Microwave-assisted synthesis and luminescent properties of triphenylamine substituted mono- and di- branched benzimidazo
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ORIGINAL PAPER
Microwave‑assisted synthesis and luminescent properties of triphenylamine substituted mono‑ and di‑ branched benzimidazole derivatives Jiaxu Fu1 · Liuqing Yan1 · Shuang Wang1 · Hongying Song1 · Qiang Gu1 · Yumin Zhang1 Received: 23 August 2020 / Accepted: 16 October 2020 © Institute of Chemistry, Slovak Academy of Sciences 2020
Abstract 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 N a2S2O5 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. Graphic Abstract
Keywords Triphenylamine-benzimidazole · Catalysis · Microwave chemistry · Reaction mechanisms · Luminescent property Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11696-020-01400-1) contains supplementary material, which is available to authorized users. Extended author information available on the last page of the article
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Introduction In recent years, benzimidazole derivatives as fluorescent organic small molecules have attracted intensive attention because of their value in technological applications referring to fluorescent probes for detecting metal ion (Saluja et al. 2012; Wang et al. 2013; Jayabharathi et al. 2012), pH probes (Sevinoç et al. 2014), electrochromic devices (Sydam et al. 2013), sensors (Wannalerse et al. 2008) and organic semiconductor materials (Lai et al. 2008) and so on. Compared with metal and inorganic compounds, organic compounds were easily modified with various functional structures. Organic fluorescent molecules such as benzimidazole derivatives are a group of heterocyclic organic compounds consist of benzene/imidazole ring structure. According to the comprehensive reports from Yamamoto et al. on n-type π-conjugated unit
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