Theoretical study of static second-order nonlinear optical properties of push-pull heteroquinonoid dimers

The static first-hyperpolarizabilities (beta) of a number of donor-acceptor substituted heteroquinonoid dinners has been calculated analytically by using the time-dependent Hartree Fock (TDHF) method and split-valence basis sets. The evolution pattern of beta of mono-substituted quinoid rings has been found to mirror the pattern of variation of beta of the corresponding polyenes. The charge transfer (CT) characteristics of the chosen quinonoid chromophores have been studied in terms of effective CT parameters (eta(XR)(f)) which have been found to fairly correlate with the calculated beta of mono-substituted quinonoids. The relative trend in beta of quinonoid dinners has been rationalized on the basis of calculated hardness parameter eta and eta(f) (= eta(DRI)(f) + eta(AR2)(f)) which exhibit linear relationships with the ZINDO-S/CI calculated vertical transition energy corresponding to HOMO -> LUMO excitation. The analytically evaluated response property, beta correlates fairly with the corresponding two-state calculated beta(0) and relevant spectroscopic quantities. The general qualitative trend in beta obtained for 3-21G and 6-31G** basis sets has been found to be same. The aromatic factor does not play any significant role in the evolution of second-order NLO responses in heteroquinonoid compounds. (c) 2006 Elsevier B.V. All rights reserved.