Engineering visible-to-ultraviolet emission switching of benzothiazole-based mechanoresponsive materials

Abstract

Introducing bulky substituents or twisted structures into luminescent molecules can effectively induce stimuli-responsive emission colour shifts. However, achieving stimuli responsiveness often requires large molecular frameworks to form many intermolecular interactions, which typically result in luminescence colour switching within the visible light region. This study used 2-(4-tert-butylphenylethynyl)benzothiazole (BPEB) to synthesise two polymorphs, BPEB-B and BPEB-N, which exhibit blue and ultraviolet emissions, respectively. Mechanical grinding of BPEB-B induced a visible-to-ultraviolet emission shift. These photophysical changes correlated with the molecular packing in the aggregated state. The visible emission of BPEB-B is attributed to dimer formation, whereas the ultraviolet emission of BPEB-N is due to staircase structures stabilised by C–H/π interactions. Analyses show that mechanical grinding disrupted the aggregates, thereby shifting the emission towards that of the monomer solutions. This result suggests that benzothiazole can serve as a versatile scaffold for visible-to-ultraviolet light-switching materials.