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Published March 17, 2010 | Supplemental Material
Journal Article Open

Combining Very Large Quadratic and Cubic Nonlinear Optical Responses in Extended, Tris-Chelate Metallochromophores with Six π-Conjugated Pyridinium Substituents

Abstract

We describe a series of nine new complex salts in which electron-rich Ru^(II) or Fe^(II) centers are connected via π-conjugated bridges to six electron-accepting N-methyl-/N-arylpyridinium groups. This work builds upon our previous preliminary studies (Coe, B. J. J. Am. Chem. Soc. 2005, 127, 13399-13410; J. Phys. Chem. A 2007, 111, 472-478), with the aims of achieving greatly enhanced NLO properties and also combining large quadratic and cubic effects in potentially redox-switchable molecules. Characterization has involved various techniques, including electronic absorption spectroscopy and cyclic voltammetry. The complexes display intense, visible d → π^* metal-to-ligand charge-transfer (MLCT) bands, and their π → π^* intraligand charge-transfer (ILCT) absorptions in the near-UV region show molar extinction coefficients as high as ca. 3.5 × 10^5 M^(-1) cm^(-1). Molecular quadratic nonlinear optical (NLO) responses β have been determined by using hyper-Rayleigh scattering at 800 and 1064 nm and also via Stark (electroabsorption) spectroscopic studies. The directly and indirectly derived β values are very large, with the Stark-based static first hyperpolarizabilities β_0 reaching as high as ca. 10^(-27) esu, and generally increase on extending the π-conjugation and enhancing the electron-accepting strength of the ligands. Cubic NLO properties have also been measured by using the Z-scan technique, revealing relatively high two-photon absorption cross sections of up to 2500 GM at 750 nm.

Additional Information

© 2010 American Chemical Society. Published In Issue March 17, 2010. Article ASAP February 18, 2010. Received: December 14, 2009. We thank the EPSRC for support (grants EP/D070732 and EP/E000738) and also the Fund for Scientific Research-Flanders (FWO-V, G.0312.08), the University of Leuven (GOA/2006/3), the NSF (grant CHE-0802907, 'Powering the Planet: an NSF Center for Chemical Innovation') and the Foundation for Polish Science. I.A. is a postdoctoral fellow of the FWO-V and M.S. is a Laureate of the FNP Welcome programme.

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