T. Christopher Corkery

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

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.

Dodecanuclear‐Ellipse and Decanuclear‐Wheel Nickel(II) Thiolato Clusters with Efficient Femtosecond Nonlinear Absorption

Thiolate ligands have been of longstanding interest for a variety of reasons: 1) their diverse binding modes give rise to an array of bonding motifs that are of fundamental importance in coordination chemistry, 2) metal–thiolate interactions are key elements of numerous metalloproteins and play a crucial role in the broader field of bioinorganic chemistry, and 3) thiolate-mediated magnetic coupling is an essential component in novel molecular magnets. Amongst the range of metal thiolate-derived structures, the synthesis, structure, and magnetic properties of toroidal (or tiara-like) architectures have raised considerable interest. However, most of the known tiara-like [M(m-SR)]n (M = Ni, Pd) clusters to date have been constructed by single thiolate ligands and possess geometrically similar ring systems, which has restricted, to some extent, the abundance of examples and structural diversity of the tiara family. The development of high-performance molecular materials with optimized nonlinear optical (NLO) properties has also been the focus of much current research. 7] Previous studies have demonstrated that the presence of large pelectron delocalization and a symmetrical planar structure play crucial roles in determining the properties of nonlinear chromophores. 8] Curiously, though, despite the quasiaromatic nature of the bonding that has been proposed in nickel toroidal species, their optical properties are little explored; in particular, no study of the NLO properties is extant. We present here the synthesis of the largest tiara-like nickel(II)–thiolate cluster thus far by a novel route that employs two different thiolate bridges, structural studies that reveal an unprecedented elliptical structure for [Ni(m-StBu)(m-etet)]12 (etet = 2-ethylthioethanethiolate) and two new decanuclear-wheel nickel(II)–thiolato clusters [Ni(m-StBu)(m-pyet)]10 (pyet = 2-(2-mercaptoethyl)pyridine) and [Ni(mStBu)(m-atet)]10 (atet = 2-aminoethanethiol), and the first NLO studies of examples from this important class of molecules, together with time-dependent DFT studies that shed light on the optical behavior. The reaction of NiCl2·6 H2O with 1 equivalent K(etet) gave, after work-up, separable [(CH3C6H5) {Ni(m-StBu)(metet)}10] (1a) and [Ni(m-StBu)(m-etet)]12·(CH3C6H5)2 (1 b), whereas similar reactions with K(pyet) or K(atet), instead of K(etet), afforded [(CH3C6H5) {Ni(m-StBu)(m-pyet)}10]·(CH3C6H5)4 (2) and [(0.5CH3C6H5) {Ni(m-StBu)(m-atet)}10]·(CH3C6H5)2 (3), respectively. The atomic arrangements and stoichiometries of 1 a, 1b, 2, and 3 were unequivocally established from low-temperature CCD area-detector X-ray diffraction studies. The single-crystal X-ray analysis of 1b reveals a heretofore unknown dodecagonal-ellipse Ni12S24 framework, as displayed in Figure 1. The top view (Figure 1 a) of the cyclic Ni12S24 architecture shows that edge-fusion of the 12 localized planar [NiS4] subunits along opposite nonbonding S–S edges gives rise to a triple-layer elliptical geometry that approximately conforms to pseudo-D2 symmetry. The transannular Ni···Ni distances of 1 b are in the range of 11.343(6)–13.528(7) , while the dihedral angles between adjoining [NiS2] planes vary from 140.32 to 157.848 because of the unsymmetrical elliptical geometry of this unique 12membered Ni ring. The side view (Figure 1b) of the toroid 1b [*] Prof. Dr. C. Zhang, Dr. S. C. Meng, Dr. J. F. Zhang Molecular Materials Research Center, Scientific Research Academy, School of Chemistry and Chemical Engineering, Jiangsu University Zhenjiang 212013 (P.R. China) Fax: (+ 86)511-8879-7815 E-mail: chizhang@ujs.edu.cn

Organobimetallic Ru(II)-Re(I) 4-ethynylpyridyl complexes: structures and non-linear optical properties.

A series of heterobimetallic complexes, [RuCp(C[triple bond]Cpy-4)(P-P)][Re(CO)3(N-N)]+ (P-P = dppf, N-N = bpy 5, Me2bpy 6, tBu2bpy 7, phen 8, tpy 9; P-P = 2PPh3, N-N = bpy 10) have been obtained from Lewis addition between the metalloligands [RuCp(C[triple bond]Cpy-4)(P-P)] (P-P = dppf 1; 2PPh3 2) and solvent-stabilised fac-[Re(CH3CN)(CO)3(N-N)]+. All new complexes 5-10, together with fac-[ReBr(CO)3(tpy)] (3) and fac-[Re(CH3CN)(CO)3(tpy)][PF6] (4), are characterized by solution spectroscopy; 3 and 5-9 are also characterized by single-crystal X-ray crystallography. The terpyridine ligands in 3 and 9 are in an unusual 2-bidentate coordination mode with a pendant pyridyl. Electrochemical studies showed successive metal-based oxidations and a ligand-centered reduction in 5-10. Significant oxidation changes are observed at the Ru(II) and Re(I) centers in 5-10 when compared with their respective monometallic components. Cubic nonlinearities of 5-10 determined by the Z-scan technique at 750 nm reveal two-photon absorption that increases significantly on progression from Ru(II) monomeric precursors to heterobimetallics, suggesting NLO enhancement upon heterometallic complex formation.

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.

Organometallic Complexes for Non-Linear Optics. 51. Second- and Third-Order Non-Linear Optical Properties of Alkynylgold Complexes*

The alkynes HC≡CC6H2-2,6-Et2-4-C≡CC6H4-4-NO2 (4) and HC≡CC6H4-4-C≡CC6H2-2,6-Et2-4-C≡CC6H4-4-NO2 (6) and gold alkynyl complexes Au{C≡CC6H2-2,5-(OEt)2-4-C≡CC6H4-4-NO2}(PPh3) (7), Au(C≡CC6H2-2,6-Et2-4-C≡CC6H4-4-NO2)(PPh3) (8), and Au(C≡CC6H4-4-C≡CC6H2-2,6-Et2-4-C≡CC6H4-4-NO2)(PPh3) (9) have been synthesized. The linear optical properties and quadratic optical non-linearities of 7–9 have been measured, the latter by hyper-Rayleigh scattering at 1064 nm, and compared with data for the previously reported complexes Au(C≡CC6H4-4-NO2)(PPh3) (10) and Au(C≡CC6H4-4-C≡CC6H4-4-NO2)(PPh3) (11). The optical absorption maximum red-shifts and the first hyperpolarizabilities increase on π-system lengthening and on introduction of electron-releasing substituents on the π-bridge ring adjacent to the metal centre. The cubic non-linear optical properties of 1,4-{(PCy3)Au(C≡C)}2C6H4 (12) and {(PCy3)Au(C≡C-4-C6H4C≡C)}6C6 (13) have been assessed by wide spectroscopic range femtosecond Z-scan studies; the maximal values of the imaginary component and the effective two-photon absorption cross-section increase markedly on proceeding from linear complex 12 to 6-fold-symmetric complex 13, an increase that is maintained when data are scaled by relative molecular weight.