Donor-Linked Di(perylene bisimide)s: Arrays Exhibiting Fast Electron Transfer for Photosynthesis Mimics

The first example of donor-linked di(perylene bisimide)s is reported. UV-vis absorption spectra of these newly synthesized dyads showed intense absorption across the entire visible region, demonstrating their excellent light-harvesting activities. The severe fluorescence quenching event probed by steady-state fluorescence spectroscopy and the free-energy calculations suggested the possibility of electron transfer (ET) in these arrays upon photoexcitation. Further femtosecond transient absorption spectra clarified that the fluorescence quenching was due to fast intramolecular ET. The rate of the charge separation (CS) was found to be as high as 10(12) s(-1) in CH2Cl2. It was suggested that the large ET driving forces, strong donor-acceptor electronic coupling, and relatively small reorganization energy of diPBI accounted for the rapid ET process in a synergic manner. The fate of the generated radical ion pair depended on the solvent used Rapid charge recombination to ground state occurred for the dyads in polar CH2Cl2 and for diPBI-TPA in nonpolar toluene. However, sufficient (3)diPBI* population was attained via efficient spin-orbit coupled intersystem crossing from the charge separated state for diPBI-PdTPP in toluene. These photophysical properties are interpreted as the cooperation between thermodynamic feasibility and kinetic manipulation.