Efficient excited‐state intramolecular proton transfer in acridone derivatives—A case study of Paratrimerin C

Abstract

Paratrimerin C is a natural acridone antioxidant that is also potent as an anti‐UV agent. The photophysical process of Paratrimerin C, including the absorption and emission and the excited state intramolecular proton transfer (ESIPT) mechanism, is studied herein with time‐dependent density functional theory. The solvent effect on ESIPT is studied for polar (water) and non‐polar (benzene) solvents employing the Integral Equation Formalism Polarization Continuum Model and adding up to three explicit molecules of solvent. The normal and tautomer forms of the Paratrimerin C at the ground‐ and excited‐state structures are studied at the M06‐2X/6‐311++G(d,p) level of theory. The potential energy curves along the reaction coordinates indicate that the ESIPT is a barrier‐less reaction, and the variation of OdOa distance in the excited state shows significant molecular structure deformation along the proton transfer process following the normal‐to‐tautomerism pathway. The obtained results suggest using of acridone derivatives as efficient and tunable fluorescence molecules besides their biological activities.