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.

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