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 aryldiazovinylidene complexes [Ru(C=CPhN=NAr)(PPh₃)₂(η-C₅H ₅)][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), Br (c), I (d), 4-MeC₆H₄SO₃ (e), NO₃ (f); not all combinations] have been assessed using hyper-Rayleigh scattering and Z-scan techniques, 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-electron 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) introduction of polyatomic anion (e, f c.f. a-d) all making significant contributions to the observed quadratic NLO responses. Absolute values for quadratic nonlinearities are lower than those of related alkynyl complexes. Complex 5d was assessed across three solvents, with the β_HRS data following the trend acetone > dichloromethane > thf, in contrast to the trend in absorption maxima in these solvents. The cubic optical nonlinearities were measured at 800 nm; real components of the nonlinearities are negative, and the imaginary components are significant, consistent with two-photon absorption contributing to the observed responses. The incorporation of nitro substituent in progressing from 1-4 to 5 results in a significant increase in both γ_real and |γ|.