UV-induced generation of free radicals in cryogenic matrices

This contribution will provide a selection of experimental and computational results, co-authored by the presenter, and dedicated to studies of photochemistry of aromatic and heteroaromatic molecules. Monomeric phenol, thiophenol, indole, benzoxazole, benzimidazole and several of their derivatives were isolated in cryogenic argon matrices and characterized by infrared spectroscopy. The samples were irradiated in situ, using either broadband or narrowband UV light. The structures of both the starting compounds and the photoproducts were identified by comparing their observed infrared spectra with vibrational spectra computed theoretically. A common feature of all the selected studies is generation and experimental identification of free radicals resulting from the cleavage of OH, NH, or SH bonds. Mechanistic analysis of the observed photochemistry will be presented. Further examples will be analyzed, where free radicals may be involved as intermediates and can explain the observed reactivity, not considered in mechanistic proposals until the date.