Quadratic nonlinear optical properties of ruthenium (II)-bipyridine complexes in crystalline powders

Quadratic nonlinear optical properties for the crystalline powders of two types of ruthenium-bipyridine Ru(bipy)₃] complexes were investigated. The nonlinear optical processes markedly depended on the molecular structures of the ruthenium complexes. Second harmonic generation (SHG) and very weak two-photon emission were observed for the alkylated ruthenium-bipyridine compexes with two long alkyl chains attached via amide bonds (RuC_nB), whereas only two-photon emission was observed for Ru(bipy)₃. The existence of two amide bonds in one bipyridine ligand for RuC_nB complexes most probably enhanced the molecular hyperpolarizability as compared with Ru(bipy)₃. The SHG intensity from RuC_nB complexes increased in the order RuC₁₈B < RuC₁₂B < RuC₁₆B. The order of SHG intensity from RuC_nB was ascribed to the difference in size of each crystalline powder estimated by X-ray diffraction methods.