Electronic Absorption Spectra of Molecular Crystals

Electronic absorption spectra of aromatic molecular crystals are reviewed from theoretical and experimental points of view. A theory of molecular exciton proposed by Davydov is described with some particular examples. A theory of electron transfer in molecular crystal is discussed in connection with the mechanism of photoconduction, and other theories relevant to optical properties of insulating crystals are briefly surveyed. Experimental results on the electronic absorption spectra of molecular crystals are presented classifying the molecules into three classes; namely, benzene and its derivatives, catacondensed aromatic hydrocarbons, and other miscellaneous molecules. It is emphasized that the measurements of the spectra of molecular crystals give valuable information on the excited states of these molecules as well as on the behaviour of exciton in these crystals.