Singlet Fission from Upper Excited Electronic States of Cofacial Perylene Dimer.

Singlet fission directly from the upper excited vibrational and electronic states of cofacial perylene dimers, bypassing the relaxed state S1, was detected within 50 fs. This process competes well with vibrational cooling in S1 (4.7-7.0 ps) and S2 → S1 internal conversion (380 fs). The singlet fission has the energy threshold E = 3.06 eV. Other competitive relaxation processes are excimer and dimer cation formation on an ultrafast time scale. Excitation to higher energy levels (4.96 eV) leads to a higher efficiency of singlet fission.