Organometallic Complexes for Nonlinear Optics. 43. Quadratic Optical Nonlinearities of Dipolar Alkynylruthenium Complexes with Phenyleneethynylene/Phenylenevinylene Bridges

The syntheses of trans-[Ru(4,4′-C≡CC6H4C≡CC6H4NO2)Cl(dppe)2] (19) and the systematically varied complexes trans-[Ru(4,4′,4′′-C≡CC6H4X2C6H4Y2C6H4NO2)Cl(L2)2] [L2 ) dppe, X2 ) C≡C, Y2 ) (E)-CH)CH (12), C≡C (18); L2 ) dppe, X2 ) (E)-CH)CH, Y2 ) C≡C (14), (E)-CH)CH (16); L2 ) dppm, X2 ) C≡C, Y2 ) (E)-CH)CH (13); L2 ) dppm, X2 ) (E)-CH)CH, Y2 ) C≡C (15), (E)-CH)CH (17)] are reported, the latter being donorbridge- acceptor complexes varying in bridge composition by replacement of yne with E-ene linkages, together with their cyclic voltammetric data, linear optical, and quadratic nonlinear optical response data. RuII/III oxidation potentials increase on replacing yne linkage by E-ene linkage at the phenylene adjacent to the metal center, and on replacing dppe by dppm co-ligands. The low-energy optical absorption maxima occur in the region 20400-23300 cm-1 and are metal-to-ligand charge-transfer (MLCT) in origin; these bands undergo a blue-shift upon π-bridge lengthening by addition of phenyleneethynylene units, and on replacing E-ene linkages by yne linkages. Time-dependent density functional theory calculations on model complexes have suggested assignments for the low-energy bands. The optical spectra of selected oxidized species contain low-energy ligand-to-metal charge transfer (LMCT) bands centered in the region 9760-11800 cm-1. Quadratic molecular nonlinearities from hyper-Rayleigh scattering (HRS) studies at 1064 nm reveal an increase in the two-level-corrected 0 value on π-bridge lengthening, a trend that is not seen with values because of the blue-shift in λmax for this structural modification. Replacing yne linkages by E-ene linkage at the phenylene adjacent to the metal center or dppm co-ligand by dppe results in an increase in and 0 values. In contrast, quadratic molecular nonlinearities by HRS at 1300 nm or electric field-induced secondharmonic generation (EFISH) studies at 1907 nm do not afford clear trends.