Phototautomerization in 9-hydroxy-5H-indeno[1,2-b]pyridin-5-one a Quantum Chemical Approach

The organic dyes undergoing excited-state intramolecular proton transfer (ESIPT) have received considerable attention during the past several decades, due to its practical and potential applications in many fields [12]. In ESIPT systems, a proton (or hydrogen atom) transfer from one the hydrogen donor group (usually a phenolic OH group or amino-type) to the acceptor of the proton (usually a heterocyclic nitrogen atom or a carbonyl group) in the electronically excited state of a molecule, through the formation of a five-, six- or seven-membered ring with a strong intramolecular hydrogen bond (H-bond) between the proton donor and acceptor group 3,4. The purpose of the present work is to explore the phototautomerization in 9-hydroxy-5H-indeno[1,2-b]pyridin-5-one (HIPO) (Scheme 1) at PBE1PBE-D/6311++G(d,p) level of theory. The stationary points on the S0 and S1 potential energy surfaces of HIPO were optimized using DFT method PBE1PBE–D in conjunction with the 6-311++G (d,p) basis set. Vibrational frequency calculations were performed at the same level to obtain vibrational zero point and thermal energies and to validate the optimized structures as the energy-minima or transition states.