Nonlinear Optical Properties Of Dicyanomethylene-Derived Heteroaromatic Dyes: Semiempirical Molecular Orbital Calculations And Experimental Investigations

The effect of conformation (E/Z isomerism), nature (donor/acceptor) of substituents, and endgroups (indandione, pyrazolone, pyrazoledione) on the molecular hyperpolarizability beta(vec) of dicyanomethylene (hetero)aromatic dyes is investigated by means of semiempirical (AM1, ZINDO) molecular orbital calculations. Unless Z isomers are stabilized by intramolecular hydrogen bonding, generally E conformers have larger beta(vec)'s. Replacement of one nitrile group of the dicyanomethylene moiety by p-aminoaryl rather than p-R-arylamino (R = NMe2, MeO, H, NO2) is found to be advantageous. Increasing the acceptor strength of 29 by successively replacing the carbonyl with dicyanovinyl groups leads to a maximum of beta(vec) for the derivative with one rather than two C(CN)(2) groups. With respect to end groups, the indandione moiety generally is the least active group. Solvent effects are treated within the framework of the self-consistent reaction field approximation. In most cases gas-phase tendencies are either parallel or even reinforced if solvent effects are taken into account. The calculated results are compared with electric field induced second harmonic generation (EFISH) measurements. (C) 2000 John Wiley & Sons, Inc. Int I Quantum Chem 79: 253-266, 2000.