One- and two-dimensionally conjugated tetrathynylethenes: Structure versus second-order optical polarizabilities

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 β by electric-field-induced second-harmonic generation (EFISH). We measured high values of up to βEFISH = (510 ± 100) × 10-40 m4/V at λ =1.907 μm. We derived structure−property relationships by performing semiempirical calculations for all compounds. We show that such calculations give the correct trend in the hyperpolarizability β, and more importantly, give information as to the tensorial structure of β for molecules which are two-dimensionally donor−acceptor conjugated.