Abstract
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 = CC(6)H(4)X(2)C(6)H(4)y(2)C(6)H(4)NO(2))Cl(L-2)(2)] [L-2 = dppe, X-2 = C = C, Y-2 = (E)-CH=CH (12), C = C (18); L-2 = dppe, X-2 = (E)-CH=CH, Y-2 = C = C (14), (E)-CH=CH (16); L-2 = dppm, X-2 = C = C, Y-2 = (E)-CH=CH (13); L-2 = dppm, X-2 = (E)-CH=CH, Y-2 = C = C (15), (E)-CH=CH (17)] are reported, the latter being donor-bridge-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. Ru-II/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 pi-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 beta(0) value on pi-bridge lengthening, a trend that is not seen with beta values because of the blue-shift in lambda(max) 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 beta(0) values. In contrast, quadratic molecular nonlinearities by HRS at 1300 nm or electric field-induced second-harmonic generation (EFISH) studies at 1907 nm do not afford clear trends.