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

Abstract

The geometrical coefficients that are involved in the nuclear relaxation time (T1) of TCNQ salts are calculated. The model uses the spin-density distribution in TCNQ-which is obtained from MO calculations. The angular dependence of T1 is computed and compared to experiment in the particular case of ($3AsCH3)(TCNQ),. 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 711 in ($3AsCHa)(TCNQ)a and its cation deuteriated homologue lead to an absolute determination of the exciton motion spectral density. Evidence is given for low-dimensional behaviour.