Received: 23 August 2020 Accepted: 16 October 2020
In the present work, the synthesis of the target products using sodium metasulfite (Na2S2O5) and p-toluenesulfonic acid (PTSA) separately as catalysts was studied. Herein, the liquid phase microwave method was chosen to synthesize triphenylamine substituted mono- and di-branched benzimidazole derivatives compared with the solid phase microwave method, and the reaction conditions were optimized using Na2S2O5 as a catalyst in N,N-dimethylformamide (DMF) solvent. A possible reaction mechanism is discussed. Ten new triphenylamine-benzimidazole derivatives were successfully synthesized. On this basis, PTSA using a catalyst was introduced into the reaction, the yields of the target products were evidently increased (the yield was enhanced 5‒22% using PTSA as a catalyst). It is found that PTSA only acted as a catalyst, while Na2S2O5 acted as both a catalyst and an oxidant, and PTSA could effectively catalyze the synthesis of benzimidazoles. Further, the luminescent properties of the synthesized compounds were comparatively studied after the structures of the synthesized compounds were confirmed. The results showed that the fluorescence quantum yield and the intensity of the synthesized compounds were enhanced with the increase in the number of substituted benzimidazole on triphenylamine, and the different substituents on 5-position of benzimidazole also have significant effect on the luminescent properties of the compound.