Donor-acceptor substituted molecules, based on the two-dimensionally conjugated tetraethynylethene (TEE) framework, have been investigated for the first time for their first-order hyperpolarizabilities beta by electric-field-induced second-harmonic generation (EFISH), We measured high values of up to beta(EFISH) = (510 +/- 100) x 10(-40) m(4)/V at lambda = 1.907 mu m. We derived structure-property relationships by performing semiempirical calculations for all compounds. We show that such calculations give the correct trend in the hyperpolarizability beta, and more importantly, give information as to the tensorial structure of beta for molecules which are two-dimensionally donor-acceptor conjugated.