Synthesis and configurational character study of novel structural isomers based on pyrene-imidazole

Article abstract of DOI:10.3390/molecules24122293

Isomers provide more possibilities for the structure of organic compounds. Molecular structures determine their corresponding properties, therefore the intrinsic relationship between structure and properties of isomers is of great research value. Isomers with a stable structure and excellent performance possess more potential for development and application. In this paper, we design and synthesize structural isomers with different molecular symmetries based on the asymmetric structure of imidazole and the symmetrical structure of pyrene. Isomers with stable molecular structures can be obtained by a simple and efficient “one-pot” reaction, involving axisymmetric configuration and centrosymmetric configuration. Using this “click-like” reaction, the structure of target molecules is controllable and adjustable. Furthermore, the effect of molecular configurations on molecular stacking of crystal is studied. The variation of the optical and thermal properties, the optimized structures, and orbital distributions of isomers depends on different molecular geometry with different symmetry, which are revealed by crystallographic analysis. This present strategy provides an efficient synthetic method for the design and synthesis of structural isomers based on pyrene-imidazole.

Full text of DOI:10.3390/molecules24122293

molecules
Article
Synthesis and Configurational Character Study of
Novel Structural Isomers Based on Pyrene–Imidazole
Yu-Long Liu 1,2 , Liu Yang , You-Quan Guo , Guo-Qiang Xu , Bin Qu
1
3
1
1,2
and Ying Fu 1,*
1
Department of Applied Chemistry, College of Science, Northeast Agricultural University, Harbin 150030,
China; liuyulong@neau.edu.cn (Y.-L.L.); yangliu@neau.edu.cn (L.Y.); xuguoqiang@neau.edu.cn (G.-Q.X.);
qubin@neau.edu.cn (B.Q.)
CAS Key Laboratory of Renewable Energy, Guangzhou Institute of Energy Conversion, Guangzhou 510640,
China
2
3
Heilongjiang Vocational College of Biology Science and Technology, Harbin 150025, China;
feilong50123146@126.com
*
Correspondence: fuying@neau.edu.cn; Tel.: +86-451-5519-0070
ꢀ
ꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀ
ꢁꢂꢃꢄꢅꢆ
Received: 4 June 2019; Accepted: 18 June 2019; Published: 20 June 2019
Abstract: Isomers provide more possibilities for the structure of organic compounds. Molecular
structures determine their corresponding properties, therefore the intrinsic relationship between
structure and properties of isomers is of great research value. Isomers with a stable structure and
excellent performance possess more potential for development and application. In this paper, we
design and synthesize structural isomers with different molecular symmetries based on the asymmetric
structure of imidazole and the symmetrical structure of pyrene. Isomers with stable molecular
structures can be obtained by a simple and efficient “one-pot” reaction, involving axisymmetric
configuration and centrosymmetric configuration. Using this “click-like” reaction, the structure of
target molecules is controllable and adjustable. Furthermore, the effect of molecular configurations
on molecular stacking of crystal is studied. The variation of the optical and thermal properties, the
optimized structures, and orbital distributions of isomers depends on different molecular geometry
with different symmetry, which are revealed by crystallographic analysis. This present strategy
provides an efficient synthetic method for the design and synthesis of structural isomers based
on pyrene–imidazole.
Keywords: one-pot reaction; pyrene–imidazole; structural isomer; molecular symmetry; crystal
structure
1
. Introduction
Isomers are one of the major research topics in chemistry and materials. In the field of medicinal
and material science, the pharmacological properties and the macroscopic properties of isomers may
be different or even dramatically distinctive [ ]. In the field of organic optoelectronics, isomers
have also drawn a lot of attention in recent years [ ]. Structural isomers, for instance, which possess
1–4
5
the same bonding mode but hold different geometric positions of related atoms in space, may not
keep similar properties necessarily, even though they have the same functional groups; therefore,
these valuable isomers can be provided as model compounds to research the relationship between
structure and properties [6,7]. Besides, structures of structural isomers are stabilized through chemical
bonds where photochemical or thermochemical isomerization could not occur suggesting excellent
stability of structural isomers. A great deal of the intensive study toward the syn-isomeric and
anti-isomeric effects on the crucial changes of photophysical properties for thiophene derivatives
has taken place and thus becomes typical [
8
–
11]. It has been shown that much higher charge
Molecules 2019, 24, 2293; doi:10.3390/molecules24122293
www.mdpi.com/journal/molecules

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mobilities appear in pure isomers with anti-configuration than their corresponding syn-counterparts
in the performance of organic field effect transistors, and this result has been reported by several
groups involved with the model compounds of anthradithiophene, dicyanomethylenedithiophene,
anthrabisbenzothiophene, and other systems [9–11]. In addition, emitters with naphthoimidazole (NI)
unit were first reported by Su’s group [12]. Combined with triphenylamine, a series of donor-accepter
molecules based on naphtho[1,2-d]imidazole structural isomers were synthesized, and their different
configuration effects on the performance of non-doped single-layer fluorescent organic light-emitting
diodes were systematically studied. 1H-naphtho[1,2-d]imidazole-based compounds emanate similar
deep-blue light emission to 3H-naphtho[1,2-d]imidazole analogues but show much higher efficiency.
The author pointed out that the best performance in single-layer devices of 3H-naphtho[1,2-d]imidazole
compounds is attributed to their much higher capacity for direct electron-injection from the cathode.
Moreover, structural isomers could be designed and synthesized through regulating the reactive sites
thus providing tremendous examples of structure–property study [13–17]. These valuable studies
have promoted the vigorous development of organic functional materials in organic electronics and
made great contributions to structure–property relationship of structural isomers in organic chemistry.
Exploiting structure and potential of novel isomers is a never-ending task for a scientist. Pyrene,
a classical polycyclic aromatic hydrocarbon which consists of four fused benzene rings, represents one of
the mostly investigated organic molecules over the past decades [18]. The planar structural motif, large
π
-system, and good mobility of
and have been thoroughly investigated according to admirable fluorescent and self-assembling property
in recent years [19 21]. Nowadays, there has also been increasing interest in utilizing the pyrene unit
as a semiconductor in the optoelectronic field [22 24]. It is widely known that the molecular structure
π-electron flow endow pyrene with attractive photophysical properties
–
–
and supramolecular structure of materials can be regulated through chemical modification at different
sites of molecules, thereby affecting their relevant performance on applications. Therefore, efficient
synthesis and novel structure of pyrene-based materials is of great interest. 1,3-Imidazole belongs
to a five-numbered-ring functional building block and is commonly used for efficient light emitting
materials such as benzimidazole, naphtho[1,2-d]imidazole, and phenanthro[9,10-d]imidazole in virtue
2
of its amphoteric characteristics originated from the two different kinds of sp hybrid nitrogen atoms.
The asymmetric structure of imidazole provides a priori condition for the construction of structural
isomers. Based on these considerations, a convenient and one-pot facile methodology is used to prepare
a novel polycyclic skeleton straightforwardly using imidazole and pyrene as the key units. Although
many efforts have been made to prepare pyrene–imidazole derivatives with different substitutions
at one side of the K-region on pyrene [25
pyrene–imidazole-based polycyclic skeleton in which the K-region of pyrene is fully modified [28
–
27], there is rarely an attempt to synthesize a bilateral
30].
–
In this study, small organic molecules with a clear structure and structural isomers with different
symmetries are selected as the research object. With this consideration in mind, novel structural isomers
with syn-/anti-configuration consisting of a rigid
imidazole are obtained through a one-pot reaction. In accordance with previous research [31
π
-structure of pyrene and nonsymmetrical unit of
33],
–
the “click-like” one-pot reaction is a modification of the general method of the Debus–Radziszewski
reaction which was presented more than 100 years ago by Debus and Radziszewski and has proved to
be a highly efficient multicomponent reaction (MCR) yielding imidazole under mild conditions [34,35].
The one-step procedure utilized in this paper is simple, efficient, and structurally controllable whereby
ammonium acetate, arylamine, pyrene-4,5,9,10-tetraones, and aromatic aldehyde in the solution of
acetic acid are treated by reflux for 2 h. Eventually centrosymmetric anti-tbu-PyDPI and axisymmetric
syn-tbu-PyDPI are readily and simultaneously generated during the synthesis process (Scheme 1). The
two structural isomers are separated successfully with high purity. Furthermore, the structures of
anti-tbu-PyDPI with centrosymmetry and syn-tbu-PyDPI with axisymmetry were both determined by
X-ray single-crystal diffraction precisely.

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Scheme 1. Synthetic approach to pyrene–imidazole based isomers.
2
. Results and Discussion
Synthesis route of the anti/syn-isomers of tbu-PyDPI is depicted in Scheme 2. Anti-tbu-PyDPI
and syn-tbu-PyDPI were synthesized through a one-pot reaction simultaneously with a moderate
yield of 35.0% and 32.5%, respectively. When separating and purifying by chromatography, the Rf
values of these two isomers varied significantly after being eluted with a mixed solvent of petroleum
ether and dichloromethane in a ratio of 1:5 v/v. This was a consequence of the differential molecular
polarities of the syn- and anti-isomers with various symmetries, leading to noticeable differences in the
molecular shape and dipole moment of these rigid polycyclic aromatic hydrocarbons. Thus, anti- and
syn-tbu-PyDPI could be obtained successfully in an approximate 1:1 ratio.
RuCl3.xH2O
8
parts of NaIO4
O
O
O
O
t-BuCl
AlCl3
CH2Cl2, CH3CN, H2O
0-40 o
3
C
O
O
O
O
CH3COONH4, CH3COOH
120 oC, 2h
+
OHC
+ H2N
N
N
N
N
N
N
N
+
N
anti-tbu-PyDPI
syn-tbu-PyDPI
Scheme 2. Synthetic routes of pyrene–imidazole based isomers.
1
2
.1. H NMR Spectrum Identification
1
As shown in the H NMR spectra (Figure 1), the resonance peaks of protons H
a
of tertiary butyl
on 2 and 7-position of pyrene in anti-tbu-PyDPI occurred at 1.31 ppm exclusively, demonstrating that
they had the same chemical atmosphere. As a result of centrosymmetric configuration, the shielding
effect of protons H
a
was merely from one phenyl ring attached to the N atom of imidazole. In contrast,
, displayed a
those relevant resonance peaks of protons in syn-tbu-PyDPI, marked as H and H
c
b

Molecules 2019, 24, 2293
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relatively high-field chemical shift of 0.84 ppm and relatively low-field chemical shift of 1.69 ppm,
respectively. This difference regarding the chemical shift of protons on tertiary butyl could be derived
from the fact that the ring-current effect [36], in which two phenyl rings connecting to the N atom of
imidazole resulted in a relatively strong shielding effect toward protons H , gaving rise to a concomitant
b
upfield chemical shift (0.84 ppm). Meanwhile, there is the weakest shielding effect of H
concomitant downfield chemical shift (1.69 ppm). Consequently, the chemical shift of H
at the middle (1.31 ppm) between that of H (0.84 ppm) and H
c
leading to a
a
was located
1
b
c
(1.69 ppm). The characteristic H NMR
resonance of protons for these two isomers remained unchanged after ultraviolet irradiation or heating
◦
to 120 C. This suggests that photochemical or thermocatalytic isomerization could not appear in
syn/anti-tbu-PyDPIs indicating the excellent stability of these structural isomers.
1
Figure 1. H NMR spectra of anti-tbu-PyDPI (a) and syn-tbu-PyDPI (b) in C D O (500 M Hz, 298 K).
4
8
2
.2. Crystal Structure
Single crystals of two isomers were grown by sublimation and the single-crystal measurement
further confirmed the configuration of syn/anti-tbu-PyDPI precisely. Their crystal structure with atomic
numbering is given in Figure 2. The numbering guide indicates a configuration of centrosymmetry for
anti-tbu-PyDPI where the phenyl planes (C(1)–C(2)–C(3) and C(1A)–C(2A)–C(3A)) make the same angle
◦
of 34 with the imidazole plane and the other phenyl planes (C(8)–C(9)–C(10) and C(8A)–C(9A)–C(10A))
◦
also make the same angle of 80 with the imidazole plane (Figures 2 and 3a). In contrast, all atomic
numbering varied for syn-tbu-PyDPI reflecting its axisymmetry with a slightly different torsion angle
between the phenyl plane and imidazole plane (Figure 3b).
(b)
(a)
Figure 2. Molecular Structure of anti-tbu-PyDPI (a) and syn-tbu-PyDPI (b), showing 30% probability of
thermal ellipsoids.

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Figure 3.
(a,b) Molecular structure top views of anti- and syn-tbu-PyDPI crystals; (c,d) Unit cell structure
side views of crystalline anti- and syn-tbu-PyDPI.
The derived crystal structures are shown in Figure 3 with selected molecular parameters provided
in Table S1. As depicted in Figure 3, both crystals crystallized in a monoclinic space group P 2 /c.
1
The anti/syn-tbu-PyDPI crystals had an essentially planar core and pyrene–imidazole ring, while
their formed molecular columns packed in a herringbone fashion for both of them. The anti-crystal
contained only two molecules in the unit cell while there are four molecules in the syn-crystal which
exhibited a more ordered arrangement of the anti-part. Due to the axisymmetric configuration of
syn-tbu-PyDPI which can create an induced dipole along the short axis direction (Figure 4), it is
proposed that formation of alternating the antiparallel arrangement in a flat dimer of one unit cell was
driven by the dipole–dipole interactions [37], referring to the pyrene–imidazole unit with an interfacial
distance of ca. 4.89 Å. Because of the steric hindrance effect of tert-butyl, the adjacent molecules adopt
a slip-stacked stacking mode along the short molecular axis and the long molecular axis synchronously
to some extent (Figure 4).
Figure 4. Molecular packing of syn-tbu-PyDPI formed by intermolecular dipole-dipole interaction.
We further analyzed the intermolecular interactions for anti/syn-crystal in unit cell. There
exist many various kinds of C-H•••π interactions between two adjacent molecules in one unit cell
3
2
(
Figure S2). These intermolecular CH(sp /sp )•••π interactions are the key forces of the stacking mode.
The CH•••π hydrogen bond in organic crystal is one of the most important weak intermolecular

Molecules 2019, 24, 2293
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forces, significant in controlling molecular configurations and playing a vital role of various natures in
chemistry [38]. In spite of the stabilization coming from a single intermolecular CH•••π interaction
being weak, the multicomponents of intermolecular CH•••π interactions can be of great importance.
As shown in Figure S3, in anti-isomer, it is C7···C13 (–x, –y, –z) of 3.44 Å (C7···H13(–x, –y, –z) of 2.63 Å),
while in syn-isomer, it is C20···C42 (1–x, –y, 1–z) of 3.65 Å (C20···H42(1–x, –y, 1–z) of 2.73 Å). Apparently,
the molecule stacking of alternating the antiparallel alignment of the pyrene–imidazole unit in the
syn-crystal is attributed to the van der Waals force derived from a weak intermolecular dipole (Figure 4).
However, no intermolecular π–π interaction upon face-to-face between pyrene units is perceived for
these structural isomers. Besides, the type and number of CH•••π interaction may influence the
photophysical properties of materials, especially for organic molecules containing a π-system [39].
2
.3. Optical Properties
The normalized UV-vis absorption spectra and photoluminescence (PL) spectra of the isomers
−5
in dilute THF with sample concentrations of 10 M are shown in Figure 5. They manifested similar
absorption and PL spectra due to their corresponding molecular organization. The absorption spectra
of the two molecules displayed complex absorption profiles dominated by a series of bands resulting
from the multiple localized
moiety [25 28 29]. The molar extinction coefficient of the peak at 304 nm for anti-tbu-PyDPI and the
peak at 314 nm for syn-tbu-PyDPI is 8.2
large for a * transition character. Moreover, the main absorption peak of syn-tbu-PyDPI (314 nm) is
π–π* transitions which originate from phenyl and the pyrene–imidazole
,
,
4
−1
−1
4
−1 −1
×
10 M cm and 6.3
×
10 M cm respectively, which is
π–π
slightly red-shifted (10 nm) compared with that of anti-tbu-PyDPI (304 nm) (Figure 5) which may be
attributed to the differentia in molecular configuration and symmetry. There is no absorption at the
low energy region demonstrating that no intramolecular charge transfer exist which further confirms
their symmetric molecular configurations. The PL spectrum of anti-tbu-PyDPI in dilute THF shows
three distinctive bands located at 392, 414, and 438 nm. The emission spectrum of syn-tbu-PyDPI
shows the same shape with a slight redshift of approximately 2 nm whose bands are located at 394, 416,
and 440 nm. Their PL spectra indicated the conformation of fluorophore of isomers from the ground
to the first excited singlet states in solutions were nearly the same which could be attributed to the
pyrene–imidazole group. The deep-blue emission with obvious vibronic structure features illustrates
the blue-fluorescence property of pyrene–imidazole based derivatives [26–28].
Figure 5. Normalized UV-vis absorption and emission spectra of anti-tbu-PyDPI and syn-tbu-PyDPI in
−5
diluted tetrahydrofuran solutions (10 M). λex = 360 nm.

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2
.4. Density Functional Theory Calculation
Density functional theory (DFT) calculations with a B3LYP/6-31G(d,p) basis set using the Gaussian
3W program were performed to further address their differentia in symmetry. The optimized
0
molecular configuration is shown in Figure 6. The pyrene–imidazole segment presented nearly
coplanar ground state geometries. The dihedral angles between the phenyl ring attached to the N atom
◦
of imidazole and imidazole ring of anti-isomer and syn-isomer are close to 80 . The twisty molecular
structure may impede the occurrence of intermolecular aggregation to some extent. The dihedral
angles between the phenyl ring attached to the C atom of imidazole and imidazole ring of anti-isomer
◦
◦
and syn-isomer are 30 and 31 , respectively. These calculations are basically consistent with the results
of monocrystalline structures mentioned above. In addition, the distributions of the front molecular
orbitals are shown in Figure 7. The highest occupied molecular orbitals (HOMOs) of anti-tbu-PyDPI
and syn-tbu-PyDPI were both delocalized over the molecule along the long molecular axis. Their
lowest unoccupied molecular orbitals (LUMOs) were delocalized over the whole molecule, while
there are more distributions on the bottom part of pyrene close to the two phenyl rings attached
to the N atom of imidazole for syn-tbu-PyDPI which probably resulted from the distinct dipole
orientation in syn-tbu-PyDPI (Figure 7). In general, the HOMO and LUMO mainly delocalized over the
pyrene–imidazole segment, indicating a typical pure π→π* transition for both of them, which can also
be confirmed from their PL spectra (Figure 5). Meanwhile, the distribution of LUMOs of syn-isomer
further prove its axisymmetric configuration whereby a certain intramolecular dipole can be formed in
the direction of molecule’s short axis [29].
Figure 6. Molecular optimized configurations of anti-tbu-PyDPI (a) and syn-tbu-PyDPI (b).
Figure 7. Highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals
(LUMOs) obtained at the B3LYP/6-31G level.
2
.5. Thermal Analysis: The DSC and TGA Graphs of Syn/Anti-tbu-PyDPI
Such a dual five-membered-ring skeleton demonstrated high thermal stability. From their
thermogravimetric analysis (TGA) graphs, anti-tbu-PyDPI and syn-tbu-PyDPI exhibited outstanding

Molecules 2019, 24, 2293
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◦
thermal stability with decomposition temperature (T ) (5% weight loss) as high as 520 and 500 C,
d
respectively (Figure 8). The single pyrene–imidazole unit already revealed high thermal stability [28,29],
and the centrosymmetric structure of anti-tbu-PyDPI further increased the thermal stability of the
◦
material. In differential scanning calorimetry (DSC) heating cycles up to 450 C, anti-tbu-PyDPI did
not show any thermal transition, which was due to its highly rigid structures and multi-intermolecular
◦
interactions (Figure S2). T
m
appeared at 420 C for syn-tbu-PyDPI, which reflects that an axisymmetric
structure shows better molecular flexibility than a centrosymmetric structure due to the comparatively
lower T of syn-tbu-PyDPI.
d
Figure 8. Differential scanning calorimetry (DSC) (
thermograms of anti-tbu-PyDPI and syn-tbu-PyDPI under nitrogen at a heating rate of 10 C min
a
) and thermogravimetric analysis (TGA) (
b
)
◦
−1
.
3
. Materials and Methods
3
.1. General
All of the solvents and reactants are commercially available and were used without purification.
1
The H NMR and spectra were recorded on Bruker AVANCZ 500 spectrometers (Bruker, Bremen,
Germany) at 298K by utilizing deuterated tetrahydrofuran (THF) as solvent and tetramethylsilane
(TMS) as the internal standard. The mass spectra were recorded on a Waters XevoTQ mass
spectrometer (Waters, VA, USA). The elemental analysis was performed on FLASH EA1112 elemental
analyzer. Absorption spectra were collected using a PERSEE UV-1900 ultraviolet spectrophotometer
(
Shimadzu, Kyoto, Japan). Fluorescence emission spectra were obtained on a Perkin Elmer LS55
fluorospectrophotometer (North Billerica, MA, USA). Diffraction data were collected on a Rigaku
RAXIS-PRID diffractometer using the -scan mode with graphite-monochromator Mo radiation.
ω
•
Kα
The structures were solved with direct methods using SHELXTL and refined with full-matrix
least-squares on F . In the case of syn-tbu-PyDPI, the tert-butyl group was found to be disordered on
three sites with an occupancy factor of 0.629/0.371 for C48/C48 , C49/C49 and C50/C50 . Thermal
gravimetric analysis (TGA) was measured on a Perkin-Elmer thermal analysis system from 50 C
to 800 C at a heating rate of 10 K min under nitrogen flow rate of 80 mL min . Differential
scanning calorimetry (DSC) was performed on a NETZSCH (DSC-204) unit from 50 C to 450 C at a
heating rate of 10 K min under a nitrogen atmosphere. The ground state geometries were optimized
at the B3LYP/6-31G(d,p) level, which is a common method to provide molecular geometries. The
HOMO/LUMO distributions are calculated on the basis of optimized ground-state.
2
0
0
0
◦
◦
−1
−1
◦
◦
−
1
3
.2. Synthesis of Isomers Anti-tbu-PyDPI and Syn-tbu-PyDPI
The starting material 2,7-di-tert-butylpyrene-4,5,9,10-tetraone was prepared according to the
literature procedures [40]. A mixture of aniline (4.6 mL, 50.0 mmol), 2,7-di-tert-butylpyrene-
,5,9,10-tetraone (1.87 g, 5.0 mmol), corresponding benzaldehyde (1.3 g, 12.0 mmol), ammonium acetate
3.1 g, 40.0 mmol), and acetic acid (20 mL) was refluxed under nitrogen in an oil bath. After 2 h, the
mixture was cooled and filtered. The solid product was washed with an acetic acid/water mixture (1:1,
4
(

Molecules 2019, 24, 2293
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1
50 mL). And then, the two isomers were separated by chromatography using CH Cl as eluent and
2 2
further purified by sublimation under vacuum.
2
,8-di-tert-butyl-4,5,10,11-tetraphenyl-4,10-dihydropyreno[4,5-d:9,10-d’]diimidazole
1
◦
(
anti-tbu-PyDPI): White powder (yield: 35.0%), H NMR (500 MHz, THF-d , 25 C,
δ): 9.00
8
(
d, J = 1.9 Hz, 2H), 7.78–7.67 (m, 14H), 7.57 (d, J = 1.9 Hz, 2H), 7.32–7.24 (m, 6H), 1.31 (s, 18H).
+
MALDI-TOF MS (mass m/z): calcd. for C H N , 698.34; found, 699.5 [M + H ]. Anal. Calcd. for
50
42
4
C H N : C. 85.93; H. 6.06; N. 8.02; Found: C, 85.74; H, 6.33; N, 7.98.
50
42
4
2
,8-di-tert-butyl-4,5,11,12-tetraphenyl-4,12-dihydropyreno[4,5-d:9,10-d’]diimidazole
1
◦
(
syn-tbu-PyDPI): White powder (yield: 32.5%), H NMR (500 MHz, THF-d , 25 C,
δ
): 8.96
8
(
s, 2H), 7.78 (dd, J = 6.5, 3.2 Hz, 4H), 7.76–7.71 (m, 6H), 7.69 (dd, J = 6.5, 3.2 Hz, 4H), 7.45–7.39 (m, 6H),
7
6
.35 (s, 2H), 1.69 (s, 9H), 0.84 (s, 9H). MALDI-TOF MS (mass m/z): calcd. for C H N , 698.34; found,
50 42 4
+
99.5 [M+H ]. Anal. Calcd. for C H N : C. 85.93; H. 6.06; N. 8.02; Found: C, 85.88; H, 6.25; N, 7.88.
50
42
4
4
. Conclusions
Two structural isomers containing pyrene–imidazole skeleton, anti-tbu-PyDPI and syn-tbu-PyDPI
with different molecular symmetries, were conveniently synthesized and successfully separated through
a one-pot reaction. The structural characteristics of anti/syn-tbu-PyDPI upon different symmetries were
1
elucidated unambiguously using H NMR spectroscopy and further confirmed from single-crystal X-ray
measurement. In addition, the similarities with differences of intermolecular interaction and packing
mode were accurately characterized by X-ray crystallography. Crystal packing in anti-configuration
with centrosymmetry strengthened intermolecular interactions displaying higher thermostability.
The preliminary fluorescence study shows that the two molecules were good candidates for blue light
emitting materials. This work provides an efficient synthesis method and experimental basis for the
construction of stable, novel, and advanced structural isomers based on pyrene–imidazole with very
convenient accessibility.
+
Supplementary Materials: The following are available online, Figure S1: Mass Spectrum (M + H ) of
anti-tbu-PyDPI (a) and syn-tbu-PyDPI (b), Figure S2: Packing form and the C-H···π intermolecular interactions
2
in crystal of anti/syn-tbu-PyDPI, Figure S3: Short CH(sp )···π interactions with phenyl groups at N atoms of
anti/syn-tbu-PyDPI, Table S1: Crystal data and structure refinements of isomers.
Author Contributions: Y.F. and Y.-L.L. developed the concept of the work. Y.-L.L. and L.Y. carried out the
synthetic work. Y.-L.L. and G.-Q.X. contributed to the single crystal culture and discussion. The computational
work was conducted by Y.-Q.G. and B.Q. The manuscript was written jointly by Y.F. and Y.-L.L.
Funding: This work was supported by the Natural Science Foundation of Heilongjiang Province (LH2019B002)
and the Postdoctoral Science Foundation of Heilongjiang Province (LBH-Z17014) and the CAS Key Laboratory of
Renewable Energy (No.Y907k71001).
Conflicts of Interest: The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds are not available from the authors.
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