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

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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.