The substituent effect on the excited state intramolecular proton transfer of 3-hydroxychromone

The excited state intramolecular proton transfer of four derivatives (FM, BFM, BFBC, CCM) of 3-hydroxychromone is investigated. The geometries of different substituents are optimized to study the substituent effects on proton transfer. The mechanism of hydrogen bond enhancement is qualitatively elucidated by comparing the infrared spectra, the reduced density gradient, and the frontier molecular orbitals. The calculated electronic spectra are consistent with the experimental results. To quantify the proton transfer, the potential energy curves (PECs) of the four derivatives in S-0 and S-1 states are scanned. It is concluded that the ability of proton transfer follows the order: FM > BFM > BFBC > CCM.