Electron-proton couplings in TCNQ compounds and dimensionality of triplet excitons in (ϕ3AsCH3)(TCNQ)2at room temperature

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Abstract
The geometrical coefficients that are involved in the nuclear relaxation time (T 1) of TCNQ salts are calculated. The model uses the spin-density distribution in TCNQ- which is obtained from MO calculations. The angular dependence of T 1 is computed and compared to experiment in the particular case of (ϕ 3AsCH3)(TCNQ)2. Although the theoretical values are rather strongly dependent on the model used for the spin-density distribution, the ratio of scalar coupling to dipolar coupling for the interaction of the electron spin with the TCNQ protons can be estimated to be 2·2–2·4. Measurements of the frequency dependence of T 1 in (ϕ 3AsCH3)(TCNQ)2 and its cation deuteriated homologue lead to an absolute determination of the excition motion spectral density. Evidence is given for low-dimensional behaviour.