Organic semiconductors: Effect of substituents and metal ions on electrical conductivity of Schiff bases

Abstract

The effect of substituents on the electrical conductivity of some crystalline anils of salicylaldehyde is reported. A correlation exists between specific conductivity (log K) and the Hammett substituent constant (σ) for both the meta and para series of substituents, and between the activation energy of conduction (Δє) and σ for the para series. In each case the relationship between conductivity and temperature can be described by the equation K = K₀exp(-Δє/2kT).    Certain current questions as to the validity of measurements ~f electrical resistivities of polycrystalline pellets and of the application of band theory considerations to organic crystals are discussed. The effect of chelating Schiff bases with divalent metal ions is to lower the conductivity considerably. Copper(II) chelates are less conductive than the corresponding nickel(II) chelates. The conductivity of the anils increases abruptly by several orders of magnitude at the melting point, and Δєc values appropriate to the super- cooled liquids are much lower than the solid state values.