Probing exciton localization/delocalization: Transient dc photoconductivity studies of excited states of symmetrical porphyrin monomers, oligomers, and supramolecular assemblies

Solution-phase transient de photoconductivity (TDCP) measurements are used to address the question of exciton localization/delocalization in strongly coupled oligomeric porphyrins and in well-defined, higherorder assemblies of oligomers (ladder and prism assemblies). The approach used is determination of the excited-state excess polarizability volume, Δα _v ^-a quantity known to report on exciton derealization. The measurements reveal for the oligomers that singlet excitons are substantially delocalized but that triplet excitons are much more localized. For each of the two higher-order assemblies, the measurements reveal that excitons are transiently confined to individual oligomeric subunits rather than being delocalized over the entire assembly.