ESIPT Fluorescent Chromism and Conformational Change of 3-(2-Benzothiazolyl)-4-hydroxy-benzenesulfonic acid by Amine Sorption

Sulfonic acid (-SO₃H)-substituted 2-(2′-hydroxyphenyl)benzothiazole (1) was designed as a new solid-state ESIPT (excited-state intramolecular proton transfer) fluorescent chromic molecule that responds to various types of organic bases and amines as a sensing device of biologically important molecules such as ammonia and histamine. Crystal 1 exhibited a reversible adsorption-desorption behavior with pyridine, aniline, thiazole, quinoline, ammonia, propylamine, octylamine, diethylamine, 1,4-diaminobutane, histamine, and other compounds. The sorption behavior of these compounds induced the fluorescent chromism of crystal 1 from non-ESIPT weak blue, to ESIPT strong green, and finally to non-ESIPT strong green emissions, which applied to the solid-state sensing devices for biologically important organic bases and amines.