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

Abstract

The complexes trans-[Ru(C C-4-C 6H 4F)X(dppe) 2] [X = Cl ( 1), C CPh ( 2), C C-4-C 6H 4NO 2 ( 3)], trans-[Ru{C C-4-C 6H 4-( E)-CH CH-4-C 6H 4NO 2}X(dppe) 2] [X = C CPh ( 4), C C-4-C 6H 4C CPh ( 5)], and [C 6H 3-1,3-{C C- trans-[RuCl(dppe) 2]} 2-5-(C C-4-C 6H 4F)] ( 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.