Proton- and metal cation-enhanced excited state intramolecular proton transfers of 2-(2-hydroxyfluorophenyl)benzoxazole having imidazole moiety

2-(2-Hydroxyfluorophenyl)benzoxazole having an imidazole moiety 1 was synthesized by the two step reactions starting from 2-(pentafluorophenyl)benzoxazole. Protonation at the 3-imidazole nitrogen atom of 1 enhances the green emission around 500 nm, where the positive character caused by the protonation is inductively communicated to the hydroxy group, to recover its intramolecular hydrogen bonding, leading to the ESIPT process. Addition of Al³⁺ or Zn²⁺ to 1 enhances both the green emission and the blue emission around 450 nm in chloroform-acetonitrile.