Resonance-Enhanced Excited-State Intramolecular Proton Transfer Emission by Base-Mediated Formation of α-Cyano-γ-lactone

This letter describes the synthesis and structural, photophysical, and theoretical properties of novel fluorescent dyes derived from 2-(2'-hydroxyphenyl)benzoxazole, functionalized by tricyanofuran or α-cyano-γ-lactone groups, prone to undergo an excited-state intramolecular proton transfer (ESIPT) process. We serendipitously found that tricyanofuran can induce the formation of the corresponding lactone in basic media, leading to a highly fluorescent derivative, owing to the formation of a merocyanine in the excited state.