Reversible alteration of spectral properties for azulene decorated multiphenyl-ethylenes by simple acid-base and redox processes

Abstract

Azulene decorated multiphenyl-ethylene derivatives were designed and synthesized where they have diphenylethene, triphenylethene, and tetraphenylethene units at the different positions of azulene spacers. All compounds exhibit aggregation-induced emission activity. UV–Vis titration experiment shows that four well-defined isoabsorptive points indicate the presence of azulenium cations in equilibrium with neutral azulene counterparts. The absorption of their neutral states can be regenerated by neutralizing the acidic solution of compounds 1–5 with triethylamine, which has been attributed to the reversible reactions and the stable products. In addition, electrochemical results demonstrate that compound 5 possesses an excellent reversible redox response at the half-wave potential of 0.37 V, indicating the presence of the stable cationic radical species. The combination of azulene spacers and AIE chromophores enable the reversible responsiveness with redox and acid-base processes. This work provides new insight into the design of potential probes by simple synthesis to detect uniform weak acids and bases at a low cost with the naked eye.