Theoretical Investigations of State Specific Hydrogen Atom Transfer in 8-Formyl-7-hydroxy-4-methylcoumarin

Abstract

Excited state intramolecular hydrogen transfer (ESIHT) reaction of 8-formyl-7-hydroxy-4-methyl coumarin (FC) in its pure and hydrated state FC-(H2O)4 (FCH) has been studied by implementing state specific time dependent density functional theory (SS-TDDFT) along with the effective fragment potential (EFP1) method for solvation with discrete water molecules. The intramolecular hydrogen bond formed between hydroxyl hydrogen (H18) and formyl oxygen (O15) and intermolecular hydrogen bonds formed due to microsolvation were explored. The studies of electrostatic potential, natural charge analysis, difference electron density map and UV-Vis spectra of both FC and FCH molecules establish the intramolecular charge transfer (ICT) states of the molecules. The vertical excitation from S0 to S1 state causes the transfer of hydroxyl hydrogen to formyl oxygen and from S1 to S3 causes the transfer of the hydrogen atom back to hydroxyl oxygen. Potential energy surface scans along intramolecular hydrogen bonding at the ground and excited states confirm the state specific ESIHT reaction in both FC and FCH molecules.