Direct Observation of the Reduction of Aryl Halides by a Photoexcited Perylene Diimide Radical Anion

摘要

The ability of the doublet excited state of perylene diimide anion radical ~2(PDI~-˙)* to reduce aromatic electron acceptors was probed by picosecond time-resolved transient absorption (TA) spectroscopy. Excitation of PDI~-˙ produces visible TA due to ~2(PDI~-˙)* that decays with ι =τ 160 ps. Aromatic electron acceptors with varying reduction potential quench ~2(PDI~-˙)* and, in some cases, give a new visible region absorption that is attributed to the products of bimolecular photoinduced electron transfer, ~2(PDI~-˙)* + Ar-X → PDI + Ar-X~-˙. Stern-Volmer quenching of ~2(PD-˙)* accomplished with a series of acceptors provides bimolecular quenching rate constants as a function of acceptor reduction potential. Rehm—Weller analysis of the electron transfer quenching data affords the potential for the (*PDI~-˙/PDI) electrochemical half-reaction as —1.87 V vs SCE.