Excited-State Dynamics of Diindenoperylene in Liquid Solution and in Solid Films

The excited-state dynamics of diindenoperylene (DIP) are investigated in dilute solution and in a solid film at room temperature using picosecond photoluminescence and femtosecond transient absorption measurements. In solution, DIP undergoes a rapid (0.89 ns) internal conversion back to its ground state, with no detectable formation of triplet or other long-lived states. In the solid state, multiple emissive species are formed. The time-resolved photoluminescence signal is dominated by an intrinsic exciton that decays on a time scale of 166 ps. Emission from lower energy excimer-like species then persists for >10 ns. Transient absorption experiments indicate that the majority of the excited-state population relaxes to the ground state on the 166 ps time scale, but a smaller fraction (<10%) survives in longer-lived trap or defect states. The rapid internal conversion leads to transient heating that results in a derivative line shape in the transient absorption signal at longer delays. DIP does not appear to support long-lived singlet exciton states or singlet fission. The implications of these results for the function of DIP in organic solar cells are discussed.