Synthesis,crystal structure and charge transport characteristics of stable peri-tetracene analogues

peri-Acenes have shown great potential for use as functional materials because of their open-shell singlet biradical character. However, only a limited number of peri-acene derivatives larger than peri-tetracene have been synthesized to date, presumably owing to the low stability of the target compounds in addition to the complicated synthesis scheme. Here, a very simple synthesis route for the tetrabenzo[a,f,j,o]perylene (TBP) structure enables the development of highly stable peri-tetracene analogues. Despite a high degree of singlet biradical character, the compounds with four substituents at the zigzag edge show a remarkable stability in solution under ambient conditions, which is better than that of acene derivatives with a closed-shell electronic configuration. The crystal structures of the TBP derivatives were obtained for the first time; these are valuable to understand the relationship between the structure and biradical character of peri-acenes. The application of peri-acenes in electronic devices should also be investigated. Therefore, the semiconducting properties of the TBP derivative were investigated by fabricating the field-effect transistors.

Highly stable peri-tetracene analogues with a high degree of singlet biradical character were synthesized in a very simple route, and their crystal structures and semiconducting properties were investigated.     

A mediator-type biosensor as a new approach to biochemical oxygen demand estimation

A novel biosensor for the determination of biochemical oxygen demand (BOD) was developed using potassium hexacyanoferrate(III) [HCF(III)] as a mediator. The sensor element consists of a three-electrode system, with both working and counter electrodes compactly integrated as a disposable using etching and electroplating processes. Pseudomonas fluorescens biovar V (isolated from a wastewater treatment plant) was immobilized on the surface of the working electrode using poly(vinyl alcohol)-quaternized stilbazol (PVA-SbQ) photopolymer gel. Synthetic wastewater described by the Organization for Economic Cooperation and Development (OECD) was used as a standard solution instead of glucose-glutamic acid synthetic wastewater. The conditions of amperometric measurement were optimized at +600 mV (vs. Ag/AgCl) operating potential, namely 40 mM HCF(III) in a 0.1 M phosphate buffer (pH 7.0) at 20 degrees C. The sensor response was linear from 15 up to 200 mg O l-1 BOD. The response time was 15 min at 200 mg O l-1 BOD. To demonstrate the wide metabolic range of activity of the sensor, the sensor response to 14 substances in four categories of organic compounds was investigated. Further, it was shown that the response of this BOD sensor was not influenced in samples with low concentrations of dissolved oxygen under the measuring conditions used. For real wastewaters, the BOD values were determined using the sensor and compared favorably with those determined by the conventional BOD5 method.     

Synthesis and inversion barriers of undeca- and dodeca-substituted saddle shaped porphyrin complexes

Synthesis and barriers to inversion of a series of highly saddle shaped complexes are reported. The ΔG^≠ has decreased by 8 kJ mol⁻¹ at 243 K when the meso phenyl groups are replaced by bulkier 2,6-dichlorophenyl groups, and by 17 kJ mol⁻¹ when one of the peripheral ethyl groups is removed.     

NMR studies of phosphinenickel(0) complexes of ethyl methacrylate Ni(PR3)2(CH2=C(CH3)COOC2H5)

¹³C NMR data are given for a series of phosphinenickel(0) complexes of ethyl methacrylate (ema), Ni(PR₃)₂(CH₂=C(CH₃)COOC₂H₅) (PR₃ = PPh₃ (Ia), PEtPh₂ (Ib), PEt₂Ph (Ic), PMe₂Ph (Id), PEt₃ (Ie)). The olefinic carbon signals of ema shift upfield by 71.5–86.5 ppm on coordination, the magnitude of the upfield shift increasing with increase in the bacisity of the phosphine ligand. The effect of the basicity of PR₃ is discussed on the basis of the back-bonding from Ni to ema. Variable temperature¹H NMR studies reveal that the ema of Id, the complex having the least sterically demanding phosphine ligands, exchanges with free ema in toluene on the NMR time scale. The dependence of the rate of exchange on the concentration of ema shows that the exchange proceeds through anS_N2 mechanism. The activation parameters are: ΔH₂₇₃^≠ 2.75 kcal/mol, ΔG₂₇₃^≠ 12.7 kcal/mol, ΔS₂₇₃^≠ ?37 e.u. The³¹P NMR spectra of the complexes show two doublets when the exchange is frozen out, indicating the inequivalence of the two phosphine ligands in the ema-coordinated complex. The difference in the³¹P chemical shifts of the two coordinated tertiary phosphines increases with increase in the basicity of the PR₃ ligand.     

Low energy asymptotics for Schrödinger operators with slowly decreasing potentials

Low energy behavior of Schrödinger operators with potentials which decay slowly at infinity is studied. It is shown that if the potential is positive then the zero energy is very regular and the resolvent is smooth near 0. This implies rapid local decay for the solutions of the Schrödinger equation. On the other hand, if the potential is negative then the resolvent has discontinuity at zero energy. Thus one cannot expect local decay faster than ordert ^–1 ast.     

Signals for scalar top quark atep collider HERA

In the framework of the minimal supersymmetric standard model (MSSM) and theR-parity breaking model (RBM), we investigate production processes of the scalar top (stop) at HERA energies. These models are characterized by the possible existence of the light stop whose mass is lighter than those of the top quark and the other squarks. It is shown that in the MSSM the stop pair production via boson-gluon fusion gives a sizeable cross section and the most serious background $ep \to ec\bar cX$ could be suppressed by appropriate kinematical cuts. We also show that in the RBM the stop is singly produced in the neutral current processes and we have a clear signal as a sharp peak in the Bjorken parameterx distribution of the scattered electron.     

Mössbauer spectroscopic study of ferrocene derivatives in the adsorption and liquid-crystalline states

Mössbauer spectra of ferrocene derivatives in the solid, adsorption and liquidcrystalline states were measured at temperatures ranging from 78 to 423 K. The peak intensities of the Mössbauer spectra of ferrocene derivatives adsorbed on silica gel decreased markedly with an increase in temperature. The Mössbauer absorption of [4-(4-methoxyphenoxycarbonyl)-phenoxycarbonyl]alkyl 4-ferrocenylbenzoate at 295 K during the cooling process was observed in what was assumed to be the liquid-crystalline state.