A combination of IR spectroelectrochemistry and DFT calculations has been used to demonstrate that the vinyl ligands in the complexes [Ru(CHdCHC 6 H 4 Me-4)Cl(CO)-(PMe 3 ) 3 ] and [{RuCl(CO)(PMe 3 ) 3 } 2 (μ-CHdCHC 6 H 4 CHd CH)] are redox noninnocent, and one-electron oxidation results in radical cations that are best described in terms of metal-stabilized organic radicals.

The electronic structures of 1,3-{trans-Cl-(dppe) 2 RuCtC} 2 C 6 H 4 (3) and 1,3-{Cp*(dppe)RuCtC} 2-C 6 H 4 (4) in their available redox states have been investigated using a combination of UV-vis-near-IR and IR spectroscopy and computational methods. In contrast to the case for closely related iron compounds, for the ruthenium complexes 3 and 4 the bridging aryl moiety is heavily involved in the oxidation process, and consequently descriptions of the electronic structures and electronic transitions in terms of the language developed for mixed-valence systems with clearly identifiable metal oxidation states are not appropriate. Consequently, the unique low-energy (near-IR) absorption bands observed for the asymmetric cations [3] þ and [4] þ are better described as arising from charge transfer transitions from a metal acetylide donor to a metal phenylacetylide acceptor rather than in terms of IVCT transitions.

Dedicated to Professor Michael I. Bruce in the year of his retirement from the Angas Professorship of Chemistry at the University of AdelaideThird-and higher-order nonlinear optical (NLO) properties of organic chromophores have been of significant recent interest, [1,2] possible applications of two-and three-photon absorption, such as optical limiting, imaging and microscopy, and 3D data storage and microfabrication, commanding particular attention.[3] Spectral dependencies of two-photon absorption (2PA) cross-sections (related to the imaginary component of the third-order nonlinearity) have been examined to help in developing structureproperty relationships for this parameter, [4] but wavelength dependencies of nonlinear refraction (related to the real component of the nonlinearity, and of interest for optical computing applications) or higher-order absorption (three-photon absorption (3PA), a fifth-order NLO process of interest for the same reasons as 2PA, but with the added benefit that the higher-order intensity dependence provides tighter spatial control) are scarce. [5] The 2PA properties of triarylamine-containing compounds have attracted interest recently, in particular 4-phenyl-substituted derivatives of triphenylamine;[6] studies exploiting two-photon excited fluorescence (TPEF) with either nanosecond or femtosecond pulses [6,7] or employing single wavelength femtosecond open-aperture Z-scan [8] have highlighted the potential of N-cored compounds. Triarylamine-based dendrimers are a logical extension, [9] one reason being that the main group atom core may facilitate electronic interaction between the constituent dendrons, and thereby influence NLO behavior, but thus far the third-order nonlinearities of main group atom-cored dendrimers remain little explored.

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