Photovoltaic properties of self-assembled monolayers of porphyrins and porphyrin-fullerene dyads on ITO and gold surfaces

A systematic series of ITO electrodes modified chemically with self-assembled monolayers (SAMs) of porphyrins and porphyrin-fullerene dyads have been designed to provide valuable insight into the development of artificial photosynthetic devices. First the ITO and gold electrodes modified chemically with SAMs of porphyrins with a spacer of the same number of atoms were prepared to compare the effects of energy transfer (EN) quenching of the porphyrin excited singlet states by the two electrodes. Less EN quenching was observed on the ITO electrode as compared to the EN quenching on the corresponding gold electrode, leading to remarkable enhancement of the photocurrent generation (ca. 280 times) in the porphyrin SAMs on the ITO electrode in the presence of the triethanolamine (TEA) used as a sacrificial electron donor. The porphyrin (H(2)P) was then linked with C(60) which can act as an electron acceptor to construct H(2)P-C(60) SAMs on the ITO surface in the presence of hexyl viologen (HV(2+)) used as an electron carrier in a three electrode system, denoted as ITO/H(2)P-C(60)/HV(2+)/Pt. The quantum yield of the photocurrent generation of the ITO/H(2)P-C(60)/HV(2+)/Pt system (6.4%) is 30 times larger than that of the corresponding system without C(60): ITO/H(2)P-ref/HV(2+)/Pt (0.21%). Such enhancement of photocurrent generation in the porphyrin-fullerene dyad system is ascribed to an efficient photoinduced ET from the porphyrin singlet excited state to the C(60) moiety as indicated by the fluorescence lifetime measurements and also by time-resolved transient absorption studies on the ITO systems. The surface structures of H(2)P and H(2)P-C(60) SAMs on ITO (H(2)P/ITO and H(2)P-C(60)/ITO) have been observed successfully in molecular resolution with atomic force microscopy for the first time.     

Vibrational structures in the photoelectron spectrum of formic acid

He I photoelectron spectra of formic acid and its deuterium substituted derivatives have been measured. The first, second and fifth bands of each molecule exhibit very fine vibrational structures. The characters of molecular orbitals from which the photoelectron bands originate are discussed by the use of results of vibrational analyses and molecular orbital calculations.     

The Effect of Ge, Ni, and Fe Doping on the Ga Activity in the CoGa B2 Phase

Gallium activity in the B2 (CsCl-type) phase of ternary Co–Ga–X (X = Ge, Ni, and Fe) alloys was measured by the EMF method with a stabilized zirconia solid electrolyte. The temperature range was 1050–1250 K and the concentrations of the added elements were 2–6 at-% Ge and Ni, and 1–3 at-% Fe. The reference electrodes were Fe,Fe_xO or Ga,Ga₂O₃. The effect on the activity of gallium in the B2 phase with the addition of other elements was found to be the largest with Ge and the smallest in the case of Ni.     

Layered assemblies composed of sulfonated cyclodextrin and poly(allylamine)

Layered assemblies containing cyclodextrin (CD) have been prepared by layer-by-layer deposition of poly(allylamine) and sulfonated α-CD or β-CD on a solid surface. A quartz crystal microbalance study revealed that α-CD and β-CD form multilayers in the films upon each deposition. The sulfonated-α-CD-containing film bound methyl orange (MO) by forming an inclusion complex, resulting in the isolation of MO as a monomer in the film, whereas MO formed aggregates in the sulfonated-β-CD and CD-free films.     

Electro- and photochemical properties of a (mu-alkoxo)bis(mu-carboxylato)diruthenium complex having two tetraphenylporphinato zinc(II) moieties

The novel (mu-alkoxo)bis(mu-carboxylato)diruthenium complex K[Ru(2)(dhpta)(mu-O(2)C-p-ZnTPP)(2)] 3 was prepared by simple ligand substitution reaction. Strong antiferromagnetic interaction between two Ru(III) ions of 3 was observed with a coupling constant of -425 approximately -404 cm(-1). The cyclic voltammogram of 3 can be explained in terms of superposition of those of ZnTPP-p-CO(2)H and K[Ru(2)(dhpta)(mu-O(2)CPh)(2)] 2, indicating no significant electrochemical interaction. The large conproportionation constant estimated from the reduction potentials for Ru(III)Ru(III) and Ru(II)Ru(III) indicates great stability of the mixed-valence state. The mixed-valence species [Ru(II)Ru(III)(dhpta)(mu-O(2)C-p-ZnTPP)(2)](2-) 4 was prepared by controlled potential electrolysis. The electronic absorption spectrum of 4 was quite similar to that of [Ru(II)Ru(III)(dhpta)(mu-O(2)CCH(3))(2)](2-) which is a typical Class II complex. The fluorescence from the S(2) state of the ZnTPP unit of 3 was significantly (78%) quenched. The electron transfer from the ZnTPP unit to Ru(III) ions in 3 is a plausible mechanism, even though energy transfer could not be ruled out completely. The free energy change for electron transfer, Delta G(CS), was estimated to be ca.-1.1 eV, which is similar to typical values for the reorganization energy lambda in polar solvents. Hence, the electron transfer scheme is situated almost at the top of the Marcus parabola, enabling ultrafast electron transfer.     

Absolute helical arrangement of sulfonamide in the crystal

[reaction: see text] 1,2-Bis(N-benzenesulfonyl-N-methylamino)benzene (2), which has no fixed asymmetric element, was crystallized from ethyl acetate as chiral crystals belonging to space group P4(1)2(1)2 (No. 92) or P4(3)2(1)2 (No. 96). The array of molecules built by the CH-pi interaction along the c-axis forms an enantiomeric helical superstructure in each individual crystal. The absolute configurations of the chiral crystals of 2 were determined by X-ray crystal structure analysis using the Flack parameter method. The solid-state CD spectra of the chiral crystals in KBr were mirror images. The equilibrium between the two enantiomers in solution is fast during crystallization at ambient temperature, and the energy barrier (DeltaG()) is estimated to be 11.7 +/- 0.3 kcal/mol (233 K).     

Reduction of isocyanates and carbodiimides via hydrosilylation

The hydrosilylation of isocyanates is promoted by palladium catalysts and affords N-silylformamides or C-silylamides. The orientation of the reaction depended upon the structure of isocyanates. The reaction of carbodiimides with silicon hydrides, catalyzed by PdCl₂ or (Ph₃P)₃RhCl, required higher temperatures to give N-silylformamidines. The adducts obtained in these reactions are precursors to formamides, formamidines, and their N-acetyl derivatives.     

Determination of phosphorus in silicate rocks by flow injection method of analysis

Summary A flow injection spectrophotometric method has been developed for the determination of phosphorus in silicate rocks. A rock solution is prepared by fusion with a mixture of lithium carbonate and boric acid and subsequent dissolution with l M hydrochloric acid. An aliquot of the sample solution is injected directly into the flow system, which consists of formation of heteropolyacids of molybdenum and antimony, reduction with ascorbic acid, and subsequent measurement of the absorbance of blue species. It permits semi-automated analysis of a variety of silicate rocks for phosphorus. Results obtained for standard rocks were in good agreement with the recommended values. The throughput comes out 20 samples per h.

---

Bestimmung des Phosphors in Silikatgestein durch Flie-Injektions-Analyse

Zusammenfassung Ein Verfahren zur spektrophotometrischen Phosphorbestimmung in Silikatgestein mittels Fließinjektion wurde entwickelt. Das Gestein wird mit einer Mischung aus Lithiumcarbonat und Borsäure aufgeschlossen und in 1 M Salzsäure gelöst. Ein aliquoter Teil der Lösung wird unmittelbar in das fließende System injiziert, worin Heteropolysäuren aus Molybdän und Antimon gebildet, mit Askorbinsäure reduziert und die Absorbanz der blauen Farbe gemessen wird. Dies ermöglicht die halbautomatische Analyse verschiedener Silikatgesteine zur Phosphorbestimmung. Die Resultate von Standardproben stimmen mit den vorgeschriebenen Werten gut überein. In der Stunde können 20 Proben durchgesetzt werden.

     

Novel 2-pyridone synthesis via nucleophilic addition of malonic esters to alkynyl imines

[reaction: see text] A novel 2-pyridone synthesis via nucleophilic addition of malonic esters to alkynyl imines has been developed. The reaction of dialkylalkyl sodiomalonates with alkynyl imines provided 2-pyridones in good to excellent yields.     

Synthesis of chiral oligopeptides by means of catalytic asymmetric hydrogenation of dehydropeptides

Asymmetric hydrogenations of Ac-ΔTyr(Ac)-(S)-Ala-Gly-OMe (6), Ac-ΔTyr(Ac)-(R)-AlaGly-(S)-Phe-OMe (7), Ac-ΔPhe-NH-CH(R) CH₂-OCH₂Ph (10), HCO-ΔPhe-(S)-Leu-OMe (16), X-AA-ΔPhe-AA'-OMe (5: X ^tBOC, CBZ, CF₃CO; AA, AA' = α-amino acid), and ^tBOC-AA-ΔPhe-AA'-NH-Y (21: Y=H, NH-AA'-ΔPhe-AA-^tBOC, NHPh), catalyzed by cationic Rh complexes, [L*Rh(NBD)]⁺ClO₄ (L* = chiral diphosphine), were performed to give the corresponding chiral oligopeptides with high stereoselectivities. It was found that the nature of the N-protecting group of dehydrotripeptides (5) exerted a significant influence on the asymmetric induction as well as catalyst efficiency. The chiral centers in AA' and AA' amino acid residues in 5 were also found to have some influence on the catalytic asymmetric induction. Possible mechanism which can accommodate these effects are discussed. Asymmetric reduction of RCOCO-AA-OMe (13) via hydrosilylation was carried out to give chiral depsipeptide units. The asymmetric hydrogenation of dehydropeptides was successfully applied to the synthesis of enkephalin analogs, Ac-(R)Tyr-(R) -Ala-Gly-(S)-Phe-(S)-Leu-OMe (23) and Ac-(S)Tyr-(R) -Ala-Gly-(S)-Phe-(S)- Leu-OMe (29)