Electrical pump-and-probe study of spin singlet-triplet relaxation in a quantum dot

Spin relaxation from a triplet excited state to a singlet ground state in a semiconductor quantum dot is studied by employing an electrical pump-and-probe method. Spin relaxation occurs via co-tunneling when the tunneling rate is relatively large, confirmed by a characteristic square dependence of the relaxation rate on the tunneling rate. When co-tunneling is suppressed by reducing the tunneling rate, the intrinsic spin relaxation is dominated by spin-orbit interaction. We discuss a selection rule of the spin-orbit interaction based on the observed double-exponential decay of the triplet state.     

Krypton fixation using KrF2 (III). Entrapment of krypton into zeolite 13x

The KrF₂ - zeolite 13X reaction at ?40 °C results in entrapment of Kr in the zeolite. On heating, a portion of the entrapped Kr is retained up to 500 °C. The Kr loading is more than 8 cc(STP)/g at a storage temperature of 100 °C. The present work has suggested a feasibiltty of the zeolite encapsulation of radioactive krypton by a chemical procedure.     

Application of photoelectron spectroscopy to the study of photochemical reactions of solids. photooxidation of rubrene (5,6,11,12-tetraphenylnaphthacene)

Photoelectron spectroscopy was applied for the first time to the study of a photochemical reaction in solids, the reaction of a rubrene film being taken as an example. The measurement of the absorption spectrum indicates that the photo-oxidation takes place in the bulk. The change of the photoelectron spectrum shows that about 50% of the original rubrene is recovered upon heating the peroxide.     

Single-walled carbon nanotubes acquire a specific lectin-affinity through supramolecular wrapping with lactose-appended schizophyllan

Single-walled carbon nanotubes can be entrapped within a helical superstructure composed of schizophyllan bearing lactoside-appendages to show an excellent water-solubility as well as a specific lectin-affinity.     

A very reliable method for determination of absolute configuration of chiral secondary alcohols by 1H NMR spectroscopy

Surprisingly stable synperiplanar conformers of CFTA esters have led us to develop a new and very reliable method for assigning absolute configurations of even secondary alcohols having minimal structural differences, such as chiral benzhydrols and alpha-monodeuterated benzyl alcohols.     

Electroytic partial fluorination of organic compounds. 52. Regio- and diastereoselective anodic fluorination of thiazolidines

Anodic fluorination of N-benzoyl, N-acethyl-, and N-formylthiazolidine derived from L-cysteine was carried out in dimethoxyethane (DME) and acetonitrile containing various supporting fluoride salts using an undivided cell. Highly regioselective fluorination proceeded to provide the corresponding 5-monofluorinated thiazolidine derivatives in good yields in DME, and the diastereoselectivitiy was moderate to high regardless of the supporting fluoride salts. The diastereoselectivitiy of the fluorination was greatly affected by the bulkyness of the subsitituent on the nitrogen atom, and N-benzoylthiazolidine gave much higher diastereoselectivity compared with N-formyl derivative. The fluorination of the thiazolidines was not achieved by commercially available fluorinating reagents such as N-fluoropyridinium salts.     

Excited quartet and doublet states in the complex of tetraphenylporphine zinc (II) and a nitroxide radical in solution: X- and W-band time-resolved EPR studies

The photoexcited quartet (Q₁) and doublet (D₁) states of the complex of tetra-phenyl-porphine zinc (II) and a nitroxide radical have been studied in toluene solution by X-(9.4 GHz) and W-band (94 GHz) time-resolved electron paramagnetic resonance spectroscopy. The spin-polarized signals of the Q₁ and D₁ states are observed and assigned by analysis of theg-values. Line broadening and spin polarization mechanisms in this system are discussed.     

High birefringence photopolymerizable phenylacetylene liquid crystals

Photopolymerizable three-ring phenylacetylene (3PA) liquid crystalline compounds were synthesized and the physical properties of the monomers and polymers were characterized in the expectation of obtaining high birefringence polymers. 3PA monomers containing acrylate substituents exhibited enantiotropic nematic phases and high δn values of around 0.35. Homogeneous alignment was retained after polymerization and high values of δn (~0.34) for the polymers were obtained. The orientation of the monomers at the photopolymerization temperature was almost fixed, such that δn and the order parameter of the polymers varied with the polymerization temperature.     

Kinetic evaluation of the reactivity of flavonoids as radical scavengers

The reactivity of flavonoids as radical scavengers was investigated under kinetic considerations using radical polymerization of methyl methacrylates initiated by benzoyl peroxide. The number of radicals which are trapped by each molecule of phenol (the stoichiometric factors, n values) decreased in the order of epigallocatechin-3- O -gallate (ECG) (5.5) > catechin (3.5) > resveratrol (2.4) > quercetin (1.9)> n -propylgallate (1.5) > hesperetin (1.0). The inhibition rate constants ( k inh ) (1-3 ‐ 10 3 l/(mol s)) for the flavonoids were not different from each other, and, therefore, the radical scavenging activity depend on n values. The n values of the fully oxidized flavonoids were estimated from the frontier orbital theory, using PM3 semiempirical molecular orbital calculation. The experimental n values were consistent with the calculated values.