Photoinduced charge separation and recombination in acridine-triarylamine-based redox cascades

In this contribution, we report on the synthesis and the photophysical characterization of redox cascades, consisting of an acridine acceptor and up to three triarylamine donor subunits. These chromophores were designed in order to study directed photoinduced electron transfer along a redox gradient which results in a long-lived charge separated state. The electronic coupling in between the redox subunits was tuned by sterical as well as electronic effects to investigate their influence on the kinetics of various deactivation pathways. Lifetime and population of intermediate charge transfer and charge separated states depend strongly on donor strength of corresponding redox centers as well as on solvent polarity. We identified a low lying localized excited triplet state as an energy trap for all deactivation mechanisms in all cascades. The rate for population and depopulation of the involved excited states were determined by stationary and time-resolved fluorescence and absorption spectroscopy, respectively.