
unstable substituted thiolated one, made it a favourable candidate for reported earlier, the β value has a close relationship with the
practical application. The temperature is high enough for the substituents, steric hindrance, and intramolecular chargeꢀtransfer, πꢀ
application in EO device preparation 38
.
conjugation length and so on 42, 43
.
Firstly, the geometrically optimized structures of the molecules
were investigated as shown in Fig.3. We found that the chromophore
zhꢀ1 showed great planarity with one substituted alkyl chain on the
donor moiety. In the optimized structures, the angle between the
phenyl ring of the julolidine moiety and the average plane of the two
chromophores zhꢀ1 and zhꢀ2 was ca. 14.29° and 30.26°,
respectively. Yet the substituted butylthio group on the isophorone
πꢀconjugation made the conjugate plane slightly bent as shown. The
poorer planarity of chromophore zhꢀ2 indicates relatively worse
electron delocalization over the whole molecule which may verify
the 6 nm blue shift compared with chromophore zhꢀ1.
Table 1 Summary of thermal and optical properties and EO
coefficients of chromophores zhꢀ1 and zhꢀ2
a
b
c
e
chromophores
Td
λmax
λmax
ꢁλd
r33
(℃)
(nm)
(nm)
(nm)
(pm/v)
zhꢀ1
zhꢀ2
256
216
763
757
671
665
92
92
170
101
a Td was determined by an onset point, and measured by TGA under
nitrogen at a heating rate of 10℃minꢀ1. b λmax was measured in
CHCl3. c λmax was measured in dioxane. d ꢁλ = b λmax ꢀ c λmax e r33
.
values (25 wt%) were measured at the wavelength of 1310 nm.
Optical properties
To explore the effect of butylthio group on the πꢀconjugation
bridge on the intramolecular charge transfer (ICT) of dipolar
chromophores, UVꢀVis absorption spectra of two chromophores (c =
1×10ꢀ5 mol L－1) were performed in a series of aprotic solvents with
different polarity (Fig.2). These two chromophores exhibited the
similar π–π* intramolecular chargeꢀtransfer (ICT) absorption band.
As shown in Fig.2, chromophores zhꢀ1 and zhꢀ2 exhibited the
maximum absorption (λmax) at 763 nm and 757 nm in chloroform,
respectively. Both of the two chromophores all showed a large
bathochromic shift of 92 nm from dioxane to chloroform, displaying
a great solvatochromism, which indicating that both chromophores
could be easily polarized. The λmax of chromophore zhꢀ2 is similar to
chromophore zhꢀ1, which may attribute to the fact that the additional
butylthio group did not change the conjugate structure. The spectrum
data are summarized in Table 1.
Fig.3 The optimized structure of chromophores zhꢀ1 and zhꢀ2.
The frontier molecular orbitals are often used to characterize the
chemical reactivity and kinetic stability of a molecule and to obtain
qualitative information about the optical and electrical properties of
molecules 41, 44, 45. Moreover, the HOMO–LUMO energy gap is also
used to investigate the charge transfer interaction occurring in a
14, 21, 45
chromophore molecule
. Fig.4 represents the frontier
molecular orbitals of chromophores zhꢀ1 and zhꢀ2. It could be seen
that the density of the ground and excited state electron was
asymmetry along the dipolar axis of the chromophores. Apparently,
the electronic distribution of the HOMO is delocalized over the
isophorone ring and the julolidine donor, whereas the electronic
distribution of LUMO is mainly constituted by the acceptor moiety
Fig. 2 UVꢀVis absorption spectra of chromophores zhꢀ1 and zhꢀ2 (c
= 1×10ꢀ5 mol Lꢀ1) in different solvents
45
.
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time, the attributions of sulfur atom on the substituent group located
in the πꢀbridge moiety were listed separately. For the chromophores
zhꢀ1 and zhꢀ2, the HOMO was mostly stabilized by the contributions
from the donor (51.97% and 52.18%) and much less contributions
from other segments. For chromophore zhꢀ1, the contribution of the
πꢀbridge was 27.83% and 41.39% to the HOMO and LUMO level,
respectively. For the chromophore zhꢀ2, the contribution of the πꢀ
bridge was 29.42% and 41.50% to the HOMO and LUMO level
respectively. However, the contribution of sulfur atom located in the
πꢀbridge moiety to the HOMO (0.91%) was obviously more than to
Fig.4 The frontier molecular orbitals of chromophores zhꢀ1 and zhꢀ2 the LUMO (0.08%). Thus, the butylthio group on the πꢀbridge
played a role of slight electron donor. But, the slightly bent plane of
chromophore zhꢀ2 may hinder the sulfur atom’s electronꢀdonating
ability.
Table 2 Results of DFT calculations for chromophores zhꢀ1 and zhꢀ
2
a
chromophores EHOMO/eV ELUMO/eV
ꢁE/eV
βmax
/
Furthermore, the theoretical microscopic Zeroꢀfrequency (static)
molecular first hyperpolarizability (β) was calculated using Gaussian
09. As a reference reported earlier, β has been calculated at the 6ꢀ
31g**(d, p) level under vacuum 47. The scalar quantity of β can be
computed from the x, y, and z components according following
10ꢀ30esu
987.9
zhꢀ1
zhꢀ2
ꢀ5.0469
ꢀ5.0447
ꢀ3.0958
ꢀ3.0934
1.9511
1.9513
985.5
a
ꢁE= ELUMO ꢀEHOMO. Results were calculated from DFT. β values
were calculated using Gaussian 09 at the B3LYP/6ꢀ31g** (d, p)
level and the direction of the maximum value is along the charge
transfer axis of the chromophores.
equation:
1/ 2
β
=
(
βx2
+
βy2
+
βz2
)
Where
1
The HOMO and LUMO energies were calculated by DFT
calculations as shown in Table 2. The gaps between HOMO and
LUMO energy level for the two chromophores were 1.9511eV and
1.9513eV, respectively. As reported, the energy gap is lower and the
charge transfer (ICT) ability is higher, thus improving the
nonlinearity 45. We can see from the DFT calculation results that the
chromophore zhꢀ1 showed lower optical gap (ꢁE) and bigger
microscopic electroꢀoptic properties (βmax) than zhꢀ2, so it may
indicate that chromophores zhꢀ1 should exhibit better ICT and
macroscopic electroꢀoptic properties than chromophore zhꢀ2. In fact,
the butylthio chain linked with the πꢀconjugation bridge makes the
whole molecule structure slightly bent which may be the reason of
broader band gap for chromophore zhꢀ2 than chromophore zhꢀ1.
These results correspond well to the UVꢀVis spectra results.
βi
=
βiii
+
(βijj
+
β jij + β jji ),i, j ∈(x, y, z)
∑
3 i≠ j
The data obtained from DFT calculations are summarized in Table
2. There was no obvious change in the β values of chromophores zhꢀ
1 and zhꢀ2 (985 and 987×10ꢀ30esu), which illustrated that the main
conjugated structures did not change under the simulated conditions.
The substituent group located in the πꢀbridge moiety plays a slight
electron donor role on the main conjugated structures according to
the analysis of the composition of the HOMOs and LUMOs, but the
bent plane of the geometrically optimized structure for chromophore
zhꢀ2 may have more obvious influence on the main conjugation
structure which resulted in larger energy gap and smaller β values. In
summary, chromophore zhꢀ1 might be the suitable combination of
donor and accepter because of its relatively large β values than zhꢀ2.
These results correspond well to the conclusion of UVꢀVis spectra
analysis.
Table 3 The molecular orbital composition (%) in the ground state
for chromophores zhꢀ1 and zhꢀ2a
zhꢀ1
zhꢀ2
Electrochemical properties
HOMO
(%)
LUMO
(%)
HOMO
(%)
LUMO
(%)
To study the redox properties of these chromophores, cyclic
voltammetry (CV) experiments were conducted in degassed
donor
51.97
27.83
20.20
17.43
41.39
41.18
52.18
29.42
18.40
0.91
18.01
41.50
40.49
0.08
anhydrous
acetonitrile
solutions
containing
0.1
M
πꢀbridge
acceptor
sulfur
tetrabutylammonium hexafluorophosphate (TBAPF) as the
supporting electrolyte. The relative data and voltammograms of
1×10ꢀ4 mol Lꢀ1 chromophores zhꢀ1 and zhꢀ2 were recorded, as shown
in Table 4 and Fig. 5.
atom
a
The molecular orbital composition was calculated using the
Multiwfn program with Ros–Schuit (SCPA) partition.
Table 4 ElectroꢀChemical properties of chromophores zhꢀ1 and zhꢀ
2a
For better investigating the influence of the butylthio group on the
πꢀbridge, the composition of the HOMOs and LUMOs were
calculated using the Multiwfn program with Ros–Schuit (SCPA)
partition46. As shown in Table 3, the chromophores zhꢀ1 and zhꢀ2
were segmented as the donor, πꢀbridge, and acceptor. At the same
chromophores
zhꢀ1
Eox
Ered
ꢁEa/eV
0.974
0.023
0.068
ꢀ0.951
ꢀ0.923
zhꢀ2
0.991
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3
a 10ꢀ3 M in CH3CN vs ferrocene/ferrocenium, glassy carbon working loading densities. cos (θ) is the acentric order parameter. θ is the
electrode, Pt counter electrode, 20℃, 0.1M Bu4NPF6, 100mV sꢀ1 angle between the permanent dipole moment of chromophores and
scan rate, ferrocene internal reference E1/2= +0.43V.
the applied electricꢀfield. To have meaningful analysis, the loading
densities of the chromophores are presented in terms of ͈, ensuring
12
As shown in Fig. 5, chromophores zhꢀ1 and zhꢀ2 all exhibited one normalization of observed r33 values for the chromophore content
quasi reversible oxidative wave with a halfꢀwave potential, E1/2
.
=
The r33 values of films containing chromophore zhꢀ1 (filmꢀA), zhꢀ2
0.5(Eox + Ered), at about 0.023 V, 0.068 V, respectively. Meanwhile, (filmꢀB) are measured in the different loading densities from 10% to
these chromophores had an irreversible reduction wave 30%. For chromophore zhꢀ1, the r33 values were gradually improved
corresponding to the acceptor moieties at Ered = ꢀ0.951 V, ꢀ0.923 V from 23 pmVꢀ1 (10 wt %) to 170 pm Vꢀ1 (25 wt %), as the
(vs. ferrocene/ferrocenium). It showed energy gap (ꢁE) values of concentration increased, and a similar trend of enhancement was also
0.974 eV, 0.991 eV, respectively. The HOMO and LUMO levels of observed for chromophore zhꢀ2, whose r33 values increased from 18
these new chromophores were calculated from their corresponding pm Vꢀ1 (10 wt %) to 101 pm Vꢀ1 (25 wt %). When the loading
oxidation and reduction potentials. The HOMO levels of increased to 30%, films showed a downward trend as shown in Fig 6.
chromophores zhꢀ1 and zhꢀ2 were estimated to be ꢀ4.823 eV and ꢀ
In contrast with chromophore zhꢀ2, the chromophore zhꢀ1 showed
4.868 eV. In the meantime, the corresponding LUMO level of much greater planarity which indicated the better electron
chromophores zhꢀ1 and zhꢀ2 were estimated to be ꢀ3.849 eV and ꢀ delocalizability and polarizability. Therefore we could obtain higher
3.809 eV, respectively. These results showed the same trend as the r33 values from films containing chromophore zhꢀ1.
DFT results.
Fig.5 Cyclic voltammograms of chromophores zhꢀ1 and zhꢀ2
Fig.6 EO coefficients of NLO thin films as
a function of
chromophore loading densities
Electric field poling and EO property measurements
In order to investigate the translation of the microscopic
hyperpolarizability into macroscopic EO response, a series of guest–
host polymers were generated by formulating the two chromophores
into amorphous polycarbonate (APC) using dibromomethane
(CH2Br2) as the solvent. The resulting solutions are filtered through
a 0.2 ꢂm PTFE filter and spinꢀcoated onto indium tin oxide (ITO)
glass substrates. Films of doped polymers are baked in a vacuum
oven at 85°C overnight to ensure the removal of the residual solvent.
The corona poling process is carried out at a temperature of 5°C
above the glass transition temperature (Tg) of the polymer. The r33
values are measured using the Teng–Man simple reflection
technique at the wavelength of 1310 nm using a carefully selected
thin ITO electrode with low reflectivity and good transparency in
Experimental
Materials
All chemicals are commercially available and are used without
further purification unless otherwise stated. Compound 1 was
purchased from Chongqing Werlchem Fine Chemical Co. Ltd. The
isophorone Oxide, nꢀbutyl mercaptan, 1ꢀchlorohexane were
purchased from J&K Chemical Co. Ltd. N,Nꢀdimethylformamide
(DMF), tetrahydrofuran(THF) and ether were distilled over calcium
hydride and stored over molecular sieves (pore size 3 Å). A 2ꢀ
dicyanomethyleneꢀ3ꢀcyanoꢀ4ꢀmethylꢀ2,5ꢀdihydrofuran(TCF)
acceptor was prepared according to the literature 50. TLC analyses
were carried out on 0.25 mm thick precoated silica plates and spots
were visualized under UV light. Chromatography on silica gel was
carried out on a Kieselgel (200–300 mesh).
order to minimize the contribution from multiple reflections 48
.
The r33 values are related to the chromophore number density (N),
β, and poling efficiency, described by the <cos 3 θ> order parameter,
as indicated by:49
Measurements and instrumentation
1H NMR and 13C NMR spectra were recorded on an Advance
r
= 2Nf (ω)β θ
cos3 / n4
33
Where N represents the aligned chromophore number density Bruker 400M (400 MHz) NMR spectrometer (tetramethylsilane as
(molecules per cm3) in the polymer host, n is the refractive index, the internal reference). The MS spectra were obtained on a MALDIꢀ
and f (ω) is the product of localꢀfield (DebyeꢀOnsager) factors. n and TOF (Matrix Assisted Laser Desorption/Ionization of Flight) on
f(ω) remain relatively constant for related chromophores at similar BIFLEXIII (Broker Inc.) spectrometer. The UVꢀVis spectra were
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performed on a Cary 5000 photo spectrometer. The TGA was gel (hexane/ethyl acetate, v/v, 10/1) to give a red solid 5b (5.5 g,
determined by using a TA5000ꢀ2950TGA (TA co) with a heating 9.72 mmol) in 75% yield.
rate of 10°C min － under the protection of nitrogen. Cyclic MS (MALDIꢀTOF): m/z (M+, C36H55NO2S): calcd: 565.40; found:
1
voltammetric data were measured on a Princeton Applied Research 564.79.
Model 283 Potentiostat/Galvanostat. The DFT calculations using 1H NMR (400 MHz, CDCl3) δ 7.86 (d, J = 16.4 Hz, 1H), 7.42 (s,
Gaussian 09 were carried out at the hybrid B3LYP level by 1H), 7.29 – 7.23 (m, 1H), 3.80 (t, J = 6.8 Hz, 2H), 3.20 (t, J = 5.6 Hz,
employing the split valence 6ꢀ31G* basis set 24
.
2H), 3.13 (t, J = 5.6 Hz, 2H), 2.73 (t, J = 6.8 Hz, 2H), 2.63 (s, 2H),
2.41 (s, 2H), 1.74 – 1.70 (m, 4H), 1.55 – 1.44 (m, 6H), 1.41 (s, 6H),
1.36 (m, 6H), 1.29 (s, 6H), 1.06 (s, 6H), 0.89 – 0.83 (m, 6H).
Synthesis
Compound 1
Compound 6a
A twoꢀphase mixture of 8ꢀhydroxyꢀ1, 1, 7, 7ꢀtetramethyljulolidineꢀ9ꢀ
carboxaldehyde (5.47 g, 20 mmol), 1ꢀchlorohexane (30 mL),
tetrabutyl ammonium bromide (0.3 g, 1 mmol), and 1 M NaOH (30
mL) was heated to reflux for 6 h. The mixture was diluted with ether
(50 mL) and washed with HCl (1 M, 15 mL) and water (25 mL). The
combined organic extracts were dried over MgSO4. After the
removal of the solvent under reduced pressure, the residue was
purified by column chromatography (hexane/acetone, 20/1, v/v) to
give a yellowish oil (6.65 g, 18.6 mmol) liquid in 93.0% yield.
MS (MALDIꢀTOF): m/z (M+, C23H35NO2): calcd: 357.27; found:
357.23.
1H NMR (400 MHz, Acetone) δ9.96 (s ,1H), 7.59 (s ,1H), 3.96 (t, J
= 6.8 Hz, 2H), 3.34 (t, J = 2.0 Hz, 2H), 3.28 (t, J = 2.0 Hz, 2H),
1.93ꢀ1.82 (m, 2H), 1.71 (m, 4H), 1.51 (tt, J = 8.6Hz, 5.6 Hz, 2H),
1.41 (d, J = 4.8 Hz, 6H), 1.40ꢀ1.33 (m, 4H), 1.23(s, 6H), 0.90 (t, J =
3.2 Hz, 3H).
A 50 mL threeꢀnecked flask was charged with NaH (0.37 g, 16.2
mmol) in dry THF (20 mL) under N2 atmosphere. Diethyl
(cyanomethyl) phosphonate (2.55 mL, 16.2 mmol) was slowly
introduced to the mixture dropwise by syringe. After the solution
became clear, compound 5a (3.09 g, 6.48 mmol) in THF (10 mL)
was added to the mixture which was then refluxed for 18 h. After
removal of THF under reduced pressure, the residue was directly
purified by the column chromatography on silica gel (hexane/ethyl
acetate, v/v, 40/1) to give an orange oil liquid 6a (2.39 g,4.79mmol)
in 74% yield. The compound 6a was cisꢀtransꢀisomer mixture,
Z/E=0.8:1.
MS (MALDIꢀTOF): m/z (M+, C34H48N2O): calcd: 500.38; found:
500.32.
1H NMR (400 MHz, CDCl3) δ 7.18 (d, J = 18.8 Hz, 1H), 6.88 (dd, J
= 3.6, 3.6 Hz, 1H), 6.67 – 6.50 (m, 2H), 4.94ꢀ4.74 (m, 1H), 3.69 (s,
2H), 3.06 (t, J = 4.8 Hz, 2H), 3.00 (s, 2H), 2.36 (s, 1H), 2.22 (s, 2H),
2.11 (s, 1H), 1.74 (dd, J = 5.2, 6.0 Hz, 2H), 1.62 (s, 4H), 1.39 (d, J =
21.4 Hz, 2H), 1.31 (s, 6H), 1.28 (d, J = 2.8 Hz, 4H), 1.19 (d, J = 8.4
Hz, 6H), 0.91 (d, J = 15.2 Hz, 6H), 0.83 (m, 3H).
Compound 5a
To a solution of compound 1 (3.57 g, 10 mmol) and 5, 5ꢀdimethylꢀ2ꢀ
cyclohexenone (1.38 g, 10 mmol) in absolute ethanol (20 mL) was
added NaOEt (2.23 g, 13 mmol). The solution was allowed to stir at
85 °C for 2 h, then water was added dropwise to quench the reaction.
After removal of the solvent under reduced pressure, the crude
product was purified using silica gel (hexane/ethyl acetate, v/v, 8/1)
to give 5a as red oil (3.7 g, 7.9 mmol) in 79.1% yield.
Compound 6b
The procedure for compound 6a was followed to prepare 6b from 5b
as orange oil with 65.7% yield.
MS (MALDIꢀTOF): m/z (M+, C38H56N2OS): calcd: 588.41; found:
588.32.
1H NMR (400 MHz, Acetone) δ 7.77 (d, J = 16.4 Hz, 1H), 7.25 (s,
1H), 7.03 (d, J = 16.2 Hz, 1H), 5.74 (d, J = 16.4 Hz, 1H), 3.67 (t, J =
6.8 Hz, 2H), 3.18 – 3.12 (m, 2H), 3.11 – 3.02 (m, 4H), 1.75 (m, 4H),
1.63 – 1.55 (m, 8H), 1.46 – 1.30 (m, 8H), 1.27 (s, 6H), 1.16 (s, 3H),
1.12 (s, 6H), 0.93 (s, 3H), 0.80 – 0.78 (m, 3H), 0.75 (t, J = 14.4 Hz,
3H).
MS (MALDIꢀTOF): m/z (M+, C32H47NO2): calcd: 477.36; found:
476.39.
1H NMR (400 MHz, Acetone) δ 7.32 (s, 1H), 7.06 (d, J = 16.2 Hz,
1H), 6.75 (d, J = 16.2 Hz, 1H), 5.80 (s, 1H), 3.67 (t, J = 12.0 Hz,
2H), 3.08 (t, J = 6.0 Hz, 2H), 3.01 (t, J = 6.0 Hz, 2H), 2.40 (s, 2H),
2.09 (s, 2H), 1.80 – 1.70 (m, 3H), 1.57 (dd, J = 6.0, 2.0 Hz, 4H),
1.44 (m, 3H), 1.31 (d, J = 3.6 Hz, 2H), 1.27 (s, 6H), 1.13 (s, 6H),
0.96 (s, 6H), 0.80 (t, J = 6.8 Hz, 3H).
Compound 7a
To a solution of compound 6a (1.5 g, 3.0 mmol) in toluene (20 mL)
was added a 1M solution of diisobutyl aluminum hydride in hexanes
(7.5 mL, 7.5 mmol) by syringe at ꢀ78 °C. The reaction was stirred at
this temperature for 2 h. Ethyl acetate (20 mL) was added to quench
the reaction which was then allowed to warm up to room
temperature. The solution was added by saturated aqueous
ammonium chloride (50 mL) and stirred vigorously for hydrolysis
until the color of organic layer became red. The organic phase was
extracted by AcOEt, washed with brine and dried over MgSO4.
After removal of the solvent under reduced pressure, the crude
product was purified by the column chromatography on silica gel
(hexane/ethyl acetate, v/v, 20/1) to give 8a as red oil (1.09g,
2.18mmol) in 72.5% yield.
Compound 5b
To a solution of ethanol (30 mL) was carefully added sodium metal
(0.31 g, 12.96 mmol) under N2 atmosphere. The solution was
vigorously stirred at room temperature until the sodium was
completely dissolved. 1ꢀButanethiol (1.52 mL, 12.96 mmol) was
added to the above solution by syringe, and the mixture was stirred
for 10 min followed by addition of isophorone oxide 236 (2 g, 12.96
mmol). The mixture became dark shortly and was stirred at room
temperature for another 1h to form intermediate compound 3.
Compound1 (4.63 g, 12.96 mmol) was added to the mixture which
was then heated to 75 °C for 6 h. After the removal of solvent, the
residue was directly purified by column chromatography on silica
6 | J. Name., 2012, 00, 1-3
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MS (MALDIꢀTOF): m/z (M+, C34H49NO2): calcd: 503.38; found: 3.07 (m, 4H), 2.54 (t, J = 6.8 Hz, 2H), 2.47 (d, J = 21.6 Hz, 4H),
502.72.
1.87 – 1.76 (m, 2H), 1.69 (s, 4H), 1.63 (s, 6H), 1.49 – 1.38 (m, 6H),
1H NMR (400 MHz, Acetone) δ 9.94 (d, J = 8.4 Hz, 1H), 7.29 (s, 1.37 (s, 6H), 1.29 (m, 4H), 1.25 (s, 6H), 0.95 (s, 6H), 0.87 – 0.79 (m,
1H), 7.27 (d, J = 12.8 Hz, 1H), 6.87 (d, J = 8.4 Hz, 1H), 6.24 (s, 1H), 6H).
5.70 (d, J = 8.2 Hz, 1H), 4.14 (t, J = 6.6 Hz, 2H), 3.07 (t, J = 6.0 Hz, 13C NMR (100 MHz, CDCl3) δ 176.34, 173.22, 157.67, 155.25,
2H), 3.01 (t, J = 1.6 Hz, 2H), 2.64 (d, J = 0.8 Hz, 2H), 2.29 (s, 2H), 152.89, 144.95, 144.56, 132.88, 129.90, 127.60, 127.09, 124.25,
1.61 – 1.54 (m, 8H), 1.50 – 1.39 (m, 4H), 1.28 (s, 6H), 1.14 (s, 6H), 122.89, 122.35, 117.87, 116.14, 112.76, 112.18, 111.88, 96.78,
0.95 (s, 6H), 0.83 (d, J = 7.6 Hz, 3H).
93.56, 76.15, 54.82, 47.52, 46.98, 41.93, 41.21, 39.84, 36.22, 35.83,
33.41, 32.68, 32.24, 31.94, 31.81, 30.93, 30.79, 30.33, 30.22, 30.04,
29.30, 28.34, 26.49, 26.04, 22.65, 21.97, 19.17, 14.09, 13.75.
Compound 7b
The procedure for compound 7a was followed to prepare 7b from 6b
as red oil with 85.7% yield.
MS (MALDIꢀTOF): m/z (M+, C38H57NO2S): calcd: 591.41; found:
591.32.
Conclusions
In this article, two novel second order nonlinear optical
chromophores zhꢀ1 and zhꢀ2 based on modified 8ꢀhydroxyꢀ1,1,7,7ꢀ
tetramethylꢀformyl julolidine as the donor, isophorone group as the
πꢀconjugated bridge and tricyanofuran (TCF) as the acceptor had
been synthesized in good overall yields (40–50%) and systematically
characterized by NMR, MS and UVꢀVis absorption spectroscopy.
What’s fascinating in this work is that we chose the stronger donor
group and the relatively weaker accepter than in the literature36 to
make the conjugation structure a balanced DꢀπꢀA molecule, yet we
obtained high thermal decomposition temperature (Td), significant
photoꢀphysical and electricꢀoptic properties. The energy gaps
between the ground state and the excited state together with
molecular nonlinearity were studied by UVꢀVis absorption
spectroscopy, DFT calculations and CV measurements. The gaps
between HOMO and LUMO energy level for the two chromophores
were 1.9511eV and 1.9513eV, respectively. At the same time, 985
and 987×10ꢀ30esu of very high β values were obtained by calculation.
Theoretical and experimental investigations suggested that planarity
of the molecule played a critical role in affecting the linear and
nonlinear properties of dipolar chromophores. The poling results of
guest–host EO polymers with 25 wt% of chromophores showed
chromophore zhꢀ1 and zhꢀ2 afforded the largest r33 values of 170 pm
Vꢀ1 and 101 pm Vꢀ1, respectively. In general, the unsubstituted
chromophore zhꢀ1 shows a bit better performances in aspects of
thermal, photoꢀphysical and r33 values prior to thiolated
chromophore zhꢀ2. All in all, these novel chromophores
accompanied by the advantages of highꢀyield synthesis, good
thermal stability and significant high nonlinear optical activity
showed brilliant broad application prospects in advanced material
devices.
1H NMR (400 MHz, CDCl3) δ 10.07 (d, J = 8.0 Hz, 1H), 7.86 (d, J =
16.4 Hz, 1H), 7.33 (s, 1H), 7.05 (d, J = 16.4 Hz, 1H), 6.95 (d, J = 8.0
Hz, 1H), 3.74 (t, J = 6.8 Hz, 2H), 3.12 (t, J = 5.2 Hz, 2H), 3.08 –
3.02 (m, 2H), 2.68 (s, 2H), 2.50 (t, J = 6.8 Hz, 2H), 2.45 (s, 2H),
1.68 – 1.63 (m, 4H), 1.43 (m, 6H), 1.34 (s, 6H), 1.28 (m, 6H), 1.22
(s, 6H), 0.96 (s, 6H), 0.85 (d, J = 6.0 Hz, 3H), 0.79 (t, J = 7.2 Hz,
3H).
Chromophore zh-1
A solution of compound 7a (0.6 g, 1.2 mmol) and TCF acceptor
(0.28 g, 1.4 mmol) in absolute ethanol (20 mL) was allowed to stir at
80 °C for 5 h, then after removal of the solvent under reduced
pressure, the crude product was purified by the column
chromatography on silica gel (hexane/ethyl acetate, v/v, 6/1) to give
zhꢀ1 as a black solid in 41.2% yield (0.34 g, 0.5 mmol).
MS (MALDIꢀTOF): m/z (M+, C45H56N4O2): calcd: 684.44; found:
684.42.
HRMS (ESI) (M + H)+: calcd: 684.4381; found: 684.4372.
1H NMR (400 MHz, Acetone) δ 8.02 (s, 1H), 7.35 (s, 1H), 6.99 (d, J
= 16.0 Hz, 1H), 6.83 (d, J = 16.4 Hz, 1H), 6.49 – 6.37 (m, 3H), 3.70
(t, J = 6.4 Hz, 2H), 3.13 (t, J = 6.4 Hz, 2H), 3.06 (t, J = 6.4 Hz, 2H ),
2.65 (s, 2H), 2.36 (s, 2H), 1.93 (t, J = 2.0 Hz, 12H), 1.65 (s, 6H),
1.63 – 1.58 (m, 4H), 1.45 (m, 2H), 1.15 (s, 6H), 0.94 (s, 6H), 0.81
(d, J = 6.4 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 176.38, 172.89, 157.45, 155.91,
150.27, 144.45, 144.08, 131.36, 130.92, 129.11, 128.86, 127.36,
126.95, 125.02, 122.70, 114.66, 112.92, 112.24, 112.03, 96.75,
96.53, 75.87, 54.35, 47.47, 46.95, 39.89, 39.71, 36.30, 32.68, 32.26,
31.94, 31.62, 31.46, 31.03, 30.90, 30.21, 30.07, 28.47, 28.26, 27.74,
26.59, 26.04, 22.66, 19.17, 14.09.
Chromophore zh-2
A solution of compound 7b (0.9 g, 1.2 mmol) and TCF acceptor
(0.28 g, 1.4 mmol) in absolute ethanol (20 mL) was allowed to stir at
80°C for 5 h, then after removal of the solvent under reduced
pressure, the crude product was purified by the column
chromatography on silica gel (hexane/ethyl acetate, v/v, 7/1) to give
zhꢀ2 as a black solid in 38.5% yield (0.36 g, 0.46 mmol).
MS (MALDIꢀTOF): m/z (M+, C49H64N4O2S): calcd: 772.47; found:
771.62.
HRMS (ESI) (M + H) +: calcd: 772.4731; found: 772.4723.
1H NMR (400 MHz, CDCl3) δ 8.13 – 8.00 (m, 1H), 7.94 (d, J = 16.0
Hz, 1H), 7.46 (d, J = 12.4 Hz, 1H), 7.39 (s, 1H), 7.16 (d, J = 16.4
Hz, 1H), 6.31 (d, J = 14.8 Hz, 1H), 3.75 (t, J = 6.4 Hz, 2H), 3.26 –
Acknowledgments
We are grateful to the National Natural Science Foundation of
China (No. 21504099 and No.21473227) for the financial support.
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