Marie P. Cifuentes

Switching the Cubic Nonlinear Optical Properties of an Electro-, Halo-, and Photochromic Ruthenium Alkynyl Complex Across Six States

The impending breakdown in Moore s law has prompted the search for molecule-based information-processing components such as molecular switches and logic gates. Bistable molecules that afford states possessing distinct linear optical properties (absorbance, fluorescence) and that can be interconverted by chemical, redox, magnetic, or photonic stimuli have attracted considerable interest for Boolean logic operations. In principle, molecular computing could exploit ternary or higher-order digit representations, which would permit smaller device components. “Switchable” molecular properties are also of intense interest for sensor applications. Despite this interest, molecules that can exist in more than two stable and independently addressable states, which could be employed for complex and higher-order logic functions, have been explored significantly less than two-state molecules. One potentially very important procedure to exploit molecular switches is to utilize their cubic nonlinear optical (NLO) properties, and in particular their nonlinear absorption. However, this avenue is also poorly explored and is to date restricted to switching between three states at most, although such switching offers 1) the prospect of broadening the available spectral range (and in particular utilizing telecommunications-relevant wavelengths) and 2) the possibility of enhanced spatial control (compared to linear optical switching) because of the higher-order dependence on the intensity of the incident light. Herein we show that a specific binuclear metal alkynyl complex incorporating a functionalized 5,5’-dithienylperfluorocyclopentene (DTE) bridge can afford six stable and switchable states that possess distinct cubic NLO properties. The complex is comprised of independently addressable modules that respond orthogonally to protic (alkynyl ligandQvinylidene ligand), electrochemical (metal-centered redox: RuQRu), and photochemical (DTE ring-openingQring-closing) stimuli. The six states are interconverted along seven pathways, all of which result in distinct changes to cubic nonlinearity for specific regions of the spectrum. Our results demonstrate that complexes of this type have the potential to be used, among other things, in the construction of multi-input logic gates responding to diverse stimuli across a broad spectral range. The synthesis of the dinuclear ruthenium alkynyl complex oa(II) is depicted in Figure S1 in the Supporting Information. The DTE unit is obtained in the “open” form as its 5,5’diethynyl derivative; the open DTE is thermally stable, and this open form persists through the preparative steps that ultimately afford oa(II). Complete synthetic and characterization details are given in the Supporting Information. Complex oa(II) can be reversibly protonated to the di(vinylidene) complex ov(II), reversibly oxidized to the Ru complex dication oa(III), and photoisomerized with UV light to the closed alkynyl complex ca(II). Complex ca(II) can be reversibly protonated to cv(II) and reversibly oxidized to ca(III) and undergoes photoreversion to oa(II) on irradiation with red light. The vinylidene forms and the oxidized forms undergo reversible photoisomerization under analogous irradiation conditions. Note that oxidation of ruthenium vinylidene complexes with these coligands is an irreversible process, as assessed by cyclic voltammetry, so there is a maximum of six switchable states for this complex. The interconversions of the six stable states of the complex are depicted in Scheme 1, and key spectral data are tabulated in the Supporting Information (Table S1). Cyclic voltammograms and UV/Vis/NIR spectral progressions for the redox processes, the latter acquired with an optically transparent thin-layer spectroelectrochemical (OTTLE) cell and demonstrating stable isosbestic points, are given in the Supporting Information, together with NMR spectra demonstrating spectroscopically complete 1) photoisomerization between the open and closed forms and 2) protonation/deprotonation to afford the vinylidene and alkynyl complex forms, and IR spectra demonstrating spectroscopically complete oxidation from the Ru to the Ru form. Several organometallic alkyne-functionalized DTE complexes have been reported, and the effect of oxidation state on photochromic behavior has been probed, although there was no assessment of the effect of protonation/deprotonation on photochromism. [CpFe(h-C5H4C C DTE C C-hC5H4)FeCp] [11] and [(dppe)CpFe(C C DTE C C)FeCp[*] K. A. Green, Dr. M. P. Cifuentes, T. C. Corkery, Prof. M. G. Humphrey Research School of Chemistry, Australian National University Canberra, ACT 0200 (Australia) Fax: (+ 61)2-6125-0760 E-mail: mark.humphrey@anu.edu.au

Organometallic Complexes for Nonlinear Optics Part 25. Quadratic and Cubic Hyperpolarizabilities of some Dipolar and Quadrupolar Gold and Ruthenium Complexes

Abstract The complexes [Au(4-CCC 6 H 4 NO 2 )(L)] [L=PCy 3 ( 1 ), PMe 3 ( 2 )], [(L)Au(μ-4-CCRCC)Au(L)] [R=C 6 H 4 , L=PCy 3 ( 4 ), PPh 3 ( 5 ); R=C 6 H 4 -4-C 6 H 4 , L=PCy 3 ( 7 ), PPh 3 ( 8 )], trans,trans -[RuCl(dppm) 2 (μ-4,4′-CCC 6 H 4 C 6 H 4 CC)RuCl(dppm) 2 ] ( 11 ), trans -[Ru(X)(Y)(dppe) 2 ] [X=Cl, Y=4-CCC 6 H 4 I ( 12 ), 4-CCC 6 H 4 CCSiMe 3 ( 13 ); X=CCPh, 4-CCC 6 H 4 CCH ( 14 )] and { trans -[Ru(CCPh)(dppe) 2 ]} 2 (μ-4,4′-CCC 6 H 4 CCCCC 6 H 4 CC) ( 15 ) have been prepared and their electrochemical (Ru complexes) and nonlinear optical properties assessed. Electronic communication between the metal centers in 10 , 11 and 15 diminishes as the π-delocalizable bridge is lengthened. Quadratic nonlinear optical (NLO) merit increases on replacing triarylphosphine by trialkylphosphine, the relative β values Au(4-CCC 6 H 4 NO 2 )(PPh 3 ) 1 3 being observed. Cubic NLO values are small for the gold complexes and much larger for the ruthenium examples. Complex 15 has the largest σ 2 /MWt (two-photon absorption cross-section/molecular weight) value observed thus far for an organometallic complex.

Organometallic complexes for nonlinear optics. Part 27. Syntheses and optical properties of some iron, ruthenium and osmium alkynyl complexes

The syntheses of the alkynyl complexes M(4-CCC6H4NO2)(dppe)(η-C5H5) [M=Fe (1), Ru (2), Os (3)], Os(4-CCC6H4NO2)(PPh3)2(η-C5H5) (4) and Ru(4-CCC6H4NO2)(CO)2(η-C5H5) (5) are reported. Structural studies reveal a decrease in RuC(1) distance on proceeding from 5 to 2, consistent with greater back-donation of electron density to the alkynyl ligand from the more electron-rich metal center in 2. Electrochemical data show that the MII/III couple for the dicarbonyl complex 5 is at a significantly more positive potential than that of the related diphosphine complex 2, consistent with ligand variation modifying the electron richness and hence donor strength of the metal center. Time-dependent density functional calculations on model complexes M(4-CCC6H4NO2)(PH3)2(η-C5H5) (M=Fe, Ru, Os) have been employed to assign the intense low-energy optical transition in these complexes as MLCT in character, the higher energy band being phenyl–phenyl* in nature. Molecular quadratic optical nonlinearities have been measured using the hyper-Rayleigh scattering procedure at 1064 nm. β values vary as Fe≤Ru≤Os for metal variation and CO<phosphines for co-ligand variation, the latter consistent with the variation in donor strength of the metal center inferred from electrochemical and crystallographic data. The observed trend in β on metal variation follows the trend in backbonding energies calculated by DFT.

Organometallic complexes for nonlinear optics. X. Molecular quadratic and cubic hyperpolarizabilities of systematically varied (cyclopentadienyl)bis(phosphine) ruthenium σ-arylacetylides: X-ray crystal structure of Ru((E)-4,4′-C CC6H4CHC6H4NO2)(PPh3)2(η-C5H5) ☆

Abstract The complexes Ru(4,4′-C  CC6H4C6H4NO2)(PPh3)2(η-C5H5) and Ru(4,4′-C  CC6H4C  CC6H4NO2)(PPh3)2(η-C5H5) have been prepared and the latter structurally characterized; they belong to a series of organometallic donor-bridge-acceptor compounds containing (cyclopentadienyl)bis(phosphine)ruthenium(II) centres as donors, conjugated arylacetylide bridges, and nitro acceptor groups. Electrochemical data for the series of complexes Ru(C  CR)(PR′3)2(η-C5H5) (R  Ph, 4-C6H4NO2, R′  Ph, Me; R = 4,4′-C6H4C6H4NO2, (E)-4,4′-C6H4CH  CHC6H4NO2, 4,4′-C6H4C  CC6H4NO2, 4,4′-C6H4N  CHC6H4NO2, R′  Ph) are consistent with an RuII/III couple whose oxidation potentials vary strongly with chain-lengthening from one-ring to two-ring acetylide ligand, but show little variation with changes at the bridging unit of the two-ring acetylide ligand. The molecular quadratic and cubic optical nonlinearities of the series of complexes have been determined by hyper-Rayleigh scattering (HRS) and Z-scan techniques, respectively. Molecular first hyperpolarizabilities by HRS at 1064 nm are dispersively enhanced; experimental and two-level corrected data suggest an increase in nonlinearity on chain-lengthening of the bridge, in proceeding from C6H4 to C6H4C6H4 and then C6H4C  CC6H4 and C6H4CH  CHC6H4, a general trend that is reproduced by semiempirical ZINDO computations. Cubic hyperpolarizabilities by Z-scan at 800 nm are negative for complexes with nitro acceptor groups, probably a result of two-photon dispersion, with absolute values (up to 850 × 10−36 esu) large for small organometallic complexes; as with quadratic nonlinearities, cubic nonlinearities increase substantially on bridge lengthening, with little variation on phosphine substitution.

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. 15. Molecular quadratic hyperpolarizabilities of trans-bis{bis(diphenylphosphino)methane}ruthenium σ-aryl- and σ-pyridyl-acetylides: X-ray crystal structure of trans-[Ru(2-CCC5H3N-5-NO2)Cl(dppm)2]

The complexes trans -[Ru(2-CCC 5 H 3 N-5-R)Cl(dppm) 2 ] [R=H ( 6 ), NO 2 ( 7 )] have been prepared and 7 has been structurally characterized; comparison with the structural study of trans -[Ru(4-CCC 6 H 4 NO 2 )Cl(dppm) 2 ] ( 3 ) reveals a decrease in Ru–C(1) distance and increase in Ru–Cl(1) distance, consistent with stronger σ -bonding by the nitropyridylalkynyl ligand in 7 compared to the nitrophenylalkynyl ligand in 3 . Electrochemical data for 3 , 6 , 7 , precursor dichloro complexes [RuCl 2 (dppm) 2 ] [ cis ( 1a ), trans ( 1b )], and related alkynyl complexes trans -[Ru(4-CCC 6 H 4 R)Cl(dppm) 2 ] [R=H ( 2 ), 4-C 6 H 4 NO 2 ( 4 ), ( E )-4-CHCHC 6 H 4 NO 2 ( 5 )] have been determined by cyclic voltammetry. Introduction of nitro substituent in progressing from 2 to 3 or 6 to 7 leads to a substantial increase in E o Ru II/III , most of which is lost on chain-lengthening the alkynyl ligand in progressing from 3 to 4 or 5 . Replacement of phenyl by pyridyl in progressing from 2 to 6 or 3 to 7 results in a 0.1 V increase in E o Ru II/III . The optical spectra of representative complexes have been examined. Introduction of a nitro substituent onto the phenylalkynyl ligand, in progressing from 2 to 3 , results in a substantial (ca. 11 000 cm −1 ) red-shift in the intense MLCT band of the Ru II –CC–Ar–NO 2 moiety. Complexes 3 , 4 and 5 exhibit sizable solvatochromic shifts, suggestive of significant optical nonlinearities. Quadratic hyperpolarizabilities for 2 – 7 were determined by hyper-Rayleigh scattering (HRS) at 1064 nm; measurements are consistent with an increase in β HRS upon incorporation of nitro substituent (progressing from 2 to 3 or 6 to 7 ), chain-lengthening the alkynyl ligand (progressing from 3 to 4 and then to 5 ) and replacing phenyl by pyridyl in progressing from 2 to 6 , general trends that are maintained with the two-level-corrected data, and which parallel shifts in λ max to low energy. The observed and two-level-corrected β HRS values for 7 are lower than expected; it is perhaps significant that λ max for 7 is close to the second-harmonic.

Organometallic complexes for nonlinear optics. Part 31. Cubic hyperpolarizabilities of ferrocenyl-linked gold and ruthenium complexes

Abstract The complexes [Fe{η-C5H4(E)CHCH4-C6H4CCX}2] [X=SiMe3 (1), H (2), Au(PCy3) (3), Au(PPh3) (4), Au(PMe3) (5), RuCl(dppm)2 (7), RuCl(dppe)2 (8)] and [Fe{η-C5H4(E)CHCH4-C6H4CHCRuCl(dppm)2}2](PF6)2 (6) have been prepared and the identities of 1 and 7 confirmed by single-crystal X-ray structural studies. Complexes 1–8 exhibit reversible oxidation waves in their cyclic voltammograms attributed to the FeII/III couple of the ferrocenyl groups, 6–8 also showing reversible (7, 8) or non-reversible (6) processes attributed to Ru-centered oxidation. Cubic nonlinearities at 800 nm by the Z-scan method are low for 1–5; in contrast, complexes 6 and 7 exhibit large negative γreal and large γimag values. A factor of 4 difference in ∣γ∣ and two-photon absorption cross-section σ2 values for 6 and 7 suggest that they have potential as protically switchable NLO materials.

Organometallic complexes for non-linear optics VII. Cubic optical non-linearities of octahedral trans-bis{bis(diphenylphosphino)methane}ruthenium acetylide complexes; X-ray crystal structure of trans-[Ru(CCPH)(4-CCC6H4NO2)(dppm)2]

Abstract Cubic molecular optical non-linearities of a systematically varied series of octahedral bis{bis(diphenylphosphino)methane}ruthenium σ-acetylide complexes have been determined by the Z-scan technique: the influence on the non-linear response of sequential replacement of chloro by acetylide ligand in trans -[RuCl 2 (dppm) 2 ] and acetylide chain length in proceeding from 4-nitrophenyl- to 4-nitrobiphenyl- and 4-nitro-( E )-stilbenylacetylide has been studied. The first X-ray structuralstudy of an unsymmetrical bis(acetylide) complex of this type, trans -[Ru(CCPh)(4-CCC 6 H 4 NO 2 )(dppm) 2 ], is reported and confirms the trans -diposed stereochemistry of the alkynyl ligands.

Covalent functionalization of reduced graphene oxide with porphyrin by means of diazonium chemistry for nonlinear optical performance

Reduced graphene oxide (RGO)-porphyrin (TPP) nanohybrids (RGO-TPP 1 and RGO-TPP 2) were prepared by two synthetic routes that involve functionalization of the RGO using diazonium salts. The microscopic structures, morphology, photophysical properties and nonlinear optical performance of the resultant RGO-TPP nanohybrids were investigated. The covalent bonding of the porphyrin-functionalized-RGO nanohybrid materials was confirmed by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and thermogravimetric analysis. Attachment of the porphyrin units to the surface of the RGO by diazotization significantly improves the solubility and ease of processing of these RGO-based nanohybrid materials. Ultraviolet/visible absorption and steady-state fluorescence studies indicate considerable π-π interactions and effective photo-induced electron and/or energy transfer between the porphyrin moieties and the extended π-system of RGO. The nonlinear optical properties of RGO-TPP 1 and RGO-TPP 2 were investigated by open-aperture Z-scan measurements at 532 nm with both 4 ns and 21 ps laser pulses, the results showing that the chemical nanohybrids exhibit improved nonlinear optical properties compared to those of the benchmark material C60, and the constituent RGO or porphyrins.

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.