Experimental and theoretical studies of 2,5-diphenyl-1,4-distyrylbenzenes with all-cis- And all-trans double bonds: Chemical structure determination and optical properties

Article abstract of DOI:10.1002/poc.935

2,5-Diphenyl-1,4-distyrylbenzene (DPDSB) with all-cis (cw-DPDSB) and all-trans double bonds (trans-DPDSB) were synthesized by Wittig reaction and the differences in structural and optical properties between the cis- and trans-isomers are discussed in detail. Both compounds were fully characterized by NMR spectroscopy, FT-IR spectroscopy, x-ray crystallography, differential scanning calorimetry (DSC) and electrochemical methods. X-ray analysis and molecular simulation revealed that the structure of cis-DPDSB obviously deviates from planarity along both the distyrylbenzene and terphenyl directions, and less intermolecular interaction exists in crystal. The cisisomer shows a large blue shift in the absorption spectrum in comparison with that of the trans-isomer, and cyclic voltammetric measurements give bandgaps of 3.16 and 2.97 eV for cis- and trans-DPDSB, respectively. Both compounds show unusually strong blue fluorescence in the solid state, probably due to the weak intermolecular interaction existing in both isomers owing to the large steric hindrance induced by the substituted phenyl groups. DSC experiments determined that both isomers have excellent thermal stability, which indicates that they can be used as active layers to make stable devices. Quantum chemical calculations for the frontier molecular orbital and the cation and anion properties reveal that the HOMO and LUMO are completely localized in the distyrylbenzene direction and the distyrylbenzene segment has more sensitive electroactivity than the terphenyl segment whether it is cis- or trans-DPDSB. Copyright

Full text of DOI:10.1002/poc.935

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2005; 18: 962–973
Published online 19 April 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/poc.935
Experimental and theoretical studies of 2,5-diphenyl-1,4-
distyrylbenzenes with all-cis- and all-trans double bonds:
chemical structure determination and optical properties
Zengqi Xie,1 Bing Yang,1 Linlin Liu,1 Mao Li,1 Dong Lin,1 Yuguang Ma,1* Gang Cheng2 and Shiyong Liu2
1Key Laboratory for Supramolecular Structure and Materials of the Ministry of Education, Jilin University, 130012 Changchun, China
2National Laboratory of Integrated Optoelectronics, Jilin University, 130023 Changchun, China
Received 20 August 2004; revised 22 October 2004; accepted 18 February 2005
ABSTRACT: 2,5-Diphenyl-1,4-distyrylbenzene (DPDSB) with all-cis (cis-DPDSB) and all-trans double bonds
(trans-DPDSB) were synthesized by Wittig reaction and the differences in structural and optical properties between
the cis- and trans-isomers are discussed in detail. Both compounds were fully characterized by NMR spectroscopy,
FT-IR spectroscopy, x-ray crystallography, differential scanning calorimetry (DSC) and electrochemical methods.
X-ray analysis and molecular simulation revealed that the structure of cis-DPDSB obviously deviates from planarity
along both the distyrylbenzene and terphenyl directions, and less intermolecular interaction exists in crystal. The cis-
isomer shows a large blue shift in the absorption spectrum in comparison with that of the trans-isomer, and cyclic
voltammetric measurements give bandgaps of 3.16 and 2.97 eV for cis- and trans-DPDSB, respectively. Both
compounds show unusually strong blue fluorescence in the solid state, probably due to the weak intermolecular
interaction existing in both isomers owing to the large steric hindrance induced by the substituted phenyl groups. DSC
experiments determined that both isomers have excellent thermal stability, which indicates that they can be used as
active layers to make stable devices. Quantum chemical calculations for the frontier molecular orbital and the cation
and anion properties reveal that the HOMO and LUMO are completely localized in the distyrylbenzene direction and
the distyrylbenzene segment has more sensitive electroactivity than the terphenyl segment whether it is cis- or trans-
DPDSB. Copyright # 2005 John Wiley & Sons, Ltd.
KEYWORDS: cis/trans isomers; 2,5-diphenyl-1,4-distyrylbenzene; luminescence; oligomeric phenylenvinylene;
theoretical calculation; Wittig reactions
INTRODUCTION
substituted phenyl (DP-PPV) have very high efficiency
since the bulky substitution effectively suppresses the
aggregation.19–21 The oligomers of the repeating unit of a
polymer are often useful in understanding the proper-
ties of a polymer system.22–27 This is due to the close
analogy of their physical properties, and as easier char-
acterization of the oligomeric system. The oligomers
themselves as active materials have been used widely
owing to their definite structure.28–31 Several papers have
reported the synthesis of a series of short-chain oligo-
meric analogues of PPVs with alkoxy groups,32–34 but to
our knowledge, discussion about oligomers correspond-
ing to phenyl-substituted PPVs is limited.35
In all kinds of PPVs, the presence of cis/trans-vinylene
units and their photochemical isomerization attracts spe-
cial attention because the cis-isomer generally shows
weak luminescence and is regarded as a cis defect.36–39
Although great efforts have been made in the investiga-
tion of relationships that exist between the cis/trans
conformation in polymer chains and the resulting lumi-
nescence properties, the understanding of these depen-
dences is still incomplete, which is partially due to a lack
Conjugated polymers are key components of a number of
advanced but fairly in expensive electronic devices.1–4
Some of the most promising candidates for the active
layer in organic light-emitting diodes (LEDs) are poly-
mers derived from poly(p-phenylenevinylene) (PPV),
such as MEH-PPV,5,6 DP-PPV7–9 and CN-PPV.10,11 The
concept behind the molecular design of such PPVs is the
use of substitutional side-chains to improve solubility in
common solvents and suppress molecular aggregation.2
Nevertheless, there still exists a significant tendency
towards molecular aggregation for PPVs with, e.g.,
alkoxy side-chains, which gives rise to strong effects on
their light emission properties.12–18 Almost all PPVs with
*Correspondence to: Y. Ma, Key Laboratory for Supramolecular
Structure and Materials of the Ministry of Education, Jilin University,
2699 Qianjin Avenue, 130012 Changchun, China.
E-mail: ygma@jlu.edu.cn
Contract/grant sponsor: National Science Foundation of China;
Contract/grant numbers: 20474024; 20125421; 90101026; 50303007.
Contract/grant sponsor: Ministry of Science and Technology of China;
Contract/grant numbers: 2002CB6134003; 2003CB314703.
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 962–973

STRUCTURE AND OPTICAL PROPERTIES OF 2,5-DIPHENYL-1,4-DISTYRYLBENZENES
963
of more definite structural information on polymer sys-
tems.40–42 So far the results on this topic have come
mostly from theoretical simulation,35 and need urgently
to be testified by experiment.
In this paper, we report the synthesis and characteriza-
tion of the most basal model compounds (oligomers) for
DP-PPV and discuss the differences between cis- and
trans-isomers in detail. Such ordinary materials them-
selves exhibit excellent optical and thermal properties,
which are useful in making luminescence devices or
lasers.
obtained directly by the optimized synthetic procedure
probably owing to the o-phenyl substituent playing the
same role as the CF3 substituent in the Witting reaction.
trans-DPDSB was prepared by refluxing a p-xylene
solution of the cis-isomer for 12 h, with a small amount
of iodine as catalyst (yield: 95%).
Structural determination of cis- and trans-DPDSB
Based on NMR and FT-IR measurements (Figs 1–3), the
two compounds are unambiguously characterized as cis-
and trans-DPDSB, respectively (shown in Scheme 2).
The 1H and 13C NMR spectra are shown in Figs 1 and 2,
which are correlated by 13C, 1H chemical shift correlation
spectroscopy, and the chemical shifts are given in Table 1.
The position, intensity and coupling patterns of the NMR
signals provide unequivocal proof of the structures of the
isomers. For example, the chemical shifts of the olefinic
RESULTS AND DISCUSSION
Synthesis of cis- and trans-DPDSB
The synthetic route toward the target materials is outlined
in Scheme 1. cis-DPDSB was synthesized by a twofold
Wittig reaction from benzyltriphenylphosphonium bro-
mide and 1,10;40,100-terphenyl-20,50-dicarbaldehyde (3) in
tetrahydrofuran (THF) solution by dropping potassium
tert-butylate (t-BuOK, dissolved in THF) over a period of
30 min, and then stirring the mixture for another 12 h at
room temperature. Colorless crystals were obtained after
the product had been deposited in methanol (yield: 87%).
Interestingly, the resulting product is determined to have
the all-cis conformation as discussed below. Previous
studies on the Witting reaction by Hwang et al. demon-
strated that reaction in the polar solvents produced
more cis products (Z-selectivity).43 They also indicate
using ortho-substituted benzaldehydes bearing electron-
withdrawing substituent such as CF3 exhibit a pro-
nounced enhancement for Z-selectivity (Z/E ratio up to
5.6). Our results indicate that pure cis-DPDSB can be
Figure 1. 1H NMR spectra of cis- and trans-DPDSB. The
numbers correspond to the numbers in Scheme 2
Scheme 1. Synthesis route to cis- and trans-DPDSB
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964
Z. XIE ET AL.
Scheme 2. Structures of cis- and trans-DPDSB
the decreased conjugation in the distyrylbenzene direc-
tion in cis-DPDSB. Also, unlike in trans-DPDSB, the ꢀ
values of the other protons [H7(H11), H8(H10) and
H13(H17), H14(H16)] in the end phenyl rings in cis-
DPDSB are all distributed in a small range from 7.27 to
7.35 ppm. In The 13C NMR spectra of cis-DPDSB, C9
and C15 are also indistinguishable and the difference in
ꢀ between C8(C10) and C14(C16) or C7(C11) and
C13(C17) in cis-DPDSB are smaller than those in trans-
DPDSB. All of the above information indicates that the
conjugation effect in the distyrylbenzene direction in
trans-DPDSB is higher than that in cis-DPDSB. The
lower conjugation effect in cis-DPDSB is caused by the
torsion conformation.
IR spectroscopy is one of the most important analytical
methods for cis/trans-isomer characterization. It provides
fast and easy criteria, albeit empirical, distinguishing
between the isomers (Fig. 3). The spectrum of trans-
DPDSB shows a strong absorption band at 964 cmꢀ1
(out-of-plane bending mode of the C—H bond in the
trans-vinylene group, ꢁ),45 which is completely absent
in the spectrum of cis-DPDSB. Unlike in cis-DPDSB,
the two double bands at about 700 and 760 cmꢀ1 (five
adjacent H on phenyl)45 in trans-DPDSB indicate the
difference in the end rings in the distyrylbenzene and
Figure 2. 13C NMR spectra of cis- and trans-DPDSB. The
numbers correspond to the numbers in Scheme 2
protons are 6.4 ppm (H4) and 6.6 ppm (H5) with coupling
constant 12 Hz in the cis configuration and 7.1 ppm (H4)
and 7.3 ppm (H5) with coupling constant 16.3 Hz in the
trans configuration.44 The reason for the signals of the
olefinic protons in trans-DPDSB shifting downfield com-
pared with those in the cis-isomer is the decreased
shielding effect of the phenyl ring on the olefinic protons
and the decreased electron cloud density on the olefinic
segments, because trans-DPDSB exhibits more planarity
and a greater conjugated effect in the distyrylbenzene
direction than that of the cis-isomer (see the discussion
below). The dispersed electron cloud also affects the
signals of protons in phenyl rings. By 1H NMR of
trans-DPDSB, we investigated the clear difference be-
tween the protons in end phenyl rings in the distyrylben-
zene direction and the terphenyl direction, e.g.
ꢀ ¼ 7.24 ppm for H9 and ꢀ ¼ 7.48 ppm for H15. Such a
difference arises because of the effective conjugation in
the distyrylbenzene direction (planar conformation) and
less conjugation in the terphenyl direction (twist con-
1
formation) in trans-DPDSB. In the H NMR spectra of
cis-DPDSB, the ꢀ values of H9 and H15 are localized in
the same range and become indistinguisable, reflecting
Table 1. 1H and 13C chemical shifts (relative to TMS) of cis-
and trans-DPDSB in DMSO solution
cis-DPDSB
C or H 13C (ppm) 1H (ppm)
trans-DPDSB
13C (ppm) 1H (ppm)
1
2
3
4
5
6
132.1
137.5
135.2
131.4
130.3
140.0
129.5
129.2
130.3
140.5
128.2
129.0
129.6
7.14(s)
—
—
6.64(d)
6.42(d)
—
128.1
138.0
134.8
130.6
126.9
140.8
130.5
129.6
128.6
141.0
127.2
129.3
128.4
7.81(s)
—
—
7.34(d)
7.08(d)
—
7.50(d)
7.33(t)
7.24(t)
—
7.39(d)
7.55(t)
7.48(t)
7(11)
8(10)
9
7.27–7.35
7.16(t)
—
7.27–7.35
12
13(17)
14(16)
15
7.16(t)
Figure 3. FT-IR spectra of cis- and trans-DPDSB
Copyright # 2005 John Wiley & Sons, Ltd.
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STRUCTURE AND OPTICAL PROPERTIES OF 2,5-DIPHENYL-1,4-DISTYRYLBENZENES
965
Table 2. Crystal data and refinement parameters for cis-
terphenyl directions, which corresponds to the result from
NMR analysis.
DPDSBa
The IR spectra of cis- and trans-DPDSB were simu-
lated using the Gaussian98w program package for Win-
dows on a PC. Both geometry optimization and actual
frequency calculation were performed with the DFT/
B3LYP method at the level of the 6–31G** basis set.
The calculated frequencies are corrected by scale factor
0.9613,46 and agree well with the experimental results. In
addition, we use the HyperChem 7.1 software to analyze
the vibrational spectra, and all normal modes are identi-
fied and confirmed. The absorption band at 783 cmꢀ1 in
cis-DPDSB, which is absent in the trans-isomer, is due to
the wagging vibration of the C—H bond in cis-vinylene
groups. Previously, Fan et al. assigned an absorption band
at about 875 cmꢀ1 to the characteristic absorption of cis-
vinylene groups.47 However, we note that this absorption
band (875 cmꢀ1) appears in the spectra of both cis- and
trans-DPDSB without a distinct difference in intensity.
Hence this 875 cmꢀ1 band cannot be used to indicate the
conformation of cis-vinylene groups at least in the
DPDSB system. In fact, this band is probably due to
the ꢁ vibration of single hydrogen (H1) connected to the
central phenyl ring.45
The single crystal (block crystal) of cis-DPDSB is
easily obtained in alcohol, whereas just a mix crystal
can be obtained from trans-DPDSB (for details, see wide-
angle x-ray diffraction and DSC discussions). The struc-
ture of cis-DPDSB in a single crystal is shown in Fig.
4(left) and the crystal data and refinement parameters are
given in Table 2. A noteworthy feature of the cis-DPDSB
crystal is its torsion conformation, which is similar to that
obtained from geometry optimization for the cis-DPDSB
molecule in the gas phase. The torsion angles between the
double bond and two adjacent phenyl rings are 43.1ꢁ (ꢂ1)
and 38.3ꢁ (ꢂ2). The torsion angle between the central
phenyl ring and the adjacent phenyl ring (in the p-
terphenyl direction) is 52.4ꢁ (ꢂ3), which is larger than
that in p-terphenyl (38.4ꢁ).48 Also, it must be noted that
Crystal parameter
Value
Chemical formula
Formula weight
Crystal system
Space group
Z
C34H26
434.55
Monoclinic
P21/c
2
˚
a (A)
10.078(4)
13.220(10)
9.756(8)
90
111.36(3)
90
˚
b (A)
˚
c (A)
ꢃ ( ꢁ)
ꢁ ( ꢁ)
ꢄ ( ꢁ)
3
˚
V (A )
1210.6(14)
1.192
ꢅ
calc (g cmꢀ3
)
Crystal dimensions (mm)
0.31 ꢂ 0.26 ꢂ 0.24
T ( ꢁC)
20(2)
2ꢂ range: min., max. ( ꢁ)
No. of data collected
No. of unique data
5.32, 50.42
3110
1956
623
0.067
0.0533, 0.0642
0.1904, 0.0860
0.782
No. of data with Fo ꢃ 4.0ꢆ(Fo)
m (mmꢀ1
)
R1(F), wR2(F2), (I > 2ꢆ(I))
R1(F), wR2(F2), all data
Goodness-of-fit on F2
a CCDC-226016 contains supplementary crystallographic data for this
paper. These data can be obtained free of charge via www.ccdc.cam.
ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (þ44) 1223 336033;
or by e-mail: deposit@ccdc.cam.ac.uk].
all end phenyl rings that connect to the double bond [e.g.
ring A shown in Fig. 4(right)] is inserted between the two
adjacent rings (shown as rings B and C) of other mole-
cules and the distance between the phenyl ring A and ring
˚
B (or ring C) is 3.609 A, which indicates some intramo-
lecular motions, e.g. twisting of the double bond and
twisting of the end phenyl ring that connect to the double
bond are not free.
The wide-angle x-ray diffraction patterns of cis- and
trans-DPDSB are shown in Fig. 5. It is noticeable that
Figure 4. Left: ORTEP drawing of cis-DPDSB. The ellipsoid probability is 25%. Right: packing arrangement of cis-DPDSB,
viewed down the a-axis. The phenyl ring A that connects to the double bond is inserted between rings B and C of the two
adjacent molecules
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966
Z. XIE ET AL.
trans-DPDSB in the crystal is attributed to the invisible
but common pedal motion as in stilbene and azobenzene
crystals.50 As for cis-DPDSB, such motion may not be
occur for the same reason as discussed above and so it
cannot transform to other rotamers in the crystal.
Thermal properties of cis- and trans-DPDSB
The thermal behavior was investigated by means of DSC
experiments, using standard heating and cooling rates of
10 ꢁC minꢀ1 under nitrogen flushing. In the scans shown
in Fig. 6, the samples were heated to 210 ꢁC for cis-
DPDSB and 265 ꢁC for trans-DPDSB. The maximum
temperatures are obviously below the range of degrada-
tion or isomerization according to the coherence of
different scan times. Indeed, the resulting samples were
examined by FT-IR spectroscopy and no difference was
observed before and after the heat treatments, which
indicates that there is no isomerization between the two
isomers at such temperatures and the difference in the
rotamers of trans-DPDSB cannot be detected in the FT-
IR experiment. For cis-DPDSB, the up and down scans in
DSC experiments are repeated accurately for the first
three times, which indicates high thermal stability. The
melting-point of cis-DPDSB is 192.5 ꢁC (peak) and no
other thermal process is observed, whereas for trans-
DPDSB there are two peaks in the exotherm of every run
shown in Fig. 6 (bottom), which indicates that there may
exist two kinds of crystals, as concluded from the wide-
angle x-ray diffraction analysis. The change in the rela-
tive intensity in the exotherms shows that the proportion
of different crystal types altered after the heating process.
Also, the endotherm in the second up scan is shifted down
by 3 ꢁC and is slightly broader than that in the first up
scan. Crystallization is found to occur at peak-to-peak
supercooling of 48 and 63 ꢁC for cis- and trans-isomers,
respectively, which are about 10 times larger than
p-bis(p-styrylstyryl)benzene.51
Figure 5. Wide-angle x-ray diffraction patterns of cis- and
trans-DPDSB
several diffractions are very strong in both cis- and trans-
DPDSB crystals. The single peak of the first diffraction at
2ꢂ ¼ 5.92 ꢁ for cis-DPDSB indicates the simplex crystal
type, whereas in trans-DPDSB the double peak of the
first diffraction at 2ꢂ ¼ 6.96 ꢁ and 7.24 ꢁ (corresponding
˚
to interplanar distances of 12.7 and 12.2 A) is observed
(shown as a1 and b1), and a2 and b2 correspond to the
second diffraction of the same interplanar distance, etc.
These double peaks indicate that the crystals obtained are
mixed crystal. As shown in Scheme 3, trans-DPDSB is
expected to exist as an equilibrium mixture of three
rotamers,49 which may cause different crystal parameters
in the crystalline state. We also performed energy opti-
mization by DFT/B3LYP/6–31G of the three rotamers to
rationalize their possible existence. The results show that
there are three local minima at the three rotamers as
expected and the rotamer a has the lowest energy. Sub-
sequently, frequency analysis was performed on the
optimized structures, and no imaginary frequency was
found, which proves that these three rotamers are real
stationary points. The existence of mixed crystals of
trans-DPDSB was further confirmed by DSC experi-
ments. The transformation between the rotamers of
Scheme 3. Equilibrium of three rotamers of trans-DPDSB
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STRUCTURE AND OPTICAL PROPERTIES OF 2,5-DIPHENYL-1,4-DISTYRYLBENZENES
967
Figure 6. DSC thermograms of cis- and trans-DPDSB, re-
corded at heating and cooling rates of 10 ꢁC minꢀ1. Both
contain series of first and second heating and cooling
processes
Figure 7. Absorption and emission spectra of the cis- and
trans-DPDSB in dilute THF solution and emission spectra of
their crystals. The emission spectra of the cis- and trans-
DPDSB in dilute THF solution were recorded under the same
conditions and the spectrum of cis-isomer is enlarged 500
times for comparison
Optical properties of cis- and trans-DPDSB
The absorption and emission spectra of the cis- and trans-
DPDSB in dilute THF solution and the emission spectra
of their crystals are shown in Fig. 7 and detailed data
are given in Table 3. The absorption spectrum of cis-
DPDSB in dilute THF solution shows an absorption
band at 316 nm with a molar absorption coefficient of
21 900 Mꢀ1 cmꢀ1, whereas for trans-DPDSB the maxi-
mum absorption band is at 354 nm with a molar absorp-
tion coefficient of 48 500 Mꢀ1 cmꢀ1. It is the torsion
conformation of cis-DPDSB that induces a large blue
shift in the absorption spectrum and a small molar ab-
sorption coefficient. trans-DPDSB in dilute THF solution
exhibits intense emission as a pure blue band with a high
photoluminescence (PL) efficiency of 0.95, whereas the
cis-DPDSB–THF solution shows almost no fluorescence
initially, but after it has been exposed under an ultraviolet
lamp (360 nm) for several seconds the fluorescence
increases dramatically. Evidently the photochemical pro-
cesses (cis–trans isomerization and photocyclization
to 7,14-diphenyldibenzo[a,h]anthracene) occur and the
trans-isomer plays the role of the following emission.52,53
Hence the reason for cis-DPDSB showing no fluores-
cence is that such complicated photochemical processes
compete with the luminescence process.52 Usually the
unsubstituted trans-OPVs (oligomeric phenylenvinylene)
show weak fluorescence in the solid due to ‘herringbone’-
type crystal packing and strong ꢇ–ꢇ interaction.51,54 The
crystals of both cis- and trans-DPDSB show strong
fluorescence with maximum emission bands at 435 and
444 nm, respectively (see Figs 7 and 8), which is probably
attributable to the weak intermolecular interaction exist-
ing in both isomers owing to the large steric hindrance
induced by the substituted phenyl groups. Especially for
cis-DPDSB the photochemical processes that exist in
solution are limited by the crystal lattice (see the crystal
analysis), that is, the energy barrier from the cis-isomer to
Table 3. Optical properties of cis- and trans-DPDSB
Material
ꢈa in solution (nm)
" ( ꢂ 103) (Mꢀ1 cmꢀ1
)
ꢈfa in solution (nm)
ꢈfb in crystal (nm)
ꢉPLc (solution)
cis-DPDSB
trans-DPDSB
276, 316
282, 354
21.9 (ꢈ ¼ 316 nm)
—
400, 423
435
444
<0.05
0.95
48.5 (ꢈ ¼ 354 nm)
a Emission spectra were recorded in dilute THF solutions, excited at 350 nm.
b In crystals, excited at 360 nm.
c In dilute THF, using quinine sulfate in 0.1 M sulfuric acid as standard.
Copyright # 2005 John Wiley & Sons, Ltd.
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968
Z. XIE ET AL.
the distyrylbenzene direction are distorted against the
central phenylene unit, which leads to a shorter conjuga-
tion length and a larger HOMO–LUMO distance.
Frontier molecular orbitals
Figure 8. Crystals of cis-DPDSB (left, block crystal) and
trans-DPDSB (right, acicular crystal) under an ultraviolet
lamp (365 nm)
The frontier orbitals of cis- and trans-DPDSB were
investigated (B3LYP/6–31G), as shown in Fig. 10. For
both isomers, the HOMO and LUMO are completely
localized on the distyrylbenzene and the node distribution
is similar to that in 1,4-distyrylbenzene.56 Obviously, the
LUMO has more nodes than the HOMO in the central
benzene rings. In the HOMO the ꢇ-bond between C4
and C5 is bonding, whereas the ꢇ-bond between C2
and C4 is antibonding. In contrast, in the LUMO the
ꢇ-bond between C2 and C4 is bonding, whereas the ꢇ-
bond between C4 and C5 is antibonding. For cis-DPDSB,
both the HOMO-1 and LUMO þ 1 are localized on the
terphenyl part, but in trans-DPDSB, the HOMO-1 loca-
lized on distyrylbenzene, which may be caused by the
planar configuration. Hence we can readily conclude that
the contribution to fluorescence is due to distyrylbenzene,
not terphenyl, whether it is in cis- or trans-DPDSB.
the trans-isomer/7,14-diphenyldibenzo[a,h]anthracene is
increased dramatically so that the photochemical pro-
cesses become impossible. Hence the excited state cannot
be decayed by isomerization or photocyclization and then
the emission process occurs.52,53 The property of strong
emission in the solid state is rare but useful in devices,
because the organics are normally used in the solid state.55
Electrochemical properties
We investigated the electrochemical behavior of cis- and
trans-DPDSB by cyclic voltammetry (CV). Through the
CV curve shown in Fig. 9, three redox steps are observed,
of which two appear in the reductive potential range (1,4-
distyrylbenzene also shows two reversible waves at
ꢀ2.48 and ꢀ2.74 V in THF)56 and one in the oxidative
potential range. The detailed data are given in Table 4.
The reduction waves of cis-DPDSB are at ꢀ2.30 and
ꢀ2.52 V and the quasi-reversible anodic wave is at
0.94 V. In contrast, the two reduction waves of trans-
DPDSB are shifted to ꢀ2.21 and ꢀ2.51 V and the oxida-
tion wave is at 0.88 V. Therefore, the bandgaps (the ene-
rgy difference between the HOMO and the LUMO, or
between the first oxidation and the first reduction poten-
tial) of cis- and trans-DPDSB can be calculated as 3.16
and 2.97 eV, respectively, which are close to the data ob-
tained from absorption spectra. The decrease of the band-
gap caused by changing cis- to trans-DPDSB can be
explained by a stronger torsion within the molecule in the
case of the cis compared with the trans configuration.57
Because of the steric hindrance, the outer phenyl rings in
Cation radical and anion radical properties
To reveal the effects of charge injection on the molecular
conformational stability, we calculated structural and
electronic properties of both the anion radical and the
cation radical. For this purpose, geometry optimization
was carried out on both molecular ions (i.e. the neutral
molecule in the presence of an extra electron and that of
an extra hole, respectively). The optimized structures for
both the cation radical and the anion radical show
dramatic structural changes relative to the neutral mole-
cule. The distribution of the extra hole in the cation
radical calculated as excess spin densities (Fig. 11) is
completely localized on the distyrylbenzene and is espe-
cially similar to the HOMO and LUMO of the neutral
molecule. A similar result is found in the anion radical,
where the distribution of the electron is also all localized
on the distyrylbenzene. These results indicate that the
distyrylbenzene has more sensitive electroactivity than
the terphenyl.
The main structural distortions in both the cation
radical and the anion radical relative to the neutral
molecule are given in Table 5. It is found that the
variation of bond lengths and torsion angles in the
distyrylbenzene are strongly affected by charge injection,
whereas few change takes place in the terphenyl. More-
over, adding a hole has nearly the same effect on
structural geometries as adding an electron, and cis-
and trans-DPDSB have the same variation tendency for
different charge injections. The C2—C4 bond lengths are
˚
˚
Figure 9. Cyclic voltammograms of cis- and trans-DPDSB
Copyright # 2005 John Wiley & Sons, Ltd.
shortened by about 0.03 A and C5—C6 by about 0.02 A.
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STRUCTURE AND OPTICAL PROPERTIES OF 2,5-DIPHENYL-1,4-DISTYRYLBENZENES
969
Table 4. Redox potentials determined by cyclic voltammetry and the HOMO–LUMO distances determined by electrochemical
(measured in DMF) and optical experiments (measured in THF)
red
b (V) Eonset (V) Eel gc (eV) Eopt gd (eV)
Material
E
1/2(Ox)a (V) E1/2(Red1) (V) E1/2(Red2) (V)
Eox
onset
cis-DPDSB
trans-DPDSB
0.94
0.88
ꢀ2.30
ꢀ2.21
ꢀ2.52
ꢀ2.51
0.90
0.84
ꢀ2.26
ꢀ2.13
3.16
2.97
3.36
3.10
a
E1/2 ¼ (Epa þ Epc)/2.
b
Eonset ¼ redox and reductive potential onset.
Eel g ¼ band gap from electrochemistry.
c
d
Eopt g ¼ band gap from UV–visible absorption spectrum (obtained from the edge).
is more than 14ꢁ in the torsion angles between the central
phenyl ring and vinylene double bond. In contrast, the
torsion angles with respect to the vinylene double bond
are increased to different extents, about 9ꢁ for cis-
DPDSB, and <1ꢁ for trans-DPDSB. Based on the struc-
tural changes for both the cation radical and the anion
radical discussed above, increased conjugation occurs on
the distyrylbenzene, and it is evident that the distyryl-
benzene appears to be more coplanar in trans-DPDSB
than in cis-DPDSB. In addition, relative structural stabi-
lity versus the injection of one charge will be expected for
cis- and trans-DPDSB molecules.
—
In contrast, the vinylene C C bonds are lengthened by
—
˚
about 0.02 A; however, the anion radical has a larger
change than the cation radical. In the central phenyl ring,
the C1—C2 and C2—C3 bond lengths increase by about
˚
0.01 and 0.02 A, respectively, and the C1—C3 bond
˚
length decreases by about 0.01 A. In the distyrylbenzene,
the torsion angles between the phenyl ring and vinylene
double bond are evidently reduced by the positive
charge or negative charge, and the maximum variation
Additional information derived from our calculations
provides insight into the interrelationship of structure and
electronic behavior, in particular the response of the
molecule to the formation of a hole or the addition of
an electron. Table 6 contains the results for ionization
potentials (IPs), electron affinities (EAs), both vertical (v:
for the geometry of the neutral molecule) and adiabatic
Figure 10. Frontier molecular orbitals of cis- and trans-
DPDSB
Figure 11. Spin density surfaces of the cation radical and
the anion radical for cis- and trans-DPDSB
Copyright # 2005 John Wiley & Sons, Ltd.
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970
Z. XIE ET AL.
Table 5. Main structural parameters of the cation radical
and anion radical of cis- and trans-DPDSB relative to the
neutral moleculesa
cis-DPDSB
trans-DPDSB
Parameter
Cation
0.014
Anion
0.017
Cation
Anion
C1—C2
C2—C3
C1—C3#
C2—C4
C4—C5
C5—C6
C3—C12
0.0224 0.0264
0.0235 0.0248 0.0233 0.0225
ꢀ0.0129 ꢀ0.0106 ꢀ0.0222 ꢀ0.0188
ꢀ0.0332 ꢀ0.0354 ꢀ0.0332 ꢀ0.0334
Figure 12. Left: EL spectra of OLEDs of cis- (circles) and
trans-DPDSB (squares), obtained when the voltage is 15 V.
Right: luminance and efficiency versus voltage of the OLEDs
0.024
0.0283 0.0239 0.0273
ꢀ0.0238 ꢀ0.0216 ꢀ0.0235 ꢀ0.021
ꢀ0.0059 ꢀ0.0009 ꢀ0.0033 ꢀ0.001
C1—C2—C4—C5 ꢀ12.64 ꢀ14.53 ꢀ14.67 ꢀ14.83
a voltage of 19 V, and efficiencies of 0.66 and 0.87 cd Aꢀ1
are achieved at voltage of 10 V for cis- and trans-DPDSB,
respectively. Obviously, although relatively lower lumi-
nance and efficiency are obtained in the device using cis-
DPDSB, the EL has a more excellent pure blue emission.
C2—C4—C5—C6
9.33
8.86
0.6
ꢀ4.6
0.07
ꢀ3.96
0.13
C4—C5—C6—C11 ꢀ6.99 ꢀ12.72
C2—C3—C12—C13 ꢀ0.83
ꢀ2.86
4.12
a The numbers of the C atoms correspond to those in Scheme 2. Bond
˚
lengths are reported in A and torsion angles in degrees.
(a: optimized structure for both the neutral and charged
molecule) and extraction potentials (HEP and EEP for
the hole and electron, respectively) that refer to the
geometry of the ions.58 IP(v) and IP(a) of cis-DPDSB
are larger about 0.2 eV than that of trans-DPDSB, and the
absolute of value of EA(v) and EA(a) for cis-DPDSB are
lower by about 0.28 and 0.15 eV than those for trans-
DPDSB, respectively. This indicates that the trans-isomer
can more easily gain or lose an electron, which is in
agreement with their energy of the HOMO and LUMO.
CONCLUSION
cis- and trans-DPDSB were synthesized and character-
ized by various spectroscopic and electrochemical
methods, including NMR spectroscopy, FT-IR spectro-
scopy, x-ray crystallography and absorption and electro-
chemical measurements. These physicochemical data
were analyzed together with the results of molecular
orbital calculations. The synthetic procedure was care-
fully optimized, allowing the unusual cis-DPDSB to be
obtained directly. The main results are summarized as
follows. (1) Syntheses of cis- and trans-DPDSB are
achieved by the Wittig reaction by using benzyltriphe-
nylphosphonium bromide and 1,10;40,100-terphenyl-20,50-
dicarbaldehyde in a 2.2:1 molar ratio at room tempera-
ture, and the yields are relatively high. Compared with
other methods, such as HPLC, controlling synthetic con-
ditions becomes a more straightforward route to obtain
cis-isomers. (2) The 1H NMR and IR spectra of the new
compounds are entirely consistent with the expected
molecular structures: cis- and trans-DPDSB give clear
NMR characteristic signals for the double bonds, and
trans-DPDSB shows the characteristic IR absorption
band of the trans-vinylene groups, which is absent
completely in cis-DPDSB. (3) The x-ray crystal structure
of cis-DPDSB indicates a deviation from planarity in the
distyrylbenzene direction, whereas trans-DPDSB tends
to form mixed crystals as revealed by wide-angle x-ray
diffraction and DSC experiments. (4) Both cis- and trans-
DPDSB have relatively high melting-points and excellent
Electroluminescence (EL) properties
To investigate the EL properties of cis- and trans-
DPDSB, we fabricated multilayer organic light-emitting
devices (OLEDs) with the structure ITO–NPB (50 nm)–
cis- or trans-DPDSB (30 nm)–BCP (10 nm)–Alq3
(10 nm)–LiF (0.5 nm)–Al, where NPB (N,N0-di-1-
naphthyl-N,N0-diphenylbenzidine) acts as a hole-trans-
porting layer, cis- or trans-DPDSB as an emitting layer,
BCP (bathocuproin) as an exciton-blocking layer and
Alq3 [tris(8-hydroxyquinolinato)aluminum] as an elec-
tron-transporting layer. The normalized EL spectra of
devices with various materials are shown in Fig. 12 (left).
It can be seen that the EL spectral features of both devices
appear in the blue emission region with peaks at 440 and
464 nm for cis- and trans-DPDSB with CIEs (Commis-
sion Internationale de l’Eclairage) of 0.1839, 0.1757 and
0.1797, 0.2189, respectively. As shown in Fig. 12 (right),
peak luminances of 1094 and 1643 cd mꢀ2 are achieved at
Table 6. Ionization potentials and electron affinities of cis- and trans-DPDSB
Material
IP(v) (eV) IP(a) (eV)
6.5930 6.4155
6.3707 6.2115
HEP (eV) EA(v) (eV) EA(a) (eV) EEP (eV) SPE(h) (eV) SPE(e) (eV)
cis-DPDSB
trans-DPDSB
ꢀ6.2341
ꢀ6.0602
ꢀ0.2633
ꢀ0.5483
ꢀ0.5701
ꢀ0.7257
0.7988
0.8934
0.1775
0.1592
0.3068
0.1774
Copyright # 2005 John Wiley & Sons, Ltd.
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STRUCTURE AND OPTICAL PROPERTIES OF 2,5-DIPHENYL-1,4-DISTYRYLBENZENES
971
thermal stability, making it possible to obtain stable
devices using these materials. (5) The cis-isomer has a
large blue shift in the absorption spectrum and a smaller
molar absorption coefficient in comparison with trans-
DPDSB, which is due to its torsion conformation and
lower conjugation length. Interestingly, although cis-
DPDSB shows very weak fluorescence in solution, strong
blue fluorescence in the crystal is observed owing to
limited photochemical processes in the crystal lattice.
(6) The HOMO and LUMO are both completely localized
on the distyrylbenzene whether it is in cis- or trans-
DPDSB, indicating that it is the distyrylbenzene, not the
terphenyl, that contributes to fluorescence in both iso-
mers. A similar result is found in the cation radical or
anion radical, where the distribution of the electron is
also all localized on the distyrylbenzene. These results
indicate that the distyrylbenzene has more sensitive
electroactivity than the terphenyl. (7) In OLEDs using
these two materials, trans-DPDSB has a higher blue
luminance and efficiency but cis-DPDSB has more ex-
cellent pure blue emission.
formed on a Netzsch ꢁDSC-204 instrument at heating
and cooling rates of 10 C minꢀ1 under nitrogen flushing.
Electrochemical measurements were performed with a
BAS 100 W instrument (Bioanalytical Systems) using a
platinum disk (È ¼ 2.0 mm) as working electrode, plati-
num wire as auxiliary electrode, with a porous ceramic
wick, and Ag/Agþ as reference electrode, standardized
for the redox couple ferricinium/ferrocene (E1/2
¼
þ0.40 V, ÁEP ¼ 76 mV). Cyclic voltammetric studies of
the cis- and trans-DPDSB were carried out at a scan rate
of 50 mV sꢀ1 on 0.01 M solutions in DMF containing
0.1 M Bu4NBF4 as supporting electrolyte. All solutions
were purged with a nitrogen stream for 10 min before
measurement. The procedure was performed at room
temperature and a nitrogen atmosphere was maintained
over the solution during measurements.
Theoretical method
The ground-state geometries of different conformations
were fully optimized using the density functional theory
(DFT), B3LYP/6–31G, as implemented in Gaussian 98.
ZINDO and TD-DFT/B3LYP calculations of the vertical
excitation energies were then performed at the optimized
geometries of the ground states. The excited geometries
were optimized by ab initio CIS/3–21G. All of Ips and
Eas in this paper are the difference energies between the
ions and molecules.
EXPERIMENTAL
Materials
p-Xylene, phenylboronic acid, t-BuOK, bromomethyl-
benzene, triphenylphosphine and tetrakis(triphenylpho-
sphine) palladium(0) were purchased from Aldrich and
used without further purification unless noted otherwise.
THF was dried and purified by fractional distillation over
sodium–benzophenone and DMF was vacuum distilled
over P2O5. Column chromatography was performed
using silica gel (200–300 mesh).
Fabrication of electroluminescent devices
The configuration of devices with multi-layers was
optimized for cis- and trans-DPDSB. Organic layers
were deposited by high-vacuum [10ꢀ6 Torr (1 Torr ¼
133.3 pa)] thermal evaporation on to a cleaned glass
substrate precoated with transparent, conductive indium
tin oxide (ITO). The layer thickness of the deposited
material was monitored in situ using an oscillating quartz
thickness monitor. Finally, an LiF buffer layer and an Al
cathode were vapor-deposited at a background pressure
of 10ꢀ6 Torr on to the organic films. EL spectra and CIE
coordination of these devices were measured with a
Spectroscan PR650 spectrometer. The luminance–current
density–voltage characteristics were recorded simulta-
neously with the measurement of the EL spectra by
combining the spectrometer with a Keithley Model
2400 programmable voltage–current source. All mea-
surements were carried out at room temperature under
ambient conditions.
General experiments
The NMR spectra were recorded on AVANCZ 500
spectrometers at 298 K by utilizing CDCl3 or DMSO-d6
as solvent and tetramethylsilane (TMS) as standard. The
compounds were characterized with a Flash EA 1112,
CHNS-O elemental analysis instrument. Single-crystal
structural analysis was performed on a Siemens SMART
CCD diffractometer with graphite-monochromated Mo
˚
Kꢃ radiation (ꢈ ¼ 0.71073 A). GC–mass spectra were
measured with a Finnigan TRACE MS instrument. IR
spectra were recorded on Perkin-Elmer spectrophot-
ometer in the 400–4000 cmꢀ1 region using a powder
sample on a KBr plate. UV–visible absorption spectra
were recorded on a UV-3100 spectrophotometer. Fluor-
escence measurements were carried out with an RF-
5301PC instrument. The mixed crystal was detected
with a Rigaku x-ray diffractometer (D/max r A, using
Syntheses
Cu Kꢃ radiation of wavelength 1.542 A). Differential
scanning calorimetric (DSC) measurements were per-
1,4-Dibromo-2,5-dimethylbenzene (1).59 Bromine (65.5 g,
0.41 mol, 2.05 equiv.) was added dropwise, over 30 min,
˚
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 962–973

972
Z. XIE ET AL.
to a stirred and ice-cooled solution of p-xylene (0.2 mol)
and iodine (0.2 g, 1.6 mmol), with rigorous exclusion of
light. After 1 day at room temperature, 20% KOH
solution (50 ml) was added and the mixture was cooled
to room temperature, the aqueous solution was decanted
and the remaining residue was recrystallized from EtOH
(2 ꢂ 200 ml) (34 g, yield 64.4%), m.p. 72–75 ꢁC. 1H
NMR (500 MHz, 25 ꢁC, CDCl3, TMS, ppm), ꢀ 7.39
(s, 2H; benzo H), 2.33 (s, 6H; CH3); FT-IR (KBr pellet,
cmꢀ1), 2978(m), 2952(m), 2916(w), 2848(w), 1749(m),
1473(s), 1433(s), 1375(m), 1342(m), 1293(w), 1186
(m), 1055(s), 982(s), 879(s), 748(s).
benzene (2.565 g) was dropped into DMF solution
containing triphenylphosphine (4.12 g) and refluxed for
12 h. The resulting solution was evaporated under de-
creased pressure and the crude product was washed with
cyclohexane (50 ml) and recrystallized from dichloro-
methane (100 ml). The white precipitates were collected
via filtration and dried under vacuum (5.65 g, yield 87%),
1
m.p. 294–295 ꢁC. H NMR (500 MHz, 25 ꢁC, CDCl3,
TMS, ppm), ꢀ 7.8–7.7 (m, 9H; benzo H), 7.64 (t, 6H;
benzo H), 7.23 (t, 1H; benzo H), 7.14 (t, 2H; benzo H),
7.09 (d, 2H; benzo H), 5.42 (d, 2H; CH2); FT-IR (KBr
pellet, cmꢀ1), 3049(m), 2985(m), 2850(m), 2777(m),
1585(m), 1495(m), 1437(s), 1161(m), 1111(s), 995(m),
875(m), 790(m), 756(s), 719(s), 690(s).
2,5-Dibromobenzene-1,4-dicarbaldehyde (2). This com-
pound was synthesized according to a published proce-
dure with minor modification.60 Sulfuric acid (28 ml) was
added dropwise to a suspension containing 1 (8.0 g),
acetic acid (40 ml) and acetic anhydride (80 ml) at 0 ꢁC.
CrO3 (12 g) was then added to the mixture in portions.
The resulting mixture was stirred vigorously at this
temperature for a further 5 h until the reaction was
completed. The greenish slurry was poured into ice–
water and filtered. The white solid was washed with
water and cold methanol. The diacetate was then hydro-
lyzed by refluxing with a mixture of water (40 ml),
ethanol (40 ml) and sulfuric acid (4 ml) for 5 h. After
the mixture had cooled, the pale yellow product was
separated by filtration. The crude product was purified by
recrystallization from chloroform (4.3 g, yield 48.6%),
2,5-Diphenyl-1,4-distyrylbenzene with two cis double
bonds (cis-DPDSB). The phosphonium salt (200 mg) and
3 (660 mg) were placed in a dry flask, which was wrapped
with tinfoil, and the flask was flushed with nitrogen. Dry,
cooled THF (30 ml) was added to the flask via an injector
and then t-BuOK in dry THF was added slowly to allow
the colored ylide formed to react with aldehyde groups
between successive additions. When no color was ob-
served upon addition of base, the mixture was stirred for a
further 12 h at room temperature. After the reaction was
completed, most of the solvent was removed under
reduced pressure and then the concentrated solution
was dropped into stirred methanol (50 ml). A 255 mg
amount of white product was obtained by filtration (yield
87%), m.p. 192.5 ꢁC. 1H NMR (500 MHz, 25 ꢁC, DMSO,
TMS, ppm), ꢀ 7.27–7.35 (m, 16H; benzo H), 7.16
[t, J(HH) ¼ 1.5 Hz, 4H; benzo H], 7.14 (s, 2H; benzo H),
6.64 [d, J(HH) ¼ 12 Hz, 2H; olefinic H] 6.42 [d,
J(HH) ¼ 12 Hz, 2H; olefinic H]; 13C NMR (500 MHz,
25 ꢁC, DMSO, TMS, ppm), ꢀ 140.5, 140.0, 137.5, 135.2,
132.1, 131.4, 130.3, 129.6, 129.5, 129.2, 129.0, 128.2;
FT-IR (KBr pellet, cmꢀ1), 3056(m), 1599(w), 1493(w),
1475(m), 1444(m), 1408(w), 1385(w), 1074(m),
1026(m), 870(vw), 783(s), 764(s), 698(vs); MS: m/z
434.2 (M). Anal. calcd for C34H26, C 93.97, H 6.03;
found, C 93.83, H 6.17%.
1
m.p. 194 ꢁC. H NMR (500 MHz, 25 ꢁC, CDCl3, TMS,
ppm), ꢀ ¼ 10.35 (s, 2H; CHO), 8.16 (s, 2H; benzo H); FT-
IR (KBr pellet, cmꢀ1), 3074(m), 2873(m), 1687(vs),
1444(m), 1342(s), 1276(m), 1157(m), 1057(s), 914(m),
812(m).
1,10;40,1-Terphenyl-20,50-dicarbaldehyde (3). This com-
pound was synthesized by the well-known Suzuki cou-
pling method.61 A mixture of 2 (1.0 g), phenylboronic
acid (1.1 g), Pd(PPh3)4 (0.2 g), toluene (12.5 ml) and 2 M
Na2CO3 solution (2.5 ml) was refluxed at 85 ꢁC for 36 h
under nitrogen, then poured into water and extracted with
dichloromethane. The organic layer was washed with
brine and water and dried over MgSO4. The crude
product was first purified by flash column chromatogra-
phy (dichloromethane as eluent) and then recrystallized
form chloroform. A 0.79 g amount of product (yield 81%)
was obtained as pale yellow crystals, m.p. 197–200 ꢁC.
1H NMR (500 MHz, 25 ꢁC, CDCl3, TMS, ppm), ꢀ 10.09
(s, 2H; CHO), 8.12 (s, 2H; benzo H), 7.53–7.44 (m, 10H;
benzo H); FT-IR (KBr pellet, cmꢀ1), 3024(w), 2889(w),
1678(vs), 1469(m), 1446(m), 1390(m), 1267(w), 1242 (w),
1149(m), 1076(w), 1022(w), 904(w), 837(s), 766 (m),
706(s).
2,5-Diphenyl-1,4-distyrylbenzene with two trans double
bonds (trans-DPDSB). This material was prepared by
refluxing a p-xylene solution of the cis-isomer (200 mg)
for 12 h in the presence of a small amount of iodine as
catalyst. The resulting solution was concentrated using a
rotatory evaporator and then dropped into stirred metha-
nol (20 ml). A 190 mg amount of yellow product was
1
obtained by filtration (yield 95%), m.p. 251–254 ꢁC. H
NMR (500 MHz, 25 ꢁC, DMSO, TMS, ppm), ꢀ 7.81(s,
2H; benzo H), 7.55 [t, J(HH) ¼ 7.36 Hz, 4H; benzo H],
7.50 [d, J(HH) ¼ 7.22 Hz, 4H; benzo H], 7.48 [t, J(HH) ¼
7.21Hz, 2H; benzo H], 7.39 [d, J(HH)¼ 7.33 Hz, 4H;
benzo H], 7.34 [d, J(HH) ¼ 16.31 Hz, 2H; olefinic H], 7.33
[t, J(HH)¼ 7.49 Hz, 4H; benzo H], 7.24 [t, J(HH)¼
7.25Hz, 2H; benzo H], 7.08 [d, J(HH) ¼ 16.35 Hz, 2H;
Benzyltriphenylphosphonium bromide. This compound
was synthesized with a molar ratio of 1:1.05 of (bromo-
methyl)benzene and triphenylphosphine. Bromomethyl-
Copyright # 2005 John Wiley & Sons, Ltd.
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STRUCTURE AND OPTICAL PROPERTIES OF 2,5-DIPHENYL-1,4-DISTYRYLBENZENES
973
13
olefinic H]; C NMR (500MHz, 25 ꢁC, DMSO, TMS,
25. Stalmach U, Schollmeyer D, Meier H. Chem. Mater. 1999; 11:
2103–2106.
ppm), ꢀ 141.0, 140.8, 138.0, 134.8, 130.6, 130.5, 129.6,
129.3, 128.6, 128.4, 128.1, 127.2, 126.9; FT-IR (KBr
pellet, cmꢀ1), 3053(m), 1595(m), 1493(m), 1477(m),
1446(m), 1396(w), 1340(w), 1072(m), 1024(m), 964(s),
922(w), 901(m), 877(vw), 852(w), 764(vs), 752(s),
704(vs); MS, m/z 434.2 (M). Anal. calcd for C34H26, C
93.97, H 6.03; found, C 93.85, H 6.15%.
26. Tian B, Zerbi G, Schenk R, Mu¨llen K. J. Chem. Phys. 1991; 95:
3191–3197.
´
¨
27. Zojer E, Knupfer M, Shuai Z, Fink J, Bredas JL, Horhold HH,
Grimme J, Scherf U, Benincori T, Leising G. Phys. Rev. B 2000;
61: 16561–16569.
28. Meier H, Gerold J, Kolshorn H, Mu¨hling B. Chem. Eur. J. 2004;
10: 360–370.
29. Syamakumari A, Schenning APHJ, Meijer EW. Chem. Eur. J.
2002; 8: 3353–3361.
30. He F, Cheng G, Zhang HQ, Zheng Y, Xie ZQ, Yang B, Ma YG,
Liu SY, Shen JC. Chem. Commun. 2003; 2206–2207.
31. Henari FZ, Manaa H, Kretsch KP, Blau WJ, Rost H, Pfeiffer S,
¨
Teuschel A, Tillmann H, Horhold HH. Chem. Phys. Lett. 1999;
307: 163–166.
Acknowledgments
¨
32. Dottinger SE, Hohloch M, Hohnholz D, Segura JL, Steinhuber E,
We are grateful for financial support from the National
Science Foundation of China. (grant numbers 20474024,
20125421, 90101026 and 50303007) and from the
Ministry of Science and Technology of China (grant
numbers 2002CB6134003 and 2003CB314703).
Hanack M. Synth. Met. 1997; 84: 267–268.
33. Strehmel B, Sarker AM, Malpert JH, Strehmel V, Seifert H,
Neckers DC. J. Am. Chem. Soc. 1999; 121: 1226–1236.
34. Barashkov NN, Guerrero DJ, Olivos HJ, Ferraris JP. Synth. Met.
1995; 74: 153–160.
35. Vromen S, Modiano A, Mandelvaum A, Ginsburg D, Hwang B,
Schlessinger RH, Cava MP. Tetrahedron 1966; 22(Suppl. 7): 203–
211.
36. Wong KF, Skaf MS, Yang CY, Rossky PJ, Bagchi B, Hu D, Yu J,
Barbara PF. J. Phys. Chem. B 2001; 105: 6103–6107.
37. Chen YS, Meng HF. Phys. Rev. B 2002; 66: 035202.
38. Summers MA, Kemper PR, Bushnell JE, Robinson MR, Bazan
GC, Bowers MT, Buratto SK. J. Am. Chem. Soc. 2003; 125: 5199–
5203.
39. Claudio GC, Bittner ER. J. Chem. Phys. 2001; 115: 9585–9593.
40. Son S, Dodabalapur A, Lovinger AJ, Galvin ME. Science 1995;
269: 376–378.
41. Yang NC, Jeong JK, Choi SJ, Rhee TH, Suh DH. Macromol.
Rapid Commun. 1999; 20: 586–590.
42. Pang Y, Li J, Hu B, Karasz FE. Macromolecules 1999; 32: 3946–
3950.
43. Hwang JJ, Lin RL, Shieh RL, Jwo JJ. J. Mol. Catal. A: Chem.
1999; 142: 125–139.
44. Jacobs S, Eevers W, Verreyt G, Geise HJ. Synth. Met. 1993; 61:
189–193.
45. Nakanishi K. Infrared Absorption Spectroscopy—Practical.
Holden-Day: San Francisco, 1962; 24, 27.
46. Wong MW. Chem. Phys. Lett. 1996; 256: 391–399.
47. Fan QL, Lu S, Lai YH, Hou XY, Huang W. Macromolecules 2003;
36: 6976–6984.
48. Cacelli I, Prampolini G. J. Phys. Chem. A 2003; 107: 8665–8670.
49. Ito Y, Uozu Y, Dote T, Ueda M, Matsuura T. J. Am. Chem. Soc.
1988; 110: 189–198.
50. Harada J, Ogawa K. J. Am. Chem. Soc. 2001; 123: 10884–10888;
J. Am. Chem. Soc. 2004; 126: 3539–3544.
51. van Hutten PF, Wildeman J, Meetsma A, Hadziioannou G. J. Am.
Chem. Soc. 1999; 121: 5910–5918.
52. Waldeck DH. Chem. Rev. 1991; 91: 415–436, and references cited
therein.
REFERENCES
1. Clery D. Science 1994; 263: 1700–1702.
2. Kraft A, Grimsdale AC, Holmes AB. Angew. Chem. 1998; 110:
416–443; Angew. Chem. Int. Ed. 1998; 37: 402–428.
3. Burroughes JH, Bradley DDC, Brown AR, Marks RN, Mackay K,
Friend RH, Burns PL, Holmes AB. Nature 1990; 347: 539–541.
4. Scherf U, List EJW. Adv. Mater. 1998; 14: 477–487.
5. Braun D, Heeger AJ. Appl. Phys. Lett. 1991; 58: 1982–1984.
6. Shi Y, Liu J, Yang Y. J. Appl. Phys. 2000; 87: 4254–4263.
7. Wan WC, Antoniadis H, Choong VE, Razafitrimo H, Gao Y, Feld
WA, Hsieh BR. Macromolecules 1997; 30: 6567–6574.
8. Hsieh BR, Antoniadis H, Bland DC, Feld WA. Adv. Mater. 1995;
7: 36–39.
9. Hsieh BR, Wan WC, Yu Y, Gao Y, Goodwin TE, Gonzalez SA,
Feld WA. Macromolecules 1998; 31: 631–636.
10. Greenham NC, Moratti SC, Bradley DDC, Friend RH, Holmes
AB. Nature 1993; 365: 628–630.
11. Chen SA, Chang EC. Macromolecules 1998; 31: 4899–4907.
12. Jenekhe SA, Osaheni JA. Science 1994; 265: 765–768.
13. Jakubiak R, Collison CJ, Wan WC, Rothberg LJ, Hsieh BR.
J. Phys. Chem. A 1999; 103: 2394–2398.
14. Yan M, Rothberg LJ, Kwock EW, Miller TM. Phys. Rev. Lett.
1995; 75: 1992–1995.
15. Chen SH, Su AC, Han SR, Chen SA, Lee YZ. Macromolecules
2004; 37: 181–186.
16. Vanden Bout DA, Yip WT, Hu D, Fu DK, Swager TM, Barbara
PF. Science 1997; 277: 1074–1077.
17. Nguyen TQ, Doan V, Schwartz BJ. J. Chem. Phys. 1999; 110:
4068–4078.
18. Nguyen TQ, Martini IB, Liu J, Schwartz BJ. J. Phys. Chem. B
2000; 104: 237–255.
53. Dou Y, Allen RE. J. Chem. Phys. 2003; 119: 10658–10666.
54. Wu CC, DeLong MC, Vardeny ZV, Ferraris JP. Synth. Met. 2003;
137: 939–940.
55. Chen J, Law CCW, Lam JWY, Dong Y, Lo SMF, Williams ID,
Zhu DB, Tang BZ. Chem. Mater. 2003; 15: 1535–1546.
56. Renak ML, Bartholomew GP, Wang S, Ricatto PJ, Lachicotte RJ,
Bazan GC. J. Am. Chem. Soc. 1999; 121: 7787–7799.
57. Lange FJ, Leuze M, Hanack M. J. Phys. Org. Chem. 2001; 14:
474–480.
58. Curioni A, Boero M, Andreoni W. Chem. Phys. Lett. 1998; 294:
263–271.
59. Rehahn M, Schlu¨ter AD, Feast WJ. Synthesis 1988; 386–388.
60. Naylor JR. J. Chem. Soc. 1952; 4085–4086.
61. Miyaura N, Suzuki A. Chem. Rev. 1995; 95: 2457–2483.
19. Hsieh BR, Yu Y, Forsythe EW, Schaaf GM, Feld WA. J. Am.
Chem. Soc. 1998; 120: 231–232.
20. Peng Z, Zhang J, Xu B. Macromolecules 1999; 32: 5162–5164.
21. Spreitzer H, Becker H, Kluge E, Kreuder W, Schenk H, Demandt
R, Schoo H. Adv. Mater. 1998; 10: 1340–1343.
22. Mu¨llen K, Wegner G. Electronic Materials: The Oligomer
Approach. Wiley-VCH: Weinheim, 1998.
23. Martinez-Ruiz P, Behnisch B, Schweikart KH, Hanack M, Lu¨er L,
Oelkrug D. Chem. Eur. J. 2000; 6: 1294–1301.
24. Liao L, Pang Y, Ding L, Karasz FE. Macromolecules 2001; 34:
7300–7305.
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