Syntheses and Optical Properties of Azo-Functionalized Ruthenium Alkynyl Complexes.

The syntheses of trans-[Ru(C≡C-1-C6 H4 -4-N=N-1-C6 H4 -4-C≡C-1-C6 H4 -4-NO2 )Cl(L2 )2 ] (L2 =dppm (Ru1), dppe) (Ru2)), trans-[Ru(C≡C-1-C6 H4 -4-N=N-1-C6 H4 -4-(E)-CH=CH-1-C6 H4 -4-NO2 )Cl(dppe)2 ] (Ru3), and trans-[Ru(C≡C-1-C6 H4 -4-(E)-CH=CH-1-C6 H2 -2,6-Et2 -4-N=N-1-C6 H4 -4-NO2 )Cl(dppe)2 ] (Ru4) are reported, together with those of precursor alkynes. Their electrochemical properties were assessed by cyclic voltammetry (CV), linear optical and quadratic nonlinear optical (NLO) properties assayed by UV/Vis-NIR spectroscopy and hyper-Rayleigh scattering studies at 1064 nm, respectively, and their linear optical properties in the formally RuIII state examined by UV/Vis-NIR spectroelectrochemistry. These data were compared to those of analogues with E-ene and yne linkages in place of the azo groups. Computational studies using time-dependent density functional theory were undertaken on model compounds (Ru2'-Ru4') to rationalize the optical behaviour of the experimental complexes.