The Rapid Transport of Excitons in Organic Crystals Can Be Regulated by the Molecular Packing Form

Long-range exciton transport is crucial for optoelectronic devices based on organic semiconductors, but the method for increasing and regulating the exciton transport rate in organic semiconductors is still underexplored. Here we have achieved rapid-transporting excitons in organic crystals assembled of difluoroboron β-diketonate (BCZ) and found that the exciton transport rate of BCZ crystals can be regulated by the molecular packing form. Using transient absorption microscopy, we find that the BCZ-Y crystal in which BCZ molecules experience uniform head-to-tail antiparallel molecular packing has anisotropic long-range exciton transport. The exciton diffusion constants along the fast and slow axes are 2.0 and 0.9 cm 2 /s, respectively. By contrast, there is no obvious exciton transport in BCZ-R crystals, in which BCZ molecules form tightly stacked dimers. Theoretical calculations prove that energy transfer in BCZ-Y is much faster than that in BCZ-R because of the different molecular arrangements.