Electronically-tuned 2-(2′-Hydroxyphenyl)-4-pyrenylthiazole through Bond Energy Transfer Donor–Acceptor Couples: Sensing and Biological Applications

A novel pyrene-conjugated 2-(2′-hydroxyphenyl)thiazole probe (HPTP, 1) was prepared, and its photophysical and sensing properties were investigated and compared to those of four model compounds. HPTP effectively detects CN⁻ and glycerol in DMSO, with “turn off” at 425 nm and “turn on” at 495 nm. The sensing ability of 1 towards CN⁻ ions in DMSO, mediated by the hydrogen bonding-induced disaggregation of aggregates, resulted in the quenching of ESIPT emission at 425 nm. By contrast, in a DMSO–glycerol mixed medium, the aggregate size increased together with the increased degree of intermolecular π–π interactions between two pyrene units located on adjacent molecules, and resulted in partial inhibition of energy/charge transfer from the pyrene unit to the thiazole unit in the excited state. Excitation energy transfer with increased photostability of the ESIPT core was effectively demonstrated in Candida albicans cell lines.