Organometallic complexes for nonlinear optics. X. 1 Molecular quadratic and cubic hyperpolarizabilities of systematically varied (cyclopentadienyl) bis(phosphine) ruthenium σ-arylacetylides

Abstract

The complexes Ru(4,4′-C ≡ CC6H4C6H4NO2)(PPh3)2(η-C5H5) and Ru(4,4′-C ≡ CC6H4C ≡ CC6H4NO2)(PPh3)2(η-C5H5) have been prepared and the latter structurally characterized; they belong to a series of organometallic donor-bridge-acceptor compounds containing (cyclopentadienyl)bis(phosphine)ruthenium(II) centres as donors, conjugated arylacetylide bridges, and nitro acceptor groups. Electrochemical data for the series of complexes Ru(C ≡ CR)(PR′3)2(η-C5H5) (R=Ph, 4-C6H4NO2, R′=Ph, Me; R=4,4′-C6H4C6H4NO2, (E)-4,4′-C6H4CH=CHC6H4NO2, 4,4′-C6H4C ≡ CC6H4NO2, 4,4′-C6H4N=CHC6H4NO2, R′=Ph) are consistent with an RuII/III couple whose oxidation potentials vary strongly with chain-lengthening from one-ring to two-ring acetylide ligand, but show little variation with changes at the bridging unit of the two-ring acetylide ligand. The molecular quadratic and cubic optical nonlinearities of the series of complexes have been determined by hyper-Rayleigh scattering (HRS) and Z-scan techniques, respectively. Molecular first hyperpolarizabilities by HRS at 1064 nm are dispersively enhanced; experimental and two-level corrected data suggest an increase in nonlinearity on chain-lengthening of the bridge, in proceeding from C6H4 to C6H4C6H4 and then C6H4C ≡ CC6H4 and C6H4CH=CHC6H4, a general trend that is reproduced by semiempirical ZINDO computations. Cubic hyperpolarizabilities by Z-scan at 800 nm are negative for complexes with nitro acceptor groups, probably a result of two-photon dispersion, with absolute values (up to 850 × 10-36 esu) large for small organometallic complexes; as with quadratic nonlinearities, cubic nonlinearities increase substantially on bridge lengthening, with little variation on phosphine substitution. Show more