Photoinduced Processes in Fluorene‐Bridged Rhenium–Phenothiazine Dyads – Comparison of Electron Transfer Across Fluorene, Phenylene, and Xylene Bridges

Abstract

AbstractThe photoinduced processes occurring after pulsed laser excitation of a series of donor–bridge–acceptor molecules comprising a phenothiazine electron donor, variable‐length fluorene bridges, and a rhenium(I) electron acceptor were investigated. A dyad with a single fluorene bridge unit exhibits electron transfer from phenothiazine to the rhenium(I) complex upon photoexcitation, whereas in dyads with fluorene oligomers bridge‐localized triplet excited states are formed rather than electron transfer products. In the monofluorene‐bridged system with a donor–acceptor distance of ca. 15 Å, electron transfer occurs with a time constant of 1.9 ns. The equidistant electron transfer between the same donor and acceptor is considerably slower across a biphenyl bridge (3.9 ns) or a bi‐p‐xylene spacer (20 ns). This finding is interpreted in terms of different tunneling barrier heights associated with the charge transfer across the three different types of molecular bridges.