Long-Lived Singlet and Triplet Charge Separated States in Small Cyclophane-Bridged Triarylamine–Naphthalene Diimide Dyads

Abstract

Two different dyads containing a triarylamine (TAA) donor and a naphthalene-1,8:4,5-bis(dicarboximide) (NDI) acceptor bridged by either a [2.2]- or a [3.3]paracyclophane (CP) were synthesized. These dyads show a high population of long-lived charge separated (CS) singlet and triplet states. The lifetimes of these different spin states vary only by 1 order of magnitude. This unique situation is a consequence of both a large electronic coupling V and a large exchange coupling 2J. The population of the different CS spin states and therefore the charge recombination (CR) and intersystem crossing (ISC) kinetics were monitored by standard ns-transient absorption spectroscopy. Together with fs-transient absorption spectroscopy supported by electrochemistry, steady state fluorescence and steady state absorption spectroscopy a detailed model of the photoinduced processes was derived.