Molecules 2019, 24, 2293
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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.