Electron Conduction in Charge-Transfer Molecular Crystals

Molecular crystals consisting of strong electron donors and strong electron acceptors in ordered array often possess electronic properties which are not found in other types of organic solids. Molecular orbital calculations have been carried out for the triethylammonium-(tetracyanoquino dimethane)2 crystal. The LCAO-MO method combined with a crystal-field splitting calculation resulted in a reasonably accurate value for the activation energy observed for electron conduction. On a basis of the results of this calculation, one would conclude that this type of organic solid should not be expected to exhibit the properties of conventional inorganic semiconductors. However, the results do provide a basis for some hypotheses concerning electron conduction processes and possible photoconduction mechanisms in these solids.