Green’s Functions of Partial Differential Equations with Involutions

In this paper we develop a way of obtaining Green''s functions of partial differential equations with linear involutions by reducing the equation to a higher-order PDE without involutions. The developed theory is applied to a model of heat transfer in a conducting plate which is bent in half.     

Effects of substituents on aryl groups during the reaction of triarylphosphine radical cation and oxygen

In a previous report (S. Yasui, S. Tojo and T. Majima, J. Org. Chem., 2005, 70, 1276), we presented the results from the laser flash photolysis (LFP) and product analysis of the 9,10-dicyanoanthracene (DCA)-photosensitized oxidation of triarylphosphine (Ar(3)P) in acetonitrile under air, which showed that the photoreaction results in the oxidation of Ar(3)P to give the corresponding phosphine oxide (Ar(3)P=O) in a nearly quantitative yield, and that the reaction is initiated by the electron transfer (ET) from Ar(3)P to DCA in the singlet excited state ((1)DCA*), producing the triarylphosphine radical cation Ar(3)P (+). This radical cation decays through radical coupling with O(2) to afford the peroxy radical cation Ar(3)P(+)-O-O*, which we proposed to be the intermediate leading to the product Ar(3)P=O. We now examined this photoreaction in more detail using ten kinds of Ar(3)P with various electronic and steric characteristics. The decay rate of Ar(3)P*(+) measured by the LFP was only slightly affected by the substituents on the aryl groups of Ar(3)P. During the photolysis of trimesitylphosphine (Mes(3)P), the peroxy radical cation intermediate (Mes(3)P(+)-O-O*) had a lifetime long enough to be spectrophotometrically detected. The quantum yields of Ar(3)P=O increased with either electron-withdrawing or -releasing substituents on the aryl groups, suggesting that a radical center is developed on the phosphorus atom during the step when the quantum yield is determined. In addition, the o-methyl substituents in Ar(3)P decreased the quantum yield. These results clearly indicated that Ar(3)P(+)-O-O* undergoes radical attack upon the parent phosphine Ar(3)P that eventually produces the final product, Ar(3)P=O.     

Naphthalene in the higher triplet excited state

Naphthalene in the higher triplet excited state Np(Tn) was generated from the two-step excitation method using two-colour two-laser flash photolysis technique and the lifetime of Np(Tn) was estimated to be 4.5 ps from the triplet energy quenching by quenchers such as p-dichlorobenzene, o-dicyanobenzene and carbon tetrachloride.     

Formation of the dimer radical cation of aromatic sulfide on the TiO2 surface during photocatalytic reactions

The formation of the dimer radical cation (D*+) of 4-(methylthio) benzoic acid on a TiO2 surface is demonstrated using the time-resolved diffuse reflectance technique. The observed time-resolved diffuse reflectance spectral shape significantly depends on the substrate concentrations. The substrate concentration dependences of the initial transient signal intensity (%abs.(t=0)) and the amount of adsorbates (n(ad)) clearly suggest that the formation of D*+ is attributableto the high local substrate concentration on the TiO2 surface. The electronic influence of substituents on the formation of D*+ is also discussed.     

Structures and phase transitions in (K<Subscript>1-x</Subscript>Rb<Subscript>x</Subscript>)<Subscript>2</Subscript>SeO<Subscript>4</Subscript>

Summary The phase diagram of the mixed crystal (K_1-xRb_x)₂SeO₄ was determined by means of thermal analysis and neutron scattering experiments. The hexagonal to orthorhombic phase transition line exists for any x. The normal-incommensurate phase transition temperature decreases continuously with increasing Rb content. However, the incommensurate-commensurate phase transition was not observed except for K₂SeO₄. According to the clear softening of the Σ₂- Σ ₃ phonon branches and the finite frequency at 0 K for x>0.34, an existence of the hypothetical phase transition was confirmed.     

Photochemical synthesis of heteroatom-containing polycyclic aromatic compounds

Anthra[2,1-b]furan, anthra[2,1-b]benzo[d]furan, anthra[2,1-b]thiophene, anthra[1,2-b]thiophene, anthra[2,1-b]benzo[d]thiophene, anthra[2,1-b]pyrrole and naphtho[2,3-c]carbazole derivatives were synthesized in fairly good yields by a one-pot photocycloaddition reaction of 2,3-disubstituted 1,4-naphthoquinone with 1,1-diarylethylene. This is the first reported synthesis of these aromatic compounds.     

Anomalous fluorescence from the azaxanthone ketyl radical in the excited state

The time-resolved absorption and fluorescence spectra of the azaxanthone (AX) ketyl radical (AXH.) in the excited state (AXH.(Dn) (n = 1 or 2)) were observed during the nanosecond-picosecond two-color two-laser flash photolysis. AXH. showed dual fluorescence peaks at 460 and 645 nm, which were assigned to the D2 --> D0 and D1 --> D0 transitions, respectively. It was found that the lifetime of the D2 --> D0 fluorescence (1.0 ns) was longer than that of the D1 --> D0 fluorescence (0.4 ns). The fluorescent quantum yields of the D1 --> D0 and D2 --> D0 fluorescence were estimated to be 0.0008 +/- 0.0002 and 0.05 +/- 0.02, respectively. These anomalous emitting properties can be attributed to the pyridine ring in AX. AXH. is a new example of a neutral radical which violates Kasha's rule.     

Kinetics of weak distance-dependent hole transfer in DNA by adenine-hopping mechanism

The kinetics of hole transfer in DNA by adenine-hopping mechanism was investigated by the combined pulse radiolysis-laser flash photolysis method. The hole transfer from Ptz*+* to oxG across the (A)n-bridge preceded by the A-hopping mechanism and the weak distance-dependent hole transfer with the rates faster than 108 s-1 over the distance range of 7-22 A was demonstrated. In contrast, hole transfer from oxG*+ to Ptz followed the single-step super exchange mechanism. Thus, two different processes for the hole transfer across the identical (A)n-bridge in DNA have been demonstrated. The results clearly show that the mechanism of hole transfer in DNA strongly depends on the redox nature of the oxidant, whether it produces only G*+ or both A*+ and G*+.