Theoretically unveiling the effect of solvent polarities on ESDPT mechanisms and photophysical properties of hydroxyanthraquinones.

Abstract

In this work, we were devoted to explore the effect of solvent polarities on the excited-state intramolecular proton transfer (ESIPT) process of 1-acetamido-4-hydroxyanthraquinone (AcHAQ) in three different polarity solvents (acetonitrile, chloroform, and cyclohexane) based on the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, and thereby regulating the distribution ratio between the dual excited-state isomers (enol and keto). The calculated geometrical parameters and infrared (IR) vibrational spectra have confirmed the excited-state intramolecular hydrogen bond (IHB) strengthening mechanism. Natural bond orbital (NBO) population analysis indicates that the intramolecular charge transfer (ICT) around IHBs has enhanced IHB, thereby triggering the ESIPT reaction. In addition, results obtained from the scanned potential energy curve (PEC) manifest that ESIPT process prefers to occur along the O3-H2…O1 IHB and energy barriers corresponding to the proton transfer in ACN are the lowest among all the studied solvents.