Photoinduced electron transfer in self-assembled dimers of 3-fold symmetric donor -: Acceptor molecules based on perylene-3,4:9,10-bis(dicarboximide)

The influence of pi-stacking on photoinduced electron transfer in a series of donor-acceptor molecules attached to a 3-fold symmetric scaffold was studied. The donor-acceptor unit is a DEA-PDI pair (DEA = N,N-diethylaniline; PDI = perylene-3,4:9,10-bis(dicarboximide)), in which the 4-position of DEA is covalently attached to the nitrogen atom of one imide of PDI. One, two, or three DEA-PDI units are attached to the para position of one of the phenyl groups of 1,3,5-triphenylbenzene, using the other PDI imide group to form mono-, his-, and tris(DEA-PDI). These molecules demonstrate an increasing tendency to self-assemble into pi-stacked dimers in solution in the order mono(DEA-PDI) much less than bis(DEA-PDI) < tris(DEA-PDI). Photoinduced electron transfer in both the monomers and self-assembled dimers was studied by femtosecond transient absorption spectroscopy. The charge separation (CS) and charge recombination time (CR) constants are found to be independent of pi-stacking aptitudes, while the transient spectral features differ significantly upon dimerization. The electronic interactions imposed by pi-stacking appear to change the energies of the ground, excited, and ionic states of DEA-PDI to a similar extent, which results in similar energies for CS and CR within the monomers and dimers.