Types Of Electronic States Research Articles

PHOTOPROCESSES IN THE ORGANIC SOLID STATE*

Summary The various known photo‐relaxation phenomena in organic crystals are reviewed. The discussion is confined to molecular crystals, and aggregates of organic molecules, in which the low‐lying excited electronic states are either πpgr;*, nπ*, or electron‐transfer type. The pathways for excitation in isolated molecules with these types of electronic states are compared with the corresponding process in solids.Particular emphasis is placed on the possible roles of intersystem crossing, triplet‐triplet energy transfer and annihilation in solid state photochemistry. Free and localized excitons, energy migration between impurity traps, and some aspects of photoconduction in organic materials are discussed.