Regioisomeric BODIPY Benzodithiophene Dyads and Triads with Tunable Red Emission as Ratiometric Temperature and Viscosity Sensors†

Abstract

Regioisomeric acceptor‐donor (AD) molecular rotors (p‐AD, m‐AD and m‐ADA) were synthesized and characterized, wherein dyads p‐AD and m‐AD, and triad m‐ADA contained 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) and benzodithiophene (BDT) as electron‐acceptor and electron‐donor, respectively. In all the compounds, the donor and acceptor moieties are electronically decoupled by a phenyl spacer, either through a para coupling or through a meta coupling. The dyad counterparts p‐AD and m‐AD showed distinct photophysical characteristics in which dyad p‐AD showed TICT band at ca. 654 nm characterized by a Stokes shift of ca. 150 nm and prominent solvatochromism. However, meta regioisomeric triad m‐ADA showed well‐defined aggregation in solution. Notably, because of the temperature‐tunable and solvent‐viscosity‐dependent emission, efficient ratiometric temperature sensing with positive and negative temperature coefficients and viscosity sensing was observed for all compounds. Interestingly, the fluorescence of dyad m‐AD (in 10/90 v/v THF/water) revealed a near‐white light emission with CIE chromaticity coordinates (x, y) of (0.32, 0.29). Furthermore, the fluorescence emission of p‐AD in THF at 0 °C also showed a near‐white light emission with chromaticity coordinates (x, y) of (0.34, 0.27). Such multifunctional rotors with readily tunable emission in the red region and prominent temperature‐ and viscosity‐sensing abilities are promising for sensing and bioimaging applications.