Electronic Properties of Phenazine

Abstract

MANY organic compounds such as naphthalene, anthracene, etc., have extremely small, but detectable, electrical conductivities, which increase exponentially with an increase in temperature according to the equation σ = σ₀ exp(−E/2kT), where σ is the specific resistivity, σ₀ is a constant, E is an activation energy generally referred to as the energy gap and T is the absolute temperature. Since it is generally held that the conductivity is electronic rather than ionic, these substances have been termed organic semiconductors¹. Lyons² has pointed out that a correlation exists between the magnitude of the energy gap and a number of molecular properties, such as the molecular ionization energy, the molecular electron affinity, and the excitation energy of the ground-triplet state transition. If it is assumed that the semiconductivity of organic compounds involves the formation of biradicals and hence participation of the triplet state in the conduction process, it becomes evident that the energy gap should be at least equal to the ground-triplet state excitation energy. Of particular interest is the fact that for a number of compounds the energy gap is roughly equal to (generally slightly larger than) the aforementioned excitation energy. Thus, the energy gaps³ for anthracene, naphthacene, chrysene, pyrene, and anthanthrene are, respectively, 1.95, 1.64, 2.04, 2.06, and 1.58 eV., which are in fair agreement with the ground-triplet excitation energies of 1.82⁴, 1.26⁵, 2.45⁴, 2.08³, and 1.32³ eV.