Steady-state and time-resolved studies on the formation of skatolyl radicals photosensitized by 2-benzoylthiophene

Abstract

Quenching of the excited triplet state of 2-benzoylthiophene (BT) by 3-methylindole (CH₃InH) leads to several neutral radicals resulting from formal hydrogen-atom abstraction. The transient absorption spectra of the BT ketyl radical (BTH) and the N-centered (CH₃In) radical are directly detected by laser flash photolysis. From the differences between the spectra in the presence and the absence of oxygen, the C-centered skatolyl radical (CH₂InH) is also observed. Accordingly, product studies demonstrate the formation of homodimers as well as cross-coupling products. They include BTH dimers (BTH–BTH, two stereoisomers), indolyl dimers (three different products) and products derived from reaction of skatolyl and BT ketyl radicals.