Hydrogen bond-induced planarity and ESPT Process: A theoretical insight into the sensing mechanism of a fluorescent probe for hypochlorous acid

Abstract

A time-dependent density functional theory is used to study photochemical properties and endogenous hypochlorous acid (HClO) recognition mechanism of a reported fluorescent probe (Chem. Sci. 2019, 10, 3715). Upon the addition of HClO, an intramolecular hydrogen bond in the oxidation product of the probe flattens the molecular geometry and leads to an excited-state proton transfer (ESPT) process, which increases the fluorescence wavelength. Frontier orbital analysis verifies that intramolecular charge transfer is the primary driving force for the ESPT process of the oxidation product. An excited-state potential energy scan further confirmed that ESPT is a spontaneous process without an energy barrier.