Organometallic complexes for nonlinear optics.66. Synthesis and quadratic nonlinear optical studies of trans-[Ru{C=C{2,5-C4H2S-( E )-CH=CH}n-2,5-C4H2S(NO2 )}Cl(dppe)2](n1/40-2)

Abstract

Oligo(2,5-thienylenevinylene)s (OTVs) end-functionalized with a ligated ruthenium alkynyl unit as adonor and a nitro as acceptor, namelytrans-[Ru{C^C-2,5-C4H2S(NO2)}Cl(dppe)2](Ru1T),trans-[Ru{C^C-2,5-C4H2S-(E)-CH]CH-2,5-C4H2S(NO2)}Cl(dppe)2](Ru2T), andtrans-[Ru{C^C-2,5-C4H2S-(E)-CH]CH-2,5-C4H2S-(E)-CH]CH-2,5-C4H2S(NO2)}Cl(dppe)2](Ru3T), have been synthesized, their elec-trochemical properties have been assessed by cyclic voltammetry (CV), their linear optical and quadratic nonlinear optical (NLO) properties have been assayed by UVeviseNIR spectroscopy and hyper-Rayleighscattering studies at 1300 nm, respectively, and their linear optical properties in the formally RuIII state have been examined by UVeviseNIR spectroelectrochemistry. The data for Ru1T-Ru3Thave beencompared to those of the oligo(p-phenylenevinylene) (OPV) analoguestrans-[Ru(C^C-1,4-C6H4NO2)Cl(dppe)2](Ru1P),trans-[Ru{C^C-1,4-C6H4-(E)-CH]CH-1,4-C6H4NO2}Cl(dppe)2](Ru2P), andtrans-[Ru{C^C-1,4-C6H4-(E)-CH]CH-1,4-C6H4-(E)-CH]CH-1,4-C6H4NO2}Cl(dppe)2](Ru3P). The RuII/IIIoxidationpotentials decrease on proceeding fromRu1TtoRu3T, while the wavelength of the UVevislmaxbandincreases on proceeding fromRu1TtoRu2T, but thereafter decreases on further progression toRu3T, similar trends to those seen proceeding fromRu1PtoRu3P. The quadratic nonlinearityb1300 increases on OTV lengthening from Ru1TthroughRu2TtoRu3T; the data are significantly larger than those of the Ru1PeRu3Panalogues which peak atRu2P. The formally RuIIIcomplexes exhibit low-energy bands thatred-shift significantly on proceeding fromRu1TtoRu3T. 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 modelcomplexesRu1T′-Ru6T′are consistent with decreasing contributions of the electron donor (ligated Ru) and acceptor (NO2) groups to the HOMO and LUMO, respectively, up n-bridge lengthening.btotvalues increase on progression fromRu1T′toRu3T′, but thereafter further bridge lengthening affords little further increase in b-tot, consistent with a saturation in quadratic NLO response.