Theoretical Evaluation of the Faraday Effect in Organic Compounds

Using hybrid exchange correlation functional and a basis set including diffuse functions, the Verdet constants of mono-substituted benzenes and oligothiophenes have been evaluated at DFT level using the quadratic response formalism in order to assess the effects of substitution and of chain size on this magneto-optical property. The amplitudes of the Verdet constant are nicely ordered as a function of increasing donor/acceptor character, as estimated using the Hammett's σ parameters, and present substantial exaltation for strong donor groups like the dimethylamino moiety. When available, experimental data supports these conclusions. From calculations on increasingly large oligothiophenes, the Verdet constant appears to evolve almost linearly with the number of thiophene units. Basis set investigations have highlighted the key role of diffuse functions and in particular p and d functions on the C and S atoms.