Executive Summary : | This research project aims to investigate the photochemical reaction pathways of dihydroxybenzenes, such as catechol, resorcinol, hydroquinones, and their derivatives, which act as primary light absorption chromophores in various biomolecules, including hormones, neurotransmitters, and natural sunscreens. The H-atom transfer reaction is considered the central chemical process for providing photo-protective properties of these pigments. Recent studies have shown that the bond dissociation reaction occurs in the ultrashort timescale, making catechol and related compounds the model systems for investigating the intrinsic photostability of these biological pigments. The project aims to investigate the light-driven reaction pathways of these aromatic systems in their small aggregated conditions. The H-bonded clusters of different dihydroxybenzenes will be prepared under an isolated and ultracold condition using the supersonic jet expansion method. The excited state O-H bond fission and other photofragmentation reactions will be probed using the resonant laser ionization mass spectrometric method, using the low-energy vibronic manifolds of the S1 state as the intermediate state. A home-built time-of-flight mass spectrometer will be used to identify fragment ions based on their mass to charge ratio. The effect of cluster size on ensuing photochemical reactions will be investigated by producing clusters with various size distributions through alteration of jet-expansion conditions. The modification of excited state reactions under micro-solvated conditions will be correlated to different electronic structure parameters, such as ionization energies and proton affinities of different neutral, anion, and radical species, and the role of vibronic excitation. The photo-induced H-atom detachment/transaction will be the central theme of the study. |