Green synthesis and photophysical properties of novel 1H-imidazo[4,5-f][1,10]phenanthroline derivatives with blue/cyan two-photon excited fluorescence

Article abstract of DOI:10.1016/j.tet.2017.03.075

A simple, rapid, and highly efficient method has been developed for the synthesis of a series of novel 1H-imidazo[4,5-f][1,10]phenanthroline derivatives (1BN, 2Py, 3BI, 4BT, and 5MOBI) via a three–component, one–pot reaction under solvent–free conditions.

Full text of DOI:10.1016/j.tet.2017.03.075

Accepted Manuscript
Green synthesis and photophysical properties of novel 1H-imidazo[4,5-f]
[1,10]phenanthroline derivatives with blue/cyan two-photon excited fluorescence
Yu-Lu Pan, Zhi-Bin Cai, Li Bai, Fei-Fei Ma, Sheng-Li Li, Yu-Peng Tian
PII:
S0040-4020(17)30333-2
10.1016/j.tet.2017.03.075
TET 28581
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 20 January 2017
Revised Date: 23 March 2017
Accepted Date: 27 March 2017
Please cite this article as: Pan Y-L, Cai Z-B, Bai L, Ma F-F, Li S-L, Tian Y-P, Green synthesis and
photophysical properties of novel 1H-imidazo[4,5-f][1,10]phenanthroline derivatives with blue/cyan two-
photon excited fluorescence, Tetrahedron (2017), doi: 10.1016/j.tet.2017.03.075.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Graphical abstract
A series of novel 1H-imidazo[4,5-f][1,10]phenanthroline derivatives were
synthesized via the solvent–free Debus–Radziszewski reaction. They display both
large two-photon absorption cross-sections and strong blue/cyan fluorescence.

ACCEPTED MANUSCRIPT
Green synthesis and photophysical properties of novel
1H-imidazo[4,5-f][1,10]phenanthroline derivatives with blue/cyan
two-photon excited fluorescence
Yu-Lu Pan a, Zhi-Bin Cai a,*, Li Bai a, Fei-Fei Ma a, 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
A simple, rapid, and highly efficient method has been developed for the synthesis
of a series of novel 1H-imidazo[4,5-f][1,10]phenanthroline derivatives (1BN, 2Py,
3BI, 4BT, and 5MOBI) via a three–component, one–pot reaction under solvent–free
1
13
conditions. Their structures were characterized by FT–IR, H NMR, C NMR, MS,
and elemental analysis. Their photophysical properties, including linear absorption,
one–photon excited fluorescence, two–photon absorption, and two–photon excited
fluorescence, were systematically investigated in various solvents. The results
demonstrate that all the compounds emit relatively strong blue/cyan fluorescence.
1BN and 5MOBI exhibit large two–photon absorption cross–sections (471 and 654
GM) in THF. In addition, the relationship between the electronic structures and
photophysical properties was investigated using density functional theory.
Keywords: Photophysical property; Blue/cyan fluorescence; Phenanthroline
derivative; Green synthesis
1

ACCEPTED MANUSCRIPT
*Corresponding author. Tel. : +86 571 88320891.
E-mail address: caizbmail@126.com (Z.-B. Cai).
1. Introduction
Two–photon absorption (TPA) is a third–order nonlinear optical process wherein
two photons are absorbed simultaneously. The development of organic materials with
large TPA cross–sections (σ) has attracted considerable interest in the past decades
due to a variety of potential applications in fields such as two–photon pumped
up–converted lasing,1,2 fluorescence imaging,3,4 three–dimensional (3D)
microfabrication,5,6 3D optical data storage,7–9 optical limiting,10–12 and photodynamic
therapy.13–15 Increasing the conjugated system is one of the commonly used strategies
in the molecular design of TPA materials.16,17 However, enhancement of the
conjugated system will lead to a conflict between nonlinearity and transparency. That
is, an increase in the conjugated system will cause a significant red–shift of the
absorption wavelength, which will lead to a red–shift of the emission wavelength,
usually to the green, yellow, or red light region. The blue–emitting TPA materials
have some important applications. For example, they promote the development of the
multi–channel two–photon induced fluorescence microscopy, which is helpful in
reducing background light scattering and auto–fluorescence when probing natural
molecules.18,19 Up till now, the number of reported TPA materials with efficient blue
emission is relatively limited. He et al.20 designed four 1,8-diazapyrenes, for which
the wavelengths of two–photon excited fluorescence (TPEF) are in the deep–blue
light region, and the maximum two–photon cross–section (σ) is 298 GM (1 GM =
1×10-50 cm4 s photon-1). Cao et al.21 synthesized a new A–π–D–π–A compound (A =
acceptor, D = donor，and π = conjugated bridge), which exhibits blue–violet TPEF
with a maximum σ value of 38 GM. Hu et al.22 synthesized two novel π–conjugated
carbazole derivatives with blue TPEF, with a maximum σ value of 49 GM. In order to
2

ACCEPTED MANUSCRIPT
realize practical applications, the σ values of this kind of materials must be further
improved. We think that appropriate conjugated structural units can play important
roles in obtaining high–performance TPA materials that emit blue fluorescence.
1H-Imidazo[4,5-f][1,10]phenanthroline has a large planar structure, high
electron–withdrawing ability, good electron transportability, high thermal stability,
and good fluorescence properties. Its derivatives are widely used as luminescent
materials,23 biomolecular probes,24 and molecular recognition.25 In this study, we
selected 1H-imidazo[4,5-f][1,10]phenanthroline as the effective conjugated structural
unit, combining trans double bonds and various electron acceptors (benzonitrile,
pyridine, benzimidazole, and benzothiazole) to synthesize four A–π–A’ compounds
(1BN, 2Py, 3BI, and 4BT) and one A–D–π–A’ compound (5MOBI). The introduction
of a trans–diarylethene at the 2–position of the imidazole leads to an appropriate
extension of the conjugated system, which may not only help to increase the
fluorescence quantum yield (Φ) and σ, but also ensure that TPEF occurs in the blue
light region. Till now, the compounds reported with similar structures are fairly rare,
26-29 and none of them exhibit blue fluorescence.
This kind of materials is usually synthesized by a Debus–Radziszewski reaction
with diketones, aldehydes, and ammonium acetate as raw materials, and AcOH as the
solvent. As this method usually produces a large amount of waste acid, it is not only
difficult to conduct, but is very environmentally unfriendly. In this study, the target
compounds were synthesized under solvent–free and catalyst–free conditions with
relatively high selectivity and yields, which protects the environment, reduces the
production cost, and simplifies the operation steps. Therefore, it can be considered as
an efficient synthesis method.
The linear and nonlinear photophysical properties of the target compounds have
been systematically investigated in different solvents. Furthermore, density functional
theory (DFT) calculations have been employed to study the structure–property
relationships of the target compounds, which provides a reference for the
development of high–performance TPA materials that emit blue fluorescence.
3

ACCEPTED MANUSCRIPT
EtO
CH(OEt)3, NH4Cl
CHO
OHC
CHO
EtO
EtOH
1
OEt
O
P
(1) 1, t-BuOK
P(OEt)3
OEt
OHC
NC
NC
CH2Br
(2)
AcOH / H2O
CN
LSZ
3a
N
Me
OHC
N
Ac2O, AcOH
3b
N
Me
N
H
OHC
CHO
OHC
OHC
N
Ac2O, AcOH
N
H
3c
3d
N
Me
S
N
S
Ac2O, AcOH
CHO
OMe
CH2Br
(HCHO)n
(1)
(2)
N4(CH2)6
MeO
OHC
MeO
BrH2C
OMe
MeO
OMe
HBr / AcOH
AcOH / H2O
2
N
OMe
Me
N
H
OHC
MeO
N
Ac2O, AcOH
N
H
3e
4

ACCEPTED MANUSCRIPT
N
N
N
N
H
CN
1BN
N
N
N
N
H
N
2Py
3BI
N
N
N
N
N
N
N
O
O
3a-3e
HNO3 / H2SO4
KBr
N
N
H
NH4Ac
N
H
N
N
N
N
S
N
H
4BT
MeO
N
N
N
N
N
H
N
H
OMe
5MOBI
Scheme 1. Synthetic route of the target compounds (1BN, 2Py, 3BI, 4BT, and
5MOBI).
2. Results and discussion
2.1. Synthesis and characterization
The synthetic routes of the target compounds (1BN, 2Py, 3BI, 4BT, and 5MOBI)
are depicted in Scheme 1. 4-[(1E)-2-(4-Formylphenyl)ethenyl]benzonitrile (3a) was
prepared by a two–step reaction, which involved the Horner–Wadsworth–Emmons
reaction
between
4-(diethoxymethyl)benzaldehyde
(1)
and
5

ACCEPTED MANUSCRIPT
[(4-cyanophenyl)methyl]phosphonic acid diethyl ester (LSZ) using potassium
tert-butoxide as the catalyst, followed by hydrolysis in acetic acid. The other four
intermediates, 4-[(1E)-2-(4-pyridinyl)ethenyl]benzaldehyde (3b), 4-[(1E)-2-(1H-
benzimidazol-2-yl)ethenyl]benzaldehyde (3c), 4-[(1E)-2-(2-benzothiazolyl)ethenyl]
benzaldehyde (3d), and 4-[(1E)-2-(1H-benzimidazol-2-yl)ethenyl]-2,5-
dimethoxybenzaldehyde(3e), were synthesized by acid condensation of
4-methylpyridine, 2-methyl-1H-benzimidazole, or 2-methylbenzothiazole with
1,4-benzenedicarboxaldehyde or 2,5-dimethoxy-1,4-benzenedicarboxaldehyde (2).
Finally, the solvent–free Debus–Radziszewski reaction of 3a–3e with
1,10-phenanthroline-5,6-dione gave the target compounds (1BN, 2Py, 3BI, 4BT, and
5MOBI) in relatively high yields (67.5%–78.9%). This solvent–free reaction offers
considerable advantages such as simplified operation, lower production cost, and
environmental friendliness, and thus significantly contributes to the practice of green
chemistry.
In the 1H NMR spectra, the chemical shifts (δ) of the target compounds (1BN, 2Py,
3BI, 4BT, and 5MOBI) at 13.02–13.89 ppm were detected as broad singlets, which
were attributed to the N-H in the imidazole moiety. In addition, the observed J
coupling constants for the vinyl protons of the compounds were in the range of
16.3–16.5 Hz, which is consistent with the expected values for an all–trans
configuration. The N-H in the imidazole moiety was also identified by FT–IR
spectroscopy as bands within the spectral region of 3332–3398 cm-1. Mass
spectrometry was used to further verify the structures of the compounds. For the five
molecules, the observed values agreed well with the calculated values.
2.2 Linear absorption and emission properties
The photophysical properties for all the target compounds (1BN, 2Py, 3BI, 4BT,
and 5MOBI) are summarized in Table 1. Their linear absorption spectra in
tetrahydrofuran (THF) are shown in Fig. 1.
6

ACCEPTED MANUSCRIPT
Table 1 Linear and nonlinear photophysical properties of the target compounds (1BN,
2Py, 3BI, 4BT, and 5MOBI).
c
b
f
10−4
ε
a
e
g
OPEF
λmax
TPEF
λmax
d
abs
max
λ
φ
σ
∆ν
(cm-1)
(mol-1 L cm-1) (nm)
Compound Solvent
(GM)
(nm)
506
(nm)
THF
376
10.97
6.09
463
467
471
473
449
456
461
469
444
447
450
452
469
472
485
488
443
452
4997
5112
5942
6636
4976
5618
6319
7331
3724
3807
4374
4573
4585
4855
5697
6175
2364
2876
0.42
0.34
0.26
0.16
0.54
0.48
0.32
0.19
0.11
0.07
0.15
0.09
0.33
0.25
0.17
0.11
0.75
0.62
471
1BN
CH2Cl2 377
CH3CN 368
CH3OH 360
10.26
10.66
11.28
4.89
508
503
251
270
THF
367
2Py
CH2Cl2 363
CH3CN 357
CH3OH 349
7.93
6.48
508
488
194
209
THF
381
13.45
9.86
3BI
CH2Cl2 382
CH3CN 376
CH3OH 375
8.67
9.53
492
515
94
THF
386
13.44
9.98
349
4BT
CH2Cl2 384
CH3CN 380
CH3OH 375
8.00
6.05
521
496
197
654
THF
401
14.10
12.19
5MOBI
CH2Cl2 400
7

ACCEPTED MANUSCRIPT
CH3CN 398
CH3OH 391
6.46
3.23
457
461
3244
3883
0.43
0.21
499
370
a
b
c
d
e
Maximum linear absorption wavelength, c = 1×10-5 mol L-1.
Maximum molar absorption coefficient.
Maximum one–photon excited fluorescence wavelength, c = 1×10-6 mol L-1.
Stokes shift.
Fluorescence quantum yield, measured by using quinine sulfate in 0.5 mol L-1
sulfuric acid as the standard (Φ = 0.546 30).
f
Maximum two–photon excited fluorescence wavelength, c = 1×10-3 mol L-1.
g
Two–photon absorption cross-section.
Fig. 1 Linear absorption spectra of the target compounds (1BN, 2Py, 3BI, 4BT, and
5MOBI) in THF with a concentration of 1 × 10-5 mol L-1.
As shown in Fig. 1, 1BN, 2Py, 3BI, and 4BT exhibit two absorption bands, while
5MOBI shows three obvious bands. The high–energy absorption bands (278–291 nm)
for all the compounds can be ascribed to the π–π* transition of the
8

ACCEPTED MANUSCRIPT
1H-imidazo[4,5-f][1,10]phenanthroline. The low–energy bands around 367–401 nm
result from the internal charge transfer (ICT) process. Whereas the absorption band at
330 nm of 5MOBI can be attributed to the n–π* transition of the oxygen atoms. The
absorption spectra of all the target compounds (1BN, 2Py, 3BI, 4BT, and 5MOBI)
exhibit obvious blue–shifts in methanol, but show only limited solvent polarity
dependencies in the other three solvents. This blue–shift could be explained by the
hydrogen bonds between the solute and methanol molecules, which results in the
energy gap increasing between the ground state S0 and the excited state S1. The
abs
absorption peak positions ( max ) of these compounds follow the order 5MOBI >
λ
4BT > 3BI > 1BN > 2Py. There is a prominent red–shift from 3BI to its methoxy
substituted compound (5MOBI), implying that the introduction of electron donor is
beneficial to reduce the absorption energy. The maximum molar absorption
coefficients (ɛmax) of the target compounds in THF are higher than those of the other
three solvents, which indicates that they have the strongest light absorbing ability in
THF.
The one–photon excited fluorescence (OPEF) spectra and fluorescence photographs
of the target compounds (1BN, 2Py, 3BI, 4BT, and 5MOBI) in THF are shown in Fig.
2 and the corresponding data are summarized in Table. 1. All the target compounds
emit blue/cyan fluorescence. Upon increasing the polarity of the solvent, their
fluorescent emission peaks ( OPEF ) show remarkable bathochromic shifts. This
λ
max
red–shifted behavior is accompanied by an increase in the Stokes shifts (ꢀν) when the
polarity of the solvent increases. This can be attributed to the fact that the excited state
may possess a higher polarity than the ground state. An increased dipole–dipole
interaction between the solute and solvent leads to a lowering of the energy level of
the excited state.31,32 The OPEF spectra of 3BI and 5MOBI exhibit two emission
peaks in the medium polar solvent (THF). The emission peaks at 422 nm (3BI) and
443 nm (5MOBI) are assigned to the locally excited (LE) state, and the longer
emission wavelengths centered at 444 nm (3BI) and 469 nm (5MOBI) are assigned to
the ICT state.
9

ACCEPTED MANUSCRIPT
The Φ values in different solvents were determined using quinine sulfate as
standard. As seen in Table. 1, the Φ values in the four solvents change slightly for
3BI. However, the Φ values of 1BN, 2Py, 4BT, and 5MOBI decrease significantly
upon increasing the solvent polarity. The origin of this phenomenon can be attributed
to “twisted intramolecular charge transfer (TICT)”33 in the excited state. The TICT
state is much less emissive and strongly dependent on the polarity of solvents. An
increase in the solvent polarity can lead to an enhanced TICT process and causes
greater energy loss from the excited state.34,35
Fig. 2 OPEF spectra and fluorescence photographs of the target compounds (1BN,
2Py, 3BI, 4BT, and 5MOBI) in THF with a concentration of 1×10-6 mol L-1.
2.3 Two–photon properties
The nonlinear photophysical data of the target compounds (1BN, 2Py, 3BI, 4BT,
and 5MOBI) are listed in Table. 1, which were measured in THF and methanol (c = 1
× 10-3 mol L-1). The representative TPEF spectra of 5MOBI in THF, pumped by
femtosecond laser pulses at 500 mW under different excitation wavelengths, are
TPEF
presented in Fig. 3. By comparing the peak positions of TPEF (
) with those of
λ
max
10

ACCEPTED MANUSCRIPT
OPEF
λTPEF
values are
OPEF (
) for the target compounds, one can observe that
λ
max
max
red–shifted by 28–54 nm. These red–shifts are attributed to the reabsorption effect of
the fluorescence within the solutions.36
As shown in Fig. 1, there is no linear absorption in the wavelength range of
500–1000 nm for the five compounds, which indicates that there are no molecular
energy levels corresponding to an electron transition in this spectral range. Therefore,
on excitation from 690 to 850 nm, it is impossible to produce one–photon excited
fluorescence. If up–converted fluorescence induced with a laser appears, it could be
ascribed to TPEF. Fig.4 shows the TPEF spectra of 5MOBI under different pump
powers and the logarithmic plot of the output fluorescence integral versus the input
powers. The logarithmic plot has a slope of 2.0673 as the input laser power is
increased, suggesting a two–photon excitation mechanism. The other compounds
(1BN, 2Py, 3BI, and 4BT) are also proved to have the same excitation mechanism.
Fig. 3 TPEF spectra of 5MOBI in THF pumped by femtosecond laser pulses at 500
mW under different excitation wavelengths.
11

ACCEPTED MANUSCRIPT
(a)
(b)
Fig. 4 (a) TPEF spectra of 5MOBI in THF at 790 nm under different input powers. (b)
Logarithmic plot of the output fluorescence integral (Iout) versus the input laser powers
(Iin).
12

ACCEPTED MANUSCRIPT
Fig. 5 TPA cross–sections of the target compounds (1BN, 2Py, 3BI, 4BT, and
5MOBI) in THF.
The σ values of the five target compounds were determined in the wavelength range
from 690 to 850 nm, using a two–photon induced fluorescence measurement
technique. As shown in Table 1 and Fig. 5, the maximum σ values in THF are 471
GM for 1BN, 270 GM for 2Py, 209 GM for 3BI, 349 GM for 4BT, and 654 GM for
5MOBI, respectively, which are larger than those in methanol (251 GM for 1BN, 194
GM for 2Py, 94 GM for 3BI, 197 GM for 4BT, and 370 GM for 5MOBI). The σ
value of 5MOBI is more than three times as large as that of 3BI, this can be attributed
to the following reasons: 3BI is an A–π–A’ compound where electron–withdrawing
imidazophenanthroline and benzimidazole are bound at opposite ends of styrene
conjugated bridge. As for 5MOBI, two electron–donating methoxy groups are
introduced at the 2– and 5–positions of the benzene ring to form an A–D–π–A’
configuration. The introduction of the electron donors produces the multidirectional
charge transfer, which results in higher degree of electron delocalization, and finally
enlarges the σ value obviously.
A three–level model is generally utilized to describe the TPA properties of the
13

ACCEPTED MANUSCRIPT
molecules, in which TPA into high–lying states is not dipole coupled to the ground
state. It can be written as Equation (1):20
M021M122
(E1 − E0 − hω)
2 Γ
σ
=
(1)
Where M01 and M12 are the transition dipole moments from S0 to S1 and S1 to S2,
respectively. ħω = (E2 – E0) / 2, E0, E1, and E2 represent the corresponding energy of S0,
S1, and S2. Γ is the damping factor.
Some studies have demonstrated that σ is related to the extent of ICT through the
π–bridge in the molecule,37 and according to the equation (1), σ shows negative
correlation with the transition energy ꢀE01 (ꢀE01 = E1 – E0). Therefore, theoretical
studies based on DFT calculations using the Gaussian 09 program38 at the
B3LYP/6–31G level39 of theory were conducted for optimization of the target
compounds in order to gain an insight into the relationship between the σ of the
compounds and the distribution of the electron densities over the molecules. The
frontier molecular orbitals for the five compounds are depicted in Fig. 6. The
corresponding ꢀE values of the target compounds were calculated to be 3.11 (1BN),
3.28 (2Py), 3.20 (3BI), 3.15 (4BT), and 3.11 (5MOBI) eV, respectively. For all the
target compounds, the electron densities in the highest occupied molecular orbital
(HOMO) are delocalized over the entire molecule, whereas the distributions of the
lowest unoccupied molecular orbital (LUMO) appear to be different. For 5MOBI, in
the LUMO, the electron clouds on imidazophenanthroline, benzimidazole, and
methoxy groups are partly transferred to the styrene π–bridge. This multidirectional
charge transfer and a relatively small ꢀE (3.11 eV) obviously improve the TPA ability,
resulting in the largest σ.
14

ACCEPTED MANUSCRIPT
Fig. 6 Molecular orbital energy level diagram for the target compounds (1BN, 2Py,
3BI, 4BT, and 5MOBI).
3. Conclusion
In this study, five new 1H-imidazo[4,5-f]phenanthroline derivatives were
synthesized by a solvent–free Debus–Radziszewski reaction. Their linear and
nonlinear photophysical properties were systematically investigated in various
solvents. All the compounds exhibit relatively large σ values and strong blue/cyan
fluorescence.
4. Experimental section
4.1. General procedures
All the reagents and solvents were commercially purchased and used without
further purification. 1H and 13C NMR spectra were recorded on a Bruker AVANCE III
500 spectrometer using DMSO-d6 as a solvent and all shifts are referred to
tetramethylsilane (TMS). FT–IR spectra were recorded on a Thermo Nicolet 6700
spectrometer using a powder sample on a KBr plate. Mass spectra were performed on
a Therm LCQ TM Deca XP plus ion trap mass spectrometry instrument. Elemental
15

ACCEPTED MANUSCRIPT
analyses were determined by a Thermo Finnigan Flash EA 1112 apparatus.
4.2. Spectroscopic measurements
The OPA spectra were recorded on a Shimadzu UV–2550 UV–visible
spectrophotometer. The OPEF spectra were performed using a RF–5301PC
fluorescence spectrophotometer. The Φ were determined by using quinine sulfate in
0.5 mol L-1 sulfuric acid as the standard (Φ = 0.54630). Φ is calculated according to
the following equation:
A ns2 F
r
s
Φs = Φr
(2)
A nr2 F
s
r
where the subscripts s and r 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.
The TPEF spectra were measured using a femtosecond laser pulse and a Ti:
sapphire system (680–1080 nm, 80 MHz, 140 fs) as the light source. σ of the target
compounds were measured using the two–photon induced fluorescence method with
the following equation :
F
ϕr nr c
s
σ s
=
r σ r
ϕs ns cs
(3)
F
r
where the subscripts s and r denote the sample and the reference, respectively.
Φ represent the TPEF integral intensity and the fluorescence quantum yield.
are the refractive index and the concentration of the solution. In this work, fluorescein
F
and
n
and c
c
in 0.1 mol L-1 sodium hydroxide ( = 1 ×10-3 mol L-1) is used as the reference (σ = 36
GM40).
4.3 Synthesis
The synthetic routes of the expected compounds are depicted in Scheme 1. 2,5-
Dimethoxy-1,4-benzenedicarboxaldehyde (2),41 1,10-phenanthroline-5,6-dione,42
[(4-cyanophenyl)methyl]phosphonic
4-[(1
)-2-(4-formylphenyl)ethenyl]benzonitrile (3a),44 4-[(1
ethenyl]benzaldehyde (3b),45 4-[(1
)-2-(1 -benzimidazol-2-yl)ethenyl]benzaldehyde
acid
diethyl
ester
(LSZ),43
E
E)-2-(4-pyridinyl)
E
H
(3c),46
4-[(1E
)-2-(2-benzothiazolyl)ethenyl]benzaldehyde
(3d),46
and
16

ACCEPTED MANUSCRIPT
4-[(1E
)-2-(1H
-benzimidazol-2-yl)ethenyl]-2,5-dimethoxybenzaldehyde (3e)47 were
synthesized according to the literature procedures.
4.3.1 4-[(1E)-2-[4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenyl]ethenyl]
benzonitrile (1BN
)
A mixture of 1,10-phenanthroline-5,6-dione (1 mmol, 0.21 g), 2a (1 mmol, 0.23g),
and ammonium acetate (5 mmol, 0.39 g) was ground into powder in a mortar and then
heated at 80 ºC for 8 h. After completion of the reaction (monitored by TLC), the
reaction mixture was cooled to room temperature and treated with water. The
resulting solid was purified by recrystallization from N,N-dimethylformamide to give
1
0.32 g orange–yellow crystalline powder. Yield 75.2 %. m.p. > 300 ºC; H NMR
(DMSO-d6, 500 MHz) δ: 13.83 (s, 1H), 9.07 (dd, J1 = 4.0 Hz, J2 = 1.2 Hz, 2H), 8.97
(dd, J1 = 8.1 Hz, J2 = 1.2 Hz, 2H), 8.35 (d,
7.89 (d, = 8.5 Hz, 2H), 7.87 (br s, 2H), 7.86 (d,
1H), 7.52 (d,
J
= 8.3 Hz, 2H), 7.92 (d,
= 8.5 Hz, 2H), 7.60 (d,
= 16.4 Hz, 1H); C NMR (DMSO-d6, 125 MHz) δ: 109.69, 119.02,
J
= 8.3 Hz, 2H),
J
J
J
= 16.4 Hz,
13
J
123.32, 126.55, 127.27, 127.61, 127.84, 129.65, 129.67, 129.70, 131.49, 132.69,
135.69, 137.54, 141.73, 143.69, 147.92, 150.07; FT–IR (KBr) ν: 3334, 3030, 2854,
2222, 1653, 1599, 1559, 1506, 1480, 1451, 1397, 1351, 1175, 1070, 949, 837, 739,
554 cm-1; ESI–MS m/z: 424.28 [M+H]+, 446.25 [M+Na]+; Anal. calcd for C28H17N5:
C 79.42, H 4.05, N 16.54; found C 79.61, H 4.12, N 16.78.
4.3.2 4-[(1E)-2-[4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenyl]ethenyl]
pyridine (2Py). 2Py was synthesized as that of 1BN. Orange-yellow crystalline
powder. Yield 71.1 %. m.p. 240–242 ºC; 1H NMR (DMSO-d6, 500 MHz) δ: 13.84 (s,
1H), 9.07 (dd, J1 = 4.3 Hz, J2 = 1.5 Hz, 1H), 9.06 (dd, J1 = 4.3 Hz, J2 = 1.5 Hz, 1H),
8.97 (dd, J1 = 8.0 Hz, J2 = 1.5 Hz, 1H), 8.96 (dd, J1 = 8.0 Hz, J2 = 1.5 Hz, 1H), 8.60
(d,
J = 6.0 Hz, 2H), 8.36 (d, J = 8.4 Hz, 2H), 7.93 (d, J = 8.4 Hz, 2H), 7.90 (dd, J1 =
8.0 Hz, J2 = 4.3 Hz, 1H), 7.85 (dd, J1 = 8.0 Hz, J2 = 4.3 Hz, 1H), 7.67 (d, J = 16.4 Hz,
13
1H), 7.63 (d,
J
= 6.0 Hz, 2H), 7.43 (d,
J
= 16.4 Hz, 1H); C NMR (DMSO-d6, 125
MHz) δ: 120.99, 121.17, 123.49, 126.60, 127.04, 127.75, 129.72, 129.77, 129.86,
132.32, 135.85, 135.89, 137.34, 143.60, 143.67, 144.17, 147.94, 150.13, 150.17;
17

ACCEPTED MANUSCRIPT
FT–IR (KBr) ν: 3332, 3076, 2850, 1624, 1600, 1560, 1501, 1484, 1424, 1399, 1195,
1072, 955, 839, 740 cm-1; ESI–MS
m/z
: 400.29 [M+H]+, 422.36 [M+Na]+; Anal.
calcd for C26H17N5: C 78.18, H 4.29, N 17.53; found C 78.41, H 4.39, N 17.82.
4.3.3 2-[(1E)-2-[4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenyl]ethenyl]-
1H-benzimidazole (3BI
). 3BI was synthesized as that of 1BN. Orange-yellow
1
crystalline powder. Yield 71.8 %. m.p. > 300 ºC; H NMR (DMSO-d6, 500 MHz) δ:
13.85 (br s, 1H), 12.72 (s, 1H), 9.06 (dd, J1 = 4.3 Hz, J2 = 1.6 Hz, 2H), 8.96 (dd, J1
8.1 Hz, J2 = 1.6 Hz, 2H), 8.37 (d, = 8.4 Hz, 2H), 7.94 (d, = 8.4 Hz, 2H), 7.87 (br s,
2H), 7.76 (d, = 16.5 Hz, 1H), 7.64 (d, = 7.7 Hz, 1H), 7.53 (d, = 7.7 Hz, 1H), 7.39
(d,
= 16.5 Hz, 1H), 7.16-7.23 (m, 2H); 13C NMR (DMSO-d6, 125 MHz) δ: 118.72,
=
J
J
J
J
J
J
119.30, 123.19, 123.49, 123.72, 126.60, 126.68, 127.68, 129.66, 129.71, 129.95,
133.45, 135.94, 135.96, 136.92, 141.90, 143.62, 143.76, 147.94, 147.99, 150.08;
FT–IR (KBr) ν: 3365, 3084, 2933, 1641, 1609, 1564, 1526, 1481, 1425, 1393, 1278,
1071, 969, 827, 740 cm-1; ESI–MS
m/z
: 439.23 [M+H]+, 461.29 [M+Na]+; Anal.
calcd for C28H18N6: C 76.70, H 4.14, N 19.17; found C 76.86, H 4.25, N 19.32.
4.3.4 2-[(1E)-2-[4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenyl]ethenyl]
benzothiazole (4BT
). 4BT was synthesized as that of 1BN. Orange-yellow crystalline
1
powder. Yield 78.9 %. m.p. > 300 ºC; H NMR (DMSO-d6, 500 MHz) δ: 13.89 (s,
1H), 9.07 (d,
(d, = 7.9 Hz, 1H), 8.07 (d,
7.88 (br s, 1H), 7.81 (d, = 16.3 Hz, 1H), 7.77 (d,
Hz, 1H), 7.47 (t,
= 7.6 Hz, 1H); 13C NMR (DMSO-d6, 125 MHz) δ: 122.20, 122.61,
J
= 4.0 Hz, 2H), 8.98 (d,
J
= 8.0 Hz, 2H), 8.37 (d,
= 8.1 Hz, 1H), 7.91 (br s, 1H),
= 16.3 Hz, 1H), 7.55 (t, = 7.6
J = 8.3 Hz, 2H), 8.14
J
J
= 8.3 Hz, 2H), 8.02 (d,
J
J
J
J
J
122.69, 123.48, 123.51, 125.55, 125.58, 126.55, 128.35, 129.96, 130.45, 134.14,
136.28, 136.55, 143.17, 143.28, 147.73, 150.04, 151.88, 153.44, 166.32; FT–IR (KBr)
ν: 3335, 3051, 2862, 1623, 1603, 1559, 1484, 1435, 1396, 1315, 1109, 1070, 951, 819,
741 cm-1; ESI–MS : 456.21 [M+H]+, 478.34 [M+Na]+; Anal. calcd for C28H17N5S:
m/z
C 73.83, H 3.76, N 15.37; found C 74.09, H 3.82, N 15.68.
18

ACCEPTED MANUSCRIPT
4.3.5 2-[(1E)-2-[4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-2,5-
dimethoxyphenyl]ethenyl]-1H-benzimidazole (5MOBI). 5MOBI was synthesized as
1
that of 1BN. Yellow crystalline powder. Yield 67.5 %. m.p. > 300 ºC; H NMR
(DMSO-d6, 500 MHz) δ: 13.02 (s, 1H), 12.75 (s, 1H), 9.23 (dd, J1 = 8.1 Hz, J2 = 1.5
Hz, 1H), 9.07 (dd, J1 = 4.7 Hz, J2 = 1.5 Hz, 1H), 9.05 (dd, J1 = 4.6 Hz, J2 = 1.5 Hz,
1H), 9.00 (dd, J1 = 8.0 Hz, J2 = 1.5 Hz, 1H), 8.00 (s, 1H), 7.99 (d,
J = 16.5 Hz, 1H),
7.86 (dd, J1 = 8.1 Hz, J2 = 4.7 Hz, 1H), 7.84 (dd, J1 = 8.0 Hz, J2 = 4.6 Hz, 1H), 7.64 (s,
1H), 7.63 (d,
J
= 7.7 Hz, 1H), 7.51 (d,
J
= 16.5 Hz, 1H), 7.50 (d, J = 7.7 Hz, 1H),
13
7.17-7.24 (m, 2H), 4.15 (s, 3H), 4.05 (s, 3H); C NMR (DMSO-d6, 125 MHz) δ:
56.29, 56.50, 110.43, 111.15, 112.47, 118.68, 119.40, 119.67, 122.96, 123.47, 123.62,
126.60, 128.26, 129.81, 130.44, 134.70, 134.86, 135.23, 140.29, 143.61, 143.82,
147.82, 147.94, 148.02, 150.78, 151.30, 151.33; FT–IR (KBr) ν: 3398, 3066, 2938,
1637, 1608, 1566, 1535, 1475, 1423, 1381, 1279, 1213, 1070, 1036, 972, 807, 741
cm-1; ESI–MS : 499.26 [M+H]+, 521.39 [M+Na]+；Anal. calcd for C30H22N6O2: C
m/z
72.28, H 4.45, N 16.86; found C 72.49, H 4.63, N 16.99.
Acknowledgements
We are grateful to the financial supports from the Natural Science Foundation of
Zhejiang province, China (Grant No. LY15B030006) and the National Natural
Science Foundation of China (Grant No. 21103151).
Supplementary data
Supplementary spectra related to this article can be found in the supporting
information.
References and notes
19

ACCEPTED MANUSCRIPT
[1] Xia, H.; Yang, J.; Fang, H. H.; Chen, Q. D.; Wang, H. Y.; Yu, X. Q.; Ma, Y. G.;
Jiang, M. H.; Sun, H. B. Chem. Phys. Chem. 2010, 11, 1871–1875.
[2] Fang, H. H.; Chen, Q. D.; Yang, J.; Wang, L.; Jiang, Y.; Xia, H.; Feng, J.; Ma, Y.
G.; Wang, H. Y.; Sun, H. B. Appl. Phys. Lett. 2010, 96, 103508-1–103508-3.
[3] Dahl, R.; Larsen, S.; Dohlmann, T. L.; Qvortrup, K.; Helge, J. W.; Dela, F.; Prats,
C. Acta Physiol. 2015, 213, 145–155.
[4] Verboven, P.; Herremans, E.; Helfen, L.; Ho, Q. T.; Abera, M.; Baumbach, T.;
Wevers, M.; Nicolai, B. M. Plant J. 2015, 81, 169–182.
[5] Lin, C. C.; Velusamy, M.; Chou, H. H.; Lin, J. T.; Chou, P. T. Tetrahedron 2010,
66, 8629–8634.
[6] LaFratta, C. N.; Fourkas, J. T.; Baldacchini, T.; Farrer, R. A. Angew. Chem. Int.
Ed. 2007, 46, 6238–6258.
[7] Christenson, C. W.; Saini, A.; Valle, B. J. Opt. Soc. Am. B 2014, 31, 637–641 .
[8] Li, L.; Wu, Y. Q.; Wang, Y. Chin. Opt. Lett. 2012, 10, 101602-1–101602-4.
[9] Hu, D. Q.; Hu, Y. L.; Huang, W. H. Opt. Commun. 2012, 285, 4941–4945.
[10] Sheng, N.; Liu, D. H.; Gu, B.; He, J.; Cui, Y. P. Dyes. Pigm. 2015, 122, 346–350.
[11] Narayanan, S.; Abbas, A.; Raghunathan, S. P.; Sreekumar, K.; Kartha, C. S.;
Joseph, R. Rsc. Adv. 2015, 5, 8657–8668.
[12] Vanyukov, V.; Mikheev, G. M.; Mogileva, T. N.; Puzyr, A. P.; Bondar, V. S.;
Svirko, Y. P. Opt. Mater. 2014, 37, 218–222 .
[13] Zou, Q. L.; Zhao, H. Y.; Zhao, Y. X.; Fang, Y. Y.; Chen, D. F.; Ren, J. J. Med.
Chem. 2015, 58, 7949–7958 .
[14] Secret, E.; Maynadier, M.; Gallud, A.; Chaix, A.; Bouffard, E.; Gary-Bobo, M.;
Marcotte, N.; Mongin, O.; Cheikh, K. E.; Hugues, V.; Auffan, M.; Frochot, C.;
Morère, A.; Maillard, P.; Blanchard-Desce, M.; Sailor, M. J.; Garcia, M.; Durand,
J. O.; Cunin, F. Adv. Mater. 2014, 26, 7643–7648.
[15] Hamed, B.; Haimberger, T.; Kozich, V.; Wiehe, A.; Heyne, K. Photochem.
Photobiol. 2014, 295, 53–56.
[16] Reinhardt, B. A. Chem. Mater. 1998, 10, 1863–1874.
20

ACCEPTED MANUSCRIPT
[17] Albota, M.; Beljonne, D.; Bredas, J. L.; Ehrlich, J. E.; Fu, J. Y.; Heikal, A. A.;
Hess, S. E.; Kogej, T.; Leven, M. D.; Marder, S. R.; McCord-Maughon, D.;
Perry, J. W.; Röckel, H.; Rumi, M.; Subramaniam, G.; Webb, W. W.; Wu, X. L.;
Xu, C. Science 1998, 281, 1653–1656.
[18] Bhawalkar, J. D.; Shih, A.; Pan, S. J.; Liou, W. S.; Swiatkiewicz, J.; Reinhardt, B.
A.; Prasad, P. N.; Cheng, P. C. Bioimaging 1996, 4, 168–178.
[19] Yin, H. Y.; Xiao, H. B.; Ding, L.; Zhang, C.; Ren, A. M.; Li, B. Mater. Chem.
Phys. 2015, 151, 181–186
[20] He, T. C.; Too, P. C.; Chen, R.; Chiba, S.; Sun, H. D. Chem. Asian J. 2012, 7,
2090–2095.
[21] Cao. D. X.; Liu, Z. Q.; Li, G. Z.; Liu, G. Q.; Zhang, G. H. J. Mol. Struct. 2008,
874, 46–50.
[22] Hu, Z. J.; Sun, P. P.; Li, L.; Tian, Y. P.; Yang, J. X.; Wu, J. Y.; Zhou, H. P.; Tao.
L. M.; Wang, C. K.; Li, M.; Chen, G, H.; Tang, H. H.; Tao, X. T.; Jiang, M. H.
Chem. Phys. 2009, 355, 91–98.
[23] Yi, X. Y.; Yang, P.; Huang, D. D.; Zhao, J. Z. Dyes. Pigm. 2013, 96,104–115.
[24] Zhang, X.; Li, L. L.; Liu, Y. K. Mater. Sci. Eng. C 2016, 59, 916–923.
[25] Rigo, R.; Bianco, S.; Musetti, C.; Palumbo, M.; Sissi, C. ChemMedChem 2016,
11, 1762–1769.
[26] Ali, S. S. Org. Chem. Indian J. 2011, 7, 270–274.
[27] Zhang, H. G.; Tao, X. T.; Chen, K. S.; Yuan, C. X.; Jiang, M. H. Synthetic Met.
2011, 161, 354–359.
[28] Gao, C.; Liu, S. Y.; Zhang, X.; Liu, Y. K.; Qiao, C. D.; Liu, Z. E. Spectrochim.
Acta, Part A 2016, 156, 1–8.
[29]Zhang, X.; Xie, R. X.; Yao, J. S.; Meng, X. L.; Liu, Y. K.; Yu, X. Q.; Jiang, M. H.
Polym. Polym. Compos. 2012, 20, 9–12
[30] Demas, J. N.; Crosby, G. A. J. Phy. Chem. 1971, 75, 991–1024.
[31]Fromherz, P. J. Phys. Chem. 1995, 99, 7188–7192.
[32] Narang, U.; Zhao, C. F.; Bhawalkar, J. D.; Bright, F. V.; Prasad, P. N. J. Phys.
Chem. 1996, 100, 4521–4525.
21

ACCEPTED MANUSCRIPT
[33] Song, Q.; Evans, C. E.; Bohn, P. W. J. Phys. Chem. 1993, 97, 13736–13741.
[34] Cao, X.; Tolbert, R.W.; McHale, J. L.; Edwards, W. D. J. Phys. Chem. A 1998,
102, 2739–2748.
[35] Nad, S.; Kumbhakar, M.; Pal, H. J. Phys. Chem. A 2003, 107, 4808–4816.
[36] Ren, Y.; Fang, Q.; Yu, W. T.; Lei, H.; Tian, Y. P.; Jiang, M. H. J. Mater. Chem.
2000, 10, 2025–2033.
[37] Chandrasekhar, V.; Pandey, M. D.; Maurya, S. K.; Sen, P.; Goswami, D. Chem.
Asian J. 2011, 6, 2246–2250.
[38] Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;
Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann, R. E.;
Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain,
M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.;
Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.;
Cui, Q.; Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko,
A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.;
Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.;
Gill, P. M. W.; Johnson, B. G.; Chen,W.;Wong, M.W.; Andres, J. L.;
Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 09; Gaussian:
Wallingford, CT, 2009.
[39](a) Hehre,W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56, 2257–2261;
(b) Lee, C.; Yang, W.; Parr, R. G. Rev. Phys. B 1988, 37, 785–789; (c) Becke, A.
D. J. Chem. Phys. 1993, 98, 5648–5652.
[40] Albota, M. A.; Xu, C.; Webb, W.W. Appl. Opt. 1998, 37, 7352–7356.
[41] (a) Imgartinger, H.; Herpich, R. Eur. J. Org. Chem. 1998, 4, 595–604; (b)
Borisenko, K. B.; Zauer, K.; Hargittai, I. J. Phys. Chem, 1996, 100
19303–19309.
,
[42] Wendlandt, A. E.; Shannon, S. S. J. Am. Chem. Soc. 2014, 136, 506–512.
[43] Nishizawa, T.; Lim, H. K.; Tajima, K.; Hashimoto, K. J. Am. Chem. Soc. 2009,
131, 2464–2465.
22

ACCEPTED MANUSCRIPT
[44] Soo, H. S.; Agiral, A.; Bachmeier, A.; Frei, H. J. Am. Chem. Soc. 2012, 134
,
17104–17116.
[45] Abbate, S.; Bazzini, C.; Caronna, T.; Fontana, F.; Gambarotti, C.; Gangemi, F.;
Longhi, G.; Mele, A.; Sora, I. N.; Panzeri, W. Tetrahedron 2005, 62, 139–148.
[46] Huang, Z. L.; Lei, H.; Li, N.; Qiu, Z. R.; Wang, H. Z.; Guo, J. D.; Luo, Y.; Zhong,
Z. P.; Liu, X. F.; Zhou, Z. H. J. Mater. Chem. 2003, 13, 708–711.
[47] Cai, Z. B.; Zhou, M.; Li, B.; Chen, Y.; Jin, F.; Huang, J. Q. New J. Chem. 2014,
38, 3042–3049.
23