Yasunori Nishijima

Moiré Patterns: Their Application to Refractive Index and Refractive Index Gradient Measurements

The general theory of moire patterns obtained from parallel rulings and concentric circles is presented. Near superposition of a regular ruling on to parallel rulings of variable spacings results in a curved moire pattern which is functionally related to the deviation in spacings. When two figures consisting of uniformly spaced concentric circles are overlapped, the resulting moire patterns are hyperbolas defined by the center-to-center distance of the figures and the inter-ring spacing.Since very small relative displacements of the figures result in large changes in the moire pattern, this technique can be a sensitive detector of minute changes in refractive index and in refractive index gradient which bring about apparent relative displacement of the figures. The technique is demonstrated for the case of a constant refractive index gradient and for a variable refractive index gradient as encountered in diffusion measurements. Birefringence and dispersion can also be determined utilizing the moire method. Demonstration of the use of the moire technique for the evaluation of lenses is also presented.

Photophysical properties of poly[2-(9-carbazolyl)ethyl methacrylate] films: Energy migration and carrier generation in films having no excimer-forming site

Abstract Photophysical properties of poly[2-(9-carbazolyl)ethyl methacrylate] film have been studied. This polymer shows a clear monomer fluorescence spectrum from carbazole chromophores and has no detectable excimer emission, even in the solid state. Highly efficient sensitized photoconductivity by electron acceptor doping shows effective electronic excitation energy migration through carbazole chromophores.

Intramolecular excimer of DI(1-pyrenylmethyleneoxycarbonyl) alkanes

Abstract Intramolecular excimer emission of a series of di(1-pyrenylmethyleneoxycarbonyl)alkanes ( n = 0–22) has been studied under photostationary conditions. The intramolecular excimer formation rate constant decreases monotonously with increasing number of methylene units of the chains in the low temperature region. The temperature dependence of the rate constant for each sample was studied to give an apparent activation energy of ca. 5 kcal/mol.

Fluorescence methods for studying molecular motions

Abstract The characteristics of photoluminescence are affected by the molecular motions in the local environment of the excited molecule. Hence, by knowing the lifetime of the excited state, various relaxation times of the molecular motions can be estimated from the emission characteristics. In the present paper the effect of the molecular motions manifested in the fluorescence emission, such as the rotational depolarization of fluorescence, the internal quenching of fluorescence due to internal rotation, and the inter-and intramolecular excimer formation, are reviewed and the possible applications of such phenomena to the study of molecular motions in polymer systems are discussed. The application of fluorescence methods provide unique information about the molecular motions in the nanosecond range in polymer solutions, melts, and solids.

Hole transport behavior of N‐phenylcarbazole‐doped poly(bisphenol A carbonate) films in a glass transition region

Hole mobility of a N‐phenylcarbazole‐doped poly(bisphenol A carbonate) system was measured by the time‐of‐flight method at −60 to 130 °C, which covers the glass transition temperature Tg of the poly(bisphenol A carbonate) matrix. The hole mobility at T=298 K and E=1.6×105 V cm−1 changes from 1.7×10−8 to 6.6×10−6 cm2 V−1 s−1 with the increase of N‐phenylcarbazole concentration from 7.5×10−4 to 2.4×10−3 mol cm−3. Above Tg, the activation energy of hole mobility is smaller than that below Tg. This implies that the micro‐Brownian motion of polymer chain in the glass transition region changes the trap level for hole transport, i.e., the trap level becomes shallower in the temperature range above Tg. The shape of the transient photocurrent was also studied at various temperatures. The value of (t1/2−tT) is used as an indicator of the trapping effect, where tT is the transit time and t1/2 is the time when the transient photocurrent becomes half of the photocurrent at tT. The slope of the plot of (t1/2−tT) vs T w...

Intramolecular [2 + 2] photocycloaddition. 2. Mechanism of intramolecular photocyclization of α,ω-bis(p-vinylphenyl)alkanes

Abstract From the photophysical measurements of the title reaction, the formation of cyclophanes is concluded to be facilitated by high microscopic concentration of styrene moieties and depressed by strain loaded at the transition state.

Photodimerization of styrene, p-methylstyrene, and α-methylstyrene in the presence of 1,2,4,5,-tetracyanobenzene

U.v. excitation of styrene, p-methylstyrene, and α-methylstyrene in the presence of the electron acceptor tetracyanobenzene produces 1,2,3,4-tetrahydronaphthalene derivatives as the main products in addition to 1,2-cis and 1,2-trans-disubstituted cyclobutanes.

Carrier photogeneration of N-phenylcarbazole doped poly(bisphenol A carbonate) film

Abstract The carrier photogeneration mechanism of N -phenylcarbazole (PhCz) doped poly(bisphenol A carbonate) film with 2,6-dimethyl- p -benzoquinone (MQ) as an electron acceptor was investigated. The carrier generation efficiency, η, was measured by a xerographic technique. The extrinsic carrier generation efficiency, η e , was calculated from η and fluorescence quenching data. The large increase of η e with increasing PhCz is attributed to excitation energy migration to the acceptor site MQ. The probability of free carrier formation at the acceptor site, A e ( E ), is nearly constant, ≈ 1.5 × 10 −3 . The electric field dependence of η e was analysed by an Onsager plot. The initial separation distance of the ion pair, r o is 1.8–2.0 nm. The slight increase of A e ( E ) and r o with increasing PhCz concentration seems to be caused by enhanced escape probability from the geminate recombination due to hole migration.

Application of a photodimerizable probe to the forced Rayleigh scattering technique for measurement of self-diffusion of polymer chains

Abstract A new type of photochromic compound, a bis-(9-anthrylmethyl) ether ((BAME), is introduced as a potential probe for the forced Rayleigh scattering (FRS) technique. Upon irradiation with ultra-violet (u.v.) light (∼360 nm), BAME undergoes intramolecular dimerization which involves a large refractive index change in the visible region. The dimerization process is known to be essentially irreversible in the absence of short u.v. light (∼250 nm) at room and moderately high temperatures. A derivative of BAME is synthesized and chemically attached to polystyrene chains. Some photochemical properties of the BAME-labelled polystyrene are reported together with the results of a preliminary diffusion measurement of polystyrene by the FRS technique.

Concentration Dependence of Diffusion Coefficient: Analysis of Skewed Diffusion Curve

Skewed diffusion curves are analytically treated in terms of the Gram‐Charlier expansion applied to the Boltzmann equation. The concentration dependence of the diffusion coefficients can be expressed in terms of moments of the diffusion curves.When the diffusion coefficient is linearly dependent on concentration, the slope is expressed in terms of three parameters of the diffusion curve, namely: (1) the third moment, (2) the height at the initial boundary, and (3) the average diffusion coefficient.