Direct Observation of Ultrafast Excimer Formation in Covalent Perylenediimide Dimers Using Near-Infrared Transient Absorption Spectroscopy

Energy transfer in perylene-3,4:9,10-bis(dicarboximide) (PDI) aggregates is often limited by formation of a low-energy excimer state. Formation dynamics of excimer states are often characterized by line shape changes and peak shift dynamics in femtosecond visible transient absorption spectra. Femtosecond near-infrared transient absorption experiments reveal a unique low-energy transition that can be used to identify and characterize this state without overlapping excited singlet-state absorption. Three covalently bound PDI dimers with differing PDI-PDI distances were studied to probe the influence of interchromophore electronic coupling on the PDI excimer transient spectra and dynamics.