Difference In Electronic States Research Articles

Effects of molecular structures on reduction properties of formyl groups in chlorophylls and pheophytins prepared from oxygenic photosynthetic organisms

Reduction of the 7-formyl groups in chlorophyll (Chl) b and its demetalated compound pheophytin (Phe) b was kinetically analyzed by using tert-butylamine–borane complex ( t-BuNH 2·BH 3), and was compared with that of the 3-formyl groups in Chl d and Phe d. Reduction kinetics of the 7-formyl group in Chl b was similar to that in Phe b in dichloromethane containing 5 mM t-BuNH 2·BH 3. Little difference of the reduction kinetics of the 7-formyl groups between Chl b and Phe b was in sharp contrast to the reduction kinetics of the 3-formyl groups in Chl d and Phe d: the 3-formyl group in Phe d was reduced 5.3-fold faster than that in Chl d. The 7-formyl groups in Chl b and Phe b were reduced more slowly than the 3-formyl groups in Chl d and Phe d, respectively. The difference of the reactivity between the 3- and 7-formyl groups was in line with 13C NMR measurements of chlorophyllous pigments, in which the chemical shifts of carbon atoms in the 7-formyl groups of Chl b and Phe b were high-field shifted compared with those in the 3-formyl groups of Chl d and Phe d, respectively. These indicate that the 7-formyl groups in chlorophyllous pigments were less reactive for reduction to the corresponding hydroxymethyl groups than the 3-formyl groups due to the difference in electronic states of the formyl groups in the A- and B-rings of the chlorin macrocycle.

In Situ Scanning Tunneling Microscopy Observation of Metal–Cluster Redox Interconversion and CO Dissociation Reactions at a Solution/Au(111) Interface

Abstract We present here an in situ scanning tunneling microscopy (STM) study of potential-induced reactions of oxo-centered acetato-bridged triruthenium clusters on Au(111) under electrochemical conditions, in which (i) reversible interconversion between two different redox states of the cluster and (ii) spontaneous dissociation of CO from the cluster were probed and visualized. It is known that the triruthenium complex [Ru3(μ3-O)(μ-CH3COO)6(CO)(4-methylpyridine){(NC5H4)CH2NHC(O)(CH2)10S}] (1), which is in the mixed-valent {(RuII–CO)RuIIIRuIII} state, on Au(111) is one-electron oxidized to cationic complex 1+ which corresponds to a {(RuIII–CO)RuIIIRuIII} oxidation state. The redox reaction is reversible on a cyclic voltammetry timescale. Complex 1+ undergoes irreversible dissociation of CO in an aqueous phase on a longer timescale (ca. minutes) to form an aqua ligand-coordinated complex, 2+, which is expressed as {(RuIII–OH2)RuIIIRuIII}. The reversible redox reaction (11+) and the irreversible ligand substitution reaction (1+ → 2+) were independently examined with in situ STM in a monolayer level by visualizing molecular-sized spots showing a different extent of brightness in STM images. We show here that the molecular-sized spots corresponding to 1, 1+, and 2+ are resolved by their brightness, which strongly depends on both the oxidation states and the ligand nature of the clusters. By employing multiple fast scans at an applied potential of +0.80 V vs. Ag/AgCl, we obtained STM images that follow the irreversible 1+ → 2+ reaction on the surface, from which a rate constant of the CO release was calculated to be 1.9 (±0.2) × 10−2 s−1 (25 °C; in contact with 0.1 mol dm−3 aqueous HClO4 solution). The difference in brightness of the molecular spots is rationalized in terms of orbital-mediated tunneling by considering the difference in electronic states of the dπ–pπ system in the μ3-O triruthenium cluster.

Electronic Structure Analysis of Interface between Support Surface and Cocatalyst for Water Splitting Layer Photocatalyst by DFT Method

Abstract The electronic structures of cocatalyst/photocatalyst interface (NiOx/K2La2Ti3O10) used for water splitting were investigated by the two-dimentional surface model DFT calculations. The difference in electronic states at the interface between the cocatalyst and photocatalyst was characterized in terms of the crystal faces of support photocatalyst. This result explains the difference in mobility of the photoexcited electron from the support photocatalyst to the cocatalyst between two different crystal surfaces of photocatalyst.

Electronic states and persistent current of nanographite ring

We present the electronic states and persistent current of nanographite ring based on the nearest-neighbor tight-binding model under periodic or Möbius boundary conditions. It is found that the parity of transverse mode and edge structures are decisive to determine the electronic spectrum of nanographite ring under the Möbius boundary condition. The electronic states Möbius strip with zigzag edges are derived in the same way as the free-electron case. However, the Möbius strip with armchair edges has loop quantization rule of wave vector due to the characteristics of their parity. The difference of electronic states between edge structures can crucially affect the behavior of the persistent current caused by Aharonov–Bohm magnetic flux passing through the nanographite ring. We also present some scaling properties concerning the persistent current and the zero-field susceptibility.

Imaging micropatterned organosilane self‐assembled monolayers on silicon by means of scanning electron microscopy and Kelvin probe force microscopy

AbstractField‐emission scanning electron microscopy (FE‐SEM) and surface potentiometry based on scanning probe microscopy, i.e. Kelvin probe force microscopy (KFM), have been applied to study microstructures consisting of organosilane self‐assembled monolayers (SAMs) terminated with ‐CH3 or ‐CF3 groups. Onto cleaned Si substrates covered with a thin oxide layer of 2 nm thick, SAMs were formed by chemical vapour deposition using n‐octadecyltrimethoxysilane (CH3(CH2)17Si(OCH3)3, ODS) or fluoroalkylsilane (CF3(CF2)7(CH2)2Si(OCH3)3, FAS) as a precursor. Through a photolithographic technique employing vacuum ultraviolet light at 172 nm, microstructures composed of ODS, FAS or both were fabricated. Micropatterns of the SAMs on SiO2/Si substrates were clearly imaged by FE‐SEM at an acceleration voltage of the electron beam below 1 kV, but image contrasts became faint with an increase in the acceleration voltage. At a voltage of 5 kV there was almost no detectable contrast. An FE‐SEM image of the ODS–FAS microstructure acquired at an acceleration voltage of 0.8 kV clearly demonstrated that the region covered with ODS was brighter and thus, emitted secondary electrons more efficiently than the region covered with FAS. Furthermore, as indicated in a KFM image, the region covered with FAS had a surface potential ∼180 mV lower than that of the region covered with ODS. The origin of these image contrasts between ODS‐ and FAS‐SAMs was the large difference in electronic states between ODS and FAS owing to the electron negativity of fluorine atoms. Copyright © 2003 John Wiley & Sons, Ltd.

Orbital-Degenerate Paramagnetic Metal Sr2MoO4: An Electronic Analogue to Sr2RuO4

We present the first systematic study on polycrystalline Sr2MoO4 as an electronic analogue to the spin-triplet superconductor Sr2RuO4. The Pauli paramagnetic susceptibility and metallic behaviors of specific heat and electrical resistivity have been observed. The density of states at the Fermi level D(EF) deduced from the results is about three times smaller than that of Sr2RuO4. Any indication of superconductivity intrinsic to Sr2MoO4 has not been observed down to 25 mK, which may correspond to the smaller D(EF). We discuss the origin of the difference in electronic states between Sr2MoO4 and Sr2RuO4.

Photoinduced charge separation in photovoltaic cell with heterojunction of p- and n-type conjugated polymers

A poly(p-pyridyl vinylene) (PpyV)/poly(3-hexylthiophene) (P3HT) heterojuction photovoltaic cell was fabricated and its photoirradiation effects have been investigated. Quenching of photoluminescence both in the PPyV and P3HT layers has been observed in the PPyV/P3HT heterojunction film. The photovoltaic characteristics of the heterojunction photovoltaic cell are also greatly improved from those in a P3HT monolayer photovoltaic cell. Its photoresponse gives evidence of the photoinduced charge transfer between PPyV and P3HT. These results are discussed by taking account of the difference in electronic states of both PPyV and P3HT.

サイアロンセラミックスの均一性

The macroscopic inhomogeneity of Sialon ceramics was studied. There were two regions in the sintered body. One of regions was green region and the other was brown region. The fracture toughness of the sintered body with two regions had large difference, and the green region had low toughness. The regions were analyzed by UV spectroscopy, EPMA, XRD, SEM, and TEM. There was no difference in microstructure, but there was difference in electronic state, chemical composition, and crystal phase. From these fact, it is considered that the origin of macroscopic inhomogeneity is due to gas generated from decomposition of Sialon. The gas is shut in sintered body when densification is fast at surface, and the chemical composition of grain boundary or grain is changed by reaction with gas.