We have measured the third-order susceptibilities chi ((3))(ijkl) of a few series of tetratiafulvalene derivatives using the degenerate four wave mixing method. From these measurements we have deduced the values of the second-order hyperpolarisabilities gamma and their corresponding molecular and electronic contributions. We compare the third-order optical properties of these new extended tetrathiafulvalene derivatives with the properties of other analogues of TTF. we have studied previously. All organic molecules studied in present work reveal large second-order non-linear optical hyperpolarisability.