Vectorial electron relay at ITO electrodes modified with self-assembled monolayers of ferrocene-porphyrin-fullerene triads and porphyrin-fullerene Dyads for molecular photovoltaic devices

Systematic series of indium tin oxide (ITO) electrodes modified covalently with self-assembled monolayers (SAMs) of ferrocene-porphyrin-fullerene triads and porphyrin-fullerene dyads were designed to gain valuable insight into the development of molecular photovoltaic devices. The structures of SAMs on ITO have been investigated by UV/Vis absorption spectroscopy, atomic force microscopy, and cyclic voltammetry. The photoelectrochemical and photophysical (fluorescence lifetime and time-resolved transient absorption) properties were also determined. The highest quantum yield of photocurrent generation (11 %) among donor-acceptor linked systems which are covalently attached to the surface of ITO electrodes was achieved with SAMs of ferrocene-zinc porphyrin-fullerene linked triad on ITO electrodes. The quantum yields of photocurrent generation correlate well with the charge-separation efficiency and the lifetime of the charge-separated state of the porphyrin-fullerene linked systems in solution. These results provide valuable information for the construction of photonic molecular devices and artificial photosynthetic systems on ITO electrodes.     

Hydroxyapatite-supported palladium nanoclusters: a highly active heterogeneous catalyst for selective oxidation of alcohols by use of molecular oxygen

Treatment of a stoichiometric hydroxyapatite (HAP), Ca10(PO4)6(OH)2, with PdCl2(PhCN)2 gives a new type of palladium-grafted hydroxyapatite. Analysis by means of powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray (EDX), IR, and Pd K-edge X-ray absorption fine structure (XAFS) proves that a monomeric PdCl2 species is chemisorbed on the HAP surface, which is readily transformed into Pd nanoclusters with a narrow size distribution in the presence of alcohol. Nanoclustered Pd0 species can effectively promote the alcohol oxidation under an atmospheric O2 pressure, giving a remarkably high turnover number (TON) of up to 236,000 with an excellent turnover frequency (TOF) of approximately 9800 h(-1) for a 250-mmol-scale oxidation of 1-phenylethanol under solvent-free conditions. In addition to advantages such as a simple workup procedure and the ability to recycle the catalyst, the present Pd catalyst does not require additives to complete the catalytic cycle. The diameters of the generated Pd nanoclusters can be controlled upon acting on the alcohol substrates used. Oxidation of alcohols is proposed to occur primarily on low-coordination sites within a regular arrangement of the Pd nanocluster by performing calculations on the palladium crystallites.     

Hydrogen bonding effect on photocurrent generation in porphyrin-fullerene photoelectrochemical devices

A hydrogen bonding effect on photocurrent generation has been evaluated successfully in a mixed film of porphyrin and fullerene with hydrogen bonding on an ITO electrode, which exhibits efficient cathodic photocurrent generation as compared to the reference system without hydrogen bonding.     

A solution to a spectral poset problem of Lewis and Ohm

We show that there is a 1-dimensional (countable) non-spectral poset X such that for all x≠y∈X, ↑x∩↑y and ↓x∩↓y are finite subsets. On the other hand, we obtain some sufficient conditions for posets to be spectral.     

Photoswitching of single association force between a pair of photoionizable spirobenzopyrans

We have measured the single intermolecular force of a typical photoionizable molecule, spirobenzopyran, by means of atomic force microscopy, which has proven to be useful in measuring directly single molecular forces. The spirobenzopyran moiety was immobilized covalently on both Au-coated probe tips and substrates by use of a self-assembled monolayer of a hexanethiol derivative incorporating a terminal spirobenzopyran moiety, 1'-(6'-mercaptohexyl)-3',3'-dimethylindolino-6-nitrospiro-(2H-1-benzopyran-2,2'-indoline). Force curve measurements were carried out using the spirobenzopyran-modified probe tip and substrate under dark conditions and in situ UV light irradiation. The adhesion force observed in a polar solvent (i.e., ethanol) was increased substantially under in situ UV light irradiation, which caused photoisomerization of the spirobenzopyran moiety bound to both tip and substrate from its electrically neutral spiropyran form to the corresponding zwitterionic merocyanine one. Statistical analyses of the observed force by autocorrelation technique have revealed that the photoionization enhanced by UV light caused a remarkable increase in the single intermolecular force of the photochromic compound.     

Creation of a chain-like cationic iron species in montmorillonite as a highly active heterogeneous catalyst for alkane oxygenations using hydrogen peroxide

A chain-like Fe3+ species containing an Fe-O-Fe unit has been prepared within the interlayer space of a montmorillonite, which showed a very high catalytic activity (turnover frequency 386 h-1 and turnover number 23,200) for the oxidation of cyclohexane with H2O2, affording cyclohexyl hydroperoxide as a major product.     

Diastereoselective protonation on radical anions of electron-deficient alkenes via photoinduced electron transfer

Diastereoselective protonations in the photoinduced electron transfer (PET) reactions of 1,1-dicyanoethene derivatives (1a-e) by use of organosilicon compounds such as allyltrimethylsilane (2) and benzyltrimethylsilane (5) are described. Irradiation of an acetonitrile-acetic acid solution containing 4-tert-butylcyclohexylidenepropanedinitrile (1a) and an excess of 2 in the presence of phenanthrene (Phen) as a sensitizer afforded reduction and allylated products (3a, 4a) in 63:37 and 57:43 ratios in a less regioselective manner. Photoreactions of 3,3,5-trimethylcyclohexylidenepropanedinitrile (1b), 2-methylcyclohexylidenepropanedinitrile (1c), bicyclo[2.2.1]-2-heptylidenepropanedinitrile (1d), and 1,7,7-trimethylbicyclo[2.2.1]-2-heptylidenepropanedinitrile (1e) with 2 showed higher diastereoselectivity via the PET process. Similar diastereoselectivities were obtained in the Phen-sensitized photoreaction of 1a-e with 5. When 2,4,6-trimethylpyridinium tosylate (7) was used as a proton source in place of acetic acid, the product ratios were substantially changed in several cases. From these results, steric and torsional effects have been postulated as important factors for the control of the diastereoselectivity in these PET reactions.     

Chemistry of renieramycins. Part 4.synthesis of a simple natural marine product, 6-hydroxy-7-methoxyisoquinolinemethanol

6-Hydroxy-7-methoxyisoquinolinemethanol (15) and mimosamycin (1) were recently isolated from a marine sponge, Haliclona sp. The former was prepared in ten steps from vanillin (22) in 26% overall yield using an isopropyl for phenol protection.