Photoconductivity of Naphthalene and Anthracene

Abstract

RECENT studies¹ of the mobility ('metallic' character) of the unsaturation electrons within molecules containing conjugated double-bond systems suggest that solid conjugated compounds should exhibit the phenomenon of photoconductivity, provided that the unsaturation electrons can acquire enough energy to penetrate the potential barriers between adjoining molecules in the crystal lattice. Photoconductivity has, in fact, been observed in proteins² and in certain dyes³. We have found that both naphthalene and anthracene, when melted and allowed to solidify between two platinum electrodes about 0·5 mm. apart, show weak photoconductivity when exposed in vacuo to the unfiltered radiation from a quartz mercury-vapour lamp. With applied voltages between 50 and 360, the photocurrents are detectable with a good galvanometer. They are of the order of magnitude of 10^-8 amp., and are superimposed on a rather variable dark current. As in the case of dyes³, the photocurrents are quenched if air is admitted to the system.