Quantum-chemical investigation of second-order nonlinear optical chromophores: Comparison of strong nitrile-based acceptor end groups and role of auxiliary donors and acceptors

We report a detailed quantum-chemical investigation of donor-acceptor substituted dipolar nonlinear optical chromophores incorporating the 4-(dimethylamino)phenyl donor end group and a variety of strong heterocyclic acceptor end groups, including tricyanofurans and tricyanopyrroles. In particular, we study the variation of the molecular second-order polarizability (Β) with the acceptor end group and when inserting auxiliary donors (thiophene) and acceptors (thiazole) into the π bridge. Both finite-field calculations (in the context of local contributions) and sum-over-states calculations were carried out in order to probe the relationship between Β and the chemical structure of the various chromophores. The trends obtained with these two methods are fully consistent. The large Β values (up to 700× 10-30 esu) as well as the observed tunability of the optical absorption maximum (λmax) make the chromophores investigated here interesting candidates for use in electro-optic applications at telecommunications wavelengths.