Syntheses and Properties of Two-Dimensional Charged Nonlinear Optical Chromophores Incorporating Redox-Switchable cis-Tetraammineruthenium(II) Centers

Abstract

In this article, we describe a series of new complex salts in which electron-donating cis-{Ru^(II)(NH_3)_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 β have been determined by using hyper-Rayleigh scattering at 800 nm and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d → π^* metal-to-ligand charge-transfer bands. These experiments reveal that these dipolar pseudo-C_(2v) chromophores exhibit two substantial components of the β tensor, β_(zzz) and β_(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.

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