Syntheses and properties of two-dimensional charged nonlinear optical chromophores incorporating redox-switchable cis-tetraammineruthenium(II) centers

In this article, we describe a series of new complex salts in which electron-donating -cis{Ru-parallel to{NH3)(4)}(2+) centers are connected to two electron-accepting N-methyl/aryl-pyridinium groups. These V-shaped complexes contain either monodentate 4,4'-bipyridyl-derived ligands or related chelates based on 2,2':4,4":4',4"'-quaterpyridyl and have been characterized by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Molecular quadratic nonlinear optical (NLO) responses Pi have been determined by using hyper-Rayleigh scattering at 800 nm and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d -> pi* metal-to-ligand charge-transfer bands. These experiments reveal that these dipolar pseudo-C-2v chromophores exhibit two substantial components of the beta tensor; beta(zzz) and beta(zyy), with the difference between them being most marked for the nonchelated systems. Time-dependent density-functional theory and finite field calculations serve to further illuminate the electronic structures and associated linear and NLO properties of the new chromophoric salts.