Organometallic complexes for nonlinear optics - Part 18. Molecular quadratic and cubic hyperpolarizabilities of aryldiazovinylidene complexes

The molecular quadratic and cubic optical nonlinearities of a series of ary ldiazovinylidene complexes [Ru(C=PhN=NAr)(PPh3)(2)(eta-C5H5)][X][Ar = Ph (1 ), C6H4OMe-n (n = 2 (2), 3 (3), 4 (4)), C6H4NO2-4 (5), 3,5-C6H3(NO2)(2) (6) ; X = BF4 (a), Cl (b), Pr (c), 1 (d), 4-MeC6H4SO3 (e), NO3 (f); not all com binations] have been assessed using hyper-Rayleigh scattering and Z-scan te chniques, respectively. The quadratic optical nonlinearities at 1064 nm are consistent with (i) introduction of polarizing substituents (NO2, OMe c.f. H); (ii) location of nitro substituent [the conjugated 4-NO2 c.f. the non- conjugated 3,5-(NO2)(2)]; (iii) dipolar composition (the strong donor-elect ron deficient bridge-strong acceptor composition of 5 and 6 c.f. the strong donor-electron deficient bridge-poor donor composition of 1-4); and (iv) i ntroduction of polyatomic anion (e, f c.f. a-d) all making significant cont ributions to the observed quadratic NLO responses. Absolute values for quad ratic nonlinearities are lower than those of related alkynyl complexes. Com plex 5d was assessed across three solvents, with the beta(HRS) data followi ng the trend acetone > dichloromethane > thf, in contrast to the trend in a bsorption maxima in these solvents. The cubic optical nonlinearities were m easured at 800 nm, real components of the nonlinearities are negative, and the imaginary components are significant, consistent with two-photon absorp tion contributing to the observed responses. The incorporation of nitro sub stituent in progressing from 1-4 to 5 results in a significant increase in both gamma(real) and \gamma\ (C) 2000 Published by Elsevier Science S.A. Al l rights reserved.