Structure-enabled long-lived charge separation in single crystals of an asymmetric donor–acceptor perylenediimide cyclophane

Abstract

We report the synthesis and characterization of a covalently linked asymmetric cyclophane comprising a 1,7-di(pyrrolidin-1′-yl)perylene-3,4,9,10-bis(dicarboximide) (pyrPDI) and 1,6,7,12-tetra(4′-t-butylphenoxy)perylene-3,4,9,10-bis(dicarboximide) (tpPDI), which absorbs light from 400–750 nm. Single crystals of pyrPDI-tpPDI were analyzed by using X-ray diffraction and transient absorption microscopy. The crystal structure contains several types of intermolecular donor–acceptor interactions (pyrPDI–pyrPDI, tpPDI–tpPDI, and pyrPDI-tpPDI) in addition to the covalently installed intramolecular interaction. Following photoexcitation of the pyrPDI-tpPDI single crystal, the transient absorption data show that charge separation occurs in τ = 21 ps, which is about nine times faster than in toluene solution, while charge recombination occurs in τ > 2 μs, which is more than 400 times longer than in solution. The faster charge separation in the single crystals results from the intermolecular donor–acceptor pyrPDI-tpPDI interactions, while the greatly enhanced charge-separated state lifetime is a consequence of charge transport through the intermolecular π-stacks. These results demonstrate the utility of pre-organizing donor–acceptor structural motifs to elicit specific crystal morphologies that can lead to enhanced photogenerated charge carrier lifetimes for solar energy conversion.