Organometallic complexes for nonlinear optics. Part 36. Quadratic and cubic optical nonlinearities of 4-fluorophenylethynyl- and 4-nitro-(E)-stilbenylethynylruthenium complexes

The complexes trans-[Ru(Ctriple bond; length of mdashC-4-C6H4F)X(dppe)2] [X = Cl (1), Ctriple bond; length of mdashCPh (2), Ctriple bond; length of mdashC-4-C6H4NO2 (3)], trans-[Ru{Ctriple bond; length of mdashC-4-C6H4-(E)-CHdouble bond; length as m-dashCH-4-C6H4NO2}X(dppe)2] [X = Ctriple bond; length of mdashCPh (4), Ctriple bond; length of mdashC-4-C6H4Ctriple bond; length of mdashCPh (5)], and [C6H3-1,3-{Ctriple bond; length of mdashC-trans-[RuCl(dppe)2]}2-5-(Ctriple bond; length of mdashC-4-C6H4F)] (6) have been synthesized and the identity of 1 confirmed by a single-crystal X-ray diffraction study. Cyclic voltammetry reveals a metal-centered oxidation, the potential of which is largely invariant on alkynyl ligand replacement across the series 1–5; the diruthenium complex 6 shows two oxidation processes, consistent with weakly interacting metal centers. Hyper-Rayleigh scattering (HRS) studies at 1064 nm using ns pulses suggest quadratic nonlinearities for 3–5 that are amongst the largest thus far for organometallic complexes, a trend maintained with the two-level-corrected data. HRS studies at 800 nm using fs pulses and amplitude modulation to remove multi-photon fluorescence contributions reveal significant fluorescence-free nonlinearities for 3–5; the frequency-independent nonlinearities calculated from the 800 nm results are suggestive of fluorescence contributions to the 1064 nm data. Z-scan studies at 820 nm reveal cubic nonlinearities that increase with the size of the π-system, although error margins are significant.