Intramolecular photoinduced proton transfer in 2-(2′-hydroxyphenyl)benzazole family: A TD-DFT quantum chemical study

•PBE1PBE/TD method was used to study the ESIPT process in the benzazole family.•Potential energy curves in ground and excited states were calculated.•Effect of substitution in benzazole ring on the ESIPT process was investigated.•In contrast to S0 state, keto form of the molecules can be formed at the S1 state.•The photophysical properties of the compounds were calculated.

In this work, intramolecular photoinduced proton transfer in 2-(2′-hydroxyphenyl)benzazole family (HBO, HBI and HBT) was investigated using TD-DFT calculations at PBE1PBE/6-311++G(2d,2p) level of theory. The potential energy surfaces were employed to explore the proton transfer reactions in both states. In contrast to the ground state, photoexcitation from S0 state to S1 one encourages the operation of the excited-state intramolecular proton transfer process. Structural parameters, H-bonding energy, absorption and emission bands, vertical excitation and emission energies, oscillator strength, fluorescence rate constant, dipole moment, atomic charges and electron density at critical points were calculated. Molecular orbital analysis shows that vertical S0 → S1 transition in the studied molecules corresponds essentially to the excitation from HOMO (π) to LUMO (π∗). Our calculated results are in good agreement with the experimental observations.

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