Electronic absorption spectra of closed and open-shell tetrathiafulvalenes: the first time-dependent density-functional study

The lowest energy transitions of tetrathiafulvalene (TTF) derivatives are calculated at different levels of theory. Whereas semiempirical (CNDO/S, ZINDO) and HF methods (CIS, TD-HF) give unrealistic excitation energies, time-dependent density-functional theory (TD-DFT) calculations provide a much improved description of the electronic absorption spectra of these compounds, including the unusual behavior of some TTF-containing nonlinear optical chromophores. Moreover, the study of radical cations of TTF derivatives allows the evaluation of the performance of TD-DFT methods on sulfur-containing open-shell species for the first time.