ConPET-Driven Aryl Halide Reduction with a Donor-Acceptor-Donor Anion Radical.

This study investigates the anion radical of a donor-acceptor-donor molecule, namely 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (TBT), as a photosensitizer for consecutive photoinduced electron transfer (conPET) reactions. Fluorescence lifetime decay and femtosecond transient absorption spectroscopy on TBT-• revealed a doublet excited state lifetime of 250 ± 6 ps. Cyclic voltammetry and excited state energy (E00) analysis determined the excited state potential, E(TBT/*TBT-•) = -2.80 V vs SCE. Rehm-Weller analysis of the excited state (*TBT-•) quenching kinetics also corroborated the estimated excited state potential. Model reactions with a series of aryl bromides monitored by 19F-NMR and HPLC confirmed that TBT-• can act as a strongly reducing photosensitizer for visible light-mediated aryl halide reduction via a conPET mechanism.