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

• We investigate the GSDPT and ESDPT of compound 1.
• The transition state for GSDPT and ESDPT of compound 1 has been located.
• GSDPT of compound 1 cannot occur due to the high energy barrier.
• ESDPT of compound 1 tends to take place stepwise.

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.

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