The syntheses of trans-[Ru{4,4'-C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(4)NO(2)}Cl(dppm)(2)] (19), trans-[Ru{4,4',4''-C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(4)NO(2)}Cl(dppm)(2)] (20), trans-[Ru{4,4',4'',4'''-C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(4)NO(2)}Cl(dppe)(2)] (21), trans-[Ru{4,4',4'',4'''-C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(4)NO(2)}Cl(dppm)(2)] (22), trans-[Ru{4,4',4'',4'''-C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(4)NO(2)}Cl(dppm)(2)] (23), and trans-[Ru{4,4',4'',4''',4''''-C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(2)[2,5-(OEt)(2)]C[triple bond]CC(6)H(4)NO(2)}Cl(dppm)(2)] (24) are reported, together with those of precursor alkynes, complexes with the donor-pi-bridge-acceptor formulation that affords efficient quadratic and cubic NLO compounds; the identity of 19 was confirmed by a structural study. The electrochemical properties of 19-24 and related complexes with shorter pi-bridge ligands were assessed by cyclic voltammetry, and the linear optical, quadratic nonlinear optical, and cubic nonlinear optical properties were assayed by UV-vis-NIR spectroscopy, hyper-Rayleigh scattering studies at 1064 and 1300 nm, and broad spectral range femtosecond Z-scan studies, respectively. The Ru(II/III) oxidation potentials and wavelengths of the optical absorption maxima decrease on pi-bridge lengthening, until the tri(phenyleneethynylene) complex is reached, further chain lengthening leaving these parameters invariant; theoretical studies employing time-dependent density functional theory have shed light on this behavior. The quadratic nonlinearity beta(1064) and two-photon absorption cross-section reach maximal values at this same pi-bridge length, a similar saturation behavior that may reflect a common importance of ruthenium-to-alkynyl ligand charge transfer in electronic and optical behavior in these molecules.

The two‐photon absorption cross‐sections of related organometallic and organic dendrimers have been compared using a basket of scaling factors, the results revealing that organometallics are highly competitive as possible nonlinear optical materials viewed from economic, size, and weight perspectives, as well as consideration of π‐electron contribution.

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.