Semiconductivity of organic substances. Part 15.—Compounds related to stilbene

Abstract

Dark conductivity in diphenyl butadiene and four analogues of stilbene has been examined. The compounds were chosen to reveal the possible effects of a donor and an acceptor group attached to opposite ends of the same molecule. In fact, intramolecular shifts do not induce a large solid-state conductivity and in this respect differ from intermolecular charge transfers. For each compound a wide range of ΔE and log ₁₀σ₀ values were recorded and each compound had its compensation line, with its own “characteristic temperature”. This probably arise from the electrode injection process postulated earlier for insulating crystals involving molecular vacancies at the organic crystal surface. In support of this view, there appears to be a rough correlation over a total of 13 simpler molecular crystals, between characteristic temperature and melting point.