SINGLET FISSION IN ORGANIC CRYSTALS

Singlet fission attracts an extensive attention in recent years due to its potential to improve the efficiency of organic solar cells. Ultrafast time-resolved measurements provide a powerful tool for direct determination of singlet fission pathways and rates. In this chapter we present and discuss the experimental data on one- and two-photon, as well as consecutive two-quantum induced singlet fission in organic crystals rubrene and perylene. Temperature and excitation wavelength dependent rates of the singlet fission are discussed in terms of the activation energy. Ultrafast singlet fission was demonstrated to proceed directly from upper vibrational states of S1, from upper excited states SN, bypassing relaxed S1 state, as well as from two-photon excited states. 1