Photophysical and (photo)electrochemical properties of a coumarin dye

A new coumarin dye, cyano-{5,5-dimethyl-3-[2-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen-9-yl)vinyl]cyclohex-2-enylidene}-acetic acid (NKX-2753), was prepared and characterized with respect to photophysical and electrochemical properties. It was employed as a dye sensitizer in dye-sensitized solar cells and showed efficient photon-to-electron conversion properties. The photocurrent action spectrum exhibited a broad feature with a maximum incident photon-to-electron conversion efficiency (IPCE) of 84% at 540 nm, which is comparable to that for the famous red dye RuL2(NCS)2 (known as N3), where L stands for 2,2'-bipyridyl-4,4'-dicarboxylic acid. The sandwich-type solar cell with NKX-2753, under illumination of full sun (AM1.5, 100 mW cm(-2)), produced 16.1 mA cm(-2) of short-circuit photocurrent, 0.60 V of open-circuit photovoltage, and 0.69 of fill factor, corresponding to 6.7% of overall energy conversion efficiency using 0.1 M LiI, 0.05 M I2, 0.1 M guanidinium thiocyanate, and 0.6 M 1,2-dimethyl-3-n-propyl-imidazolium iodide in dry acetonitrile as redox electrolyte. In comparison with its analogue NKX-2586 (Langmuir 2004, 20, 4205), NKX-2753 with an extra side ring on the alkene chain produced much higher IPCE values at the same conditions. The side ring acted as a spacer to efficiently prevent dye aggregation when adsorbed on the TiO2 surface, resulting in significant improvements of short-circuit photocurrent, open-circuit photovoltage, and fill factor compared with NKX-2586 that aggregated on the TiO2 surface.     

Photoelectron and penning ionization electron spectroscopic investigation of trimethylsilyl- and t-butyl-thiophenes

Penning ionization electron spectroscopy and CNDO/S calculations have been successfully applied to the analyses of the UV photoelectron spectra of 2- and 2,5-bistrimethylsilylthiophene and 2-t-butylthiophene. The relative intensities of the π type bands are greatly enhanced in the Penning spectra compared with those of the UV photoelectron spectra.     

Synthesis and nanostructure of strong polyelectrolyte brushes in amphiphilic diblock copolymer monolayers on a water surface

We synthesized an ionic amphiphilic diblock copolymer, poly(hydrogenated isoprene)-b-poly(styrenesulfonic acid) (PIp-h2-b-PSS), by living anionic polymerization, and the nanostructure of its monolayer spread on a water surface was directly investigated by the in situ X-ray reflectivity technique. The monolayer of the diblock copolymer on a water surface had a smooth hydrophobic PIp-h2 layer on water and a "carpet"/polymer brush double layer in a hydrophilic sodium polystyrene sulfonate (PSSNa) layer under the water. The surface pressure dependence and PSSNa chain length dependence of the PIp-h2 layer thickness and the brush nanostructure were quantitatively studied. The effect of salt concentration in the subphase was also investigated in aqueous solutions containing 0-2 M NaCl. The salt effect on monolayer structure occurred at around 0.2 M. The thickness of the PSS brush layer decreased at salt concentrations above 0.2 M, while no structural change was observed below 0.2 M. This critical salt concentration is thought to be related to the balance of ionic concentrations inside the brush and in bulk solution.     

Triethylborane-mediated hydrogallation and hydroindation: novel access to organogalliums and organoindiums

Hydrogallation of carbon[bond]carbon multiple bonds proceeds in the presence of triethylborane as a radical initiator. Several functionalities do not interfere with this reaction. Resulting alkenyl- and alkylgallium species can be trapped by several electrophiles. Highly regioselective radical addition of an indium hydride reagent to alkynes is also achieved. Various functionalities are tolerant under the reaction conditions. The reaction proceeds with complete anti stereoselectivity. Alkenylindiums obtained via hydroindation can be employed for the following cross-coupling reaction with aryl halides in one pot.     

Self-crosslinkable polymers. I. Copolymerization of glycidyl methacrylate with 2-vinylpyridine and 2-vinyl-5-ethylpyridine

A soluble and self-crosslinkable linear copolymer with pendant epoxy and pyridyl groups was obtained from glycidyl methacrylate (M₁) and 2-vinylpyridine (M₂) or 2-vinyl-5-ethylpyridine (M₂) by the action of azobisisobutyronitrile. The monomer reactivity ratios were determined in tetrahydrofuran at 60°C: r₁ = 0.510, r₂ = 0.620 with 2-vinylpyridine and r₁ = 0.57, r₂ = 0.62 with 2-vinyl-5-ethylpyridine. These were consistent with the calculated values with the reported Q and e values for these monomers. The intrinsic viscosities of the copolymers with 2-vinylpyridine and with 2-vinyl-5-ethylpyridine were found to be 0.17–0.19 and 0.26–0.38, respectively, in tetrahydrofuran at 30°C; they were independent of the copolymer composition. The copolymers were amorphous, had no clear melting points, and became insoluble crosslinked polymers under heating without further addition of any curing agents.     

Effect of intramolecular pi-pi and CH-pi interactions between ligands on structure, electrochemical and spectroscopic properties of fac-[Re(bpy)(CO)3(PR3)]+(bpy = 2,2'-bipyridine; PR3= trialkyl or triarylphosphines)

Intramolecular pi-pi and CH-pi interactions between the bpy and PR3 ligands of fac-[Re(bpy)(CO)3(PR3)]+ affect their structure, and electrochemical and spectroscopic properties. Intramolecular CH-pi interaction was observed between the alkyl groups on the phosphine ligand (R =nBu, Et) and the bpy ligand, and intramolecular pi-pi and CH-pi interactions were both observed between the aryl group(s) on the phosphorus ligand (R =p-MeOPh, p-MePh, Ph, p-FPh, OPh) and the bpy ligand, while no such interactions were found in the trialkylphosphite complexes (R = OiPr, OEt, OMe). The intramolecular interactions distort the pyridine rings of the bpy ligand as long as 3.7 x 10(-2)A in crystals. Molecular orbital calculations of the bpy ligand suggest that this distortion decreases the energy gap between its pi and pi* orbitals. An absorption band attributed to the pi-pi*(bpy) transition of the distorted rhenium complexes, measured in a KBr pellet, was red-shifted by 1-5 nm compared to the complexes without the distorted bpy ligand. Even in solution, similar red shifts of the pi-pi*(bpy) absorption were observed. The redox potential E1/2(bpy/bpy*-) of the complexes with the trialkylphosphine and triarylphosphine ligand are shifted positively by 110-120 mV and 60-80 mV respectively, compared with those derived from the electron-attracting property of the phosphorus ligand. In contrast with these properties, three nu(CO) IR bands, which are sensitive to the electron density on the central rhenium because of pi-back bonding, were shifted to higher energy, and a Re(I/II)-based oxidation wave was observed at a more positive potential according to the electron-attracting property of the phosphorus ligand.     

Dioxo-molybdenum(VI) and mono-oxo-molybdenum(IV) complexes supported by new aliphatic dithiolene ligands: new models with weakened Mo=O bond characters for the arsenite oxidase active site

The cis-dioxo-molybdenum(VI) complexes, [MoO2(L(H))2]2- (1b), [MoO2(L(S))(2)]2- (2b), and [MoO2(L(O))2]2- (3b) (L(H) = cyclohexene-1,2-dithiolate, L(S) = 2,3-dihydro-2H-thiopyran-4,5-dithiolate, and L(O) = 2,3-dihydro-2H-pyran-4,5-dithiolate), with new aliphatic dithiolene ligands were prepared and investigated by infrared (IR) and UV-vis spectroscopic and electrochemical methods. The mono-oxo-molybdenum(IV) complexes, [MoO(L(H))2]2- (1a), [MoO(L(S))2]2- (2a), and [MoO(L(O))2]2- (3a), were further characterized by X-ray crystal structural determinations. The IR and resonance Raman spectroscopic studies suggested that these cis-dioxo molybdenum(VI) complexes (1b-3b) had weaker Mo=O bonds than the common Mo(VI)O2 complexes. Complexes 1b-3b also exhibited strong absorption bands in the visible regions assigned as charge-transfer bands from the dithiolene ligands to the cis-MoO2 cores. Because the oxygen atoms of the cis-Mo(VI)O2 cores are relatively nucleophilic, these complexes were unstable in protic solvents and protonation might occur to produce Mo(VI)O(OH), as observed with the oxidized state of arsenite oxidase.     

Chemistry of organosilicon compounds 118. Novel ring contraction reaction of (η4-1,2-disilacyclohexadiene)iron tricarbonyls

1,1,2,2-Dimethyl-3,6-diphenyl-1,2-disilacyclohexadiene reacts with iron pentacarbonyl or diiron nonacarbonyl to give the corresponding (diene)iron tricarbonyl complex which undergoes novel ring contraction reaction to (η⁴-1,1-dimethyl-2,5-diphenyl-1-silacyclopentadiene)iron tricarbonyl on thermolysis at 160°C. Similar results were observed with 1,1,2,2-tetramethyl-3,4,5,6-tetraphenyl-1,2-disilacyclohexadiene.     

Computer simulation study of metastable ice VII and amorphous phases obtained by its melting

Molecular dynamics simulations of metastable ice VII and cubic ice Ic are carried out in order to examine (1) the ability of commonly used water interaction potentials to reproduce the properties of ices, and (2) the possibility of generating low-density amorphous (LDA) structures by heating ice VII, which is known to transform to LDA at approximately 135 K at normal pressure [S. Klotz, J. M. Besson, G. Hamel, R. J. Nelmes, J. S. Loveday, and W. G. Marshall, Nature (London) 398, 681 (1999)]. We test four simple empirical interaction potentials of water: TIP4P [W. L. Jorgensen, J. Chandrasekhar, J. D. Madura, R. W. Impey, and M. L. Klein, J. Chem. Phys. 79, 926 (1983)], SPC/E [H. J. C. Berendsen, J. R. Grigera, and T. P. Straatsma, J. Phys. Chem. B 91, 6269 (1987)], TIP5P [M. W. Mahoney and W. L. Jorgensen, J. Chem. Phys. 112, 8910 (2000)], and ST2 [F. H. Stillinger and A. Rahman, J. Chem. Phys. 60, 1545 (1974)]. We have found that TIP5P ice VII melts at 210 K, TIP4P at 90 K, and SPC/E at 70 K. Only TIP5P water after transition has a structure similar to that of LDA. TIP4P and SPC/E have almost identical structures, dissimilar to any known water or amorphous phases, but upon heating both slowly evolve towards LDA-like structure. ST2 ice VII is remarkably stable up to 430 K. TIP4P and SPC/E predict correctly the cubic ice collapse into a high-density amorphous ice (HDA) at approximately 1 GPa whereas TIP5P remains stable up to approximately 5 GPa. The densities of the simulated ice phases differ significantly, depending on the potential used, and are generally higher than experimental values. The importance of proper treatment of long-range electrostatic interactions is also discussed.     

1H-NMR Relaxation of Water Molecules in the Aqueous Microcrystalline Cellulose Suspension Systems and Their Viscosity

An intensive study for aqueous microcrystalline cellulose (MCC) suspensions was carried out in view of the relationship between a viscosity and a 1H spin-spin relaxation time (T2) of water. An investigation was carried out for four suspension systems with the different particle size distributions. The proton mole ratio () of bound water against MCC particles and T2 of bound water (T2,b) were evaluated from the T2 values obtained by Carr-Purcell- Meiboom-Gill (C.P.M.G) method and those by solid echo method, respectively. As a result of these analyses, the T2,b value for the aqueous MCC suspension was evaluated as 5 × 10–3 s and it was found that the system having a larger tended to show a higher viscosity. By relating the above results to the observation of the suspensions by an optical microscope, it was concluded that a network formed by MCC particles plays an important role in generating a high viscosity of MCC suspension, and that an averaged mobility of water molecules is sensitively affected by the network structure.