Coumarin-based photoacid as a dual-state probe for studying proton transfer dynamics from solute to solvents

Abstract

In present work, we have developed a coumarin based water-soluble photoacid (3-acetyl-7-hydroxy-2H-chromen-2-one: HyCAc) which acts as a dual-state probe for investigating proton transfer processes from solute to solvents at ground and excited state. Intermolecular hydrogen bonding interactions significantly enhance the proton transfer process. A solvent-dependent proton transfer is evident from the relative intensity of the ICT band in UV–Vis spectra at the ground state. Polar aprotic and protic and aprotic solvents participate in the proton transfer from solute to solvent through intermolecular hydrogen bonding interactions at ground state. Additionally, HyCAc exhibits solvent-specific dual fluorescence and photodissociation behavior in solution at excited states. Photodissociation of HyCAc is observed due to the proton transfer process from solute to solvents at excited state. To deepen the mechanistic understanding, we performed Natural Bond Orbital (NBO) analysis to explore intermolecular interactions through second-order perturbation energy calculations. Atoms in Molecules (AIM), Non-Covalent Interaction (NCI) analysis, Electron Localization Function (ELF), and Localized Orbital Locator (LOL) analyses to elucidate the nature of non-covalent interactions and are also carried out to explore solvent-dependent solute–solvent interactions. © 2024