A TDDFT study of the excited-state intramolecular proton transfer of 1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole

The ground and excited state geometries, as well as the excitation and emission energies of 1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole (1), a derivative of 1,3-bis(2-pyridylimino)isoin-doline (BPI), are investigated in dichloromethane using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The theoretical results are in good agreement with the experimental data of the ground state geometries and the absorption and emission spectrum of BPI derivatives. Particularly, we investigate the ground and excited state double proton transfer (GSDPT and ESDPT) processes of compound 1 by using the relaxed potential energy surface scan and optimization of transition states. The theoretical energy profile indicates that the ESDPT of compound 1 is inclined to take place stepwise rather than concertedly.