Organometallic complexes for nonlinear optics. 66. Synthesis and quadratic nonlinear optical studies of trans-[Ru{C[tbnd]C{2,5-C4H2S-(E)-CH[dbnd]CH}n-2,5-C4H2S(NO2)}Cl(dppe)2] (n = 0–2)

Abstract

Oligo(2,5-thienylenevinylene)s (OTVs) end-functionalized with a ligated ruthenium alkynyl unit as a donor and a nitro as acceptor, namely trans-[Ru{CC-2,5-C4H2S(NO2)}Cl(dppe)2] (Ru1T), trans-[Ru{CC-2,5-C4H2S-(E)-CHCH-2,5-C4H2S(NO2)}Cl(dppe)2] (Ru2T), and trans-[Ru{CC-2,5-C4H2S-(E)-CHCH-2,5-C4H2S-(E)-CHCH-2,5-C4H2S(NO2)}Cl(dppe)2] (Ru3T), have been synthesized, their electrochemical properties have been assessed by cyclic voltammetry (CV), their linear optical and quadratic nonlinear optical (NLO) properties have been assayed by UV–vis–NIR spectroscopy and hyper-Rayleigh scattering studies at 1300 nm, respectively, and their linear optical properties in the formally RuIII state have been examined by UV–vis–NIR spectroelectrochemistry. The data for Ru1T-Ru3T have been compared to those of the oligo(p-phenylenevinylene) (OPV) analogues trans-[Ru(CC-1,4-C6H4NO2)Cl(dppe)2] (Ru1P), trans-[Ru{CC-1,4-C6H4-(E)-CHCH-1,4-C6H4NO2}Cl(dppe)2] (Ru2P), and trans-[Ru{CC-1,4-C6H4-(E)-CHCH-1,4-C6H4-(E)-CHCH-1,4-C6H4NO2}Cl(dppe)2] (Ru3P). The RuII/III oxidation potentials decrease on proceeding from Ru1T to Ru3T, while the wavelength of the UV–vis λmax band increases on proceeding from Ru1T to Ru2T, but thereafter decreases on further progression to Ru3T, similar trends to those seen proceeding from Ru1P to Ru3P. The quadratic nonlinearity β1300 increases on OTV lengthening from Ru1T through Ru2T to Ru3T; the data are significantly larger than those of the Ru1P–Ru3P analogues which peak at Ru2P. The formally RuIII complexes exhibit low-energy bands that red-shift significantly on proceeding from Ru1T to Ru3T. Computational studies employing time-dependent density functional theory were undertaken on model complexes to rationalize the optical observations and explore the impact of further OTV bridge lengthening. Computational studies on model complexes Ru1T′-Ru6T′ are consistent with decreasing contributions of the electron donor (ligated Ru) and acceptor (NO2) groups to the HOMO and LUMO, respectively, upon π-bridge lengthening. βtot values increase on progression from Ru1T′ to Ru3T′, but thereafter further bridge lengthening affords little further increase in βtot, consistent with a saturation in quadratic NLO response.