Optical properties of organic semiconductors

Abstract Organic semiconductors are often called excitonic materials since their optical properties derive from the photogeneration of excitons, that is, bound electron–hole pairs. Organic excitons are either Frenkel or charge-transfer-like with binding energies of 0.5–1.0 eV, making them stable at room temperature. This chapter describes the fundamental optical properties of organics, starting with those of individual molecules, and then building the solid from pairs of molecules (dimers) and oligomers. Theoretical approaches to describe optical properties start by introducing the Born–Oppenheimer approximation and the Franck–Condon principle. Calculational approaches to understanding optical characteristics based on the linear combination of atomic orbitals are described. Both theory and experimental observation of optical phenomena are discussed in detail. Also, electron spin, spin–orbit coupling, fluorescence, and phosphorescence are quantitatively described. Finally, long and short range energy transfer, exciton diffusion, and annihilation processes ae described.