Solvates of a dianisyl-substituted donor–acceptor-type benzothiadiazole: mechanochromic, vapochromic, and acid-responsive multicolor luminescence

Abstract

Recently, great advances have been made in the mechanochromic luminescence (MCL) of organic crystals that can switch their emission colors upon exposure to mechanical stimuli. Although several polymorphic crystals and solvates have exhibited multicolor MCL properties, a further deep understanding of the relationship between crystal structures and stimuli-responsive properties is required for rationally generating multicolor-emissive polymorphic crystals and solvates from a single luminescent compound. Herein, multicolor luminescence switching has been achieved for solvates of a phenanthroimidazolylbenzothiadiazole derivative with dianisyl groups. Four types of solvates with different luminescence properties changed their emission colors upon amorphization induced by mechanical stimuli. The amorphous state was recrystallized into solvates when exposed to solvent vapors. Furthermore, the solvate containing pyridine molecules showed a bathochromic shift in emission wavelength upon exposure to acid vapor. Typical acid-responsive luminescence switching is characterized by the protonation of the basic moiety of luminescent molecules, whereas in this study, the change in luminescence color could be induced by protonating non-luminescent pyridine molecules in the solvate. The present study potentially provides useful insights for the development of smart luminescent sensors.