Synthesis and two-photon absorption properties of novel 2-substituted-4,5-diphenyl-1H-imidazoles

Article abstract of DOI:10.1016/j.tet.2016.04.015

Novel 2-substituted-4,5-diphenyl-1H-imidazoles (M1-M4) were synthesized via a three-component, one-pot reaction under solvent-free conditions. The structures were characterized by infrared, hydrogen-1 nuclear magnetic resonance, carbon-13 nuclear magnetic

Full text of DOI:10.1016/j.tet.2016.04.015

Accepted Manuscript
Synthesis and two-photon absorption properties of novel 2-substituted-4,5-diphenyl-
1H-imidazoles
Guo-Chuang Zheng, Zhi-Bin Cai, Yu-Lu Pan, Li Bai, Yan-Tao Zhou, Sheng-Li Li, Yu-
Peng Tian
PII:
S0040-4020(16)30268-X
10.1016/j.tet.2016.04.015
TET 27658
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 22 January 2016
Revised Date: 31 March 2016
Accepted Date: 6 April 2016
Please cite this article as: Zheng G-C, Cai Z-B, Pan Y-L, Bai L, Zhou Y-T, Li S-L, Tian Y-P, Synthesis
and two-photon absorption properties of novel 2-substituted-4,5-diphenyl- 1H-imidazoles, Tetrahedron
(2016), doi: 10.1016/j.tet.2016.04.015.
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ACCEPTED MANUSCRIPT
Graphical Abstract
Novel 2-substituted-4,5-diphenyl-1H-imidazoles (M1-M4) have been synthesized via
the solvent-free Debus-Radziszewski reaction. They emit up-converted fluorescence,
and the two-photon absorption cross-sections are 585, 31, 34, and 1193 GM in DMF,
respectively.

ACCEPTED MANUSCRIPT
Synthesis and two-photon absorption properties of novel 2-substituted-4,5-diphenyl-
1H-imidazoles
Guo-Chuang Zheng a, Zhi-Bin Cai a,*, Yu-Lu Pana, Li Baia, Yan-Tao Zhoua, and Sheng-Li
Li b, Yu-Peng Tian b
a College of Chemical Engineering, Zhejiang University of Technology, Hangzhou
310014, PR China
b Department of Chemistry, Anhui Province Key Laboratory of Functional Inorganic
Materials, Anhui University, Hefei 230039, PR China
Abstract
Novel 2-substituted-4,5-diphenyl-1H-imidazoles (M1-M4) were synthesized via a
three-component, one-pot reaction under solvent-free conditions. The structures were
characterized by infrared, hydrogen-1 nuclear magnetic resonance, carbon-13 nuclear
magnetic resonance, mass spectrometry and elemental analysis. Their UV-visible
absorption, single-photon excited fluorescence, two-photon absorption, and two-photon
excited fluorescence were systematically investigated in different solvents. Pumped by
femtosecond laser pulses, M1 and M4 exhibit large two-photon absorption cross-sections
(585 and 1193 GM in DMF, respectively). The quantum chemical density functional
theory calculations offer complementary information regarding the frontier orbitals and
the molecular structures, which confirm that the degree of intramolecular charge transfer
plays an important role in enhancing two-photon absorption properties.
Keywords: Two-photon absorption; Solvent-free; Imidazole; Synthesis
*Corresponding author. Tel. : +86 571 88320891.
E-mail address: caizbmail@126.com (Z.-B. Cai).
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1. Introduction
In recent years, a tremendous amount of interest has been attracted to materials with
two-photon absorption (TPA) properties for their potential applications, such as
two-photon dynamic therapy,1-3 up-converted lasing,4 optical power limiting,5-7
three-dimensional data storage,8-9 three-dimensional microfabrication,10-12 and fluorescent
probes in living cell imaging studies.13-15 So far, much effort has been devoted to
designing and synthesizing TPA materials with large TPA cross-sections (σ) as well as
high fluorescence quantum yields (Φ).16-18
Among the reported TPA systems, the heterocycle-based chromphores represent a
growing class of TPA materials, and have evoked special attention.19-22 Imidazole, the
N-heterocycle molecule, has high electron-withdrawing ability, good coplanarity, and
good thermal stability, which render it to be an ideal building block for nonlinear optical
materials.23-25 In addition, imidazole derivatives have been shown to exhibit interesting
biological activities, including anti-allergy,26 anti-tumor,27 anti-inflammatory,28
anti-bacterial,29 and analgesic.30 Hence, imidazole plays an important role in biochemistry,
medical science, nonlinear optical materials and so on.
Organic solvents occupy a very large part on the list of damaging chemicals. In recent
years, solvent-free organic reactions have caused great interest. Debus-Radziszewski31
reaction is a commonly used method to synthesize imidazoles, most of which were
prepared using solvents. So the development of synthetic methods enabling
environment-friendly
access
to
this
heterocycle
is
still
desirable.
2-Substituted-4,5-diphenyl-1H-imidazoles are generally synthesized by three-component
cyclocondensation of benzil with an aldehyde and ammonium acetate, which comprises
the use of refluxing in AcOH.32 Obviously, this method usually produces a large amount
of waste acid that limits its utility.
In this paper, a simple, mild, environmentally benign, and efficient method has been
used for the preparation of four new 2-substituted-4,5-diphenyl-1H-imidazole derivatives
2

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M1-M4 (scheme 1) starting from benzil, ammonium acetate and various aromatic
aldehydes under solvent-free conditions.33 The target imidazole derivatives are in the
form of A-π-A (M1), A-π-D (M2), A-D-A (M3), and A-π-D-π-A (M4), respectively. (D:
electron donating group, A: electron accepting group, π: conjugated pathway). Their
linear and nonlinear optical properties have been systematically investigated in different
solvents. Meanwhile, the quantum chemical calculations have been performed to provide
deep insight into the electronic structures and the optical properties of these imidazole
derivatives. Detailed results and discussion are presented in the following sections.
2. Results and discussion
2.1. Synthesis and characterization
The detailed synthetic routes of four imidazole derivatives M1-M4 are described in
Scheme 2. 4-[(1E)-2-(4-Formylphenyl)ethenyl]benzonitrile (3a) was achieved following
a one-pot two-step reaction, involving the Horner-Wadsworth-Emmons (HWE) reaction
between 4-(diethoxymethyl)benzaldehyde (1a) and [(4-cyanophenyl)methyl]phosphonic
acid diethyl ester (2a) with high trans-stereoselectivity and subsequent hydrolysis under
mild acidic conditions with aqueous acetic acid. Using potassium tert-butoxide as catalyst
and DMF as solvent, 4-(9H-carbazol-9-yl)benzaldehyde (1b) was prepared by direct
reaction of 9H-carbazole with 4-fluorobenzaldehyde. 9-ethyl-9H-Carbazole-3,6-
dicarboxaldehyde (1c) was obtained by the Vilsmeier formylation reaction of
9-ethyl-9H-carbazole
dimethoxybenzene (1d) was prepared via the Blanc reaction of 1,4-dimethoxybenzene
with (HCHO)n and HBr, then reacted with P(OEt)3 to yield
with
DMF
and
POCl3.
1,4-Bis(bromomethyl)-2,5-
[(2,5-dimethoxy-1,4-phenylene)bis(methylene)]bisphosphonic acid tetraethyl ester (2d).
4,4'-[(2,5-Dimethoxy-1,4-phenylene)di-(1E)-2,1-ethenediyl] bisbenzaldehyde (3d) was
synthesized by the similar experimental conditions described for 3a. M1-M4 were
prepared from benzil, the corresponding aromatic aldehydes (3a, 1b, 1c, and 3d), and
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ammonium acetate under solvent-free conditions as shown in Scheme 2. It is noteworthy
that the target compounds are easily collected and purified.
The FT-IR spectra of M1-M4 exhibit absorption frequencies at 3398-3420 cm-1 for NH
1
group of the imidazole ring. The H NMR spectra of M1-M4 exhibit one singlet at
12.66-12.90 ppm due to the NH group of the imidazole ring. For M1 and M4, the
(E)-configurations of the C-C double bonds are certified by the coupling constants 3J (H,
H) = 16.5 Hz for the olefinic AB spin systems. In addition, it is striking to note a signal at
m/z 316.8 for M3 and 390.5 for M4, this can be interpreted as doubly protonated
molecular ion ([M+2H]2+) of M3 and M4.
CN
N
N
H
M1
N
N
N
H
M2
N
N
HN
NH
N
Et
M3
4

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OMe
N
N
H
N
N
H
MeO
M4
Scheme 1. Molecular structures of M1-M4.
EtO
CH(OEt)3
CHO
OHC
CHO
EtO
1a
OEt
O
(1) 1a
P
P(OEt)3
NC
OEt
NC
NC
CH2Br
(2) CH3COOH
CHO
3a
2a
F
CHO
N
CHO
N
H
1b
OHC
CHO
DMF
N
POCl3
N
Et
Et
1c
5

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OMe
OMe
EtO
OMe
O
(HCHO)n
HBr
P(OEt)3
O
P
BrH2C
MeO
CH2Br
EtO
OEt
P
MeO
MeO
OEt
1d
2d
OMe
CHO
(1) 1a
OHC
(2) CH3COOH
MeO
3d
3a
M1
M2
CH3COONH4
1b
O
O
CH3COONH4
1c
M3
M4
CH3COONH4
3d
CH3COONH4
.
Scheme 2. Synthesis of M1-M4.
2.2 Linear absorption and single-photon excited fluorescence
The linear photophysical data of M1-M4 in various solvents with different polarity are
listed in Table 1. The corresponding linear absorption spectra and single-photon excited
fluorescence (SPEF) spectra are displayed in Fig. 1 and Fig. 2.
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Table 1. Linear absorption and single-photon excited fluorescence properties of M1-M4.
d
Φ e
c
b
a
10−4
ε
∆
ν
λSPEF
abs
λ
max
Compound Solvent
max
(nm)
(mol-1 L cm-1) (nm)
(cm-1)
M1
M2
M3
M4
THF
378
374
378
373
331
331
331
329
312
310
311
307
426
428
429
424
7.65
8.46
3.60
6.92
3.69
9.09
10.28
6.63
2.85
8.08
14.75
8.63
8.93
8.09
15.69
1.77
486
492
517
519
391
396
398
400
413
416
418
421
478
481
483
487
5879
6413
7113
7542
4636
4959
5086
5396
7838
8220
8231
8820
2554
2574
2606
3051
0.49
0.35
0.28
0.21
0.51
0.55
0.52
0.61
0.43
0.48
0.38
0.46
0.72
0.64
0.51
0.32
CH2Cl2
DMF
CH3CN
THF
CH2Cl2
DMF
CH3CN
THF
CH2Cl2
DMF
CH3CN
THF
CH2Cl2
DMF
CH3CN
a Maximum linear absorption wavelength, c = 1×10-5 mol L-1.
b Maximum molar absorption coefficient.
c Maximum single-photon excited fluorescence wavelength, c = 1×10-6 mol L-1.
d Stokes shift.
e Fluorescence quantum yield, measured by using quinine sulfate in 0.5 mol L-1 sulfuric acid (M1-M3)
and fluorescein in 0.1 mol L-1 sodium hydroxide (M4) as the standards.
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M1
M2
8

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M3
M4
Fig. 1. Linear absorption spectra of M1-M4 in various solvents with a concentration of
1×10-5 mol L-1.
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M1
M2
10

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M3
M4
Fig. 2. Single-photon excited fluorescence spectra of M1-M4 in various solvents with a
concentration of 1×10-6 mol L-1.
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As shown in Fig. 1, two absorption peaks can be observed, the one in the shorter
wavelength region is attributed to the π-π* transition arising from the phenyl rings
attached at positions 4 and 5 of the imidazole ring, and that in the longer wavelength
region can be classed into two types: M1 and M4 show the absorption peaks around
abs
max
375 and 426 nm, respectively, which are accredited to intramolecular charge
λ
=
transfer (ICT) character. Moreover, the second bands of M2 and M3 in the UV region
(around 330 and 310 nm, respectively) are characteristic of carbazole π-π* transition.
There is only slight shift (±5 nm) for the absorption spectra of M1-M4 upon changing
the solvents from THF to CH3CN, indicating that the polarity of solvents has little effect
on the absorption transition. Compared with M2 and M3, a prominent red-shift in
absorption spectra of M1 and M4 is attributed to the longer π-conjugated chain by
introducing a styrene π-bridge. In highly polar DMF, M2-M4 possessing one or two
donors display the strongest light absorption capacity, whose molar absorption
coefficients (ε
) are 10.28×104, 14.75×104, and 15.69×104 mol-1 L cm-1, respectively.
While M1 without any donor manifests the poorest absorption capacity in DMF (ε =
3.60×104 mol-1 L cm-1).
The SPEF spectra of M1-M4 in different solvents were obtained under the excitation at
their maximum absorption wavelengths. It is noticeable that the effect of solvent polarity
on the emission behavior is more pronounced than that on the absorption behavior. As
shown in Fig. 2, all the target compounds are sensitive to four different solvents ranging
from THF to CH3CN: the higher polarity the solvent has, the greater red-shift the
compounds display. The Stokes shift (∆ν) of each compound shows the same tendency
SPEF
max
with the
λ
as the polarity of solvents increases. These observations suggest that the
excited state of the compounds is more polar than the ground state. In THF and CH2Cl2
with medium polarity, M4 exhibits dual emission behavior. The emission peak around
479 nm is assigned to the locally excited (LE) state and the longer emission wavelength
centered around 510 nm is assigned to the ICT state. In DMF and CH3CN with high
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polarity, the emission peak of M4 around 510 nm degenerates into a shoulder, which can
be explained by the intense ICT between the electron donor and the electron acceptor
resulting from the strong solute-solvent interaction. Different from the absorption
SPEF
max
properties, the
λ
of M1-M4 can be sequenced as M1 > M4 > M3 > M2, which
implies that the molecular polarity in the excited state changes in the same order.
The fluorescence photos of M1-M4 in DMF are displayed in Fig. 3, from which one
can clearly see that under the irradiation of UV light at 365 nm, M1 and M4 emit green
(517 nm) and cyan (483 nm) fluorescence, respectively. While M2 and M3 emit violet
(398 nm) and blue (418 nm) fluorescence, respectively.
Fig. 3. Fluorescence photos of M1-M4 in DMF.
The fluorescence quantum yield (
mol L-1 sulfuric acid ( = 0.546)34 (M1-M3) and fluorescein in 0.1 mol L-1 sodium
= 0.9)34 (M4) as the standards. The
was obtained as follows:
Ф) was determined by using quinine sulfate in 0.5
Ф
hydroxide (
Ф
Ф
ns2 F A
s
r
Φs = Φr
nr2 F A
r
s
where the s and r subscripts designate the sample and the reference, respectively. A is the
absorbance at the excitation wavelength, n is the refractive index of the relevant solution,
and F is the integrated area under the corrected emission spectrum.
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As shown in Table 1, the
While one can see that the
Ф
of M2 and M3 are slightly susceptible to solvent polarity.
Ф
of M1 and M4 decrease consistently and significantly as the
polarity of solvents increases. This fluorescent behavior can be ascribed to ‘‘twisted
intramolecular charge transfer (TICT)’’ upon the excited state.35 TICT is a process of
intramolecular transfer from the donor to the acceptor on the excited state accompanied
by the twisted structure geometry. It is much less emissive and strongly dependent on the
polarity of solvents. An increase in the polarity of solvents can decrease the activation
barrier and enhance the TICT process.
2.3 Two-photon absorption properties
Taking advantage of the fluorescent properties of M1-M4, their TPA properties in the
near infrared (NIR) range (680-1000 nm) could be determined by using the two-photon
induced fluorescence technique with femtosecond laser pulses. The nonlinear
photophysical properties of M1-M4 in THF and DMF were recorded under 500 mW
from 680 nm to 930 nm, and the corresponding data are listed in Table 2 and shown in
Fig. 4.
(a)
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(b)
Fig. 4. Two-photon absorption cross-sections of M1-M4 in THF (a) and DMF (b) in the
680-930 nm region.
Table 2
Two-photon absorption and two-photon excited fluorescence properties of M1-M4.
b
a
TPEF
max
σmax
λ
Compound
Solvent
(GM)
(nm)
525
561
431
445
458
471
M1
THF
DMF
THF
DMF
THF
DMF
373
585
25
M2
M3
31
28
34
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M4
THF
530
535
733
DMF
1193
a Maximum two-photon excited fluorescence wavelength, c = 1×10-3 mol L-1.
b Two-photon absorption cross-section, 1 GM = 1×10-50 cm4 s photon-1.
The
σ value was obtained by comparing the two-photon excited fluorescence (TPEF)
intensity of the sample with that of a reference compound by the following equation.
Fs Φr nr c
σ s
=
r σ r
Fr Φs ns cs
where the subscripts s and r denote the sample and the reference. F and
Ф
represent the
TPEF integral intensity and the fluorescence quantum yield. n and c are the refractive
index and the concentration of the solution. In this work, we selected fluorescein in 0.1
mol L-1 sodium hydroxide (c = 1×10-3mol L-1) as the reference (
As observed from Fig. 4, the excitation wavelengths of M1-M4 at maximum
in THF and DMF are both at 750 nm, 680 nm, 680 nm, and 850 nm, respectively. The
corresponding maximum values are 585 GM for M1, 31 GM for M2, 34 GM for M3,
σ
= 36 GM36).
σ
values
σ
and 1193 GM for M4 in DMF with the sequence of M4 > M1>>M3 > M2, which is
better than those in THF.
In an effort to understand the relationship between the σ of M1-M4 and the distribution
of electron densities over the molecules and hence the electronic properties, the density
functional theory (DFT) calculations were performed and the energy gap between the
highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital
(LUMO) of the M1-M4 were analyzed. The calculation results are shown in Fig. 5.
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Optimized Structure
HOMO
LUMO
M1
-0.196 eV
-0.081 eV
M2
M3
-0.191 eV
-0.046 eV
-0.179 eV
-0.037 eV
M4
-0.174 eV
-0.103 eV
Fig. 5. Optimized geometrical structures, HOMO and LUMO distributions of M1-M4.
Clearly, the
σ values of M2 and M3 are much smaller than those of M1 and M4,
probably because our wavelengths of light source range from 680 nm to 1080 nm. This
abs
max
range cannot meet their relative twofold
. On the other hand, M2 and M3 have
λ
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non-planar geometries that interfere with electron transfer across the molecule, the more
largely the electron transfer is impeded, the smaller
σ the molecule should have. For M1,
Fig. 5 shows that the electron clouds of the HOMO are mainly localized on the styrene
π-bridge, the imidazole unit, and the C-5 benzene ring. However, it is notable that the
electron clouds of the LUMO are spread over the styrene π-bridge and the electron-poor
benzonitrile due to the strong electron-withdrawing ability of the cyano group. The result
indicates that there is a good charge-separated state between the HOMO and the LUMO
of M1, which leads to the relatively large
σ
value. Though the HOMO-LUMO transitions
value of M4 is
of M1 and M4 both bear ICT nature besides the π-π* transition, the
σ
about 2 times as large as that of M1, suggesting that the longer conjugation length, the
pseudo-one-dimensional geometry, and the bidirectional charge transfer obviously
improve the TPA ability. The
σ value shows negative correlation with energy gap
between the HOMO and the LUMO. The corresponding energy gaps of M1-M4 were
calculated to be 0.115, 0.145, 0.142, and 0.103 eV, respectively, which is in agreement
with the sequence of σ (M4 > M1>>M3 > M2).
It can be seen from Table 2 that the fluorescence peak wavelengths of TPEF are
evidently red-shifted by 39-52 nm compared with those of SPEF in THF and DMF, which
can be explained by the reabsorption effect.
The representative TPEF spectra of M4 in DMF pumped by femtosecond laser pulses
at 500 mW under different excitation wavelengths are presented in Fig. 6. One can see
that M4 exhibits various TPEF intensity under different excitation wavelengths. For M1,
the optimal excitation wavelength is 850 nm. Fig. 7a and 7b show the TPEF intensities of
M4 under different pump powers and the logarithmic plot of the output fluorescence
integral versus the input powers. The logarithmic plot has a slope of 2.01 when the input
laser power is increased. It provides the direct evidence for the squared dependence of the
fluorescence intensity and the input power, suggesting a two-photon excitation
mechanism. As the nonlinear absorption is observed in the range from 680 nm to 930 nm,
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so the emission can also be attributed to the TPEF mechanism. The other compounds
(M1-M3) are also proved to have the same excitation mechanism.
Fig. 6. Two-photon excited fluorescence spectra of M4 in DMF (c = 1×10-3 mol L-1)
pumped by femtosecond laser pulses at 500 mW under different excitation wavelengths.
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(a)
(b)
Fig. 7. (a) Two-photon excited fluorescence spectra of M4 in DMF (c = 1×10-3 mol L-1)
at 850 nm under different input powers. (b) Logarithmic plot of the output fluorescence
integral (Iout) of M4 versus the input laser powers (Iin).
3. Conclusion
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In conclusion, four novel imidazole derivatives containing different electron donors
and acceptors were synthesized by the solvent-free Debus-Radziszewski reaction. Their
linear and nonlinear optical properties were systematically investigated in various
solvents. Measured by the two-photon induced fluorescence method, M4 is found to
exhibit the largest
of extending the π-conjugated system, improving the molecular planarity, and possessing
the multi-directional charge transfer can enhance the value. We believe that the
σ value (1193 GM). The study further demonstrates that the strategies
σ
fabrication strategy is potentially applicable to the derivatization of analogous TPA
materials.
4. Experimental
4.1. General
1a,37 2a,38 1b,39 1c,40 1d,41 and 2d42 were synthesized according to the previous
literature procedures. The solvents THF and DMF were disposed by primary procedures
before use. Other materials were commercially available, which were used without
further purification.
Melting points were measured on an X-4 micromelting point apparatus without
1
correction. H and 13C NMR spectra were recorded at room temperature on a Bruker
AVANCEIII 500 spectrometer in CDCl3 or DMSO-d6 solvent with tetramethylsilane
(TMS) as internal standard. FT-IR spectra were measured on KBr pellets with a Thermo
Nicolet 6700 spectrometer. Mass spectra were taken on a Therm LCQ TM Deca XP plus
ion trap mass spectrometry instrument. Elemental analyses were conducted on a Thermo
Finnigan Flash EA 1112 apparatus.
The linear absorption spectra were measured on a Shimadzu UV-2550 UV-visible
spectrophotometer. The SPEF spectrum measurements were performed using a
RF-5301PC fluorescence spectrophotometer with the maximum absorption wavelengths
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as the excitation wavelengths. The TPEF spectra were measured using a femtosecond
laser pulse and Ti: sapphire system (680-1080 nm, 80 MHz, 140 fs) as the light source.
The DFT calculations were carried out using the Gaussian 09 program. The nonlocal
density function of B3LYP with 6-31G basis sets was used for the calculations.
4.2 4-[(1E)-2-(4-Formylphenyl)ethenyl]benzonitrile (3a)
1a (1.25 g, 6 mmol), 2a (1.52 g, 6 mmol), and potassium tert-butoxide (0.81 g, 7.2
mmol) in dry THF (25 mL) were added into a dry round-bottom flask under a nitrogen
atmosphere with ice bath cooling. The reaction mixture was stirred at room temperature
for 12 h and the reaction was monitored by TLC. Then, acetic acid (3.60 g, 60 mmol) in
water was added and stirred vigorously. After stirring at room temperature for 6 h, the
reaction mixture was neutralized cautiously with saturated aqueous sodium hydrogen
carbonate solution, and extracted with CH2Cl2 (2×30 mL). The combined organic layers
were washed with water (20 mL) and brine (20 mL), dried with anhydrous sodium sulfate,
and then filtered. The filtrate was concentrated under vacuum. The crude products were
purified by silica gel column chromatography to provide bright yellow crystalline powder
1
(1.25 g). Yield: 89.2%. Mp: 211-213 . H NMR (CDCl3, 500MHz)
δ: 10.04 (s, 1H),
7.92 (d, J = 8.2 Hz, 2H), 7.70 (d, J = 8.2 Hz, 2H), 7.69 (d, J = 8.4 Hz, 2H), 7.64 (d, J =
8.4 Hz, 2H), 7.26 (s, 2H).
4.3 4,4'-[(2,5-Dimethoxy-1,4-phenylene)di-(1E)-2,1-ethenediyl]bisbenzaldehyde (3d)
1a (2.08 g, 10 mmol), 2d (2.19 g, 5 mmol), potassium tert-butoxide (1.23 g, 11
mmol) in dry THF (50 mL), and the synthetic method was similar to that of 3a. 3d was
1
obtained as orange-red crystalline powder (1.63 g). Yield: 82.1%; Mp: 230-232 . H
NMR (CDCl3, 500MHz) δ: 10.02 (s, 2H), 7.89 (d, J = 8.2 Hz, 4H), 7.71 (d, J = 8.2 Hz,
4H), 7.67 (d, J = 16.5 Hz, 2H), 7.21 (d, J = 16.5 Hz, 2H), 7.18 (s, 2H), 3.98 (s, 6H)
4.4 4-[(1E)-[2-[4-(4,5-Diphenyl-1H-imidazol-2-yl)phenyl]ethenyl] benzonitrile (M1)
Benzil (0.21 g, 1 mmol), 3a (0.23 g, 1 mmol), acidic alumina (1.02 g, 10 mmol ), and
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ammonium acetate (0.39 g, 5 mmol) were ground into powder in a mortar, and then
heated in a thermostatic reactor at 110◦C for 10 h. After completion of the reaction
confirmed by TLC, the reaction mixture was treated with water to furnish the crude
products. Further purification was done by silica gel column chromatography to provide
1
M1 as yellow needle crystals (0.34 g). Yield: 81.4%; Mp: 294-296 ; H NMR
(DMSO-d6, 500MHz) δ: 12.77 (s, 1H), 8.13 (d, J = 8.3 Hz, 2H), 7.86 (d, J = 8.4 Hz, 2H),
7.82 (d, J = 8.4 Hz, 2H), 7.77 (d, J = 8.3 Hz, 2H), 7.57 (d, J = 7.5 Hz, 2H), 7.53 (d, J =
16.5 Hz, 1H), 7.52 (d, J = 7.7 Hz, 2H), 7.46 (t, J = 7.4 Hz, 2H), 7.44 (d, J = 16.5 Hz, 1H),
7.40 (t, J = 7.3 Hz, 1H), 7.32 (t, J = 7.6 Hz, 2H), 7.24 (t, J = 7.3 Hz, 1H); 13C NMR
(DMSO-d6, 500MHz)
130.11, 128.66, 128.54, 128.45, 128.19, 127.84, 127.36, 127.13, 127.09, 127.03, 126.58,
125.45, 119.03, 109.48; FT-IR (KBr) : 3398, 3028, 2226, 1598, 1504, 1490, 1439, 1174,
δ: 145.14, 141.86, 137.44, 136.14, 135.09, 132.63, 131.70, 130.99,
ν
964, 841, 765, 697, 559 cm-1; ESI-MS m/z: 424.2 [M+H]+; HRESI-MS calcd for
C30H22N3 [M+H]+: 424.1814; found: 424.1823; Anal. calcd for C30H21N3: C 85.08, H
5.00, N 9.92; found C 85.27, H 5.13, N 10.18.
4.5 9-[4-(4,5-Diphenyl-1H-imidazol-2-yl)phenyl]- 9H-carbazole (M2)
The compound was synthesized by the same procedure described for M1 using 1b,
benzil, acidic alumina and ammonium acetate as the starting materials. M2 was obtained
1
as white crystalline powder. Yield: 85.6%; Mp: 302-303 ; H NMR (DMSO-d6,
500MHz) δ: 12.90 (s, 1H), 8.39 (d, J = 8.4 Hz, 2H), 8.28 (d, J = 7.8 Hz, 2H), 7.77 (d, J =
8.4 Hz, 2H), 7.61 (d, J = 7.4 Hz, 2H), 7.56 (d, J = 7.4 Hz, 2H), 7.47-7.50 (m, 6H), 7.41 (t,
J = 7.3 Hz, 1H), 7.31-7.36 (m, 4H), 7.26 (t, J = 7.3 Hz, 1H); 13C NMR (DMSO-d6,
500MHz)
δ: 144.86, 140.00, 136.58, 129.40, 128.45, 127.07, 126.82, 126.31, 122.84,
120.55, 120.17, 109.75; FT-IR (KBr)
ν: 3420, 3059, 1601, 1494, 1451, 1316, 1230, 750,
697 cm-1; ESI-MS m/z: 462.2 [M+H]+; HRESI-MS calcd for C33H24N3 [M+H]+: 462.1970;
found: 462.1984; Anal. calcd for C33H23N3: C 85.87, H 5.02, N 9.10; found C 85.96, H
5.09, N 9.21.
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4.6 3,6-Bis(4,5-diphenyl-1H-imidazol-2-yl) -9-ethyl-9H-carbazole (M3)
The compound was synthesized by the same procedure described for M1 using 1c,
benzil, acidic alumina and ammonium acetate as the starting materials. M3 was obtained
as white crystalline powder. Yield: 83.9%; Mp >300 ; 1H NMR (DMSO-d6, 500MHz)
δ:
12.66 (s, 2H), 8.98 (d, J = 1.3 Hz, 2H), 8.27 (dd, J1 = 8.6 Hz, J2 = 1.5 Hz, 2H), 7.76 (d, J
= 8.6 Hz, 2H), 7.62 (d, J = 7.2 Hz, 4H), 7.56 (d, J = 7.2 Hz, 4H), 7.47 (t, J = 7.6 Hz, 4H),
7.39 (t, J = 7.4 Hz, 2H), 7.33 (t, J = 7.6 Hz, 4H), 7.24 (t, J = 7.3 Hz, 2H), 4.53 (q, 2H),
1.40 (t, J = 7.1 Hz, 3H); 13C NMR (DMSO-d6, 500MHz)
135.45, 131.34, 128.65, 128.31, 128.17, 127.69, 127.57, 127.11, 126.41, 123.75, 122.50,
121.93, 117.24, 109.60, 37.36, 13.92; FT-IR (KBr) : 3411, 3055, 2975, 1605, 1484, 1450,
δ: 146.66, 140.04, 136.88,
ν
1382, 1295, 1226, 1127, 1072, 767, 703 cm-1; ESI-MS m/z: 632.4 [M+H]+, 316.8
[M+2H]2+; HRESI-MS calcd for C44H34N5 [M+H]+: 632.2814; found: 632.2831; Anal.
calcd for C44H33N5: C 83.65, H 5.26, N 11.09; found C 83.91, H 5.41, N 11.26.
4.7 2,2'-[(2,5-Dimethoxy-1,4-phenylene)bis[(1E)-2,1-ethenediyl-4,1-phenylene]]bis(4,5
-diphenyl-1H-imidazole) (M4)
The compound was synthesized by the same procedure described for M1 using 3d,
benzil, acidic alumina and ammonium acetate as the starting materials. M4 was obtained
1
as orange-yellow crystalline powder. Yield: 76.5%; Mp >300 ; H NMR (DMSO-d6,
500MHz)
= 7.4 Hz, 8H), 7.53 (d, J = 16.5 Hz, 2H), 7.42 (d, J = 16.5 Hz, 2H), 7.39 (s, 2H),
7.33-7.44 (m, 12H), 3.95 (s, 6H); 13C NMR (DMSO-d6, 500MHz)
: 151.12, 149.17,
145.31, 137.31, 135.13, 131.03, 129.61, 129.26, 128.65, 128.41, 128.19, 127.78,
127.08,126.87, 126.73, 125.86, 125.52, 122.84, 115.11, 109.33, 56.18; FT-IR (KBr)
δ: 12.85 (bs, 2H), 8.12 (d, J = 8.3 Hz, 4H), 7.72 (d, J = 8.3 Hz, 4H), 7.54 (d, J
δ
ν:
3401, 3050, 2934, 2829, 1602, 1492, 1448, 1406, 1208, 1043, 967, 764, 696 cm-1;
ESI-MS m/z: 779.4 [M+H]+, 390.5 [M+2H]2+; HRESI-MS calcd for C54H43N4O2 [M+H]+:
24

ACCEPTED MANUSCRIPT
779.3386; found: 779.3405; Anal. calcd for C54H42N4O2: C 83.26, H 5.43, N 7.19; found
C 83.53, H 5.61, N 7.45.
Acknowledgements
We are grateful to the Natural Science Foundation of Zhejiang province, China (Grant
No. LY15B030006) and the National Natural Science Foundation of China (Grant No.
21103151) for financial support.
Supplementary data
Supplementary data (1H NMR, 13C NMR, and MS spectra of M1-M4.) can be
found in the supporting information.
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