To provide an insight into the third-order nonlinear optical (NLO) behaviour of a series of tetrathiafulvalene (TTF)-based molecules, the third-order NLO properties and two-photon absorption characterizations have been theoretically investigated by means of the time-dependent Hartree-Fock method. According to ab-initio calculation results, the examined molecules exhibit second hyperpolarizabilities (γ) with non-zero values, implying microscopic third-order optical nonlinearity. Our computed results are also in good agreement with the previous experimental observations on the title compounds. © 2013 Springer Science+Business Media New York.