Influence of ethynyl extension on the dual-state emission properties of pyridinium-substituted ESIPT fluorophores

We describe the synthesis and photophysical properties in both solution solid-state of dual-state emitters undergoing an Excited-State Intramolecular Proton Transfer (ESIPT) process. These fluorophores, built around 2-(2?-hydroxyphenyl)benzoxazole (HBO) scaffold incorporate a N-methylpyridinium unit, at 3 or 5 position phenol ring, prone to reduce vibrational relaxation excited-state thanks resonance effects consequently allowing increasing solution-state quantum yield (QY). In order further optimize their optical properties, additional ethynyl-extended triisopropylsilyl (TIPS) spacer was introduced with aim combine molecular rigidification ?-delocalization, as cooperative enhance emission (DSE) properties. Molecular engineering studies comparison unsubstituted compounds reveal significant impact ethynyl-TIPS moiety on especially fluorescence color. As several phenomena can compete ESIPT process, all dyes were modelled using ab initio calculations rationalize nature excited-states.