Synthesis And Properties Of Multi-Phenyl Substituted Pyrido [1,2-a]Benzimidazole Derivatives

Pyrido [1,2-a]benzimidazole is a kind of important Small organic molecules in both medical field and luminescent material field. In recent decades, the reports on the synthesis of PBIs are uninterrupted. More and more methods that are higher yields and cheaper catalysts are found. However, the study on luminescent properties is really seldom. As it is a material which exhibit excellent fluorescence in both solid and liquid, the development is hesitant. Undeniably, it has important prospects in luminescent material field. We did not have achieved the tunable fluorescence emission wavelength which excellent fluorescent skeleton must be owned.Based on the above issue, we used previous work and summarized the structural features of organic molecular with solid and liquid fluorescence. And we used the disconnection approach to design a new method to synthetic PBIs in this paper. The main contents are shown as following:1. We regarded the synthesis of 1,3,4-triphenyl-prido[1,2-a]benzimidazole as the model reaction, and found the best reaction conditions. With the best reaction cinditiions in hand, we got many PBIs with different substituents. This indicates that the reaction is universal. Until now, we found a mild, higher yield method to synthetic PBIs.2. In order to achieve the tunable fluorescence, we designed three different types of molecules:the PBIs with electron-withdrawing substituents, the PBIs with conjugate plane and the PBIs with D-?-A structure. At last, we successfully achieved the fluorescence emission wavelength changes from blue to yellow. In addition, DFT is used to illustrate the result we got from the experiment.3. We analysis the halochromism of PBIs with unsubstituted, electron-donating substituents and electron-withdrawing substituents. The results are expressed as quenching and blue shift, blue shift, quenching respectively. And they are all reversible when added base. This indicates that PBIs is a kind of Halochromism materials. Among the three PBIs, the PBI with electron-withdrawing substituents is a kind of polarity sensor, because it exhibit very sensitive response when we changed the solvent polarity.