Opposite ESIPT characteristic of two AIE-active isomers with different linkage sites

Article abstract of DOI:10.1016/j.tet.2019.03.041

In this work, we report two isomers composed of 1-phenyl-1H-phenanthro[9,10-d]imidazole (PI), hydroxyl and tetraphenylethylene (TPE), abbreviated as m-PITPE and p-PITPE. It is found that they exhibit similar aggregation-induced emission (AIE) behavior but totally different excited-state intramolecular proton transfer (ESIPT) characteristic, as a result of the different linkage sites of PI on TPE moiety. Theoretical calculations and their different experimental responses to F^? demonstrate that only the para-linkage isomer displays ESIPT. In m-PITPE with meta-linkage, the electron cloud distribution only locates at the TPE part in the singlet excited (S₁) states, which results in the localized excited state without ESIPT characteristic.

Full text of DOI:10.1016/j.tet.2019.03.041

Accepted Manuscript
Opposite ESIPT characteristic of two AIE-active isomers with different linkage sites
Yujie Dong, Junjie Shen, Weijun Li, Ruiyang Zhao, Yuyu Pan, Qingbao Song, Cheng
Zhang
PII:
S0040-4020(19)30338-2
https://doi.org/10.1016/j.tet.2019.03.041
TET 30227
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 21 December 2018
Revised Date: 20 March 2019
Accepted Date: 23 March 2019
Please cite this article as: Dong Y, Shen J, Li W, Zhao R, Pan Y, Song Q, Zhang C, Opposite ESIPT
characteristic of two AIE-active isomers with different linkage sites, Tetrahedron (2019), doi: https://
doi.org/10.1016/j.tet.2019.03.041.
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Opposite ESIPT characteristic of two AIE-
active isomers with different linkage sites
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Yujie Donga, Junjie Shena, Weijun Lia , Ruiyang Zhaob, Yuyu Panc,*, Qingbao Songa, and Cheng Zhanga,
a State Key Laboratory Breeding Base of Green Chemistry Synthesis Technology, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, 310014, P. R. China
b College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao, 266042, P. R. China
c School of Petrochemical Engineering, Shenyang University of Technology, 30 Guanghua Street, Liaoyang, 111003, P. R. China.

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Tetrahedron
journal homepage: www.elsevier.com
Opposite ESIPT characteristic of two AIE-active isomers with different linkage sites
Yujie Donga, Junjie Shena, Weijun Lia , Ruiyang Zhaob, Yuyu Panc,*, Qingbao Songa, and Cheng Zhanga,
a State Key Laboratory Breeding Base of Green Chemistry Synthesis Technology, College of Chemical Engineering, Zhejiang University of Technology,
Hangzhou, 310014, P. R. China
b College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao, 266042, P. R. China.
c School of Petrochemical Engineering, Shenyang University of Technology, 30 Guanghua Street, Liaoyang, 111003, P. R. China.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
In this work, we report two isomers composed of 1-phenyl-1H-phenanthro[9,10-d]imidazole
(PI), hydroxyl and tetraphenylethylene (TPE), abbreviated as m-PITPE and p-PITPE. It is
found that they exhibit similar aggregation-induced emission (AIE) behavior but totally different
excited-state intramolecular proton transfer (ESIPT) characteristic, as a result of the different
linkage sites of PI on TPE moiety. Theoretical calculations and their different experimental
responses to F- demonstrate that only the para-linkage isomer displays ESIPT. In m-PITPE
with meta-linkage, the electron cloud distribution only locates at the TPE part in the singlet
excited (S1) states, which results in the localized excited state without ESIPT characteristic.
Available online
keywords:
ESIPT
AIE
2009 Elsevier Ltd. All rights reserved
.
Tetraphenylethylene
Isomer
1. Introduction
characteristics undergo the photoautomerization process, i.e.,
from excited-state enol (E*) to excited state keto (K*) and then
back to the ground states, there is a stronger fluorescence
emission with an extraordinary Stokes shift from the decay of K*.
Organic luminogens with strong solid-state emission have
been of immense scientific and technological interests to studies
of molecular electronics and photonics. They also exhibited wide
applications in the fields of organic light-emitting devices
Therefore, ESIPT molecules also have the potential to exhibit
25, 26
intense emission in solid state.
Some excellent work about
(OLEDs) 1-3, organic laser 4-6, sensor and so on. To overcome
7-9
introducing ESIPT into AIEgens have been reported 27-34. Up to
now, however, studies on AIEgens with ESIPT characteristic and
strong solid-state emission are still limited.
the well-known aggregation-caused quenching (ACQ) effect and
extend the application scope of these materials, the concept of
aggregation-induced emission (AIE) was put forward in 2001
10
.
A recent study indicated that the intramolecular linkage of
TPE not only affects molecular luminescence20, but also has a
strong impact on the AIE mechanism 17. The effects caused by
different linkage sites between a typical ESIPT unit and TPE
moiety haven’t been well studied. In this work, we choose
hydroxyl as the proton donor group and 1-phenyl-1H-
phenanthro[9,10-d]imidazole (PI) as the proton acceptor group to
build two isomers, i.e. p-PITPE and m-PITPE, which are
abbreviated according to the linkage sites of PI on TPE. It is
found that both isomers show AIE phenomenon, but different
ESIPT characteristic. Our experimental results on the responses
to F- and theoretical calculations demonstrate that only p-PITPE
undergoes ESIPT process. In m-PITPE, the theoretical
calculation results on the S1 state indicate there is no ESIPT
characteristic in its radiative transition of the localized excited
state.
AIE luminogens (AIEgens) show low luminescence in solution,
but “lighting up” with enhanced fluorescence emission upon
aggregation. The AIE effect is mainly attributed to the
11
“restriction of intramolecular motions” (RIM) in most of the
reported AIEgens, but some other factors such as molecular
planarization, specific aggregation mode 12, photo/thermal E/Z
16
isomerization 13-15, formation of photocyclized intermediates
and rotation restriction around elongated C=C bond at excited
state 17 have also been confirmed to be responsible for AIE effect.
As a star AIE-active molecule structure, tetraphenylethylene
(TPE) has been utilized to construct many AIEgens and is still
the most popular candidate for studying AIE phenomena 18-20
.
The excited-state intramolecular proton transfer (ESIPT)
reactions in organic molecules have been widely investigated
21, 22
because of its promising practical applications in laser dyes
and fluorescent probes 23, 24. When the molecules with ESIPT
———
Corresponding author. Tel.: +86-571-88320508; e-mail: czhang@zjut.edu.cn (C. Z), qbsong@zjut.edu.cn (Q. S)
Corresponding author. Tel.: +86-419-5319409; e-mail: pyy39518768@163.com (Y. P)

2
Tetrahedron
which prevents the formation of strong π-π interactions and
ACCEPTED MANUSCRIPT
ensures the higher-efficiency fluorescence emission in crystal.
2.3. Photophysical properties
Photophysical properties of compounds m-PITPE and p-
PITPE were investigated in solution and solid state. As shown in
Fig. 3, the UV-vis absorption spectra of the two compounds in
dilute THF solutions exhibit a consecutive broad band centered
around 310 and 370 nm, which should be attributed to the π-π*
transition of the conjugated skeleton. Compared with m-PITPE,
p-PITPE showed the red-shifted absorption spectrum because
the para-linkage enjoys a better conjugation effect than meta-
linkage does. Both of the two compounds exhibit weak
fluorescence in their dilute THF solutions with λmax at 488 nm for
m-PITPE and 474 nm for p-PITPE. In comparison with their PL
spectra in solution, the PL spectrum of the coated m-PITPE film
does not show substantial changes, while that of p-PITPE film
displays a red-shift of 23 nm (λmax= 497 nm). The Stokes shifts in
THF were calculated to be as large as 6535 cm-1 and 5713 cm-1
for m-PITPE and p-PITPE, respectively.
Fig. 1 Molecular structures and synthetic routes of m-PITPE and p-PITPE
2. Results and discussion
2.1. Design and synthesis
The synthetic routes of TPE derivatives are shown in Fig. 1.
The intermediates of compound 1, 2a and 2b can be readily
prepared in good yields. The isomers of m-PITPE and p-PITPE
were obtained by the Suzuki reaction between compound 1 and
the corresponding reactants of 2a and 2b, respectively. The
1
structures of all the compounds were well characterized by H
NMR, 13C NMR and mass spectroscopy (ESI†).
2.2. Crystal structure
Single crystals of m-PITPE and p-PITPE were obtained by
slowly diffusing methanol into their chloroform solutions. Both
of the two isomers are crystallized in a triclinic space group P-1,
and the crystal data refinement parameters are listed in Table. S1
(ESI†).
Fig. 2 X-ray crystal structure, intramolecular hydrogen bonds (Left) and the
crystal packing diagram (Right) of compounds m-PITPE (a) and p-PITPE
(b). (CCDC: 1886490 for m-PITPE and 1886491 for p-PITPE)
Fig. 3 Normalized absorption and PL spectra of m-PITPE (a) and p-PITPE
(b) in THF and PL spectra in their solid state
.
As shown in Fig. 2a, there is only one molecular configuration
in the crystal of m-PITPE. In the m-PITPE crystal, the hydroxyl
group points to the proton acceptor N in imidazole ring due to the
intramolecular hydrogen bonding (H-bond 1: N-H 1.80 Å, angle
O-H···N 147.3°). The adjacent molecules pack together and form
weak π-π interactions between the less overlapped
phenanthroimidazole units. As shown in Fig. 2b, there are two
molecules in one asymmetric unit in p-PITPE, but their
geometric parameters are not significantly different. The
intramolecular hydrogen bonding (O-H···N) can also be
observed in both configurations (H-bond 2: N-H 1.71 Å, angle O-
H···N 146.8°; H-bond 3: N-H 1.83 Å, angle O-H···N 140.6°). It
is obvious that no coaxial strong π-π interactions in p-PITPE
crystal due to the large intermolecular distance and dihedral
angle between phenanthroimidazole units. Both of the two
isomers in their crystal display highly twisted configurations,
2.4. AIE effect
The AIE effect of m-PITPE and p-PITPE were verified by
testing their PL spectra in the THF/water mixture. As shown in
Fig. 4, the emission intensities of m-PITPE and p-PITPE remain
unchanged until the ratio of water increases to 70%. Upon further
increasing the water fraction to 90%, the remarkable emission
enhancement was observed for both of the two isomers, i.e. 14-
fold and 22-fold enhancement in PL intensities of m-PITPE and
p-PITPE, respectively. The changes of the spectra indicate that
both of the isomers show the typical AIE properties. The
formation of nanoparticle aggregates in THF/water mixture with
higher water fractions, which could block the intramolecular free
rotation and thus inhibit the non-radiative transition, is
responsible for the observed AIE phenomenon.

(LUMO) for m-PITPE, and -5.04 eV (HOMO) and -1.43 eV
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(LUMO) for p-PITPE, respectively. Compared with m-PITPE,
the higher HOMO level and smaller band gap of p-PITPE should
be ascribed to the more effective conjugation of para-linkage in
p-PITPE. These results are well consistent with the
aforementioned absorption spectra.
In order to examine the nature of the electronic transitions in
m-PITPE and p-PITPE and further verify whether the ESIPT
exists in both of the two isomers, their optimized molecular
configurations of the excited states and natural transition orbitals
(NTOs) were evaluated in Fig. 6. Surprisingly, in S1 state, the
molecular structure of m-PITPE is highly twisted, and the
dihedral angle between imidazole ring and hydroxyl-linked
phenyl is as large as 35°. What’s more, the hydroxyl rotates to
the opposite side of the proton acceptor, indicating it is
impossible to transfer proton from hydroxyl to nitrogen atom in
m-PITPE. However, in p-PITPE, the imidazole ring and
hydroxyl-linked phenyl are almost coplanar. (the dihedral angle:
~4°), and the bond length of O-H is 1.60 Å, which is shorter than
those observed in crystal. All of these observations suggest that
the proton transfers from hydroxyl to the nitrogen atom in the S1
state of p-PITPE. For the NTOs of the S1 state, the holes and
particles of m-PITPE only locate on the TPE part, and there is
not any distribution on nitrogen atom (which is hydrogen
acceptor during the ESIPT process). For p-PITPE, on the other
hand, there is a small fraction of holes and particles located on
the imidazole ring, though most of them still locate on the TPE.
The theoretical results demonstrate that p-PITPE undergoes
ESIPT process, while m-PITPE relaxes from localized excited
state without ESIPT.
Fig. 4 The PL spectra at different solvent ratios (v/v) for (a) m-PITPE and
(b) p-PITPE in the THF/water mixture.
2.6. Response to F-
2.5. Theoretical calculation
The density functional theory (DFT) analysis of the optimized
molecular configurations for m-PITPE and p-PITPE in the
ground state revealed the similar structural characteristics to
those in their single crystal. As shown in Fig. 5, the imidazole
ring and hydroxyl-linked phenyl are almost co-planar in both m-
PITPE and p-PITPE, and the hydroxyl bends toward the
nitrogen atom of PI group. The calculation of the frontier
molecular orbitals showed that HOMOs of both m-PITPE and p-
PITPE are delocalized on the whole molecules, while LUMO of
m-PITPE mainly locates at the TPE part and that of p-PITPE
distributes on the whole molecules. These results demonstrate
differences in the conjugations of m-PITPE and p-PITPE,
caused by the different linkages between PI and TPE. Thus, it
was reasonable to have the totally different calculated energy
levels between them, i.e. -6.00 eV (HOMO) and -1.99 eV
It is well known that ESIPT luminogens are sensitive to
surrounding factors, especially F-, which can form strong F-H
interaction with hydrogen-bond donors. So far, many ESIPT
35, 36
luminogens have displayed excellent detectivity to F-.
Inspired by this characteristic, we tested their responses to F- to
studied their ESIPT properties. As shown in Fig. 7a and 7b, there
is almost no change in the absorption and PL spectra of m-
PITPE with the addition of F-. This phenomenon is consistent
with the theoretical calculation that the hydroxyl does not
participate in its fluorescence emission. By contrast, a different
phenomenon was observed in p-PITPE (Fig. 7c and 7d). Upon
addition of F-, the absorption spectra of p-PITPE did not show
noticeable change, but the PL spectra showed a slight red-shift
(~10 nm) and fluorescence intensity increased at first and then
descended,
as
F-
concentration
increased.
Fig. 5 Optimized structures, HOMO and LUMO (eV) of respective isomers in the ground state (B3LYP/6-31G (d, p)).

4
Tetrahedron
ACCEPTED MANUSCRIPT
Fig. 6 Optimized geometries of m-PITPE and p-PITPE in the S1 state and their natural transition orbital distributions (TD-DFT//M06-2X/6-31+G (d, p)).
This phenomenon demonstrated the ESIPT process only
happened in p-PITPE. Compared with m- PITPE, p-PITPE has
both enol (E*) and keto (K*) emission, where K* emission
formed through ESIPT but is too weak to be observed. These PL
spectral changes should be resulted from the combination of
ESIPT and AIE effect. At low concentration of F-, the
intramolecular hydrogen bond, O-H···N, partially deprotected,
which induces a temporary fluorescence enhancement due to the
increased E*/K* emission ratio via ESIPT process 30. As F-
concentration increases further, excess F- induce the complete
deprotonation of p-PITPE by formation of [HF2]- 35, relieving the
locked phenyl and leading to the weakened emission. Their
different responses to F- suggest the ESIPT only occur in p-
PITPE, but not in m-PITPE.
3. Conclusions
In summary, we have presented two AIE-active isomers with
different linkage sites (para- or meta-) of PI on TPE unit. The
theoretical calculation results and the different responses to F-
demonstrate only para-linkage isomer shows ESIPT
characteristic. The results are crucial to the investigation of the
relationship between the linkage sites, conjugation and
luminescent properties of organic molecules, and provide new
insight
into
the
factors
influencing
ESIPT.
Fig 7. Effect of addition of F- on UV–vis absorption spectra and PL spectra of m-PITPE (Up) and p-PITPE (Down) (10 µM in THF).

The compound 2b was synthesized by the same procedure as
2a but using 4-bromo-2-hydroxybenzaldehyde instead of 5-
4. Experimental section
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4.1. General remarks
bromosalicylaldehyde. The product is yellow powder. Yield:
1
85%. H NMR (400 MHz, Chloroform-d), δ [ppm]: 14.17 (s,
All the reagents or chemicals were commercial products
without further purification. NMR spectra of the synthesized
compounds were recorded on Bruker AVANCE III instrument
(Bruker, Switzerland) and BRUKER Ascend 400. Mass spectra
analysis was recorded using a ThermoFisher LCQ Deca XP plus
instrument. Photophysical properties were investigated by a
Shimadzu UV-1800 spectrophotometer (Shimadzu, Japan) and a
Perkin-Elmer LS-55 luminescence spectrophotometer (the
integration time were set to be 0.01s in order to shorten the
measurement time to be less than 20s). The response toward F-
was conducted with tetrabutylammonium as counter cation
dissolved in a THF solution. The calculation method for
geometry optimization in the ground state is B3LYP/6-31G (d, p)
functional 37. The excited state calculations in this paper are
calculated using the TD-DFT// M06-2X/6-31+G (d, p) functional
38-40. All quantum chemical calculations were carried out using
1H), 8.80 (d, J = 8.3 Hz, 1H), 8.76-8.67 (m, 2H), 7.85-7.73 (m,
4H), 7.72 (ddd, J = 8.4, 7.0, 1.5 Hz, 1H), 7.68-7.62 (m, 2H), 7.56
(ddd, J = 8.3, 7.0, 1.3 Hz, 1H), 7.33 (d, J = 2.1 Hz, 1H), 7.30-
7.20 (t, 1H), 7.08 (d, J = 8.3 Hz, 1H), 6.67 (dd, J = 8.7, 2.1 Hz,
1H), 6.57 (d, J = 8.7 Hz, 1H). 13C NMR (126 MHz, Chloroform-
d), δ [ppm]: 160.03, 147.68, 138.72, 134.27, 131.01, 130.82,
129.56, 128.95, 128.48, 127.54, 127.08, 126.78, 126.60, 126.19,
125.57, 125.44, 124.21, 123.23, 122.53, 122.45, 121.30, 121.12,
120.85, 112.07. HRMS (ESI): m/z 465.0606 (M++1).
4.2.4. 2-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)-4-
(1,2,2-triphenylvinyl)phenol (m-PITPE)
0.4 g (0.86 mmol) compound 2a, 0.4 g (1.05 mmol)
compound 1, 0.12 g K2CO3 and 0.02 g Pd(PPh3)4 catalyst were
added into a 50 mL two necked flask, and then 12 mL toluene
and 8 mL deionized water was added. The mixture was refluxed
for 24 h under N2 atmosphere. After cooling to room
temperature, the product was extracted with dichloromethane and
Gaussian 09 (version D.01) package on a PowerLeader cluster 41
.
4.2. Synthesis
purified
using
SiO2
column
chromatography
with
4.2.1. 4,4,5,5-tetramethyl-2-(1,2,2-triphenylvinyl)-1,3,2-
dichloromethane/petroleum ether (v/v, 1/2) as eluent to afford a
light yellow powder. Yield: 13%. 1H NMR (500 MHz,
Chloroform-d), δ [ppm]: 13.82 (s, 1H), 8.76 (d, J = 8.4 Hz, 1H),
8.73-8.67 (m, 2H), 7.77 (td, J = 7.5, 1.1 Hz, 2H), 7.69 (ddd, J =
8.4, 7.0, 1.5 Hz, 1H), 7.59-7.53 (m, 1H), 7.50 (ddd, J = 10.6, 8.8,
7.2 Hz, 3H), 7.39-7.35 (m, 2H), 7.22 (ddd, J = 8.3, 7.0, 1.2 Hz,
1H), 7.13-7.03 (m, 9H), 7.00 (dd, J = 8.5, 1.3 Hz, 1H), 6.91 (dt, J
= 5.7, 2.0 Hz, 5H), 6.87 (d, J = 8.4 Hz, 1H), 6.83-6.79 (m, 2H)
6.49 (d, J = 2.0 Hz, 1H). 13C NMR (126 MHz, Chloroform-d), δ
[ppm]: 157.91, 148.37, 143.90, 143.48, 143.43, 140.41, 140.07,
138.66, 134.28, 134.11, 133.77, 131.37, 131.33, 131.27, 130.89,
130.65, 130.29, 129.41, 129.32, 129.10, 128.58, 128.40, 127.60,
127.55, 127.50, 126.95, 126.48, 126.42, 126.30, 126.25, 126.04,
125.74, 125.22, 124.13, 123.21, 122.57, 120.86, 117.31, 112.47.
HRMS (ESI): m/z 641.2584 (M++1).
dioxaborolane (1)
1.0 g (3 mmol) (2-bromoethene-1,1,2-triyl)-tribenzene was
dissolved in 20 mL distilled THF at -78 under N2 atmosphere,
and then 3.0 mL (7.5 mmol) n-BuLi (1.6 M) was added dropwise
into the mixture. After stirred for 1 h, 2.2 mL (10.7 mmol) 2-
isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane was added
dropwise into the mixture, and then the system was stirred for 8 h
under room temperature. The mixture was quenched with
saturated NH4Cl solution and extracted with dichloromethane.
After evaporation of the solvent, the product was purified by
SiO2 column chromatography with ethyl acetate/petroleum ether
1
(v/v, 50/1) as eluent to give a white solid. Yield: 70%. H NMR
(500 MHz, Chloroform-d), δ [ppm]: 7.37-7.29 (m, 5H), 7.17-7.03
(m, 8H), 6.99-6.93 (m, 2H), 1.13 (s, 12H). 13C NMR (126 MHz,
Chloroform-d), δ [ppm]: 151.38, 144.66, 141.83, 141.69, 130.92,
129.72, 129.42, 127.98, 127.94, 127.57, 127.51, 126.76, 125.84,
83.68, 24.55. MS (ESI): m/z 383.2 (M++1).
4.2.5. 2-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)-5-
(1,2,2-triphenylvinyl)phenol (p-PITPE)
The compound p-PITPE was synthesized by the same
procedure as m-PITPE but using compound 2b instead of
compound 2a. The product is yellow powder. Yield: 44%. H
4.2.2. 4-bromo-2-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-
yl)phenol (2a)
1
NMR (500 MHz, Chloroform-d), δ [ppm]: 13.69 (s, 1H), 8.78 (d,
J = 8.3 Hz, 1H), 8.73-8.66 (m, 2H), 7.76 (ddd, J = 8.0, 7.0, 1.1
Hz, 1H), 7.73-7.66 (m, 4H), 7.62-7.57 (m, 2H), 7.52 ((ddd, J =
8.3, 7.0, 1.3 Hz, 1H), 7.27-7.23 (m, 1H), 7.15-6.98 (m, 15H),
6.83 (d, J = 1.8 Hz, 1H), 6.46 (d, J = 8.4 Hz, 1H), 6.20 (dd, J =
8.4, 1.8 Hz, 1H); 13C NMR (126 MHz, Chloroform-d), δ [ppm]:
158.59, 148.47, 146.44, 143.55, 143.41, 143.20, 141.68, 140.12,
138.98, 134.40, 131.32, 131.30, 131.15, 130.80, 130.52, 129.45,
129.05, 128.59, 128.42, 127.73, 127.68, 127.62, 127.50, 126.95,
126.69, 126.50, 126.05, 125.73, 125.21, 124.18, 123.20, 122.61,
122.58, 121.51, 120.86, 120.74, 111.27. HRMS (ESI): m/z
641.2584 (M++1).
0.56 g (2.4 mmol) 9,10-phenanthraquinone, 0.5 g (2.18 mmol)
5-bromosalicylaldehyde, 1.0 g (12 mmol) ammonium acetate and
0.30 mL aniline were added into a 100 mL two necked round-
bottom flask. 30mL acetic acid was added sequentially, and then
the mixture was heated at 120 for 12 h. After cooling to room
temperature, the product was extracted with dichloromethane and
purified
using
SiO2
column
chromatography
with
dichloromethane/ petroleum ether (v/v, 1/2) as eluent to afford a
1
white powder. Yield: 62%. H NMR (500 MHz, Chloroform-d),
δ [ppm]: 13.98 (s, 1H), 8.80 (d, J = 8.4 Hz, 1H), 8.75-8.68 (m,
2H), 7.88-7.84 (m, 1H), 7.83-7.76 (m, 3H), 7.73-7.69 (m, 1H),
7.68-7.62 (m, 2H), 7.59-7.53 (m, 1H), 7.34-7.28 (m, 2H), 7.18-
7.12 (m, 1H), 7.03 (d, J = 8.8 Hz, 1H), 6.75(d, J = 2.4 Hz, 1H).
13C NMR (126 MHz, Chloroform-d), δ [ppm]: 158.22, 147.00,
138.54, 134.27, 133.21, 131.07, 130.94, 129.63, 128.84, 128.66,
128.50, 127.58, 127.10, 126.63, 126.24, 125.60, 125.55, 124.21,
123.24, 122.54, 122.44, 120.94, 119.71, 114.53, 109.73. HRMS
(ESI): m/z 465.0607 (M++1).
Acknowledgments
This work was supported by China Postdoctoral Science
Foundation
(2018M632498),
the
Zhejiang
Provincial
Postdoctoral Fellowship (Z71101009), Zhejiang Provincial
Natural Science Foundation of China (LQ19E030016,
LY19E030006, LZ17E030001), and Natural Science Foundation
of China (51603185, 51673174, 21875219).We thank Dr.
Zhenghui Wu for his help.
4.2.3. 5-bromo-2-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-
yl)phenol (2b)

6
Tetrahedron
ACCEPTED MANUSCRIPT
Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F.
Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara,
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