7-hydroxy-3-methyleneisoindolin-1-one as a new ESIPT-fluorescent probe to monitor aqueous environments

Abstract

A 7-hydroxy derivative of 3-methyleneisoindolin-1-one 1 was synthesized and its properties as a new fluorophore undergoing excited-state intramolecular proton transfer (ESIPT) were investigated. In alcohols and dimethylsulfoxide, 1 exhibited dual emission at ca. 380 and 525−540nm when excited at ca. 336nm, which agreed well with the density functional theory (DFT) and time-dependent (TD)-DFT-calculated emission predictions of 1 and its ESIPT tautomer. In aqueous solutions at near neutral pH, 1 exhibited a broad emission band at ca. 497nm, presumably caused by the overlap of emissions from 1 and the excited state phenolate species of 1. In binary mixtures of H2O and EtOH, the wavelength and intensity of fluorescence maxima were dependent on the dielectric constant of the solvent, suggesting that 1 could be applied as a fluorescent probe to monitor aqueous environments.