Synthesis and spectral tuning of novel triphenylamine-based derivatives containing electron donor-acceptor groups

Article abstract of DOI:10.1002/cjoc.201090177

This paper presents the investigation of tuning the color and photoluminescence of a range of triphenylaminebased derivatives with various substituent groups. The ultraviolet/visible absorption and fluorescence spectroscopy of the derivatives showed remarkable difference. The molecular geometry optimization demonstrated that the properties of the ground state and the excited state of the compounds have a close relationship with the substituent groups. Therefore, it is possible to tune the color and photoluminescence of the derivatives at molecular level. The cyclic voltammograms of these compounds were detected in methylene chloride at various scan rates. The thermal stabilities of the compounds were analyzed with the different scanning calorimetry and the thermogravimetry.

Full text of DOI:10.1002/cjoc.201090177

FULL PAPER
Synthesis and Spectral Tuning of Novel Triphenylamine-Based
Derivatives Containing Electron Donor-Acceptor Groups
Gao, Fang*(高放)
Liu, Jian(刘建)
Yang, Long(杨龙)
Wang, Qi(王琪)
Li, Hongru*(李红茹)
Zhang, Shengtao(张胜涛)
College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, China
This paper presents the investigation of tuning the color and photoluminescence of a range of triphenylamine-
based derivatives with various substituent groups. The ultraviolet/visible absorption and fluorescence spectroscopy
of the derivatives showed remarkable difference. The molecular geometry optimization demonstrated that the prop-
erties of the ground state and the excited state of the compounds have a close relationship with the substituent
groups. Therefore, it is possible to tune the color and photoluminescence of the derivatives at molecular level. The
cyclic voltammograms of these compounds were detected in methylene chloride at various scan rates. The thermal
stabilities of the compounds were analyzed with the different scanning calorimetry and the thermogravimetry.
Keywords spectroscopy, triphenylamine-core, stilbene derivatives, internal molecular charge transfer, molecular
geometry optimization
Introduction
The electron-donating substituent groups, the conju-
gated length, and the medium have been successfully
used to tune the optical properties of triphenylamine-
cored dyes.22,23 However, the comparable investigations
on the tuning spectroscopy of diphenylamine-cored dyes
with electron-donating and electron-withdrawing groups
were seldomly reported,24 in particular, whether it is fea-
sible to tune the color and photoluminescence of the dyes
with electron donor-acceptor substituent groups has not
been explored. In this paper, we employed various
push-pull substituent groups, including nitro, formyl and
methoxy groups, to tune the properties of the electron
density distribution and the electron transition of the
frontier orbitals of triphenylamine-cored stilbene deriva-
tives with the aim to regulate their spectroscopic proper-
ties. As well known, nitro and formyl groups have elec-
tron-withdrawing nature, and methoxy group has elec-
tron-donating nature. Consequently, the extent of inter-
nal charge transfer of the derivatives could be different
from each other. This means that the electron density
distribution of chromophore part (i.e. stilbene part) of
the dyes could be different from each other, which could
cause different characteristics of the absorption and
fluorescence spectroscopy. In order to deeply under-
stand interrelationship between the chemical structures
and the spectroscopic properties, the molecular geome-
try optimization and the electrochemical properties of
the dyes were investigated in this article.
In recent years, the development of novel organic
dyes with different color and photoluminescence has re-
ceived considerable attention due to their applications in
various areas such as material and biomedical fields.1-14
In the search for high quality organic dyes with ideal
spectroscopic nature, it was found that the spectral char-
acteristics and applications of the dyes have a strong rela-
tionship with their chemical structures.15,16 Hence, the
investigation of the effects of the chemical structures on
the absorption and fluorescence spectroscopy of the
compounds emerges as very important subjects in organic
photochemistry and photophysics.17-20
Bis(styryl)benzene derivatives with donor-π-donor,
donor-π-acceptor and donor-acceptor-donor structural
motifs have excellent optical properties,21 while two fac-
tors play key roles in the regulation of their molecular
spectroscopic properties: (1) the conjugated length of the
molecules, which could be tuned by the insertion of
phenylene-vinylene or phenylene-butadienylene groups,
(2) the extent of the symmetrical charge transfer from
the ends of the molecules to the middle, or vice versa.
These regulations could lead to a shift of the absorption
and emission to longer wavelength compared to those of
stilbene. In other words, the spectroscopic properties of
these molecules could be affected by the extent of in-
tramolecular charge transfer, which could be regulated
by the substituent groups. Thus, the HOMO-LUMO
gaps of the compounds can be tuned.
*
E-mail: fanggao1971@gmail.com; hrli@cqu.edu.cn
Received November 1, 2009; revised January 6, 2010; accepted March 4, 2010.
Project supported by the National Natural Science Foundation of China (Nos. 20776165, 20702065, 20872184), Chongqing Science & Technology
Commission (Nos. CSTC2008BA4020, CSTC2009BB4216), A Foundation for the Author of National Excellent Doctoral Dissertation of PR China
(No. 200735) and Innovative Talent Training Project, the Third Stage of “211 Project” of Chongqing University (No. S-09103).
950
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 950— 960

Synthesis and Spectral Tuning of Novel Triphenylamine-Based Derivatives
Figure 1 Chemical structures of the compounds studied in this paper.
Experimental
The fluorescence quantum yields of the compounds
in solvents with different polarities were measured
based on the following equation:27,28
Reagents and materials
Organic solvents were obtained from Chongqing
Medical and Chemical Corporation. Other chemicals
and reagents were purchased from Aldrich unless oth-
erwise specified. The organic solvents were dried using
standard laboratory techniques according to well-
known methods.25 The starting materials were further
purified with redistillation or recrystallization before use.
Triphenylamine-cored stilbene derivatives (Figure 1)
were synthesized in our laboratory.
n02 A0 If (λf )dλf
∫
0
Фf＝Фf
n2 A If0 (λf )dλf
∫
wherein n0 and n are the refractive indices of the sol-
vents, A0 and A are the optical densities of the reference
and the sample at excitation wavelength respectively, Φ
f
0
and Φ are the quantum yields of the reference and the
f
sample respectively, and the integrals denote the area of
the fluorescence bands for the reference and the sample
respectively.
Instruments
－5
The UV/visible absorption spectra (1×10 mol/L)
were recorded with a Cintra spectrophotometer. The
－5
Molecular geometry optimization
fluorescence spectra (1×10
mol/L) were checked
The calculations were performed by means of the
Gaussian 03 program package.29 The geometry optimi-
zation on the ground electronic state (S0) was carried out
with HF method and at the DFT level using the B3LYP
to calculate the energies;30-32 while the CIS (Configura-
tion Interaction Singles-excitation) has been employed
to optimize the geometries of the first singlet excited
state (S1), and TDDFT (time-dependent DFT) was used
to obtain the energies of 1 to 4.
with Shimadzu RF-531PC spectrofluorophotonmeter.
－6
－5
Rodamin 6G in ethanol (Φ＝0.94, 1×10 —1×10
mol/L) was used as reference to determine the fluores-
cence quantum yields of the compounds herein.26 To
avoid self-quenching of fluorescence emission, low
－6
concentration of the samples (1×10 mol/L) was pre-
pared for the survey of fluorescence quantum yields.
The melting point was detected using a Beijing Fukai
melting point apparatus. Nuclear magnetic resonance
(NMR) spectroscopy was conducted at room tempera-
ture on a Bruker 500 MHz apparatus with tetramethyl-
silane (TMS) as an internal standard and CDCl3 as sol-
vent. Elemental analysis was performed by a CE440
elemental analysis meter from Exeter Analytical Inc.
Electrochemistry
Electrochemical measurement was carried out using
a Shanghai Chenhua working station. Two Pt work
electrodes and an Ag/Ag＋ reference electrode, namely
Chin. J. Chem. 2010, 28, 950— 960
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
951

Gao et al.
FULL PAPER
three electrodes system, were included in cell. Typically,
a 0.05 mol/L solution of tetra-n-butylammonium
hexafluorophosphate in methylene chloride containing
of dyes was bubbled with argon for 15 min before the
measurement.
solvent was removed in vacuum after the filtration of the
solid materials. The crude product was washed using
water for five times. 3,4,5-Trimethoxyl-benzyl alcohol
was purified with column chromatography using ben-
zene as eluent. Yield 90%, color: light yellow, 1H NMR
(CDCl3, 500 MHz) δ: 6.42 (s, 2H, ArH), 5.10 (s, 1H,
ArCH2OH), 4.52 (s, 2H, CH2), 3.95 (s, 3H, ArOCH3),
3.83 (s, 6H, ArOCH3). Bromination of 3,4,5-trimethoxyl-
benzyl alcohol was carried out in tetrahydrofuran using
phosphorus tribromide as bromine reagent under reflux.
The solvent and excess phosphorus tribromide were re-
moved in vacuum. The crude product was washed using
distilled water for 5 times. 3,4,5-Trimethoxyl-benzyl
bromide was purified with recrystallization in ben-
zene/cyclohexane (V∶V＝3∶1). Yield 70%, color:
Thermal analysis
The differential thermal analysis (DTA) and thermo-
graving (TGA) were conducted under nitrogen flow in
Shimad－zu DTG-60H equipment at the heating rate 10
1
℃•min .
Preparation of 1— 4
The derivatives 1 to 4 are depicted in Scheme 1.
4-Formyl-triphenylamine and 4',4'-diformyl-triphenyl-
amine were prepared according to well-known methods
with modified procedure.33
3,4,5-Trimethoxyl-benzylbromide 3,4,5-Trimeth-
oxyl-benzaldehyde (30.6 mmol, 6.00 g) was deoxidized
with sodium borohydride (40.7 mmol, 1.55 g) in 60 mL
methyl alcohol. The reaction was performed at room
temperature under argon for 2 h. After the reaction, the
1
white, m.p. 45—47 ℃; H NMR (CDCl3, 500 MHz) δ:
6.35 (s, 2H, ArH), 4.10 (s, 2H, CH2), 3.77 (s, 3H,
ArOCH3), 3.31 (s, 6H, ArOCH3).
3,4,5-Trimethoxyl-4-benzylphosphonate (8) The
compound was prepared by making 3,4,5-trimeth-
oxyl-benzylbromide (11.53 mmol, 3.00 g) react with
Scheme 1 Synthesis route of derivatives 1 to 4
952
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 950— 960

Synthesis and Spectral Tuning of Novel Triphenylamine-Based Derivatives
triethyl phosphite (10 mL) at 130—160 ℃ for 6 h. Af-
ter excess triethyl phosphite was removed in vacuum,
the obtained crude 3,4,5-trimethoxyl-4-benzylphos-
phonate was directly used in the next step without fur-
ther purification.
After evaporated in vacuum, 3 was purified with column
chromatography using V(benzene)∶V(AcOEt)＝45∶1
as eluent, which was further purified with recrystalliza-
tion in methylene chloride. 3: Yellow solid, yield 50%,
m.p. 61—63 ℃; 1H NMR (CDCl3, 500 MHz) δ: 9.83 (s,
1H, ArCHO), 7.70 (d, J＝8.5 Hz, 2H, ArH), 7.46 (d, J
＝8.5 Hz, 2H, ArH), 7.36 (t, J＝8.0 Hz, 2H, ArH), 7.17
—7.21 (m, 3H, ArH), 7.14 (d, J＝8.0 Hz, 2H, ArCH＝
CH), 7.07 (d, J＝8.5 Hz, 2H, ArH), 6.99 (s, 2H, ArH),
6.74 (s, 2H, ArH), 3.92 (s, 6H, ArOCH3), 3.87 (s, 3H,
ArOCH3); 13C NMR (CDCl3, 125 MHz) δ: 56.165,
60.990, 103.576, 119.922, 125.263, 125.981, 126.358,
127.193, 127.622, 128.419, 129.441, 129.805, 131.324,
133.022, 133.876, 138.044, 145.509, 146.029, 153.099,
153.451, 190.449. Anal. calcd for C30H27NO4: C 77.40,
H 5.85, N 3.01; found C 77.33, H 5.93, N 3.06.
4-(p-Nitro-phenylethylene)yl-4'-formyl-triphenyl-
amine (4) 4,4'-Diformyl-triphenylamine (1.70 mmol,
0.51 g) and p-nitro-phenylacetic acid (5.10 mmol, 0.91 g)
were mixed fully and piperdine (0.5 mL) was added into
the mixture. The resultant mixture was heated at 100 ℃
for 2 h, than at 120 ℃ for 1 h till black solid was
formed. The product was purified with column chroma-
tography using V(benzene)∶V(ethyl acetate)＝45∶1 as
eluent. Further purification was conducted with recrys-
tallization in anhydrous ethanol. 4: Red solid, yield 45%,
m.p. 172—173 ℃; 1H NMR (CDCl3, 500 MHz) δ: 9.84
(s, 1H, ArCHO), 8.21 (d, J＝9.0 Hz, 2H, ArH), 7.72 (d,
J＝9.0 Hz, 2H, ArH), 7.62 (d, J＝9.0 Hz, 2H, ArH),
7.50 (d, J＝8.5 Hz, 2H, ArH), 7.37 (t, J＝6.8 Hz, 2H,
ArH), 7.26 (d, J＝3.0 Hz, 1H, ArCH＝CH), 7.22 (d, J＝
6.0 Hz, 1H, ArCH＝CH), 7.17 (t, J＝11.0 Hz, 5H, ArH),
7.10 (d, J＝8.5 Hz, 2H, ArH); 13C NMR (CDCl3, 125
MHz) δ: 120.522, 124.198, 125.496, 125.529, 125.738,
126.525, 126.770, 128.314, 129.866, 129.924, 131.334,
132.373, 132.410, 143.898, 145.925, 146.676, 146.781,
190.445. Anal. calcd for C27H20N2O3: C 77.13, H 4.79,
N 6.66; found C 77.20, H 4.83, N 6.59.
4-(3',4',5'-Trimethoxyphenylethylene)yl-triphenyl-
amine (1)
3,4,5-Trimethoxyl-4-benzylphosphonate
(4.1 mmol, 1.32 g) was first mixed with 4-formyl-
triphenylamine (3.0 mmol, 0.82 g) in 50 mL dry tetra-
hydrofuran, then sodium methoxide (7.3 mmol, 0.39 g)
was added as bases to initiate the reaction, which was
proceeded at room temperature overnight. After the fil-
tration of solid materials and vacuum evaporation of the
solvent, the reactant mixture was dissolved in chloro-
form and washed by water. The organic layer was dried
with anhydrous magnesium sulphate. After evaporated
in vacuum, 1 was purified with column chromatography
using benzene as eluent, which was further purified with
recrystallization in methylene chloride. 1: Yellow solid,
1
yield 55%, m.p. 62—63.5 ℃; H NMR (CDCl3, 500
MHz) δ: 7.37 (d, J＝8.5 Hz, 2H, ArH), 7.26 (t, J＝8.0
Hz, 4H, ArH), 7.12 (s, 2H, ArCH＝CH), 7.10 (s, 2H,
ArH), 7.02—7.06 (m, 4H, ArH), 9.94 (d, J＝7.5 Hz, 2H,
ArH), 6.72 (s, 2H, ArH), 3.91 (s, 6H, ArOCH3), 3.87 (s,
3H, ArOCH3); 13C NMR (CDCl3, 125 MHz) δ: 56.152,
60.994, 103.403, 123.083, 123.577, 124.532, 126.974,
127.290, 127.708, 129.316, 131.370, 133.433, 147.374,
147.559, 153.426. Anal. calcd for C29H27NO3: C 79.61,
H 6.22, N 3.20; found C 79.55, H 6.29, N 3.13.
4-(p-Nitro-phenylethylene)yl-triphenylamine (2)
4-Formyl-triphenylamine (1.00 mmol, 0.30 g) and
p-nitro-phenylacetic acid (1.25 mmol, 0.23 g) were first
thoroughly mixed, piperdine (0.3 mL) was then added.
The mixture was heated at 100 ℃ for 2 h, than at 120
℃ for 1 h until black solid was formed. The product
was purified with column chromatography using ben-
zene/ethyl acetate (V∶V＝45∶1) as eluent. Further
purification was conducted with recrystallization in pure
alcohol. 2: Red solid, yield 50%, m.p. 136—138 ℃; 1H
NMR (CDCl3, 500 MHz) δ: 8.20 (d, J＝9.0 Hz, 2H,
ArH), 7.60 (d, J＝9.0 Hz, 2H, ArH), 7.41 (d, J＝7.0 Hz,
2H, ArH), 7.18—7.22 (m, 4H, ArH), 7.11 (s, 1H, ArCH
＝CH), 7.07 (d, J＝4.50 Hz, 4H, ArH), 7.06 (s, 1H,
ArCH＝CH), 7.04 (t, J＝2.25 Hz, 4H, ArH); 13C NMR
(CDCl3, 125 MHz) δ: 122.715, 123.600, 124.188,
124.986, 126.336, 128.001, 129.425, 132.896, 144.341,
146.399, 147.228, 148.580. Anal. calcd for C29H20N2O2:
C 79.57, H 5.14, N 7.14; found C 79.65, H 5.20, N 7.06.
4-(3",4",5"-Trimethoxyl-phenylethylene)yl-4'-for-
myl-triphenylamine (3) 3,4,5-Trimethoxyl-4-benzyl-
phosphonate (4.5 mmol, 1.43 g) reacted with
4,4'-diformyl-triphenylamine (1.5 mmol, 0.45 g) in 60
mL dry tetrahydronfuran using sodium methoxide (10.0
mmol, 0.85 g) as base at room temperature overnight.
After the filtration of solid materials and the evaporation
of solvents in vacuum, the reactant mixture was dis-
solved in chloroform and washed by water. The organic
layer was dried with anhydrous magnesium sulphate.
Results and discussion
Synthesis
Among the different strategies to synthesize dyes,
the most important factor is the choice of the base in the
reaction. More byproducts were generated when sodium
hydride was used to prepare 1 and 3 due to its strong
alkalinity. While the alkalinity of sodium ethoxide was
not strong enough to make the reaction occurred, so-
dium methoxide was demonstrated to be effective for
the preparation of 1 and 3. Owing to the electron-
withdrawing effect of nitro group of p-nitro-
phenylacetic acid and the electron-donating of
triphenylamine core, 2 or 4 could be synthesized by
heating condensation reaction of p-nitro-phenylacetic
acid and 6 or 7 in very weak base such as piperidine.
One of the key tricks for the preparation of 3 and 4 is the
molar ratios of the starting materials. Although the cul-
tivation of single crystals was failed, the pure products
Chin. J. Chem. 2010, 28, 950— 960
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
953

Gao et al.
FULL PAPER
were obtained by flash column chromatography and
Table 1 Maximal absorption wavelength (λa) and the molar
extinction coefficients (ε) of 1 to 4a
1
recrystallization. Clean H NMR and 13C NMR spectra
as well as narrow-range melting temperature of the dyes
were obtained.
Solvent
Compound
Benzene THF EtOAc CH2Cl2 CH3CN
10－
ε
ε
ε
ε
0.234
359.2
0.284 0.231
364.0 364.8
0.248
365.6
0.327
364.0
5
UV/visible absorption spectroscopy
1
2
3
λa
10－
A typical UV/visible absorption spectroscopy of 1 to
5 in benzene was presented in Figure 2. 1 and 2 exhibit
double absorption peaks from 280 nm to 550 nm. The
first absorption peak of 1 and 2 is similar to the absorp-
tion of triphenylamine-core, which indicates that this
absorption band could be mainly from local electron
transition of triphenylamine core. The second absorption
peak of 1 and 2, namely the maximal absorption peak,
could be ascribed to molecular (π, π*) electron transi-
tion.34 While as contrast, 3 and 4 display only one broad
absorption band. The results imply that electron of for-
myl group could participate in the overall molecular
electron hybridization to form π orbital, which causes a
considerably broad absorption band. The results demon-
strate that the electron transition of the derivatives could
be altered by the substituent groups. The absorption
spectral data of 1 to 4 in various solvents are listed in
Table 1. The data show that the maximal absorption
wavelength of the derivatives bearing with elec-
tron-withdrawing groups is much red-shifted, especially
for 2 and 4 (2 to 1: ca. 60 nm red-shift). This is a strong
indication that the long-wavelength absorption of
triphenylamine-based stilbene derivatives could be as-
signed to highly allowed (π, π*) electron transition with
internal charge transfer.35 Owing to the role of elec-
tron-accepting substituent group, the extent of internal
charge transfer of 3 could be larger than that of 1. Like-
wise, the extent of internal charge transfer of 2 and 4
could be larger than that of 1 as well. This could lower
the HOMO-LUMO energy gap of 2, 3 and 4, which
could lead to the red-shift of the maximal absorption
wavelength of 2, 3 and 4, and cause the different colors,
as shown in Figure 3(a).
5
5
5
0.322
420.2
0.261 0.310
422.8 428.0
0.300
429.2
0.310
419.2
λa
10－
λa
10－
λa
0.320
364.0
0.344 0.362
368.8 370.4
0.415
376.0
0.410
372.0
0.330
0.368 0.320
406.0 402.0
0.387
410.0
0.343
408.8
4
410.0
－
－
a
1
1
λa: nm, ε: mol •L•cm .
Fluorescence spectroscopy and fluorescence quan-
tum yields
The maximal emission wavelength of the derivatives
Figure 3 (a) Colors of 1 to 4 in benzene and (b) photolumines-
cence of 1 to 4 in benzene photoexcited by 365 nm.
with electron-withdrawing groups is red-shifted. Typical
comparison of the fluorescence emission is presented in
Figure 4. The fluorescence intensity of 2, 3 and 4 is
much lower than that of 1, but their maximal emission
wavelength is red-shifted with respect to that of 1. It is
interesting that the fluorescence intensity of 4 is higher
than 2, while its maximal absorption and fluorescence
emission is blue-shifted with respect to that of 2, which
indicates that the extent of internal charge transfer of 4
could be lower than that of 2.
Figure 2 UV/visible absorption spectra of 1 to 5 in benzene. c:
1× 10－ 5 mol/L.
954
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 950— 960

Synthesis and Spectral Tuning of Novel Triphenylamine-Based Derivatives
Figure 4 Fluorescence spectra of 1 to 4 in benzene. c: 5× 10－
6
mol/L. Excited at 350 nm, slit widow: Ex: 1.5 nm, Em: 3 nm.
The maximal fluorescence emission wavelength and
the fluorescence quantum yields of these compounds are
presented in Table 2. As compared with 1, 2 exhibits
100—150 nm red-shift and 3 shows 50—60 nm batho-
chromic shift in various solvents. On the other hand, 1
has much larger relative fluorescence quantum yields
than 2, 3 and 4. This could be ascribed to the greater
extent of internal charge transfer of 2, 3 and 4, thus the
electron density distribution in the stilbene part of the
Figure 5 Typical fluorescence spectra of 1 and 3 in various
three derivatives is lowered, and the (π, π*) electron
transition is thus decreased, and the internal conversion
(S1, S0) is increased.36,37 However, methoxy group in-
creases the electron density distribution in stilbene part
of 1, and its (π, π*) electron transition is thus increased.
Hence, 1 exhibits exceptionally excellent photolumi-
nescence nature, as shown in Figure 3(b). Table 2 also
suggests that the fluorescence emission of 2, 3 and 4 is
much more sensitive to the polarity of the solvents. A
typical comparison of the variation of fluorescence
spectroscopy of 1 and 3 with the increasing of acetoni-
trile ratio in benzene/acetonitrile binary solvents is
shown in Figure 5. The fluorescence spectroscopy of 3
shows remarkable change with the increasing ratio of
acetonitrile. It is well known that intramolecular charge
transfer is strongly dependent on the solvent po-
volume ratios of benzene/acetonitrile. (a) Excited at 350 nm, slit
window: Ex: 1.5 nm, Em: 1.5 nm; (b) excited at 350 nm, slit
window: Ex: 3 nm, Em: 3 nm.
larity.38 Because 2, 3 and 4 could have greater internal
charge transfer properties, the fluorescence emission of
these compounds is more sensitive to the solvent polar-
ity.
Changes on the dipole moments between the excited
state and the ground state
We further estimated the changes of the dipole mo-
ments between the excited state and the ground state
based on Lippert equation:39,40
2
2 µ －µ
(
)
e
g
(2)
(3)
hc(ν －ν )
∆f＋const
＝
abs
em
4πε0a3
Table 2 Maximal fluorescence emission wavelength (λe: nm)
and the fluorescence quantum yields (Φ) of 1 to 4
Solvent
2
Compound
⎛
⎞
ε－1
n －1
Benzene
THF EtOAc CH2Cl2 CH3CN
∆f＝
－
⎜
⎟
2n2＋1
2ε＋1
⎝
⎠
λe
Φ
418.0
0.78
431.0
0.86
430.0
0.81
442.0
0.99
451.0
0.77
1
2
wherein h is Planck’s constant, c is the speed of light,
and ∆ƒ is called the orientation polarizability. ν
ν
λe
Φ
540.0
0.504
582.0
589.0
abs, em
are the wavenumbers of the absorption and emission, n
is the refractive index, and ε is the relative low-
frequency dielectric constant of the solvents.
Lippert equation considers the chromophore group as
a dipole, which locates in a cavity with a radius of a in a
continuous solvent-dipole environment, and this equa-
tion describes a solvent effect of the index of refraction
0.0623 0.0738 weak
weak
510.0
λe
Φ
471.0
0.760
480.0
0.175
486.0
498.0
3
4
0.160 0.0251 0.00894
λe
Φ
526.0
0.677
564.0
0.127
558.0
0.107
weak
weak
Chin. J. Chem. 2010, 28, 950— 960
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
955

Gao et al.
FULL PAPER
and relative dielicetric constant. Consequently, the lin-
ear correlation between Stokes shifts and ∆ƒ do not re-
flect some special interaction between the fluorophore
and solvent molecules such as hydrogen bonding. Be-
cause 2 and 4 exhibit too weak photoluminescence in
polar solvents, we did not perform Lippert equation for
these two derivatives. Figure 6 plotted the Stokes shift
as a function of the solvent orientation polarizability (∆ƒ)
for the derivatives 1 and 3. The linear correlations be-
tween Stokes shift and orientational polarizability indi-
cates the dipolar solvent effects. The equations were
obtained as follows:
should be larger than that of 1. The main reason is that
the theoretical calculation is based on the single mole-
cule in vacuum, thus the solvent effect and solute-solute
interaction is not considered. In vacuum, some negative
charges are supposed to be transferred to carbon atom of
formyl group and it results in the abnormally decreasing
of dipole moment at the excited state in theory.41 The
results in turn imply that the intramolecular charge
transfer states of 3 could be destabilized by the solvents.
The HOMO and LUMO orbitals in the ground and
excited states are further analyzed. Obvious internal
charge transfer occurs in LUMO for the derivatives, as
shown in Figure 7. We emphasize the comparison of 1/3
and 2/4 respectively. Figure 7 shows that the electron
density distribution is extensively distributed in formyl
group of LUMO. As a consequence, the overlap extent
of HOMO and LUMO of 3 is lower than that of 1, and
the probability of (π, π*) electron transition is decreased,
and the fluorescence emission is diminished. Obviously,
the electron density distribution of stilbene part 1 is
higher and the (π, π*) electron transition was thus
strengthened,42,43 and the fluorescence is much enhanced.
While for 2 and 4, formyl group offsets partly the elec-
tron-withdrawing effect of nitro group in the opposite
position of LUMO, and the electron density distribution
is distributed largely. Consequently, the overlapping
extent of HOMO and LUMO of 4 is higher than that of
2, and the probability of (π, π*) electron transition is
enhanced, and thus 4 has a stronger emission than 2.
Furthermore, Figure 7 demonstrates that the electron
hybridization of π orbital of phenyl ring and n orbital
(including the lone pair electrons of triphenylamine core
and formyl group) takes place, and the emission is origi-
nal from (π, π*) electron transition.
1: Y 4392.5X 3809.6, 3: Y 3272.3X 6089.7
＝
＋
＝
＋
Thus, the dipole moment changes between the excited
state and ground state could be calculated from the
slopes. Table 3 shows that 3 does have larger dipole
moment changes than 1, which confirms that it has more
internal charge transfer at the excited state.
Figure 6 Relationship between Stokes’ shifts of 1, 3 and the
orientation polarizability (∆ƒ) of solvents respectively.
Table 4 lists the theoretically calculated HOMO-
LUMO gap in the S0 and S1. As compared with that of 1,
the smaller HOMO-LUMO energy gaps in the S0 and S1
of 2 and 4 could account for the red-shift of the maximal
absorption and emission. It is interesting that the energy
gaps of 4 are higher than those of 2 in the S0 and S1,
which interprets why the maximal absorption and emis-
sion of 4 is blue-shifted with respect to that of 2. While
in theory, the HOMO-LUMO energy gaps of 3 are a
little bigger than those of 1. The result was somewhat
abnormal because that the absorption and emission
spectroscopy of 3 are red-shifted with respect to 1. The
reason could be the same as that which lead to abnormal
dipole moment change of 3 in the excited state, which
further indicates that the internal charge transfer state of
3 could be destabilized by the solvent effects and the
HOMO-LUMO gaps are thus reduced in the solvents.
Table 3 Change of dipole moment between the excited state
and ground state respectively obtained from experiments and
theoretical calculations
Dipole moment change ∆µ/D
From experiment
1
2
3
4
2.419
2.433
From theorya
0.581 3.068 － 0.221 2.579
1 D＝ 3.336× 10－ 30 C•m, a in vacuum, for single molecule.
Geometry optimization
We utilized quantum chemical method to theoreti-
cally calculate the dipole moment changes between the
excited state and ground state. Table 3 shows that the 2
and 4 have much larger dipole moment changes between
the excited state and the ground state than 1, and the
dipole moment change of 2 is larger than that of 4. The
results suggest that the extent of internal charge transfer
has an order of 1＞2＞4. We shall point out that the
dipole moment changes between the excited state and
ground state of 3 is smaller than that of 1 in theory, even
it is a minus number. It is strange because the maximal
absorption and emission wavelength of 3 is longer than
that of 1, which means that dipole moment change of 3
Cyclic voltammograms
The cyclic voltammograms of 1 to 4 were acquired
－
1
at the scan rates from 50 to 200 mV•s . As shown in
Figure 8, no corresponding redox potentials are ob-
served which demonstrates that redox processes of the
derivatives dyes are characterized with irreversible na-
956
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 950— 960

Synthesis and Spectral Tuning of Novel Triphenylamine-Based Derivatives
Figure 7 Electron density distributions of frontier orbitals of 1 to 4 in the S0 and S1.
Table 4 Energy gaps of HOMO and LUMO obtained from theoretical calculations in the ground state (S0) and the excited state (S1)
1
2
3
4
S0
S1
S0
S1
S0
S1
S0
S1
EHOMO/eV
ELUMO/eV
－
－
4.878
1.108
3.770
－
－
5.656
1.505
4.151
－
－
5.174
2.189
2.985
－
－
5.034
2.375
2.659
－
－
5.224
1.446
3.778
－
－
5.863
1.784
4.079
－
－
5.491
2.369
3.122
－
－
6.409
2.565
3.844
Energy gap/eV
ture under all sweeping rates. The redox processes of 1
to 4 are dominated by the diffusion-controlled electron
transfer reactions resulting from linear increasing of
peak currents with the square root of scan rates.44 The
redox potentials of 1 to 4 at 0.1 V•s－ 1 scan rate are listed
in Table 5. For comparison, the cyclic voltammograms
of 5, 6 and 7 were detected. Seen from Table 5, the oxi-
dation potentials of 1 to 4 (0.689, 1.102, 1.282, 1.111 V)
could be assigned to triphenylamine-core. Firstly, we
particularly compare the redox potentials of 1 and 2.
Because nitro group is a powerful electron-withdrawing
part and methoxy group is an electron-donating group,
the first oxidation peak potentials of 2 (1.102 V) is
higher than that of 1 (0.689 V). While, the first reduc-
tion peak of 1 (0.664 V) is higher than that of 2 (0.578
V). This implies that the electron-donating group lowers
the oxidation peak potential of triphenylamine-core,
while the electron-withdrawing group lowers the reduc-
tive potential of triphenylamine-core derivatives. Thus,
the higher oxidation potential of 6 (1.229 V) and 7
(1.338 V) than 5 (1.028 V) could be ascribed to the
electron-withdrawing role of formyl group as well. This
is also explain why the first oxidation potential of 3
(1.282 V) and 4 (1.111 V) is higher than that of 1 (0.689
V) respectively.
onset of the longest absorption wavelength at ten percent
of the maximal UV peak.47,48 Table 6 shows clearly that
the HOMO energy of 2 is higher than that of 1, but its
LUMO is smaller than that of 1. While, the energies of
the HOMO and LUMO of 3 are lower than those of 1
respectively. Furthermore, the HOMO-LUMO gaps of 2
and 4 are lower than that of 1. The HOMO-LUMO gap
of 3 is lower than that of 1, and the HOMO-LUMO gap
of 4 is lower than that of 2 too. This suggests that not
only the HOMO and LUMO energies of the derivatives
could be mediated, but the HOMO-LUMO gaps could
be regulated. These make it possible to tune the color
and photoluminescence of the derivatives.
Thermal analysis
The analysis of the thermal properties was conducted
with differential thermal analysis (DTA) and thermo-
gravimetric analysis (TGA) under a nitrogen atmosphere.
The endothermic peaks determined by DTA were de-
tected at 65.41, 144.11, 70.54 and 180.49 ℃ for 1 to 4
respectively as presented in Figure 9. If we consider that
－
1
the heating rate was 10 ℃•min , the DTA data are
fairly close to the melting points of these compounds
determined with melting point apparatus. As shown in
Figure 9, the exothermic peaks were detected at 397.41,
382.74, 403.90 and 331.89 ℃ for 1 to 4 respectively.
Interestingly, 1 and 3 exhibit more thermal stability than
We further estimated HOMO-LUMO gap from the
optical band gap (Eg), which was calculated from the
Chin. J. Chem. 2010, 28, 950— 960
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
957

Gao et al.
FULL PAPER
Figure 8 Cyclic voltammetries of 1 to 4 in methylene chloride at various scan rates.
Table 5 Redox potentials of 1 to 7 determined in methylene
chloride at 0.1 V•s－ 1 scan rate
with nitrogen gas. The weight loss of 2 (MW＝392.45)
was 52.65% at 382.74 ℃, which is also close to the loss
of nitro-styrene part (MW＝225.24), meaning that the
part of triphenylamine-core could be left. The weight
loss of 3 (MW＝465.54) was 51.29% at 403.90 ℃,
which is close to the loss of branches of 3 including
(trimethoxystyrene)yl and formyl groups (MW: total＝
252.30). Thus, the part of triphenylamine (MW＝245.32)
could be left. The weight loss of 4 (MW＝420.46) was
40.54%, which is close to the loss of the branches of 4
including (nitrostyrene)yl and formyl groups (MW:
total＝207.22) as well. Likewise, the part of chemical
composition of triphenylamine (MW＝245.32) could be
left. The analysis shows that the derivatives have good
thermal stabilities, and the thermal stabilities of the de-
rivatives have an interrelationship with their chemical
structures.
Derivative Oxidation potential/V
Reduction potential/V
0.664, － 0.718
1
2
3
4
5
6
7
0.689, 0.263
1.102
0.578, － 0.194, － 0.609
0.526, － 0.354
1.282, 0.818
1.111, 0.916
1.028
0.762, 0.686
0.42, － 0.257, － 0.567
0.601, － 0.468, － 0.897
0.707, － 0.386, － 0.749
1.299
1.388
2 and 4, which indicates that formyl group could be an
important factor on the enhancement of thermal stability.
The weight loss of 1 (MW ＝ 437.53) reached
81.244% at 397.41 ℃ , indicating the most of its
chemical composition was decomposed and moved out
Table 6 Estimated HOMO and LUMO energies of compounds 1 to 4 from cyclic voltammograms
λonset/nm Gap/eV ELUMO/eV EHOMO/eV
EOX
412.0 3.00 0.69 5.03 8.03
5.44 7.85
Derivative
ELUMO-HOMO
3.00
1
2
3
4
－
－
514.4
427.2
458.6
2.41
2.90
2.70
1.10
1.28
1.11
－
－
2.41
－
5.62
－
8.52
2.90
－
5.45
－
8.15
2.70
Eg＝ 1240/λ, LUMO (eV)＝
－ －
EOX 4.34,45,46 HOMO (eV)＝ LUMO－ Eg, λonset: the longest absorption wavelength at ten percent of the
maximal UV peak.
958
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 950— 960

Synthesis and Spectral Tuning of Novel Triphenylamine-Based Derivatives
Figure 9 DTA and TGA of compounds 1 to 4.
Conclusions
3
4
5
6
7
Ning, Z. J.; Zhang, Q.; Wu, W. J.; Pei, H. C.; Liu, B.; Tian,
H. J. Org. Chem. 2008, 73, 3791.
Velusamy, M.; Thomas, K. R. J.; Lin, J. T.; Hsu, Y. C.; Ho,
K. C. Org. Lett. 2005, 7, 1899.
Horiuchi, T.; Miura, H.; Uchida, S. J. Am. Chem. Soc. 2004,
126, 2218.
New triphenylamine-core stilbene derivatives with
various electron donor-acceptor groups were developed.
The absorption and fluorescence spectroscopy of the
derivatives could be efficiently tuned by the substituent
groups. The substituent groups play significant roles on
the electron transition properties of the derivatives. The
electron density distribution in the frontier orbitals of
the derivatives has a close relationship with the sub-
stituent groups, and thus the HOMO-LUMO gap could
be mediated. These could be the deep reasons on the
regulation of the spectroscopic properties of the deriva-
tives. The measurements of DTA and TGA show that
the thermal stability of the derivatives has a close rela-
tionship with their chemical structures.
Mustroph, H.; Stollenwerk, M.; Bressau, V. Angew. Chem.,
Int. Ed. 2006, 45, 2016.
Hara, K.; Sato, T.; Katoh, R.; Furube, A.; Yoshihara, T.;
Murai, M.; Kurashige, M.; Ito, S.; Shinpo, A.; Suga, S.;
Arakawa, H. Adv. Funct. Mater. 2005, 15, 246.
Kwong, R. C.; Lamansky, S.; Thompson, M. E. Adv. Mater.
2000, 12, 1134.
8
9
Ning, Z.; Chen, Z.; Zhang, Q.; Yan, Y.; Qian, S.; Cao, Y.;
Tian, H. Adv. Funct. Mater. 2007, 17, 3799.
10 Song, X.-R.; Wang, W.-B.; Zhang, X.-H.; Li, C.; Wang,
X.-S.; Zhang, B.-W. Acta Chim. Sinica 2008, 66, 1687 (in
Chinese).
Acknowledgements
11 Resch-Genger, U.; Grabolle, M.; Cavaliere-Jaricot, S.;
Nitschke, R.; Nann, T. Nat. Methods 2008, 5, 763.
12 Bai, M. F.; Wyatt, S. K.; Han, Z. Q.; Papadopoulos, V.;
Bornhop, D. J. Bioconjugate Chem. 2007, 18, 1118.
13 Pham, W.; Medarova, Z.; Moore, A. Bioconjugate Chem.
2005, 16, 735.
14 Zhang, M.; Yu, M. X.; Li, F. Y.; Zhu, M. W.; Li, M. Y.;
Gao, Y. H.; Li, L.; Liu, Z. Q.; Zhang, J. P.; Zhang, D. Q.; Yi,
T.; Huang, C. H. J. Am. Chem. Soc. 2007, 129, 10322.
15 Peng, X. J.; Song, F. L.; Lu, E. H.; Wang, Y. N.; Zhou, W.;
We thank supports on the laser determination from
the Key Laboratory of Functional Crystals and Laser
Technology, Technical Institute of Physics and Chemis-
try (TIPC), Chinese Academy of Sciences.
References
1
2
Ning, Z. J.; Tian, H. Chem. Commun. 2009, 5483.
Ning, Z. J.; Zhang, Q.; Pei, H. C.; Luan, J. F.; Lu, C. G.; Cui,
Y. P.; Tian, H. J. Phys. Chem. C 2009, 113, 10307.
Chin. J. Chem. 2010, 28, 950— 960
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
959

Gao et al.
FULL PAPER
Fan, J. L.; Gao, Y. L. J. Am. Chem. Soc. 2005, 127, 4170.
16 Shao, J.; Lin, H.; Lin, H. K. Talanta 2008, 77, 273.
17 Umezawa, K.; Matsui, A.; Nakamura, Y.; Citterio, D.;
Suzuki, K. Chem. Eur. J. 2008, 15, 1096.
18 Meng, G.; Velayudham, S.; Smith, A.; Luck, R.; Liu, H. Y.
Macromolecules 2009, 42, 1995.
19 Ji, S. M.; Yang, J.; Yang, Q.; Liu, S. S.; Chen, M. D.; Zhao,
J. Z. J. Org. Chem. 2009, 74, 4855.
20 Zheng, Q. D.; Xu, G. X.; Prasad, P. N. Chem. Eur. J. 2008,
14, 5812.
21 (a) Pond, S. J. K.; Rumi, M.; Levin, M. D.; Parker, T. C.;
Beljonne, D.; Day, M. W.; Bredas, J. L.; Marder, S. R.;
Perry, J. W. J. Phys. Chem. A 2002, 106, 11470.
(b) Rumi, M.; Ehrlich, J. E.; Heikal, A. A.; Perry, J. W.;
Barlow, S.; Hu, Z.; McCord-Maughon, D.; Parker, T. C.;
Rockel, H.; Thayumanavan, S. J. Am. Chem. Soc. 2000, 122,
9500.
Yazyev, O.; Austin, A. J.; Cammi, R.; Pomeli, C.; Ochterski,
J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador,
P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.;
Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Orti, J.
V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowshi, J.;
Stetanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Ko-
maromi, I.; Martin, R. L.; Fox, J. D.; Keith, T.; Allaham, M.
A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P.
M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.;
Pople, J. A., Gaussian 03, Revision B. 03, Gaussian, Inc.,
Pittsburgh, PA, 2003.
30 Zgiershi, M. Z.; Grabowska, A. J. Chem. Phys. 2000, 112,
14.
31 Yi, P.; Liang, Y.-H.; Cao, C. Chem. Phys. 2005, 315, 297.
32 Liang, Y.-H.; Yi, P. Chem. Phys. Lett. 2007, 438, 173.
33 Mallegol, T.; Gmouh, S.; Meziane, M. A. A.; Blanchard-
Desce, M.; Mongin, O. Synthesis 2005, 11, 1771.
34 Laane, J. Int. Rev. Phys. Chem. 1999, 18, 301.
35 Wang, S.; Kim, S. H. Curr. Appl. Phys. 2009, 9, 783.
36 Harriman, A.; Hosie, R. J. J. Chem. Soc., Faraday Trans.
1981, 77, 1695.
(c) Kim, O.; Lee, K.; Woo, H. Y.; Kim, K. S.; He, G. S.;
Swiatkiewicz, J.; Prasad, P. N. Chem. Mater. 2002, 12, 284.
(d) Rumi, M.; Ehrlich, J. E.; Heikal, A. A.; Perry, J. W.;
Barlow, S.; Hu, Z.; McCord-Maughon, D.; Parker, T. C.;
Rockel, H.; Thayumanavan, S. J. Am. Chem. Soc. 2000, 122,
9500.
37 Dvornikov, S. S.; Kachura, T. F.; Knyukshto, V. N.; Kuz-
mitskii, V. A.; Solovev, K. N.; Shushkevich, I. K. Opt.
Spectrosc. 1986, 61, 768.
22 (a) Wei, P.; Bi, X. D.; Wu, Z.; Xu, Z. Org. Lett. 2005, 7,
3199.
(b) Fang, Z.; Teo, T. L.; Cai, L. P.; Lai, Y. H.; Samoc, A.;
Samoc, M. Org. Lett. 2009, 11, 1.
38 Maus, M.; Rettig, W.; Bonafoux, D.; Lapouyade, R. J. Phys.
Chem. A 1999, 103, 3388.
23 De, S.; Girigoswami, A.; Mandal, S. Spectrochim. Acta,
Part A 2002, 58, 2547.
24 Chen, A. S.; Li, Y. M.; Zhang, H. Acta Chim. Sinica 2005,
63, 460 (in Chinese).
25 Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification
of Laboratory Chemicals, Pergamon Press, New York,
1966.
26 Fischer, M.; Georges, J. Chem. Phys. Lett. 1996, 260, 115.
27 Maus, M.; Reitigg, W.; Bonafoux, D.; Lapouyade, R. J.
Phys. Chem. A 1999, 103, 3388.
39 Lippert, V. E. Z. Electrochemistry 1957, 61, 962.
40 Lakowicz, J. R. Principles of Fluorescence Spectroscopy,
Kluwer Academic, New York, 1999.
41 Turro, N. J. Modern Molecular Photochemistry, Benjamin/
Cummings, Menlo Park, 1978.
42 Barlow, S.; Bunting, H. E.; Ringham, C.; Green, J. C.; Bub-
litz, G. U.; Boxer, S. G.; Perry, J. W.; Marder, S. R. J. Am.
Chem. Soc. 1999, 121, 3715.
43 Fabian, J.; Diaza, L. A.; Seifert, G.; Niehaus, T. J. Mol.
Struct.: Theochem 2002, 594, 41.
28 Lukeman, M.; Veal, D.; Wan, P.; Ranjit, V.; Munasinghe,
N.; Corrie, J. E. T. Can. J. Chem. 2004, 82, 240.
29 Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G.
E.; Robb, M. A.; Cheesman, J. R.; Montgomery, J. A.; Vre-
ven, Jr. T.; Kudim, K. N.; Burant, J. C.; Millam, J. M.;
Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi,
M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.;
Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.;
Klene, M.; Li, X.; Knox, J. E.; Hratchi, H. P.; Cross, J. B.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stramann, R. E.;
44 Aoki, K.; Guo, Y.; Chen, J. Y. J. Electroanal. Chem. 2009,
73, 629.
45 Liu, J.; Tu, G.; Zhou, Q.; Cheng, Y.; Geng, Y.; Wang, L.;
Ma, D.; Jing, X.; Wang, F. J. Mater. Chem. 2006, 16, 1431.
46 Bard, A. J.; Faulkner, L. A. Electrochemical Methods—
Fundamentals and Applications, Wiley, New York, 1984.
47 Domagalska, B. W.; Wilk, K. A.; Wysocki, S. Phys. Chem.
Chem. Phys. 2003, 5, 696.
48 Ndaykengurukiye, H.; Jacobs, S.; Tachelet, W.; Looy, J. V.
D.; Pollars, A.; Geise, H. J.; Claeys, M.; Kauffmann, J. M.;
Janietz, S. Tetrahedron 1997, 53, 13811.
(E0911011 Cheng, B.; Zheng, G.)
960
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 950— 960