Tunable Chiral Second-Order Nonlinear Optical Chromophores Based on Helquat Dications.

Fourteen new dipolar cations have been synthesized, containing methoxy or tertiary amino electron donor groups attached to helquat (Hq) acceptors. These Hq derivatives have been characterized as their TfO- salts by using various techniques including NMR and electronic absorption spectroscopies. UV-vis spectra show intense, relatively low energy absorptions with λmax ≈ 400-600 nm, attributable to intramolecular charge-transfer (ICT) excitations. Single-crystal X-ray structures have been solved for two of the chromophores, one as its PF6- salt, revealing centrosymmetric packing arrangements (space groups Pbca and P1̅). Molecular quadratic nonlinear optical (NLO) responses have been determined directly by using hyper-Rayleigh scattering (HRS) with a 800 nm laser, and indirectly via Stark (electroabsorption) spectroscopy for the low energy absorption bands. The obtained static first hyperpolarizabilities ß0 range from moderate to large: (9-140) × 10-30 esu from HRS in MeCN and (44-580) × 10-30 esu from the Stark data in PrCN. The magnitude of ß0 increases upon either extending the π-conjugation length or replacing a methoxy with a tertiary amino electron donor substituent. Density functional theory (DFT) and time-dependent DFT calculations on selected tertiary amino chromophores confirm that the low energy absorptions have ICT character. Relatively good agreement between the simulated and experimental UV-vis absorption spectra is achieved by using the CAM-B3LYP functional with the 6-311G(d) basis set. The ßtot values predicted by using DFT at the same level of theory are large ((472-1443) × 10-30 esu in MeCN). Both the theoretical and experimental results show that para-conjugation between Hq and electron donor fragments is optimal, and enlarging the Hq unit is inconsequential with respect to the molecular quadratic NLO response.

Ferrocenyl helquats: unusual chiral organometallic nonlinear optical chromophores.

Three new dipolar cations have been synthesised, containing ferrocenyl (Fc) electron donor groups attached to helquat (Hq) acceptors. These organometallic Hq derivatives have been characterised as their TfO- salts by using various techniques including NMR and electronic absorption spectroscopies and electrochemical measurements. UV-vis spectra show multiple intense low energy absorptions attributable to intramolecular charge-transfer (ICT) excitations. Each compound displays a reversible Fc+/0 redox process, together with two reversible one-electron reductions of the Hq fragment. Molecular quadratic nonlinear optical (NLO) responses have been determined by using hyper-Rayleigh scattering at 1064 nm, and Stark (electroabsorption) spectroscopic studies on the visible absorption bands. The obtained first hyperpolarizabilities ß are moderate, consistent with the relatively short π-conjugation lengths between the Fc and attached pyridinium group. A single-crystal X-ray structure has been solved for one of the complexes as its PF6- salt, revealing a centrosymmetric packing in the triclinic space group P1[combining macron]. Density functional theory (DFT) and time-dependent DFT calculations indicate that the lowest energy absorption bands have mainly metal-to-ligand charge-transfer character. The donor orbitals involved in the electronic transitions forming the next lowest energy ICT band also have substantial contributions from the Fe atom. Good agreement between the simulated and experimental UV-vis absorption spectra is achieved by using the PBE0 functional with the 6-311++G(d)/LANL2DZ mixed basis set, and the theoretical ß values are reasonably large. Oxidation of the Fc unit is predicted to cause the ßtot value to decrease by more than 80% in one of the complexes.

Helquat Dyes: Helicene-like Push-Pull Systems with Large Second-Order Nonlinear Optical Responses.

Helquat dyes combine a cationic hemicyanine with a helicene-like motif to form a new blueprint for chiral systems with large and tunable nonlinear optical (NLO) properties. We report a series of such species with characterization, including determination of static first hyperpolarizabilities ß0 via hyper-Rayleigh scattering and Stark spectroscopy. The measured ß0 values are similar to or substantially larger than that of the commercial chromophore E-4'-(dimethylamino)-N-methyl-4-stilbazolium. Density functional theory (DFT) and time-dependent DFT calculations on two of the new cations are used to probe their molecular electronic structures and optical properties. Related molecules are expected to show bulk second-order NLO effects in even nonpolar media, overcoming a key challenge in developing useful materials.

Synthesis, structures, and optical properties of ruthenium(II) complexes of the tris(1-pyrazolyl)methane ligand.

Four new complex salts [Ru(II)Cl(Tpm)(L(A))2][PF6]n [Tpm = tris(1-pyrazolyl)methane; n = 1, L(A) = pyridine (py) 1 or ethyl isonicotinate (EIN) 2; n = 3, L(A) = N-methyl-4,4'-bipyridinium (MeQ(+)) 3 or N-phenyl-4,4'-bipyridinium (PhQ(+)) 4] have been prepared and characterized. Electronic absorption spectra show intense d → π* metal-to-ligand charge-transfer (MLCT) absorption bands, while cyclic voltammetry reveals a reversible Ru(III/II) wave, accompanied by quasireversible or irreversible L(A)-based reductions for all except 1. Single crystal X-ray structures have been obtained for 1•Me2CO, 2, and 3•Me2CO. For 2-4, molecular first hyperpolarizabilities ß have been measured in acetonitrile solutions via the hyper-Rayleigh scattering (HRS) technique at 800 nm. Stark (electroabsorption) spectroscopic studies on the MLCT bands in frozen butyronitrile allow the indirect estimation of static first hyperpolarizabilities ß0. The various physical data obtained for 3 and 4 are compared with those reported previously for related cis-{Ru(II)(NH3)4}(2+) species [ Coe, B. J. et al. J. Am. Chem. Soc. 2005 , 127 , 4845 ]. TD-DFT calculations on the complexes in 1-4 confirm that their lowest energy absorption bands are primarily Ru(II) → L(A) MLCT in character, while Ru(II) → Tpm MLCT transitions are predicted at higher energies. DFT agrees with the Stark, but not the HRS measurements, in showing that ß0 increases with the electron-accepting strength of L(A). The 2D nature of the chromophores is evidenced by dominant ßxxy tensor components.

Tris-[4-(di-methyl-amino)-pyridine][tris(pyra-zol-1-yl)methane]--ruthenium(II) bis-(hexa-fluorido-phosphate) diethyl ether monosolvate.

In the title compound, [Ru(C10H10N6)(C7H10N2)3](PF6)2·C4H10O, the Ru(II) cation is coordinated by one tris-(1-pyrazol-yl)methane (Tpm) and three dimethylaminopyridine (dmap) ligands in a slightly distorted octa-hedral geometry. The asymmetric unit consists of one complex cation, two hexa-fluorido-phosphate anions and one diethyl ether solvent mol-ecule in general positions. Although quite a large number of ruthenium complexes of the facially coordinating tridentate Tpm ligand have been structurally characterized, this is only the second one containing three pyridyl co-ligands. The average Ru-N(Tpm) distance is 2.059 (12) Å, while the average Ru-N(dmap) [dmap = 4-(di-methyl-amino)-pyridine] distance is somewhat longer at 2.108 (13) Å. The orientation of the dmap ligands varies greatly, with dihedral angles between the pyridyl and opposite pyrazolyl rings of 14.3 (2), 23.2 (2) and 61.2 (2)°.

Heptametallic, octupolar nonlinear optical chromophores with six ferrocenyl substituents.

New complexes with six ferrocenyl (Fc) groups connected to Zn(II) or Cd(II) tris(2,2'-bipyridyl) cores are described. A thorough characterisation of their BPh4(-) salts includes two single-crystal X-ray structures, highly unusual for such species with multiple, extended substituents. Intense, visible d(Fe(II))→π* metal-to-ligand charge-transfer (MLCT) bands accompany the π→π* intraligand charge-transfer absorptions in the near UV region. Each complex shows a single, fully reversible Fe(III/II) wave when probed electrochemically. Molecular quadratic nonlinear optical (NLO) responses are determined by using hyper-Rayleigh scattering and Stark spectroscopy. The latter gives static first hyperpolarisabilities ß0 reaching as high as approximately 10(-27)  esu and generally increasing with π-conjugation extension. Z-scan cubic NLO measurements reveal high two-photon absorption cross-sections σ2 of up to 5400 GM in one case. DFT calculations reproduce the π-conjugation dependence of ß0, and TD-DFT predicts three transitions close in energy contributing to the MLCT bands. The lowest energy transition has octupolar character, whereas the other two are degenerate and dipolar in nature.

Synthesis, characterization, and sorption properties of amorphous titanium phosphate and silica-modified titanium phosphates.

Amorphous titanium hydroxyphosphate with formula Ti(OH)(1.36)(HPO(4))(1.32).2.3H(2)O and a new silica-modified titanium hydroxyphosphate with a general formula Ti(OH)(2x)(HPO(4))(2-x).ySiO(2).nH(2)O are synthesized and characterized using IR, TG, XRD, SEM, solid-state NMR, and BET techniques. It is concluded that SiO(2) is evenly distributed within the titanium phosphate (TiP) agglomerates and that neither the separate silica phase nor the titanium silicates are formed during the synthesis of silica-modified titanium hydroxyphosphate. Correlations between the texture, ion-exchange properties of the amorphous titanium hydroxyphosphate, and the amount of SiO(2) present within the TiP matrix are established. Sorption properties of silica-modified titanium hydroxyphosphate toward Cs(+) and Sr(2+) are studied in a series of samples with an increasing amount of silica, at different pH, and in NaCl solutions with a varying ionic strength. It is found that sorption of Cs(+) does not depend practically on the amount of SiO(2) present, whereas the Sr(2+) uptake drastically decreases with an increase of silica amount. The effects of pH and of the electrolyte concentration on the sorption behavior of titanium phosphate are discussed in terms of ionic hydration shell and titanium phosphate structural specificity. The kinetics of sorption processes is also investigated, and the diffusion coefficients for cesium and strontium are obtained.

Solid-state NMR and EXAFS spectroscopic characterization of polycrystalline copper(I) O,O'-dialkyldithiophosphate cluster compounds: Formation of copper(I) O,O'-diisobutyldithiophosphate compounds on the surface of synthetic chalcocite.

A number of polycrystalline copper(I) O,O'-dialkyldithiophosphate cluster compounds with Cu4, Cu6, and Cu8 cores were synthesized and characterized by using extended X-ray absorption fine-structure (EXAFS) spectroscopy. The structural relationship of these compounds is discussed. The polycrystalline copper(I) O,O'-diisobutyldithiophosphate cluster compounds, [Cu8{S2P(OiBu)2}6(S)] and [Cu6{S2P(OiBu)2}6], were also characterized by using 31P CP/MAS NMR (CP = cross polarization, MAS = magic-angle spinning) and static 65Cu NMR spectroscopies (at different magnetic fields) and powder X-ray diffraction (XRD) analysis. Comparative analyses of the 31P chemical-shift tensor, and the 65Cu chemical shift and quadrupolar-splitting parameters, estimated from the experimental NMR spectra of the polycrystalline copper(I) cluster compounds, are presented. The adsorption mechanism of the potassium O,O'-diisobutyldithiophosphate collector, K[S2P(OiBu)2], at the surface of synthetic chalcocite (Cu2S) was studied by means of solid-state 31P CP/MAS NMR spectroscopy and scanning electron microscopy (SEM). 31P NMR resonance lines from collector-treated chalcocite surfaces were assigned to a mixture of [Cu8{S2P(OiBu)2}6(S)] and [Cu6{S2P(OiBu)2}6] compounds.

Solid-state 31P CP/MAS and static 65Cu NMR characterization of polycrystalline copper(I) dialkyldithiophosphate clusters.

Polycrystalline tetra-nuclear Cu4[S2P(O-i-C3H7)2]4, hexa-nuclear Cu6[S2P(OC2H5)2]6, and octa-nuclear Cu8[S2P(O-i-C4H9)2]6(S) complexes were synthesized and analyzed by means of solid-state 31P CP/MAS and 65Cu static NMR spectroscopy. The symmetries of the electronic environments around each P-site were estimated from the 31P chemical shift anisotropy (CSA) parameters, Deltaaniso and eta. The 65Cu chemical shift and quadrupolar splitting parameters obtained from the experimental 65Cu NMR spectra of the polycrystalline Cu(I)-complexes are presented. A solid-state NMR approach for the elucidation of the stereochemistry of poly-nuclear Cu(I) dithiophosphate complexes, when the structural analysis of the systems by single-crystal X-ray diffraction is not readily available, is proposed.

Formation of {Cu6[S2P(OC2H5)2]6} on Cu2S surfaces from aqueous solutions of the KS2P(OC2H5)2 collector: scanning electron microscopy and solid-state 31P cross-polarization/magic angle spinning and static 65Cu NMR studies.

The interactions of synthetic chalcocite surfaces with diethyldithiophosphate, potassium salt, K[S2P(OC2H5)2], were studied by means of 31P cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy and scanning electron microscopy (SEM). To identify the species formed on the Cu2S surfaces, a polycrystalline {CuI6[S2P(OC2H5)2]6} cluster was synthesized and analyzed by SEM, powder X-ray diffraction techniques and solid-state 31P CP/MAS NMR and static 65Cu NMR spectroscopy. 31P chemical shift anisotropy (CSA) parameters, delta(cs) and eta(cs), were estimated and used for assigning the bridging type of diethyldithiophosphate ligands in the {CuI6[S2P(OC2H5)2]6} cluster. The latter data were compared to 31P CSA parameters estimated from the spinning sideband patterns in 31P NMR spectra of the collector-treated mineral surfaces: formation of polycrystalline {CuI6[S2P(OC2H5)2]6} on the Cu2S surfaces is suggested. The second-order quadrupolar line shape of 65Cu was simulated, and the NMR interaction parameters, CQ and etaQ, for the copper(I) diethyldithiophosphate cluster were obtained.