title: Electron-rich iron/ruthenium arylalkynyl complexes for third-order nonlinear optics: redox-switching between three states.
abstract: The new [(η(2)-dppe)(η(5)-C(5)Me(5))Fe(C≡C-1,4-C(6)H(4)C≡C)Ru(η(2) -dppe)(2) C≡C(C(6)H(5))] complex (3-H) and its hexanuclear relative [{(η(2)-dppe)(η(5)-C(5) Me(5))Fe(C≡C-1,4-C(6)H(4)-C≡C)Ru(η(2)-dppe)(2)(C≡C-1,4-C(6)H(4)C≡C)(3)(1,3,5-C(6)H(3))] (4) have been synthesized and characterized. The linear and cubic nonlinear optical properties of these compounds in their various redox states have been studied along with those of the analogous complexes [(η(2)-dppe)(η(5)-C(5)Me(5))Fe(C≡C-1,4-C(6)H(4)C≡C)Ru(η(2)-dppe)(2)R][PF(6)](n) (n=0-2; R=Cl, 2-Cl; R=C≡C(4-C(6)H(4)NO(2)),3-NO(2)). We show that molecules exhibiting large third-order nonlinearities can be obtained by assembling such dinuclear Fe/Ru units around a central 1,3,5-substituted C(6)H(3) core. These data are discussed with a particular emphasis on the large changes in their nonlinear (third-order) optical properties brought about by oxidation. Experimental and computational (DFT) evidence for the electronic structures of these compounds in their various redox states is presented using 3-H(n+) as a prototypical model. Single crystals of this complex in its mono-oxidized state (3-H[PF(6)]) provide the first structural data for such carbon-rich Fe(III) /Ru(II) heteronuclear mixed-valent (MV) systems. Although experimental evidence for the structure of the dioxidized states was more difficult to obtain, the theoretical study reveals that 3-H(2+) can be considered to have a biradical structure with two independent spins. The low-lying absorptions that appear in the near-infrared (NIR) range for all these compounds following oxidation correspond to intervalence charge-transfer (IVCT) bands for the mono-oxidized states and to ligand-to-metal charge-transfer (LMCT) transitions for the dioxidized states. These play a crucial role in the strong optical modulation achieved. The possibility of accessing additional states with distinct linear or nonlinear optical properties is also briefly discussed.
authors.affiliation: Sciences Chimiques de Rennes, CNRS (UMR 6226), Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Gauthier
authors.forename: Gilles
authors.initials: G
authors.lastname: Argouarch
authors.forename: Frédéric
authors.initials: F
authors.lastname: Paul
authors.forename: Loic
authors.initials: L
authors.lastname: Toupet
authors.forename: Abdelkader
authors.initials: A
authors.lastname: Ladjarafi
authors.forename: Karine
authors.initials: K
authors.lastname: Costuas
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Halet
authors.forename: Marek
authors.initials: M
authors.lastname: Samoc
authors.forename: Marie P
authors.initials: MP
authors.lastname: Cifuentes
authors.forename: T Christopher
authors.initials: TC
authors.lastname: Corkery
authors.forename: Mark G
authors.initials: MG
authors.lastname: Humphrey