Electronic properties of aromatic hydrocarbons I. Electrical conductivity

Abstract

An account is given of an experimental stud y of the conductivity of pure aromatic hydro ¬ carbons, and of solid solutions in which one hydrocarbon is introduced into another as an impurity. A method is described for preparing evaporated films of solid solutions with a know n concentration of impurity. They are suitable for electrical or optical measurements. From the temperature-dependence of conductivity a characteristic activation energy can be derived for each pure com pound; this is equal to, or greater than , the trip let state energy of the free molecules. The conductivity of a solid solution is greater than that of the pure solvent, and has an activation energy which is characteristic of the solute only. The activation energies of impurities are approximately equal to the calculated trip let state energies of the free molecules, where such data exist. In the one case where comparison can be made with an experimental phosphorescence energy the agreement is excellent. A mechanism of conduction is proposed from a consideration of the electronic excited states of a hydro ¬ carbon crystal.