The Investigation of Excited-State Intramolecular Proton Transfer Mechanism of 2-Acetylindan-1, 3-Dion: The Solvation Effect

Density functional theory (DFT) and time-dependent DFT are employed to investigate the solvent dependent excited-state intramolecular proton transfer (ESIPT) mechanism of 2-acetylindan-1,3-dion (AID) in hexane and acetonitrile (ACN). The electronic spectra of AID in the polar ACN solvent observed in the experiment are reproduced well by our calculation, but the results in nonpolar hexane are different from the experimental values. Our theoretical investigation illustrates why the emission peak of Enol-A located at about 457 nm with a weak oscillator strengthen is absent from the latest experimental report (Verma et al. in J Struct Dyn 3:023606, 2016), as the fluorescence emission from the proton-transferred product of AID in the first excited state. Thus, the single fluorescence mechanism is well explained. Moreover, the potential energy curves along the O-3-H-5 bond for the ground state (S-0) and the first excited state (S-1) are constructed. In the S-1 state, the absence of the potential barrier of AID in ACN, compared with the result of hexane (0.57 kcal/mol), indicates that the ESIPT process of AID molecule is more likely to accomplish in the ACN, highlighting the solvation effect on ESIPT mechanism of AID chromophore. [GRAPHICS] .