Thousand-Fold Enhancement of Charge-Separated State Lifetimes Caused by an Adamantane Bridge in Dimethylaniline–Anthracene and Dimethylaniline–Pyrene Dyads

A long-standing challenge in photoinduced electron transfer research is the design of compact donor–acceptor dyads that can generate long-lived charge-separated (CS) states for use as sensitizers in solar energy harvesting. Reports of dyads exhibiting CS state lifetimes in the microsecond time domain are very rare. Herein, we report two compact donor–bridge–acceptor dyads exhibiting lifetimes in the microsecond domain. We employed an adamantane moiety as a bridge, and the lifetimes obtained are nearly 1000-fold larger when compared to those of the same donor–acceptor dyads bridged through C3-alkyl chains. In addition to long-lived CS state decays, slow formation of acceptor triplets was also observed via nanosecond flash photolysis. The long lifetime of the CS state is attributed to the extremely small value of the electronic coupling matrix element for the charge recombination compared to charge separation.