Two-dimensional, pyrazine-based nonlinear optical chromophores with ruthenium(ii) ammine electron donors

Six new nonlinear optical (NLO) chromophores with pyrazinyl-pyridinium electron acceptors have been synthesized by complexing a known pro-ligand with electron donating {RuII(NH3)5}2+or trans-{RuII(NH3)4(py)}2+(py = pyridine) centers. These cationic complexes have been characterized as their PF6-salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. The visible d → π* metal-to-ligand charge-transfer (MLCT) absorptions gain intensity on increasing the number of RuIIcenters from one to two, but remain at constant energy. One or two RuIII/IIredox processes are observed which are reversible, quasi-reversible, or irreversible, while all of the ligand-based reductions are irreversible. Molecular first hyperpolarizabilities β have been determined by using hyper-Rayleigh scattering (HRS) at 1064 nm, and depolarization studies show that the NLO responses of the symmetric species are strongly two-dimensional (2D) in character, with dominant "off-diagonal" βzyycomponents. Stark (electroabsorption) spectroscopic measurements on the MLCT bands also allow the indirect determination of estimated static first hyperpolarizabilities β0. Both the HRS and the Stark-derived β0values increase on moving from mono-to bimetallic complexes, and substantial enhancements in NLO response are achieved when compared with one-dimensional (1D) and 2D monometallic RuIIammine complexes reported previously. © 2010 American Chemical Society.