External Stimuli Responsive Bis(anthryl)borylaniline AIEgens for Viscosity and Temperature Sensing: The Game of Molecular Flexibility

Abstract External stimuli‐responsive luminogens have attracted a lot of attention in the recent years owing to their potential applications in various fields such as sensing, bio‐probes, and optical devices. In this work, the design and synthesis of a new class of external stimuli‐responsive anthracene based fluorescent bis‐(anthryl)boryl anilines 1 and 2 are disclosed. The electronic and optical properties of these compounds are fine‐tuned by varying the amine donor strength. Using steady‐state and time‐resolved photoluminescnece studies in both solution and condensed state together with computational studies (both ground and excited state), it is established that both 1 and 2 exhibit molecular motion dependent emission characteristics. Owing to their molecular conformational flexibility and inherent charge transfer characteristics, 1 and 2 show intriguing optical features such as aggregation induced emission enhancement, viscochromism, temperature sensing, and mechanoluminescence as compared to structurally rigid tris(9‐anthryl)boron without amine donor moieties. These unique properties of 1 and 2 are utilized for detecting local viscosity and temperature sensing over a wide range from 190–300 K. Compound 2 emits pure white light ((Commission internationale de l'éclairage) CIE 0.33, 0.33) at 250 K.