Crystal structures, two-photon absorption and theoretical calculation of a series of bis-vinylpyridine compounds synthesized by one-step solid state reaction

Article abstract of DOI:10.1007/s11426-010-4141-6

Three bis-vinylpyridine compounds (4,4′-bis(2-vinylpyridine)biphenyl L ₁, 4,4′-bis(3-vinylpyridine) biphenyl L ₂, and 4,4′-bis (4-vinylpyridine)biphenyl L ₃) were synthesized by one-step solid-state reactions at room tempe

Full text of DOI:10.1007/s11426-010-4141-6

SCIENCE CHINA
Chemistry
May 2011 Vol.54 No.5: 730–736
doi: 10.1007/s11426-010-4141-6
• ARTICLES •
Crystal structures, two-photon absorption and theoretical
calculation of a series of bis-vinylpyridine compounds synthesized
by one-step solid state reaction
LI DongMei1, ZHANG Qiong1, A. M. Showkot HOSSAIN1, SUN Mei1, WU JieYing1,
YANG JiaXiang1, ZHOU HongPing1*, TAO LiMin2, WANG ChuanKui2 & TIAN YuPeng1,3,4*
1Key Laboratory of Functional Inorganic Materials Chemistry of Anhui Province; Department of Chemistry,
Anhui University, Hefei 230039, China
2Department of Physics, Shandong Normal University, Jinan 250014, China
3State Key Laboratory of Crystal Materials; Shandong University, Jinan 250100, China
4State Key Laboratory of Coordination Chemistry; Nanjing University, Nanjing 210093, China
Received July 12, 2010; accepted August 12, 2010; published online October 16, 2010
Three bis-vinylpyridine compounds (4,4′-bis(2-vinylpyridine)biphenyl L1, 4,4′-bis(3-vinylpyridine) biphenyl L2, and 4,4′-bis
(4-vinylpyridine)biphenyl L3) were synthesized by one-step solid-state reactions at room temperature, giving nearly quantita-
tive yields. The compounds obtained were fully characterized by IR, MS and NMR spectroscopies. The structures of L2 and L3
were determined by single crystal X-ray diffraction analysis. No noticeable solvatochromism was observed in either
one-photon absorption or one-photon excited fluorescence spectra. All of the compounds have high fluorescence quantum
yields and long fluorescence lifetime. The linear and nonlinear optical properties of the compounds were investigated both ex-
perimentally and theoretically. Interestingly, the position of the nitrogen atom from pyridine influences their two-photon ab-
sorption across-sections.
two-photon absorption, one-step solid-state reaction, high quantum yield, pyridine derivatives
[16]. In particular, a framework for mobile -electrons with
electron donor/acceptor groups at the terminal sites with or
without donors/acceptors in the middle of the conjugated
framework provides the potential application for symmetric
charge displacement upon excitation and enhancing TPA.
With the above consideration, although some of these
materials exhibited large TPA cross-sections and good TPA
properties, most of them were obtained through complicated
routes, including our recent work [17]. Investigating simple
and efficient synthesis of TPA chromophores would be
beneficial to the development of TPA materials. In this pa-
per, we present a series of novel TPA chromophores based
on pyridine as a terminal group, L1, L2, and L3 (Figure 1),
which were prepared through one-step solid-state reactions
and gave quantitative yields. It is noteworthy here that the
1 Introduction
Two-photon absorption (TPA) has many applications over
recent years, including 3D fluorescence microscopy, optical
limiting, 3D optical data storage and 3D microfabrication
[1–5] . Up to now, many efforts have been paid to develop
efficient two-photon chromophores. A large number of re-
searches on synthesis, structures and theory have revealed
the importance of certain basic structural motifs for TPA-
active organic materials [6, 7] which typically are charac-
terized in the following classes: dipoles [8], quadrupoles
[9–11], multibranched molecules [12–15], and dendrimers
*Corresponding author (email: zhpzhp@263.net; yptian@ahu.edu.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2010
chem.scichina.com
www.springerlink.com

Li DM, et al. Sci China Chem May (2011) Vol.54 No.5
731
methods with SHELXS-97 and refined with SHEXLX-9720.
All the non-hydrogen atoms were refined by full-matrix
techniques with anisotropic displacement parameters. The
hydrogen atoms were geometrically fixed at calculated
positions attached to their parent atoms, and treated as riding
atoms. Additional crystallographic details and complete
listings of the compounds have been deposited with the
Cambridge Crystallographic Data Center as supplementary
publications with reference number 227584 for L2 and
227582 for L3.
Figure 1 ORTEP diagram with the atomic numbering scheme of L2.
Thermal ellipsoids are shown at the 50% probability level.
novel chromophores possess potential application perspec-
tive due to their simple preparation, TPA activity and coor-
dinating ability [18, 4, 19]. Furthermore, the structure-
property relationship of the chromophores has been system-
atically investigated.
2.4 Preparations and characterization
In this research, all the bis-vinylpyridine compounds were
synthesized by one-step solid-state reactions (see Scheme 1).
The mixture of biphenyl bisphosphonates (1 mmol, 0.364 g),
pyridine carboxaldehyde (3 mmol, 0.32 g) and excess po-
tassium t-butoxide were manually milled for 10 min at room
temperature. The reaction mixture was poured into water
and filtered. The precipitates were washed with water to
give the yellow product in a quantitative yield. Through the
one-step solid-state reactions, the target compounds were
isolated as pure with trans-configuration.
2 Experimental
2.1 Materials and apparatus
All chemicals and solvents were dried and purified by usual
methods. Elemental analysis was performed with a Perkin-
Elmer 240 analyzer. IR spectra (4000–400 cm1), as KBr
pellets, were recorded on a Nicolet FT-IR 170 SX spectro-
photometer. The mass spectra were obtained on a Micro-
mass GCT-MS Spectrometer (EI source). Proton nuclear
magnetic resonance (1H NMR) was performed on a Bruker
500 spectrometer with TMS as internal standard.
Compound L1
Yield: 90%. Anal. Calcd. for C26H20N2: C, 86.64; H, 5.59; N,
7.77. Found: C, 86.58; H, 5.53; N, 7.89. IR (KBr, cm1)
1
selected bands: 3049 (m), 1435 (m). H NMR (CDCl3), 
(ppm): 8.59 (d, J = 4.25 Hz, 2H), 7.77–7.82 (m, 10H), 7.73
2.2 Optical measurements
(d, J = 16.10 Hz, 2H), 7.58 (d, J = 7.78 Hz, 2H), 7.39 (d,
J
= 16.07 Hz, 2H), 7.26–7.28 (m, 2H). ESIMS, m/z (%): 361.3
All the solvents used for absorption and fluorescence meas-
urements were HPLC grade. For diluted solutions of c =4.0
× 105 M, in quartz cuvettes of 1 cm path length, one-photon
absorption (OPA) spectra were recorded on a UV-265 spec-
trometer. One-photon excited fluorescence (OPEF) spectra
were recorded on a PerkinElmer LS55 fluorescence spec-
trometer equipped with a 450 W Xe lamp. The concentra-
tions are 1.0 × 106 mol/L. The fluorescence lifetime meas-
urements of the compounds in DMF were performed on the
Edinburgh FLS920 spectrofluorometer with a Hydrogen
flash lamp (pulse duration < 1 ns) as the excitation source.
Two-photon emission fluorescence (TPEF) spectra were
measured using a streak camera (C5680-01, Hamamatsu) and
imaging spectrograph (C5094, Hamamatsu). The pump la-
ser beam came from a mode-locked Ti: sapphire laser sys-
tem operating from 710 to 790 nm, pulse duration 200 fs,
repetition rate of 76 MHz (Coherent Mira900-D).
([M+H]+, 100). mp 298.8 °C.
Compound L2
Yield: 92%. Anal. Calcd. for C26H20N2: C, 86.64; H, 5.59; N,
2.3 X-ray crystallography
In the determination of the structure of the single crystal,
X-ray intensities were recorded by a Bruker SMART CCD
area detector diffractometer equipped with MoK radiation
using - scan mode. The structure was solved by direct
Scheme 1 The synthesis of the three TPA chromophores.

732
Li DM, et al. Sci China Chem May (2011) Vol.54 No.5
7.77. Found: C, 86.71; H, 5.50; N, 7.79. IR (KBr, cm1)
selected bands: 3014 (m), 1566 (m). H NMR (CDCl3), 
(ppm): 8.81 (s, 2H), 8.46 (d, J=4.4 Hz, 2H), 8.10 (d, J=7.9
Hz, 2H), 7.79 (d, J = 8.2 Hz, 4H), 7.73 (d, J = 8.3 Hz, 4H),
7.47 (d, J = 16.5 Hz, 2 H), 7.41–7.43 (m, 2 H), 7.36 (d, J=
16.6 Hz, 2 H). ESIMS, m/z (%): 361.3 ([M+H]+, 100). mp
305.8 °C.
and 2, respectively. The crystallography data were listed
in Tables 1 and S1, respectively. From the figures, it can
be seen that the two molecules adopted the same arrange-
ments to form the central symmetrical species. In each
molecule, the central benzene ring and the terminal
pyridinium are nearly coplanar with the dihedral angle of
7.8˚. The bond lengths of the benzene and pyridinium rings
are all of aromatic character. The linkage bond lengths be-
tween the benzene rings and the pyridinium units are quite
conjugated, for example, C2C6 (1.464 Å), C6=C7 (1.316
Å) and C7C8 (1.465 Å). The structural features suggest
that all nonhydrogen atoms are highly conjugated and
nearly coplanar, which will favour the electronic delocaliza-
tion in the molecules.
1
Compound L3
Yield: 92%. Anal. Calcd. for C26H20N2: C, 86.64; H, 5.59; N,
7.77. Found: C, 86.55; H, 5.63; N, 7.82. IR (KBr, cm1)
1
selected bands: 3023 (m), 1506 (m). H NMR (CDCl3), 
(ppm): 8.57 (d, J = 4.7 Hz, 4H), 7.59–7.83 (m, 12H)
7.23–7.36 (m, 4H). ESIMS, m/z (%): 361.3 ([M+H]+, 100).
mp 312.5 °C.
3.3 One-photon absorption (OPA) and one-photon
excited fluorescence (OPEF)
3 Results and discussion
One-photon absorption and emission parameters, fluores-
cence lifetimes for all the compounds have been summarized
in Table 2. It can be seen that the linear spectra confirm that
all the compounds are only marginally solvatochromic, both
in absorption and emission (5 nm excursions in a wide
3.1 Synthesis
L1 has been synthesized using diazonium and 2-vinylpyridine
by Ganushchak et al. [21]. The process is much more com-
plicated and the yield is not high (33%–70%) while L3 was
obtained through Heck reaction with diiodobiphenyl and
vinylpyridine which gave the product by 30% yield [22–24].
However, the compounds were synthesized through one-
step solid-state reactions and gave quantitative yields.
3.2 Crystallographic studies
Figure 2 ORTEP diagram with the atomic numbering scheme of L3.
The crystal structures of L2 and L3 are shown in Figures 1
Thermal ellipsoids are shown at the 50% probability level.
Table 1 Crystallographic data for L2 and L3
Formula
Formula weight
C26H20N2
C26H20N2
360.44
360.44
Crystal system
Space group
a, b, c (Å)
monoclinic
P21/c
monoclinic
P21/c
13.11(22), 5.562(9), 12.92(2)
12.898(6), 5.714(3), 12.723(6)
90.00, 93.25(3), 90.00
90.00, 92.486(8), 90.00
a, , (º)
V [Å3]
940(3)
936.8(7)
Z
2
2
D (calc) (g/cm3)
1.273
1.278
F(000)
380
380
Crystal size (mm)
Temperature (K)
Radiation (Å) MoK
0.32 × 0.17 × 0.13
293(2)
0.43 × 0.31 × 0.07
293(2)
0.71073
0.71073
2.0, 28.57
1.58, 25.02
15: 12; 6: 6; 15: 15
1661

min-max (º)
Data set
19: 20; 18: 20; 21: 20
1652
Observed data [I > 2.0  (I)]
Nref, Npar
3694, 543
4679, 673
R, wR2, S
0.0510, 0.0889, 0.716
0.0580, 0.1419, 0.857

Li DM, et al. Sci China Chem May (2011) Vol.54 No.5
733
Table 2 One-photon absorption and emission parameters, fluorescence lifetimes for L1–L3
max (nm) a)
347

max (nm) b)

max (nm) c)
 d)
0.90
0.94
0.95
 (ns) e)
Compound
Solvent
CHCl3
CH3CN
Ethanol
DMF

L1
404, 424
401, 419
423
348
347
354
423
442, 487
434, 483
440, 488
0.84
L2
CHCl3
CH3CN
ethanol
DMF
348
404, 423
420
349
347
427
353
426
0.86
L3
CHCl3
CH3CN
ethanol
DMF
354
399, 420
395, 415
399, 418
421
351
352
357
0.81
a) Absorption peak position in nm (1 × 105 mol/L); b) OPEF peak position in nm; c) TPEF peak position in nm; d) quantum yields determined by using
naphthalene as the standard; e) OPEF lifetime.
range of solvents polarities). For the chromophores are cen-
trosymmetry, only weak solvatochromism is to be expected.
The optical properties of the three compounds are very
similar. The quantum yields () (see in supporting informa-
tion) of L1 to L3 in different solvents were determined by
using naphthalene as standard. From Table 2, the chromo-
phores obtained possess high quantum yields, and long
fluorescence life time with the sequence of L2 >L1 >L3, the
lifetimes of which in DMF were longer than previous work
[25]. Meanwhile, they also had similar trend by comparison
with previous pyridine derivatives [26]. One-photon absorp-
tion spectra of L2 in four solvents with different polarity are
shown in Figure S4. It can be seen that the absorption
maxima show little differences with the increasing solvent
polarity. In Figure 3 (left), the three curves show that the
absorption maxima at 347 nm for L1 (with the correspond-
ing mole absorption coefficient  = 4.0 × 104 M1 cm1), 348
nm for L2 (= 3.0 × 104 M1 cm1), and 354 nm for L3 (=
5.3 × 104 M1 cm1) are assigned as the -* transition of
the whole molecule. The OPA peak position of L3 show ca.
5-nm red shift compared to those of L1 and L2 in all the
solvents, resulting from the higher electron-accepting ability
of the 4-pyridyl moiety.
The one-photon fluorescence spectra of L1 in four or-
ganic solvents are shown in Figure S5. As shown in Figure
S5 (or see the emission maxima in Table 2), two bands were
clearly seen when the three compounds were in the solvents
with low polarity. But with the increasing of the solvent
polarity, each L tends to show one emission peak. In fact,
there exists a single emission of each compound, whereas
the vibronic structure changes somewhat from solvent to
solvent. The emission spectra of all the compounds in chlo-
roform were also given in Figure 3 (right). In accordance
with OPA, the OPEF intensities of the three compounds
also exhibit the sequence of L3 > L1 > L2.
3.4 Two-photon excited fluorescence (TPEF) and TPA
cross-section
The two-photon fluorescence spectra of compounds in DMF
with c = 1.0 × 103 mol/L are shown in Figure 4. As men-
tioned above, no linear absorption occurs in the spectral
range from 450 to 1000 nm, and the emission exited by 710 nm
laser wavelength can be attributed to the TPEF mechanism.
By tuning the pump wavelengths incrementally from 710 to
790 nm, keeping the input power fixed, and then recording
the TPEF intensity, the two-photon emission spectra of
L1–L3 were shown in Figure 4 (the excitation wavelength is
710 nm). The spectra of the TPA cross-sections of L1–L3
were obtained with the excitation wavelength ranging from
710 to 790 nm, as shown in Figure 5.
The TPA cross-section  was obtained by comparing the
TPEF intensity of the sample with that of the reference
compound by the following equation [27],
Figure 3 Linear absorption and one-photon fluorescence spectra of
L1–L3 in CHCl3.

734
Li DM, et al. Sci China Chem May (2011) Vol.54 No.5
that, quite unfortunately, is not accessible with our experi-
mental set up. At the excitation wavelength of 710 nm, the
max values are 106, 98 and 55 GM for L3, L1 and L2, which

are smaller than those of other A--A chromophores with
similar structures [28]. But in this case, these chromophores
are much easily prepared in high yield. The intensities of
the TPEF spectra and the max values show obvious ten-
dency of L3 > L1 > L2, which corresponds to the order in the
electron-accepting ability of the terminal groups (


).
3.5 Theoretical calculation
Figure 4 The two-photon emission fluorescence spectra of L1–L3 in
DMF (c = 1.0 × 103 M, the excitation wavelength is at 720 nm).
In terms of sum-over-state formula, the two-photon matrix
element for the two-photon resonant absorption of identical
energy is written as [29]




0 
j
j 
f
0 
j
j 
f
S


(2)

j f
2
j f
2
j




where |0 and |f denote the ground state and the final state,
respectively. |j means all the intermediate states, including
the ground state. j is the excitation energy of the excited
states and  is the electronic dipole moment. In general, the
total TPA probability requires the information of all the
excited states that is uneasy to be obtained clearly. On the
other hand, a few-state model can often provide satisfying
results for TPA cross-section in a visible region [9, 30–32].
The TPA cross-section is given by orientational averaging
over the two-photon absorption probability [27].
Figure 5 The spectra of the two-photon absorption cross-sections of
L1–L3 (from a 200 fs, 76 MHz Ti:sapphire laser) in DMF vs. excitation
wavelengths ranging from 710 to 790 nm.

*
*


tpa

F  S S  G S S  H  S S
(3)



  r Fr cr nr F cn
(1)
r
where the coefficients F, G and H are related to the incident
radiation. For the linearly polarized light, F, G and H are 2,
2 and 2, but for the circular case, they are 2, 3 and 3, re-
spectively. In the present work, we only consider the results
with the linearly polarized laser beam. The summation goes
over the molecular axe ,  = {x, y, z}.
where the subscript r denotes the reference compound and F
stands for the integral intensity of TPEF peak,  is the
OPEF quantum yield, n is the refractive index of solution,
and c is the concentration of solution in mol/L. The experi-
mental errors are estimated to be ± 15% from the variations
of laser energies and sample concentrations. From Figures 4,
5 and Table 2, it can be seen that the curves of two-photon
emission fluorescence (in DMF) and OPEF (in solvent with
low polarity) are similar. They both exhibit two peaks and
the intensities also follow the sequence of L3 > L1 > L2. The
TPEF maxima of L3 and L1 are red-shifted relative to that
of L2, caused by the weeker electron-accepting ability of
3-pyridyl group. The peak positions around 430 and 480 nm
for the three compounds show a 30-nm red shift compared
to the OPEF maxima in the same solvent, which can be ex-
plained by the effect of re-absorption [28, 29]. As shown in
Figure 5, the peak at 730 nm in each spectrum did not cor-
respond to the maxima of the TPA band. It is just a shoulder
of a much more intense TP transition placed below 710 nm
The TPA cross-section directly comparable with experi-
mental measurements is defined as [28]
2 g 
 
2
5
4 a0
15c0
tp

tp
(4)
 f
Here a0 is the Bohr radius, c0 is the speed of light,  is
the fine structure constant,  is the photon energy of the
incident light, g() denotes the spectral line profile, here it
is assumed to be a -function. f is the lifetime broadening
of the final state, which is assumed to be 0.1 eV.
We utilized the Gaussian-98 program package to opti-
mize the molecular geometrical structure with the hybrid
density functional theory (DFT/B3LYP) and a basis set

Li DM, et al. Sci China Chem May (2011) Vol.54 No.5
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4 Conclusions and outlooks
In summary, three compounds with two-photon absorption
activity were synthesized by the one-step solid-state reac-
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photophysical properties were systematically studied both
experimentally and theoretically. Indeed, no noticeable sol-
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OPA or OPEF spectra. Interestingly, the position of the ni-
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It is supported by a grant for the National Natural Science Foundation of
China (20771001, 50703001, 50873001), Department of Education of
Anhui Province (KJ2010A030), Team for Scientific Innovation Foundation
of Anhui Province (2006KJ007TD), Key Laboratory of Opto-Electronic
Information Acquisition and Manipulation (Anhui University). Crystallo-
graphic data for the structure reported in this paper have been deposited
with Cambridge Crystallographic Data Center as supplementary publica-
tion no. CCDC：227584，227582. Copies of the data can be obtained free
of charge CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax (44)
1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
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