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The synergistic effect of five 8-quinolinol derivatives (HQs) on the extraction of gallium(III) with di(2-ethylhexyl)-phosphoric acid (D2EHPA or HA) from weak nitric acid into supercritical carbon dioxide (SC-CO(2)) was investigated. 8-Quinolinol (Hq), 5-ethoxymethyl-8-quinolinol (HO(2)q), 5-hexyloxymethyl-8-quinolinol (HO(6)q), 5-(2,2,2-trifluoroethoxymethyl)-8-quinolinol (HFO(2)q), and 5-chloro-8-quinolinol (5-Cl-Hq) were used as synergists. Synergism was observed for all of the HQs. The synergistic effect increased in the following order: Hq < HO(2)q < HFO(2)q < 5-Cl-Hq ≍ HO(6)q. The extent of synergism can be related to both the distribution constant and the acid dissociation constant of the HQ. The synergistic extraction equilibrium of gallium(III) with D2EHPA and 5-Cl-Hq into SC-CO(2) was investigated; the results suggest that the composition of the extracted complex is as GaA(2)Q·HA. The synergistic extraction mechanism was the same for both SC-CO(2) and n-heptane. The synergistic extraction equilibrium constants in both cases were calculated based on the experimental results.

The solubilities of several cobalt(III) chelates (CoL3) with in supercritical carbon dioxide (SC-CO2) were investigated in the presence of fluorine- and trifluoromethyl-substituted phenols (PhOH) using UV–vis spectrophotometry. Solubility enhancement of CoL3 complexes in SC-CO2 was accomplished by adding PhOH. The association constants for tris(pentane-2,4-dionato)cobalt(III) (Co(acac)3) with various PhOH in SC-CO2 were determined from the relationship between the solubility enhancement and the PhOH concentration for each corresponding phenol. For compounds with no fluorine or trifluoromethyl groups in the ortho position, the association constants decreased as the pKa values of the PhOH compounds increased. In addition, the association constants for the PhOH compounds bearing a fluorine or trifluoromethyl group in the ortho position were less than the values expected based on their pKa values. These results are ascribed to the occurrence of the steric hindrance of the ortho-fluorine or trifluoromethyl group. Furthermore, the association constants for various CoL3 complexes and 3,5-bis(trifluoromethyl)phenol (BTMP) increased as the basicity of the chelating ligand increased. Finally, the thermodynamic parameters and the numbers of CO2 molecules released upon association of Co(acac)3 and BTMP were calculated using data for the dependence of the association constant on the pressure and temperature.

A polymer microchannel chip with a symmetrical or unsymmetrical zigzag-side-walled structure was fabricated by an imprinting method, and applied to study shape effects on solution flow characteristics as well as on the liquid/liquid extraction efficiency of an aluminium(III) chelate complex (Al-DHAB: DHAB = o,o'-dihydroxyazobenzene) in a microchannel chip. In an unsymmetrical zigzag-side-walled channel chip (us-channel), an oil/water interface was sinusoidal, while that in a symmetrical zigzag-side-walled channel chip (s-channel) was flat as long as the observation was made under an optical microscope. It was demonstrated that the efficiency of the water-to-oil (1-butanol) extraction of Al-DHAB in the microchannel was governed by the contact time between the two phases. As the most important results, furthermore, the extraction efficiency was higher in the us-channel, as compared with that in the s-channel, owing to the sinusoidal liquid/liquid interfacial structure and, therefore, to the high interfacial area between the two phases.

A CS4−:(RuB32+)2 hybrid complex as a new class of a chemosensor was prepared by an ion-exchange reaction, where CS4− and RuB32+ were calix[4]arenetetrasulfonate and a tris(2,2′-bipyridine)ruthenium(II) dication, respectively. In the solid state, one RuB32+ was shown to bury partly in the cavity of CS4− from the upper rim, while other RuB32+ sits near the CS4−:RuB32+ ion-pair to balance the total electric charge of the hybrid. In methanol, on the other hand, two RuB32+ molecules in the hybrid complex located in the vicinity of a CS4− molecule at analogous microenvironments as suggested by 1 H -NMR. Spectroscopic and excited-state properties of RuB32+ in the hybrid were influenced by CS4− through the ion-excited dipole interaction and photoinduced electron transfer quenching. In the presence of a foreign cation as a guest, the emission intensity and lifetime of RuB32+ increased, demonstrating that CS4−:(RuB32+)2 hybrid complex acted as a luminescent chemosensor. The mechanism of ion recognition was discussed in terms of changes in the photophysical properties of the hybrid complex.

Ru(bpy)2(CE-bpy)2+ was prepared where bpy and CE-bpy were 2,2'-bipyridine and bpy having a crown-ether moiety at the 3,3'-positions, respectively. Although Ru(bpy)2(CE-bpy)2+ showed only very weak emission in acetonitrile, recognition of Na+, Li+, or K+ by the crown-ether moiety in CE-bpy resulted in increases in both the emission intensity and the lifetime of the complex, demonstrating that it acted as a photoreceptor. The results were discussed in terms of a steric hindrance between the 3,3'-substituents on CE-bpy and structural changes in both CE-bpy and the complex upon ion recognition, as studied by variable-temperature 1H-NMR and steady-state/dynamic emission spectroscopy of the complex.

A series of the octahedral hexarhenium(III) complexes containing a variable number of diphosphine (diphos) or diphosphine-monoxide (diphosO) ligands have been prepared by the substitution of the diphosphine Ph2P(CH2)nPPh2 (n = 1 to 5) for the iodide ions in the parent octahedral hexarhenium cluster compound [Re6Se8I6]3-. The diphosphine Ph2P-(CH2)nPPh2 ligands adopt an eta1-bonding mode with the Re6(mu3-Se)8 core, and the P donor atom in the pendant arm is noncoordinated and oxygenated in most cases. The series of new hexarhenium(III) complexes have been well-defined by 1H, 13C, and 31P NMR spectroscopic and FAB-MS data. Four compounds among the series were characterized by X-ray structural determination. Geometrical isomers were identified by NMR spectroscopy as well as by the structural determinations. The apical ligand substitution induces significant change in the redox potentials and the photophysical properties of the Re6(mu3-Se), core. The E1/2 value of the reversible process ReIII6/ReIII5ReIV becomes more positive with the increasing number of the coordinated P donors. The phosphine-substituted hexarhenium(III) derivatives are highly luminescent, with microsecond scale emissive lifetime at ambient temperature, and the fully substituted derivatives with the formula [Re6Se8-(eta1-diphosO)6]2+ display the strongest luminescence with the longest emission lifetimes.

We explored optical trapping-spectrophotometry of ion-exchange polymer microparticles in water and, determined the dye (tris(2, 2′-bipyridine)ruthenium(II) complex; Ru2+) concentration adsorbed on an individual particle (diameter (d)=20-140μm). The absorbance of Ru2+ on the particle increased with an increase of the dye concentration in the aqueous phase, while it was essentially independent of d. The results indicate that adsorption of the complex takes place in the surface layer of the particle, but not homogeneously in the entire particle. A possible role of the optical trapping- spectrophotometry method in direct analyses of trace amounts of molecules concentrated on single microparticles in olution is discussed.

Polymer diffusion in latex films prepared from two pairs of poly(butyl methacrylate) (PBMA) latex particles is investigated. One set contains only a small amount of sulfate groups at the surface; the other contains a significant amount of carboxylic acid groups at the surface. Neutralization of these acid groups with ammonium, sodium, and barium hydroxide retards the interdiffusion rate at 100°C but does not suppress it. In these experiments, we employ pairs of particles identical in size, with very similar molecular weights, molecular weight distributions, and surface charge densities, that differ only in the fluorescent chromophore [phenanthrene (Phe) or anthracene (An)] used to label the polymer

A measuring method for the distribution behavior between supercritical carbon dioxide and water by a microchip was developed. A surface modification of the microchannel by dichlorodimethylsilane induced a spontaneous phase separation of the supercritical carbon dioxide and aqueous phases in the microchip. The maximum contact time of the aqueous phase to the supercritical carbon dioxide phase was obtained as 0.58 s. This device withstood pressure up to 12.8 MPa. The distribution of tris(acetylacetonato)cobalt(III) (Co(acac)(3)) from the supercritical carbon dioxide phase to the aqueous phase in a microchannel could be measured. The concentration of Co(acac)(3) distributed into the aqueous phase was increased by lengthening the contact time of both phases. These demonstrations showed that the method developed in this study could be used to measure the distribution behavior between supercritical carbon dioxide and water.

Spectral fitting was done on time- and temperature-dependent emission spectra of Ru(bpy){sub 3}{sup 2+} (bpy = 2,2{prime}-bipyridine) around the glass-to-fluid transition temperature of ethanol-methanol (4/1 v/v). With increasing time after excitation or with increasing temperature, the emission spectrum showed (i) a low-energy shift of the maximum, (ii) an increase in the intensity of the 0-1 vibrational band relative to that of the 0-0 band, and (iii) broadening the vibrational bands. These changes in the spectrum were ascribed to dynamic solvation change, leading to stabilization of the metal-to-ligand charge-transfer (MLCT) excited state and an increase in distortion between the ground and excited states. The time-dependent emission shift is accompanied by time-dependent nonradiative decay from the MLCT excited state.

Ru(bpy)2(CE-bpy)2+ was prepared where bpy and CE-bpy were 2,2′-bipyridine and bpy having a crown-ether moiety at the 3,3′ positions, respectively. Although the Ru(II) complex showed only very weak ...

The pressure (P = 0.06-1.1 GPa) and temperature (T = 100-200 K) dependence of the emission spectrum and lifetime of Ru(bpy){sub 3}{sup 2+} (bpy = 2,2{prime}-bipyridine) was studied in ethanol-methanol (4/1, v/v) by means of nanosecond time-resolved emission spectroscopy. In contrast to a pressure-induced lower energy shift of the emission spectrum at room temperature, application of pressure brings about a distinct sharpening and a higher energy shift of the spectrum at low temperature (100-200 K). The phenomena observed with increasing P were quite analogous to the spectral changes upon cooling at a fixed pressure. Both P and T effects on the emission characteristics are explained by the variation of solvent viscosity. A time-dependent lower energy shift of the emission was observed in the T regions between 100 and 200 K depending on P while it was observed in a narrow T region between 115 and 150 K at atmospheric pressure. Although the emission lifetime of Ru(bpy){sub 3}{sup 2+} increases sharply upon cooling, the lifetime was found to be almost independent of P up to {approx} 1 GPa (100-160 K). The energy and band shapes of the emission spectrum of Ru(bpy){sub 3}{sup 2+} are exclusively determined by viscosity-dependent solvent relaxation while more » the lifetime is governed by deactivation processes involving the upper lying metal-to-ligand charge-transfer (MLCT) excited state(s) and therefore directly by T. The important role of viscosity-dependent solvent relaxation in the MLCT excited state is also discussed. « less

Oxidative quenching of *Ru(bpy){sub 3}{sup 2+} (bpy = 2,2{prime}-bipyridine) by neutral organic electron acceptors such as quinones, nitroaromatics, and aromatic esters in acetonitrile was studied in detail. The quenching exhibited an anomalous negative temperature dependence at {Delta}G{sub 23} (free energy change of an electron-transfer step, k{sub 23}) > {minus}3 kcal/mol, which accompanied large and negative activation entropies ({minus}18 to {minus}44 eu). The abnormal behavior was explained satisfactorily by the large contribution of back electron transfer regenerating the excited-state reactants (k{sub 32}). In a narrow {Delta}G{sub 23} region between {minus}2 and 0 kcal/mol, a bell-shaped Eyring plot was observed for several quenchers. The activation parameters for the forward (k{sub 23}) and backward (k{sub 32}) electron-transfer processes were determined on the basis of the bell-shaped Eyring plot and the standard enthalpy and entropy changes of the process. Although the temperature dependence of the quenching is anomalous, the activation parameters for the elementary process, k{sub 23} or k{sub 32}, are quite normal. The mechanism of the quenching was discussed on the basis of the rate constant as well as of the activation parameters relevant to k{sub 23}, k{sub 32}, and k{sub 30} (deactivation from the product ion pairs).

Time-resolved emission spectroscopy of Ru(bpy)/sub 3/Cl/sub 2/ and cis-Ru(bpy)/sub 2/(CN)/sub 2/, where bpy is 2,2'-bipyridine, was conducted in an ethanol-methanol mixture above 80 K. The emission spectra of both complexes shifted to the red with increasing temperatures (>80 K) as well as with the delay time after excitation (110-150 K). The apparent activation energies for the time-dependent red shift of the emission (110-130 K) were calculated to be 570 and 1360 cm/sup -1/ for Ru(bpy)/sub 3/Cl/sub 2/ and cis-Ru(bpy)/sub 2/(CN)/sub 2/, respectively. It was concluded that charge localization in the excited state was not an intrinsic property of the complex but was induced by solvent relaxation processes. 17 references, 4 figures, 1 table.

An anomalous temperature dependence of the rates was observed for both reductive and oxidative quenching of excited cis-dicyanobis(1,10-phenanthroline)ruthenium(II), *RuCN, by aromatic amines and nitroaromatics, respectively, in acetonitrile. The observed activation enthalpies and entropies were more positive than those observed for oxidative quenching of the excited Ru(bpy){sub 3}{sup 2+} (bpy = 2,2{prime}-bipyridine). The results were satisfactorily explained by the standard and/or electrostatic enthalpy and entropy changes of the electron-transfer step. Efficient back electron transfer from product ion pairs to the excited-state reactants in the redox quenching of *RuCN is ascribable to a favorable entropy change of the process as well as to electrostatic attraction within the ion pairs. The electrostatic interactions within the product ion pairs (repulsive or attractive) determine the overall quenching paths and, thus, the temperature dependence of the quenching.

The rate constants (k{sub q}) and activation parameters for reductive quenching of *Ru(bpy){sub 3}{sup 2+} (bpy = 2,2{prime}-bipyridine) by 19 aromatic amines were determined in acetonitrile. The activation enthalpies ({Delta}H{sub 23}{double dagger}) increased from +1 to +6 kcal/mol with decreasing k{sub q} while the activation entropies were almost constant around {minus}15 eu for all quenchers except for those of highly exoergic reactions. The mechanism of the reductive quenching is discussed on the basis of k{sub q} as well as of the activation parameters. The quenching was shown to depend on the nature of the aromatic amine; the quenching by tertiary amines was always faster than that by primary and secondary amines when k{sub q} are compared at the same free energy change. The results are explained by the variation of outer-sphere reorganization energy with the nature of a quencher. For the quenching by tertiary and primary/secondary amines, the radii of the quenchers (r{sub Q}{sup ex}) were estimated to be 3 and 2.4 {angstrom}, respectively, by analyzing free energy relationships of the activation free energy of the quenching. The difference in r{sub Q}{sup ex} between tertiary and primary or secondary amines (0.5-0.6 {angstrom}) was in good agreement with that between N,N-dimethylaminomore » and anilino groups estimated by the space-filling model (0.7 {angstrom}). The solvent reorganization around the amino group is more relevant than that around an aromatic ring or a whole molecule to the actual outer-sphere reorganization energy.« less

Electron transfer quenching reactions of excited tris(2,2'-bi-pyridine)ruthenium(II), *Ru(bpy)/sub 3//sup 2 +/, have received special attention as tests of Marcus theory as well as in their application to redox photosensitization. Nevertheless, the mechanism of oxidative quenching of *Ru(bpy)/sub 3//sup 2 +/ in acetonitrile, exhibiting negative temperature dependence in endoergic and moderately exoergic regions, is not explicitly understood. They now report the origin of the negative temperature dependence and the reaction mechanism of oxidative quenching of *Ru(bpy)/sub 3//sup 2 +/. The quenching rate constant (k/sub q/) at a given temperature was obtained by conventional Stern-Volmer plots based on both the emission intensity and the lifetime of *Ru(bpy)/sub 3//sup 2 +/. The effect of diffusion on the observed quenching rate constant was corrected.

The rates of both reductive and oxidative quenching of excited cis-dicyanobis(1,10-phenanthroline)ruthenium(II) by aromatic amines and nitroaromatics in acetonitrile (ionic strength = 0), respectively, exhibited a negative temperature dependence. Comparing the present results with those for Ru(bpy)/sub 3//sup 2 +/ (bpy = 2,2'-bipyridine), the authors concluded that the electrostatic interaction (repulsive or attractive) within product ion pairs decided the quenching mechanism and, consequently, the temperature dependence of the quenching.

Ruthenium(II) complexes are widely investigated electron transfer sensitizers (Kalyanasundaram 1982). The main reasons are ; i) the appropriate oxidation and reduction potentials, ii) the long excited state lifetime, iii) the negligible photoanation, and iv) the handy wavelength of photoabsorption. While the factors determining the properties mentioned above are in principle determined by energy levels of various electronic states and interactions between any two energy levels (i.e., transition moment, overlap, and coupling which decide absorption and radiative/nonradiative processes), the photophysics of Ru(II) complexes is not yet fully understood. The major parameters to determine the electronic state is certainly the nature of ligands. In the past, we synthesized a series of Ru(II) complexes with various diazadiimine ligands and showed that the redox potentials in the ground and excited states, the wavelength of absorption and emission, and the excited state lifetime could be altered (Kitamura 1983a, 1983b; Kawanishi 1984; Tazuke 1985). While the redox potentials and the absorption and emission energies were correlated with ligand properties, the dynamics of the relaxation from the excited state was puzzling.

Energy migration among chromophores of identical nature is one of the simplest but most fundamental photophysical processes in particular in molecular aggregate systems. Nevertheless, its quantitative rate analysis has not been reported until very recently. The energy transfer process involving either the singlet or triplet state is highly relevant to material science, photoreactions, and expected photonic devices. In the last case, the controlled one-dimensional flow of energy and/or electrons is a key process, which has hardly been surveyed. To test the possibility, we chose X{sub 4}(Pt{sub 2}(P{sub 2}O{sub 5}H{sub 2}){sub 4}) (X = Na{sup +}, K{sup +}, Et{sub 4}N{sup +}, and (n-Bu){sub 4}N{sup +}) crystals and measured the laser-induced phosphorescence.