Organic semiconductors. Part 18.—Electrical and magnetic properties of (NN′-dimethyl-4,4′-bipyridylium)2+(7,7,8,8-tetracyanoquinodimethane) 2–4

Abstract

Electrical conductivity, thermoelectric power and paramagnetic susceptibility from e.s.r. data of polycrystalline samples of NN′-dimethyl-4,4′-bipyridylium(TCNQ)₄ are reported. Departure from linearity of a log σ against 10³ K/T plot above 300 K is interpreted in terms of temperature dependences of T^–2 and T^–3.5 for the pre-exponential factor and mobility respectively, rather than the onset of a semiconductor to metal transition. This interpretation is supported by magnetic measurements which fit a singlet-triplet model. The singlet-triplet excitation energy is 0.048 eV and the delocalised triplet exciton bandwidth 0.03 eV.