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