Millisecond Lifetime Free Carriers from Symmetry-Breaking Charge Separation in Morphology-Engineered...

Photodriven symmetry-breaking charge separation (SB-CS) has been proposed as a method for producing free charge carriers in organic electronic materials because charge separation can occur with minimal photon energy loss. The challenge in achieving this goal lies in minimizing the rapid charge recombination of the initial charge transfer (CT) exciton to permit charge diffusion away from the site at which the CT exciton is created. Here, we leverage specific crystal packing motifs elicited by hydrogen-bonding core-twisted 1,6,7,12-tetrachloroperylenediimide derivatives substituted at their imide nitrogen atoms with 2-(2-hydroxyethoxy)ethyl or 5-hydroxypentyl chains. Femtosecond transient absorption microscopy reveals that photoexcitation of these derivatives in single crystals results in subpicosecond SB-CS. The initial CT exciton then separates to give mobile charge carriers that live for over 1 ms, as determined by time-resolved microwave conductivity. This investigation shows how controlling crystal morphology and environment can generate high-energy free charge carriers following SB-CS in solid-state organic materials.