Syntheses and Quadratic Optical Nonlinearities of Ruthenium(II) Complexes with Ethynyl-ConnectedN-Methylpyridinium Electron Acceptors

We have prepared a number of new dipolar complexes containing ethynyl or buta-1,3-diynyl units linking electron-rich {RuII(NH3)5}2+, trans-{RuII(NH3)4L}+ (L = pyridine or N-methylimidazole), or trans-{RuIICl(pdma)2}+ [pdma = 1,2-phenylenebis(dimethylarsine)] centers to pyridinium electron acceptors. In acetonitrile solutions at 295 K, the new complexes display unusual blue-shifting of their metal-to-ligand charge-transfer (MLCT) bands as the conjugation is extended, in a fashion similar to that of the corresponding ethenyl systems. Hyper-Rayleigh scattering (HRS) and Stark spectroscopic measurements provide direct and indirect estimates of static first hyperpolarizabilities β0, and both the linear and nonlinear optical (NLO) properties are temperature- and medium-dependent. Thus, at 77 K in butyronitrile glasses, the MLCT bands display more normal red shifts upon conjugation extension. While the Stark-derived β0 values generally increase as n (the number of ethynyl units) increases from 0 to 2, the HRS da...