Transition metal complex/gold nanoparticle hybrid materials.

Gold nanoparticles (AuNPs) are of considerable interest for diverse applications in areas such as medicine, catalysis, and sensing. AuNPs are generally surface-stabilized by organic matrices and coatings, and while the resultant organic compound (OC)/AuNP hybrids have been explored extensively, they are not suitable for certain applications (e.g. those necessitating reversible redox behaviour and/or long excited-state lifetimes), and they often suffer from low photo- and/or thermal stability. Transition metal complex (TMC)/AuNP hybrids have recently come to the fore as they circumvent some of the aforementioned shortcomings with OC/AuNP hybrids. This review summarizes progress thus far in the nascent field of TMC/AuNP hybrids. The structure and composition of extant TMC/AuNP hybrids are briefly reviewed and the range of TMCs employed in the shell of the hybrids are summarized, the one-phase, two-phase, and post-nanoparticle-synthesis synthetic methods to TMC/AuNP hybrids are discussed and contrasted, highlighting the advantages of variants of the last-mentioned procedure, and the utility of the various characterization techniques is discussed, emphasizing the need to employ multiple techniques in concert. Applications of TMC/AuNP hybrids in luminescence, electrochemical, and electro-optical sensing are described and critiqued, and their uses and potential in imaging, photo-dynamic therapy, nonlinear optics, and catalysis are assessed.

Exceptional Two-Photon Absorption in Alkynylruthenium-Gold Nanoparticle Hybrids.

Ruthenium alkynyl "star" complexes with tri(2-thienyl)-, tris(1,2,3-triazolyl)-, or triphenyl-benzene cores stabilize gold nanoparticles (AuNPs). Cyclic voltammetry, transmission electron microscopy, molecular modeling, dynamic light scattering, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy studies are consistent with ca. 5 trithienyl- or triazolyl-benzene-cored star complexes decorating the exterior of each AuNP. The ca. 2.5 nm diameter (by transmission electron microscopy) trithienylbenzene-cored gold nanoparticle hybrids are significantly less absorbent than classical Brust nanoparticles stabilized by 1-dodecanethiol; with femtosecond pulsed radiation, they exhibit exceptionally strong saturable absorption and two-photon absorption across the visible range and into the near-infrared region (3 000 000 GM at 500 nm and 46 000 GM at 750 nm; 1 GM is equal to 10-50 cm4 s photon-1).

Quadratic and Cubic Optical Nonlinearities of Y-Shaped and Distorted-H-Shaped Arylalkynylruthenium Complexes.

Straightforward syntheses of bis[bis{1,2-bis(diphenylphosphino)ethane}ruthenium]-functionalized 1,3,5-triethynylbenzene-cored complexes via a methodology employing "steric control" permit facile formation of Y-shaped Sonogashira coupling products and distorted-H-shaped homo-coupled quadrupolar products. Cyclic voltammetric data from these products reveal two reversible metal alkynyl-localized oxidation processes for all complexes. The wavelengths of the linear optical absorption maxima are dominated by the nature of the peripheral alkynyl ligand rather than the substituent at the unique arm of the "Y" or at the quadrupolar complex "core". The quadratic optical nonlinearities of the Y-shaped complexes were assessed by the hyper-Rayleigh scattering technique at 800 nm and employing 100 fs light pulses; introduction of donor NEt2 and/or acceptor NO2 to the wedge periphery resulted in non-zero nonlinearities, with the largest ßHRS,800 values being observed for the complexes containing the 4-nitrophenylalkynyl ligands. Depolarization ratios are consistent with substantial off-diagonal first hyperpolarizability tensor components and 2D nonlinear character. Computational studies employing time-dependent density functional theory have been employed to assign the key low-energy transitions in the linear optical spectra and to compute the quadratic nonlinear optical tensorial components. Cubic optical nonlinearities of the quadrupolar complexes were assessed by the Z-scan technique over the range 500-1600 nm and employing 130 fs light pulses; two-photon absorption cross-sections for these distorted-H-shaped complexes are moderate to large in value (up to 5500 GM at 880 nm), while one example displays significant three-photon absorption (1300×10-80  cm6 s2 at 1200 nm).

Stellar Multi-Photon Absorption Materials: Beyond the Telecommunication Wavelength Band.

Very large molecular two- and three-photon absorption cross-sections are achieved by appending ligated bis(diphosphine)ruthenium units to oligo(p-phenyleneethynylene) (OPE)-based "stars" with arms up to 7 phenyleneethynylene (PE) units in length. Extremely large three- and four-photon absorption cross-sections, through the telecommunications wavelengths range and beyond, are obtained for these complexes upon optimizing OPE length and the ruthenium-coordinated peripheral ligand. Multi-photon absorption (MPA) cross-sections are optimized with stars possessing arms 2 PE units in length. Peripheral ligand variation modifies MPA merit and, in particular, 4-nitrophenylethynyl ligand incorporation enhances maximal MPA values and "switches on" four-photon absorption (4PA) in these low molecular-weight complexes. The 4-nitrophenylethynyl-ligated 2PE-armed star possesses a maximal four-photon absorption cross-section of 1.8×10-108  cm8 s3 at 1750 nm, and significant MPA activity extending beyond 2000 nm.

Dynamic Permutational Isomerism in a closo-Cluster.

Permutational isomers of trigonal bipyramidal [W2RhIr2(CO)9(η(5)-C5H5)2(η(5)-C5HMe4)] result from competitive capping of either a W2Ir or a WIr2 face of the tetrahedral cluster [W2Ir2(CO)10(η(5)-C5 H5)2] from its reaction with [Rh(CO)2(η(5)-C5HMe4)]. The permutational isomers slowly interconvert in solution by a cluster metal vertex exchange that is proposed to proceed by Rh-Ir and Rh-W bond cleavage and reformation, and via the intermediacy of an edge-bridged tetrahedral transition state. The permutational isomers display differing chemical and physical properties: replacement of CO by PPh3 occurs at one permutational isomer only, while the isomers display distinct optical power limiting behavior.

Blue-shifted emission and enhanced quantum efficiency viaπ-bridge elongation in carbazole-carborane dyads.

Carbazole-carborane linear dyads and di(carbazole)-carborane V-shaped dyads with phenyleneethynylene-based bridges have been synthesized. The V-shaped dyads display the expected red-shifts in the location of their UV-Vis absorption maxima on bridge-lengthening, but show unusual blue-shifts in charge-transfer (CT) emission on the same π-system lengthening. These blue-shifts can be attributed to the 2n + 3 electron count within the carborane cluster in the excited state. The linear dyads luminesce via a combination of local excited (LE) and CT emission, with a red-shift in LE emission and a blue-shift in CT emission accompanying π-bridge elongation. A quantum efficiency as high as 86% in the solution state is achieved from the hybrid LE/CT emission. Time-dependent density functional theory (TD-DFT) calculations at the excited state of these compounds have clarified the photoluminescence blue-shift and suggested a typical cluster C-C bond elongation in the V-shaped dyads. Calculations on the elongated linear dyads have suggested that the electron density is localized at the phenyleneethynylene-containing bridge.

Record Multiphoton Absorption Cross-Sections by Dendrimer Organometalation.

Large increases in molecular two-photon absorption, the onset of measurable molecular three-photon absorption, and record molecular four-photon absorption in organic π-delocalizable frameworks are achieved by incorporation of bis(diphosphine)ruthenium units with alkynyl linkages. The resultant ruthenium alkynyl-containing dendrimers exhibit strong multiphoton absorption activity through the biological and telecommunications windows in the near-infrared region. The ligated ruthenium units significantly enhance solubility and introduce fully reversible redox switchability to the optical properties. Increasing the ruthenium content leads to substantial increases in multiphoton absorption properties without any loss of optical transparency. This significant improvement in multiphoton absorption performance by incorporation of the organometallic units into the organic π-framework is maintained when the relevant parameters are scaled by molecular weights or number of delocalizable π-electrons. The four-photon absorption cross-section of the most metal-rich dendrimer is an order of magnitude greater than the previous record value.

Tetrazine chromophore-based metal-organic frameworks with unusual configurations: synthetic, structural, theoretical, fluorescent, and nonlinear optical studies.

Three unusual three-dimensional (3D) tetrazine chromophore-based metal-organic frameworks (MOFs) {(Et4 N)[WS4 Cu3 (CN)2 (4,4'-pytz)0.5 ]}n (1), {[MoS4 Cu4 (CN)2 (4,4'-pytz)2 ]⋅CH2 Cl2 }n (2), and {[WS4 Cu3 (4,4'-pytz)3 ]⋅[N(CN)2 ]}n (3; 4,4'-pytz=3,6-bis(4-pyridyl)tetrazine) have been synthesized and characterized by using FTIR and UV/Vis spectroscopy, elemental analysis, powder X-ray diffraction, gel permeation chromatography, steady-state fluorescence, and thermogravimetric analysis; their identities were confirmed by single-crystal X-ray diffraction studies. MOF 1 possesses the first five-connected M/S/Cu (M=Mo, W) framework with an unusual 3D (4(4) ⋅6(6) ) topology constructed from T-shaped [WS4 Cu3 ](+) clusters as nodes and single CN(-) /4,4'-pytz bridges as linkers. MOF 2 features a novel 3D MOF structure with (4(20) ⋅6(8) ) topology, in which the bridging 4,4'-pytz ligands exhibit unique distorted arch structures. MOF 3 displays the first 3D MOF structure based on flywheel-shaped [WS4 Cu3 ](+) clusters with a non-interpenetrating honeycomb-like framework and a heavily distorted "ACS" topology. Steady-state fluorescence studies of 1-3 reveal significant fluorescence emissions. The nonlinear optical (NLO) properties of 1-3 were investigated by using a Z-scan technique with 5 ns pulses at λ=532 nm. The Z-scan experimental results show that the π-delocalizable tetrazine-based 4,4'-pytz ligands contribute to the strong third-order NLO properties exhibited by 1-3. Time-dependent density functional theory studies afforded insight into the electronic transitions and spectral characterization of these functionalized NLO molecular materials.

Syntheses, Spectroscopic, Electrochemical, and Third-Order Nonlinear Optical Studies of a Hybrid Tris{ruthenium(alkynyl)/(2-phenylpyridine)}iridium Complex.

The synthesis of fac-[Ir{N,C1'-(2,2'-NC5H4C6H3-5'-C≡C-1-C6H2-3,5-Et2-4-C≡CC6H4-4-C≡CH)}3] (10), which bears pendant ethynyl groups, and its reaction with [RuCl(dppe)2]PF6 to afford the heterobimetallic complex fac-[Ir{N,C1'-(2,2'-NC5H4C6H3-5'-C≡C-1-C6H2-3,5-Et2-4-C≡CC6H4-4-C≡C-trans-[RuCl(dppe)2])}3] (11) is described. Complex 10 is available from the two-step formation of iodo-functionalized fac-tris[2-(4-iodophenyl)pyridine]iridium(III) (6), followed by ligand-centered palladium-catalyzed coupling and desilylation reactions. Structural studies of tetrakis[2-(4-iodophenyl)pyridine-N,C1'](µ-dichloro)diiridium 5, 6, fac-[Ir{N,C1'-(2,2'-NC5H4C6H3-5'-C≡C-1-C6H2-3,5-Et2-4-C≡CH)}3] (8), and 10 confirm ligand-centered derivatization of the tris(2-phenylpyridine)iridium unit. Electrochemical studies reveal two (5) or one (6­10) Ir-centered oxidations for which the potential is sensitive to functionalization at the phenylpyridine groups but relatively insensitive to more remote derivatization. Compound 11 undergoes sequential Ru-centered and Ir-centered oxidation, with the potential of the latter significantly more positive than that of Ir(N,C'-NC5H4-2-C6H4-2)3. Ligand-centered π­π* transitions characteristic of the Ir(N,C'-NC5H4-2-C6H4-2)3 unit red-shift and gain in intensity following the iodo and alkynyl incorporation. Spectroelectrochemical studies of 6, 7, 9, and 11 reveal the appearance in each case of new low-energy LMCT bands following formal IrIII/IV oxidation preceded, in the case of 11, by the appearance of a low-energy LMCT band associated with the formal RuII/III oxidation process. Emission maxima of 6­10 reveal a red-shift upon alkynyl group introduction and arylalkynyl π-system lengthening; this process is quenched upon incorporation of the ligated ruthenium moiety on proceeding to 11. Third-order nonlinear optical studies of 11 were undertaken at the benchmark wavelengths of 800 nm (fs pulses) and 532 nm (ns pulses), the results from the former suggesting a dominant contribution from two-photon absorption, and results from the latter being consistent with primarily excited-state absorption.

Facile synthesis and enhanced nonlinear optical properties of porphyrin-functionalized multi-walled carbon nanotubes.

Two multi-walled carbon nanotube (MWCNT)-based nanohybrids, MWCNT-ZnTPP and MWCNT-TPP (TPP=5-[4-{2-(4-formylphenoxy)- ethyloxy}phenyl]-10,15,20-triphenylporphyrin, ZnTPP=5-[4-{(4-formylphenyl)ethynyl}phenyl]-10,15,20-triphenylporphinatozinc(II)), were prepared directly from pristine MWCNTs through 1,3-dipolar cycloaddition reactions. Covalent attachment of the porphyrins to the surfaces of the MWCNTs was confirmed by Fourier transform infrared spectroscopy, ultraviolet/visible absorption, fluorescence, Raman, and X-ray photoelectron spectroscopy, elemental analysis, transmission electron microscopy, and thermogravimetric analysis. Attachment of the porphyrin moieties to the surface of the MWCNTs significantly improves the solubility and ease of processing of these MWCNT-porphyrin composite materials. Z-scan studies reveal that these MWCNT-porphyrin nanohybrids exhibit enhanced nonlinear optical properties under both nanosecond and picosecond laser pulses at λ=532 nm in comparison with free MWCNTs and the free porphyrin chromophores, whereas superior optical limiting performance was displayed by MWCNT-porphyrin composite materials rather than MWCNTs/ZnTPP and MWCNTs/TPP blends, which is consistent with a remarkable accumulation effect as a result of the covalent linkage between the porphyrin and the MWCNTs.

Syntheses of pentanuclear group 6 iridium clusters by core expansion of tetranuclear clusters with Ir(CO)2(η5-C5Me4R) (R = H, Me).

Metal cluster core expansion at tetrahedral group 6-group 9 mixed-metal clusters MIr3(µ-CO)3(CO)8(η(5)-L) (M = W, Mo, L = C5H5; M = Mo, L = C5Me5) with the iridium capping reagents Ir(CO)2(η(5)-L') (L' = C5Me5, C5Me4H) in refluxing toluene afforded the trigonal-bipyramidal clusters MIr4(µ-CO)3(CO)7(η(5)-C5H5)(η(5)-L') (M = Mo, L' = C5Me5, 1a; M = W, L' = C5Me5, 1b; M = Mo, L' = C5Me4H, 1c; M = W, L' = C5Me4H, 1d) and MoIr4(µ3-H)(µ-CO)2(µ-η(1):η(5)-CH2C5Me4)(CO)7(η(5)-C5Me5) (2). Related reactions with M2Ir2(µ-CO)3(CO)7(η(5)-L)2 (M = W, Mo, L = C5H5; M = Mo, L = C5Me5) afforded M2Ir3(µ-CO)3(CO)6(η(5)-C5H5)2(η(5)-L') (M = Mo, L' = C5Me5, 3a; M = W, L' = C5Me5, 3b; M = Mo, L' = C5Me4H, 3c; M = W, L' = C5Me4H, 3d), W2Ir3(µ-CO)4(CO)5(η(5)-C5H5)2(η(5)-C5Me4H) (4), and Mo2Ir3(µ-CO)3(CO)6(η(5)-C5Me5)3 (5). Single-crystal X-ray diffraction studies of 1a-1d, 2, 3a-3d, and 4 confirmed their molecular structures, including the µ-η(1):η(5)-CH2C5Me4 ligand at hydrido cluster 2, derived from a C-H bond activation of one of the methyl groups. Density functional theory (DFT) studies were employed to suggest the structure of 5. The redox behavior of the new clusters was examined through cyclic voltammetry; all clusters exhibit oxidation and reduction processes (with respect to the resting state), with the oxidation processes being the more reversible, and increasingly so on decreasing Ir content of the clusters, replacing W by Mo, and increasing alkylation of the cyclopentadienyl ligands. In situ IR and UV-vis-near-IR spectroelectrochemical studies of the reversible oxidation processes in 1a and 3a were undertaken, with the spectra of the former suggesting progression to an all-terminal CO geometry concomitant with the first oxidation and a significant structural change upon the second oxidation step. DFT studies of 1a revealed that its crystallographically-confirmed Mo-equatorial core geometry is essentially isoenergetic with a possible Mo-apical isomer, and identified several bridging CO structures for the charged states.

Cooperative enhancement of optical nonlinearities in a porphyrin derivative bearing a pyrimidine chromophore at the periphery.

A novel porphyrin derivative bearing one D-π-A-π-D pyrimidine chromophore at the periphery was designed, prepared, and studied using the Z-scan technique, the results showing that this compound exhibits enhanced nonlinear optical (NLO) absorption, refraction and optical limiting responses. The significant NLO properties can be ascribed to an effective combination of distinct nonlinear mechanisms.

Syntheses and spectroscopic, structural, electrochemical, spectroelectrochemical, and theoretical studies of osmium(II) mono- and bis-alkynyl complexes.

The syntheses of trans-[Os(C≡C-4-C(6)H(4)X)Cl(dppe)(2)] [X = Br (3), I (4)], trans-[Os(C≡C-4-C(6)H(4)X)(NH(3))(dppe)(2)](PF(6)) [X = H (5(PF(6))), I (6(PF(6)))], and trans-[Os(C≡C-4-C(6)H(4)X)(C≡C-4-C(6)H(4)Y)(dppe)(2)] [X = Y = H (7), X = I, Y = C≡CSiPr(i)(3) (8)] are reported, together with improved syntheses of cis-[OsCl(2)(dppe)(2)] (cis-1), trans-[Os(C≡CPh)Cl(dppe)(2)] (2), and trans-[Ru(C≡C-4-C(6)H(4)I)(NH(3))(dppe)(2)](PF(6)) (9(PF(6))) (the last-mentioned direct from trans-[Ru(C≡C-4-C(6)H(4)I)Cl(dppe)(2)]), and single-crystal X-ray structural studies of 2-4, 5(PF(6)), 6(PF(6)), and 7. Ammine complexes 5(PF(6))/6(PF(6)) are shown to afford a facile route to both symmetrical (7) and unsymmetrical (8) osmium bis(alkynyl) complexes. A combination of cyclic voltammetry, UV-vis-NIR spectroelectrochemistry, and time-dependent density functional theory (TD-DFT) has permitted identification and assignment of the intense transitions in both the resting state and the oxidized forms of these complexes. Cyclic voltammetric data show fully reversible oxidation processes at 0.32-0.42 V (3, 4, 7, 8) (with respect to ferrocene/ferrocenium 0.56 V), assigned to the (formal) Os(II/III) couple. The osmium(III) complex (di)cations 5(2+) and 7(+) were obtained by in situ oxidation of 5(+) and 7 using an optically transparent thin-layer electrochemical (OTTLE) cell. The UV-vis-NIR optical spectra of 5(2+) and 7(+) reveal low-energy bands in the near IR region, in contrast to 5(+) and 7 which are optically transparent at frequencies below 22,000 cm(-1). TD-DFT calculations on trans-1, 2, 5(+), and 7 and their oxidized forms suggest that the lowest-energy transitions are chloro-to-metal charge transfer (trans-1), chloro-to-phenylethynyl charge transfer (2), and metal-to-phenylethynyl charge transfer (5(+), 7) in the resting state and chloro-to-metal charge transfer (trans-1(+)), phosphorus-to-metal charge transfer (5(2+)), alkynyl-to-metal charge transfer (7(+)), or phenylalkynyl-centered π → π* (2(+)) following oxidation. The presence of intense CT bands in the resting states and oxidized states and their significantly different nature across the two states, coupled to their strong charge displacement suggest that these species have considerable potential as electrochemically switchable nonlinear optical materials, while the facile unsymmetrical bis(alkynyl)osmium(II) construction suggests potential in construction of multistate heterometallic modular assemblies.

Divergent synthesis of ruthenium alkynyl dendrimers and a two-photon absorption cross-section dendritic effect.

Ruthenium alkynyl dendrimers up to second generation in size have been prepared by a divergent route and exploiting Sonogashira coupling. The cubic NLO properties have been examined by wide spectral range fs Z-scan studies, revealing an NLO dendritic effect. The significant increase in NLO properties seen on generation increase is maintained when the coefficients are scaled by the number of metal atoms, the dendrimer molecular weights, or the number of "effective" (delocalizable π) electrons in the dendritic structures.

Electron-rich iron/ruthenium arylalkynyl complexes for third-order nonlinear optics: redox-switching between three states.

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.

Organometallic complexes for nonlinear optics, 47 - synthesis and cubic optical nonlinearity of a stilbenylethynylruthenium dendrimer.

The synthesis of the 1st generation dendrimer 1,3,5-{trans-[Ru(C≡C-3,5-(trans-[Ru(C≡CPh)(dppe)(2) (C≡CC(6) H(4) -4-(E)-CHCH)])(2) C(6) H(3) )(dppe)(2) (C≡CC(6) H(4) -4-(E)-CHCH)]}(3) C(6) H(3) proceeds by a novel route that features Emmons-Horner-Wadsworth coupling of 1,3,5-C(6) H(3) (CH(2) PO(OEt)(2) )(3) with trans-[Ru(C≡CC(6) H(4) -4-CHO)Cl(dppe)(2) ] and 1-I-C(6) H(3) -3,5-(CH(2) PO(OEt)(2) )(2) with trans-[Ru(C≡CPh)(C≡CC(6) H(4) -4-CHO)(dppe)(2) ] as key steps. The stilbenylethynylruthenium dendrimer is much more soluble than its ethynylated analog 1,3,5-{trans-[Ru(C≡C-3,5-(trans-[Ru(C≡CPh)(dppe)(2) (C≡CC(6) H(4) -4-C≡C)])(2) C(6) H(3) )(dppe)(2) (C≡CC(6) H(4) -4-C≡C)]}(3) C(6) H(3) and, in contrast to the ethynylated analog, is a two-photon absorber at telecommunications wavelengths.

Length-dependent convergence and saturation behavior of electrochemical, linear optical, quadratic nonlinear optical, and cubic nonlinear optical properties of dipolar alkynylruthenium complexes with oligo(phenyleneethynylene) bridges.

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.

Organometallic complexes for nonlinear optics. 42. Syntheses, linear, and nonlinear optical properties of ligated metal-functionalized oligo(p-phenyleneethynylene)s.

A combination of UV-vis-NIR spectroscopy, femtosecond Z-scan measurements, and time-dependent density functional theory (TD-DFT) calculations have been used to comprehensively investigate the linear optical and nonlinear optical (NLO) properties of pi-delocalizable metal-functionalized oligo(phenyleneethynylene)s. A range of unsymmetrically or symmetrically end-functionalized mono-, di-, tri-, penta-, hepta-, and nona(phenyleneethynylene)s were synthesized, with larger examples bearing varying numbers of 2,5-di(hexyloxy)phenyl groups to ensure sufficient solubility of the metal complex derivatives. The effect of incorporating varying numbers of solubilizing substituents in the OPE bridge, peripheral group modification, OPE lengthening, coligand variation, and metal location in the OPE on the linear optical properties has been established, with the first three molecular modifications resulting in significant changes in the optical absorption maxima. TD-DFT calculations reveal that the most intense transition in the linear optical spectra is localized on the OPE bridge and involves excitation from acetylenic to cumulenic molecular orbitals that are not greatly spatially separated from one another. The nonlinear optical properties are dominated by two-photon absorption, which for all but 1,4-{trans-[RuCl(dppm)(2)]C[triple bond]C}(2)C(6)H(4) appears as a band around 11,400 cm(-1) and a sharp increase of nonlinear absorption at frequencies >17,000 cm(-1). Surprisingly, there is relatively little influence of the length of the OPE bridge on the magnitude of the two-photon absorption cross sections, which are in the range 300-1000 GM.

Organometallic complexes for nonlinear optics. 43. Quadratic optical nonlinearities of dipolar alkynylruthenium complexes with phenyleneethynylene/phenylenevinylene bridges.

The syntheses of trans-[Ru(4,4'-C[triple bond]CC(6)H(4)C[triple bond]CC(6)H(4)NO(2))Cl(dppe)(2)] (19) and the systematically varied complexes trans-[Ru(4,4',4''-C[triple bond]CC(6)H(4)X(2)C(6)H(4)Y(2)C(6)H(4)NO(2))Cl(L(2))(2)] [L(2) = dppe, X(2) = C[triple bond]C, Y(2) = (E)-CH=CH (12), C[triple bond]C (18); L(2) = dppe, X(2) = (E)-CH=CH, Y(2) = C[triple bond]C (14), (E)-CH=CH (16); L(2) = dppm, X(2) = C[triple bond]C, Y(2) = (E)-CH=CH (13); L(2) = dppm, X(2) = (E)-CH=CH, Y(2) = C[triple bond]C (15), (E)-CH=CH (17)] are reported, the latter being donor-bridge-acceptor complexes varying in bridge composition by replacement of yne with E-ene linkages, together with their cyclic voltammetric data, linear optical, and quadratic nonlinear optical response data. Ru(II/III) oxidation potentials increase on replacing yne linkage by E-ene linkage at the phenylene adjacent to the metal center, and on replacing dppe by dppm co-ligands. The low-energy optical absorption maxima occur in the region 20,400-23,300 cm(-1) and are metal-to-ligand charge-transfer (MLCT) in origin; these bands undergo a blue-shift upon pi-bridge lengthening by addition of phenyleneethynylene units, and on replacing E-ene linkages by yne linkages. Time-dependent density functional theory calculations on model complexes have suggested assignments for the low-energy bands. The optical spectra of selected oxidized species contain low-energy ligand-to-metal charge transfer (LMCT) bands centered in the region 9760-11,800 cm(-1). Quadratic molecular nonlinearities from hyper-Rayleigh scattering (HRS) studies at 1064 nm reveal an increase in the two-level-corrected beta(0) value on pi-bridge lengthening, a trend that is not seen with beta values because of the blue-shift in lambda(max) for this structural modification. Replacing yne linkages by E-ene linkage at the phenylene adjacent to the metal center or dppm co-ligand by dppe results in an increase in beta and beta(0) values. In contrast, quadratic molecular nonlinearities by HRS at 1300 nm or electric field-induced second-harmonic generation (EFISH) studies at 1907 nm do not afford clear trends.

Syntheses and quadratic nonlinear optical properties of 2,7-fluorenylene- and 1,4-phenylene-functionalized o-carboranes.

o-Carboranes C-functionalized by (4-substituted-phen-1-yl)ethynyl-1,4-phenyl groups or (2-substituted-fluoren-7-yl)ethynyl-2,7-fluorenyl groups, in which the pendant functionalization is electron-withdrawing nitro or electron-donating diphenylamino groups, have been synthesized and in many cases structurally characterized. Diphenylamino-containing examples coupled via the two π-delocalizable bridges to the electron-accepting o-carborane unit exhibit the greater quadratic optical nonlinearities at 1064 nm (hyper-Rayleigh scattering, ns pulses), the nonlinearities also increasing on proceeding from 1,4-phenylene- to 2,7-fluorenylene-containing bridge. The most NLO-efficient example 2-(n-butyl)-1-(2-((9,9-di(n-butyl)-2-(N,N-diphenylamino)-9H-fluoren-7-yl)ethynyl)-9,9-di(n-butyl)-9H-fluoren-7-yl)-1,2-ortho-carborane, consisting of diphenylamino donor, fluorenyl-containing bridge, o-carborane acceptor, and solubilizing n-butyl units, exhibits large 〈ß〉HRS (230 × 10-30 esu) and frequency-independent (two-level model) 〈ß0〉 (96 × 10-30 esu) values. Coupling two (2-((9,9-di(n-butyl)-2-(N,N-diphenylamino)-9H-fluoren-7-yl)ethynyl)-9,9-di(n-butyl)-9H-fluoren-7-yl) units to the 1,2-ortho-carborane core affords a di-C-functionalized compound with enhanced nonlinearities (309 × 10-30 esu and 129 × 10-30 esu, respectively).