Search

The cubic hyperpolarizabilities of 1,3,5-(trans-[RuCl(dppe) 2(C≡CC6H4-4-C≡C)])3C 6H3 (1), 1,3,5-(trans-[Ru(C≡CPh)(dppe) 2(C≡CC6H4-4-C≡C)])3C 6H3 (2), 1,3,5-(trans-[Ru(C≡CC6H 4-4-NO2)(dppe)2(C≡CC6H 4-4-C≡C)])3C6H3 (3), 1,3,5-{trans-[Ru(C≡C-3,5-(trans-[Ru(C≡CPh)(dppe)2(C≡CC 6H4-4-C≡C)])2C6H 3)(dppe)2(C≡CC6H4-4-C≡C)]} 3C6H3 (4), and 1,3,5-{trans-[Ru(C≡C-3,5- (trans-[Ru(C≡CC6H4-4-NO2)(dppe) 2(C≡CC6H4-4-C≡C)])2C 6H3)(dppe)2(C≡CC6H4-4- C≡C)]}3C6H3 (5) have been assessed over the spectral range 5201600nm using the Z-scan technique and ∼150 fs pulses. All complexes exhibit negative values of γreal (corresponding to self-defocusing behaviour) and significant positive values of imag (corresponding to two-photon absorption) at short wavelengths (up to 1000nm). The maximal values of γreal and γimag increase in magnitude on dendrimer generation increase (proceeding from 2 to 4 or 3 to 5). The open-aperture Z-scan results have been used to confirm and contrast the two-photon (2PA) and three-photon absorption (3PA) behaviour of 1-5, the data being consistent with the existence of 2PA at the short wavelength range, but with significant 3PA at longer wavelengths for 1-3 and 5, a record 3PA coefficient for an inorganic complex for 5 at 1180nm, and appreciable 3PA at the telecommunications wavelength of 1300nm. © 2011 CSIRO.

A combination of cyclic voltammetry (CV), UV-vis-NIR spectroscopy and spectroelectrochemistry, hyper-Rayleigh scattering (HRS) [including depolarization studies], Z-scan and degenerate four-wave mixing (DFWM) [including studies employing an optically transparent thin-layer electrochemical (OTTLE) cell to effect electrochemical switching of nonlinearity], pump-probe, and electroabsorption (EA) measurements have been used to comprehensively investigate the electronic, linear optical, and nonlinear optical (NLO) properties of nanoscopic π-delocalizable electron-rich alkynylruthenium dendrimers, their precursor dendrons, and their linear analogues. CV, UV-vis-NIR spectroscopy, and UV-vis-NIR spectroelectrochemistry reveal that the reversible metal-centered oxidation processes in these complexes are accompanied by strong linear optical changes, "switching on" low-energy absorption bands, the frequency of which is tunable by ligand replacement. HRS studies at 1064 nm employing nanosecond pulses reveal large nonlinearities for these formally octupolar dendrimers; depolarization measurements are consistent with lack of coplanarity upon π-framework extension through the metal. EA studies at 350-800 nm in a poly(methyl methacrylate) matrix are consistent with the important transitions having a charge-transfer exciton character that increases markedly on introduction of peripheral polarizing substituent. Time-resolved pump-probe studies employing 55 ps, 527 nm pulses reveal absorption saturation, the longest excited-state lifetime being observed for the dendrimer. Z-scan studies at 800 nm employing femtosecond pulses reveal strong two-photon absorption that increases significantly on progression from linear complex to zero- and then first-generation dendrimer with no loss of optical transparency. Both refractive and absorptive nonlinearity for selected alkynylruthenium dendrimers have been reversibly "switched" by employing the Z-scan technique at 800 and 1180 nm and 100-150 fs pulses, together with a specially modified OTTLE cell, complementary femtosecond time-resolved DFWM and transient absorption studies at 800 nm suggesting that the NLO effects originate in picosecond time scale processes. © 2006 American Chemical Society.

International audience

A series of new acetylide complexes of the type [Fe(eta(5)-C5H5)(Pboolean ANDP)(p-Cequivalent toCC(6)H(4)R)] (Pboolean ANDP = DPPE (=1,2-bis(diphenylphosphino)ethane), (R)-PROPHOS (=(R)-(+)-1,2-bis(diphenylphosphino)propane), R = NO2, C6H4NO2, (Z)-C(H) C(H)C6H4NO2, (E)-C(H)=C(H)C6H4NO2) have been synthesized by halide abstraction from the precursors [Fe(eta(5)-C5H5)(Pboolean ANDP)(1)] and fully characterized. Quadratic hyperpolarizabilities (beta) for the complexes have been determined by hyper-Rayleigh scattering at 1064 nm. The influence on the nonlinear response of acetylide chain length in proceeding from 4-nitrophenylethynyl to 4-nitrobiphenylethynyl and 4-nitro(E)-stibenylethynyl has been studied, revealing values of the first hyperpolarizabilities among the highest reported for organometallic molecular materials. Comparisons on the nonlinear efficiencies are drawn with the related well-known families of compounds [Ru(eta(5)-C5H5)(PR3)(2)(P-Cequivalent toC-(aryl)-NO2)] and [Fe(eta(5)-C6H5)(Pboolean ANDP)(P-Nequivalent toC-(aryl)-NO2)](+), Cubic hyperpolarizabilities (gamma) determined by Z-scan at 800 nm are consistent with an increase in) upon replacing Ru by the more easily oxidizable Fe and upon chain-lengthening the delocalizable pi-bridging unit (proceeding from 4-C6H4 to (E)-4,4'-C6H4CH=CHC6H4). X-ray C5H5)(DPPE)(P-Cequivalent toCC(6)H(4)NO(2))] and [Fe(eta(5)-crystallographic structures of complexes [Fe(eta(5)-C5H5)DPPE)((E)-p-Cequivalent toCC(6)H(4)C(H)=C(H)C6H4NO2)] were studied in order to investigate the existence of T-back-donation suggested by spectroscopic and electrochemical data. Crystal packing was analyzed with the aim of assessing the alignment of the molecules in the lattice and hence suggesting the magnitude of NLO properties at the macroscopic level.

A range of dipolar and quadrupolar gold and ruthenium acetylides have been prepared and their electrochemical (Ru complexes) and nonlinear optical properties assessed; electronic communication between the metal centers diminishes as the ?-delocalizable bridge is lengthened and quadratic NLO merit increases on replacing triarylphosphine by trialkylphosphine. One diruthenium example has the largest two-photon absorption cross-section/molecular weight value observed thus far for an organometallic complex.

A soluble, oxidatively and thermally very stable alkynylruthenium dendrimer 1,3,5-C6H3(4-C≡C-C6H 4C≡C-trans-[Ru(dppe)2]C≡C-3,5-C 6H3-{4-C≡CC6-H 4C≡C-trans-[Ru(C≡CPh)(dppe)2]} 2)3, containing a large two-dimensional π-delocalized system, has been prepared using an experimentally straightforward convergent synthetic approach. The first third-order nonlinear optical (NLO) measurements of an organometallic dendrimer have been obtained using the Z-scan technique at a wavelength of 800 nm. Progression from 1,3,5-C6H3-(4-C≡CC6H 4C≡C-trans-[Ru(dppe)2]C≡CPh)3 to the dendrimer results in (i) no loss of optical transparency, (ii) an increase in the second hyperpolarizability, γ, which is proportionately greater than either the increase in the number of phenylethynyl groups or the extinction coefficient for the important MLCT band, and (iii) a dramatic enhancement of two-photon absorption.