Singlet fission

In the area of spectroscopy, singlet fission is a spin-allowed process whereby a singlet excited state converts to two triplet states. The phenomenon is observed in molecular crystals where the molecules are appropriately oriented such that one excited molecule can share energy with a neighboring ground state molecule. The process often occurs on a picosecond timescale. The overall process is related to intersystem crossing whereby, in a single molecule, an excited singlet state converts to a lower energy excited triplet.