Exciton polariton in an organic–inorganic multiple-quantum-well crystal (C4H9NH3)2PbBr4

Exciton polariton in an organic–inorganic multiple-quantum-well (MQW) single crystal (C₄H₉NH₃)₂PbBr₄ at low temperature has been investigated by photoluminescence excitation (PLE), reflection, and time-resolved photoluminescence measurements. Since (C₄H₉NH₃)₂PbBr₄ has ideal two-dimensional excitons with an extremely large oscillator strength and forms self-organized MQW with a very short well-period (d～10 Å), polaritonic coupling among excitons is strong and extends over a large number of wells. Therefore, observed MQW polariton features were the same as those of bulk polaritons. We have also investigated relaxation dynamics of the MQW polariton in the same framework as discussions on bulk polaritons.     

Evaluation of bandgap energy and carrier density of InN nanocolumns

We have measured the optical properties of wurtzite InN nanocolumns and film by photoluminescence (PL) measurements at temperatures from 5 to 300 K and analyzed the PL spectra by fitting with the free-electron recombination bound (FERB) model. For the top-linked InN nanocolumns, we observed strong PL intensity compared to the InN film sample. The PL spectra were asymmetrical with low-energy tails and a red-shift of the PL peak energy position was observed with increasing temperature. However, for the separated InN nanocolumns, we observed weak PL intensity and symmetrical PL spectra. Analyzing the spectra shape of the top-linked InN nanocolumns at 5 K using the FERB model, we evaluated the intrinsic bandgap energy and carrier density of InN nanocolumns to be 0.69 eV and 2.5×10¹⁷ cm⁻³, respectively.     

Multivariate data analysis for Raman spectroscopic imaging

This article reviews the analytic techniques for Raman spectroscopic imaging with emphasis on chemometrics. Key information included in Raman spectra is often distributed broadly throughout the dataset. It is possible to condense the information into a very compact matrix representation by a chemometric technique of factor analysis such as principal component analysis (PCA) or self‐modeling curve resolution (SMCR). PCA yields two matrices called scores and loadings which complementarily represent the entire features broadly distributed in the dataset. This concept can be further extended to other forms of data transformation schemes, including bilinear data decomposition based on SMCR analysis. SMCR offers a firmer model which is chemically or physically interpretable. The information derived from these techniques readily brings useful insight into building a mechanistic model for understanding complex phenomena studied by Raman spectroscopy. Illustrative examples are given for applications of both PCA and SMCR to Raman imaging of pharmaceutical tablets. Copyright © 2009 John Wiley & Sons, Ltd.     

Recent progress on catalytic Heck carbonylations using carbon monoxide surrogates

Ongoing efforts toward the development of carbon monoxide (CO) surrogates have changed the way in which carbonylative transformations are conducted. For synthesizing carboxylic acid derivatives, Heck carbonylation using CO surrogates in slight excess has become a more efficient and practical method than the conventional one using large excess of CO gas. To supply CO for the reaction, both in-situ and ex-situ methods has been considered. Herein, we summarize recent progress in catalytic Heck carbonylation using CO surrogates, including discussion of the mechanism for CO generation from recently developed CO surrogates.     

Dioxacyclophanes as a Scaffold for Silicon-based Circularly Polarized Luminescent Materials

Planar chiral dioxacyclophanes were designed and synthesized as a key scaffold for materials with circularly polarized luminescence (CPL). Representative planar chiral 1,12-dioxa[12](1,4)naphthaleneophane-derived organosilane compounds (?)-(R)-1, (+)-(R)-2, and (?)-(R)-3 were prepared by (+)-sparteine-mediated aryl metalation and an electrophilic reaction with chlorosilanes. The absolute configurations of the planar chirality were determined in the R form by single-crystal X-ray analysis. Optically active compound (+)-(R)-2 exhibited blue fluorescence and a CPL signal with a dissymmetry factor (g_lum value) of 0.001 in solution. The electronic structure was corroborated by DFT and TD-DFT calculations rationalizing the observed spectroscopic properties.     

Designing a Polymer Blend with Phase Separation Tunable by Visible Light for Computer‐Assisted Irradiation Experiments

Summary: A mixture of poly(vinyl methyl ether) (PVME) and a polystyrene derivative bearing cinnamate groups (PSC) was chemically designed so that its phase separation can be tunable by visible light for computer‐assisted irradiation (CAI) experiments. This PSC/PVME blend exhibits a lower critical solution temperature (LCST) and undergoes phase separation upon irradiation with 405 nm visible light. The phase separation was induced by photodimerization of the cinnamate moieties in the presence of 5‐nitroacenaphthene used as a photosensitizer. It was found that for visible light with high intensity, phase separation process was almost frozen by photodimerization of the cinnamate groups which act as a photo‐cross‐linker for the PSC component. It is demonstrated in this work that by using this PSC/PVME blend, phase separation restricted to the micrometer scales can be induced and manipulated by irradiation using a computer‐controlled digital projector. These preliminary results open a new route for spatio‐temporal manipulation of phase separation in photo‐reactive polymer blends.

Computer‐assisted irradiation method for a polymer blend with phase separation drivable by visible light.     

Interpenetrating Polymer Networks with Spatially Graded Morphology Controllable by UV-Radiation Curing

Interpenetrating Polymer Networks (IPNs) composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA) were synthesized from a precursor mixture by using dissimilar photo-cross-link reactions. When the reation yields exceeded a certain threshold, the mixture was quenched from one-phase region into two-phase region, leading to phase separation. Upon irradiation with strong UV-light, an intensity gradient was formed along the propagating direction of the exciting light, generating a gradient of quench depth via the spatial inhomogeneity of the cross-link reactions. As a consequence, a gradient of the characteristic length scales was continuously generated from the top to the bottom of the mixture. The resulting three-dimensional (3-D) morphology was in-situ observed at different depths of the mixture by using a laser-scanning confocal microscope (LSCM). From this 3-D observation, it was found that phase separation was accelerated at the bottom of the mixture and proceeded in an autocatalytic fashion. The mechanism for the formation of the graded morphology was discussed in conjunction with the kinetics of the autocatalytic phase separation.     

A novel promoter, heteropoly acid, mediated chemo- and stereoselective sulfoxide glycosidation reactions

The chemo- and stereoselective glycosidations of sulfinylglycosides and alcohols using a heteropoly acid, H₃PW₁₂O₄₀, as a new promoter have been developed.     

Intense THz-radiation from semiconductors under magnetic field irradiated with femtosecond laser pulses

The THz-radiation power from InAs reaches sub-mW level in a 1.7-T magnetic field irradiated with femtosecond laser pulses of 1.5-W average power. The THz-radiation power is related almost quadratically both to the magnetic field and to the excitation laser power. Furthermore, the THz-radiation spectrum is found to be controlled by the excitation pulsewidth, chirp direction of the excitation pulse, and the magnetic field.     

A kinetic study on Rh/binap-catalyzed 1,4-addition of phenylboronic acid to enones: negative nonlinear effect caused by predominant homochiral dimer contribution

A kinetic study on the Rh/binap-catalyzed 1,4-addition of phenylboronic acid using reaction calorimetry revealed that the catalytically inactive dimeric hydroxorhodium complex [Rh(OH)((R)-binap)]2 (RR-4) is the resting state. A negative NLE in eeprod and an amplified reaction rate were predicted and observed in the present reaction system characterized by the preferential formation of homochiral dimer.