Photoinduced Charge Separation and Recombination in Acridine−Triarylamine-Based\nRedox Cascades

Abstract

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