Effect of Hyperconjugation on Photovoltaic Performance in Pseduo-2D Perylene Diimide Derivatives

The pi-pi interaction is acknowledged as the predominant factor to determine the molecular packing in organic photovoltaic materials, while other non-covalent intermolecular interactions especially the sigma-pi hyperconjugation are often ignored. Herein, a perylene diimide (PDI) derivative named FIDT-PDI is designed and synthesized to shed light into the effect of hyperconjugation on the molecular packing and further the photovoltaic performance. Dynamic NMR and 2D NOE NMR demonstrate the formation of intermolecular sigma-pi hyperconjugation between the C-H bond of the PDI moiety in one molecule and the phenyl sidechain in another molecule of FIDT-PDI. Benefiting from the sigma-pi hyperconjugation, FIDT-PDI with twisted backbone reversely exhibits more ordered packing and stronger crystallinity compared with another PDI derivative FIDTT-PDI which has better planarity, consequently achieving superior PCE and higher carrier mobility. This contribution is the first paradigm to unravel the structure-property relationship between sigma-pi hyperconjugation of conjugated materials and corresponding photovoltaic performance.