title: Combining very large quadratic and cubic nonlinear optical responses in extended, tris-chelate metallochromophores with six pi-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 pi-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 --> pi* metal-to-ligand charge-transfer (MLCT) bands, and their pi --> pi* intraligand charge-transfer (ILCT) absorptions in the near-UV region show molar extinction coefficients as high as ca. 3.5 x 10(5) M(-1) cm(-1). Molecular quadratic nonlinear optical (NLO) responses beta 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 beta values are very large, with the Stark-based static first hyperpolarizabilities beta(0) reaching as high as ca. 10(-27) esu, and generally increase on extending the pi-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.
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. b.coe@manchester.ac.uk
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Coe
authors.forename: John
authors.initials: J
authors.lastname: Fielden
authors.forename: Simon P
authors.initials: SP
authors.lastname: Foxon
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Brunschwig
authors.forename: Inge
authors.initials: I
authors.lastname: Asselberghs
authors.forename: Koen
authors.initials: K
authors.lastname: Clays
authors.forename: Anna
authors.initials: A
authors.lastname: Samoc
authors.forename: Marek
authors.initials: M
authors.lastname: Samoc
mesh_terms: D015082:2,2'-Dipyridyl / Q000031:analogs & derivatives* / Q000737:chemistry; D002614:Chelating Agents / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D005296:Ferrous Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D017711:Nonlinear Dynamics; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011726:Pyridinium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*; D012542:Scattering, Radiation; D013056:Spectrophotometry, Ultraviolet / Q000379:methods
chemical_list: D002614:Chelating Agents; D005296:Ferrous Compounds; D009942:Organometallic Compounds; D011726:Pyridinium Compounds; D015082:2,2'-Dipyridyl; D012428:Ruthenium