Unprecedented Intramolecular Electron Transfer from Excited Perylenediimide Radical Anion

Radical anions in the excited states can be treated as stronger reductants than those in the ground states. In this study, the intramolecular electron transfer (ET) processes from the excited perylene-3,4,9,10-tetracarboxydiimide radical anion (PDI center dot-*) were examined for the first time by applying the femtosecond laser flash photolysis to the dyads of PDI and acceptors (PDI-A). Efficient intramolecular ET from PDI center dot-* was detected upon the excitation of PDI(center dot-)p-yromellitimide (PI) and PDI center dot- naphthalenediimide (NDI) because of the sufficient driving forces. In particular, unprecedented ET processes were confirmed in a PDI-PDI dimer. Excitation of PDI center dot--PDI gave the shortest PDI center dot-* lifetime due to the fastest intramolecular ET. Surprisingly, an intramolecular disproportionation reaction generating the dianion of PDI and neutral PDI was confirmed upon the excitation of PDI center dot--PDI center dot-. These processes successfully simulated the photocarrier (polaron and bipolaron) generations in PDI-based n-type semiconducting materials for various organic molecular devices. Comparing the NDI-A and PDI-A dyad systems, the significant difference found in the intramolecular ET rate constants can be explained by the energy required to form the reduced spacer and the distances between the electron donors and acceptors.