Toshiaki Koga

Liquid crystalline properties and photochromism of 4-alkyl-N-(4-alkloxysalicylidene)anilines

Eight new homologous series of 4-alkyl-N-(4-alkloxysalicylidene)anilines were synthesized. The phase transitions of these homologues were determined using differential scanning calorimetry and polarizing optical microscopy. The homologues began to exhibit liquid crystalline phases as the terminal alkyl or alkoxyl chains were lengthened. In addition, some members of these homologues series exhibited photochromism in the solid state.

Raman spectroscopy of liquid crystalline N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]-3-aminopyridines

New homologous series of N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]-3-aminopyridines were synthesized, they exhibited a nematic phase. The temperature dependence of their Raman spectra has been observed in the spectral range 900–1800 cm−1. Some Raman bands show a marked change in their intensity and frequency through the phase transition from crystalline solid to nematic. These bands are ascribed to the vibrational modes related to the core part of the molecule. Such behaviour can be explained by the change of molecular conformation related to the core. Some members of these series exhibited photochromism in the solid state.

Fluorescence spectroscopic characterization of 4,7-bis(2-thienyl)-1,2,5-oxadiazolo[3,4-c]pyridine; lead structure of new red-emitting EL material

Abstract The spectroscopic parameters of 4,7-bis(2-thienyl)-1,2,5-oxadiazolo[3,4- c ]pyridine (DTOP) were determined which was designed as a red-emitting dye for the electroluminescent (EL) device. The main optical transition of DTOP is attributable to 1 L a , and therefore, the fluorescence maximum shifted to the red side to reach to 630 nm according to the solvents. Although the non-radiative transition rate was enhanced, when the fluorescence maximum shifts to the longer than 610 nm, DTOP maintains the higher radiation transition probability.

study of liquid crystalline N -[4-(4- n -alkoxybenzoyloxy)-2-hydroxybenzylidene]methylanilines

New homologous series of N-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]methylanilines [nAHmM(n=1-8/10; m=2: ortho, m=3: meta, m=4: para)] were synthesized. They exhibited a nematic phase except for 1AH3M. The temperature dependence of their Raman spectra was observed in the spectral range of 900–1700 cm-1. In one group of nAHmM compounds, the Raman band at about 1360 cm-1 abruptly decreased in intensity and wavenumber when the crystalline solid-liquid crystal phase transition was approached. In another group, the corresponding band increased through the phase transition. The bands have been assigned to the coupling mode between the in-plane CCH deformational vibration and the ring-N stretching vibration. Such a behaviour can be explained by the molecular conformation with different twist angles of the aniline ring in relation to the Schiffs base plane of the molecule. Some nAHmMs exhibited photochromism.

Measurement of mechanically induced luminescence from microparticles

We developed an AFM-based new apparatus with a photomultiplier in order to measure the weak light emission from a single microparticle induced by applying a micro force and measured the emission intensity as a function of the applied micro force and speed. The emission intensity was approximately proportional to the speed of the applied micro- force and the square of the micro stress.

Liquid crystalline properties of 4-isopropyl- and 4-isopropoxy- N -(4- n -alkoxysalicylidene)anilines

New homologous series of 4-isopropyl- and 4-isopropoxy-N-(4- n -alkoxysalicylidene)anilines were synthesized. The phase transitions of these homologues were determined by differential scanning calorimetry and polarizing optical microscopy. No enantiotropic liquid crystalline phases were observed for homologues having a terminal isopropyl group; as the terminal alkoxyl chain is lengthened, smectic C and nematic phases occur monotropically. The members with an isopropoxy substituent exhibit an enantiotropic nematic phase as the terminal alkoxyl chain is lengthened; the octyloxy member exhibits a monotropic smectic C phase as well as an enantiotropic nematic state.

Mechanoluminescence Studies upon Single Nanoparticles by AFM-photomeasurement System

We successfully measured the mechanoluminesence (ML) from a single ML nanoparticle at the first time. In order to measure the weak light emission from a single nanoparticle induced by applying a micro force, we developed an AFM-based new apparatus with a photomultiplier. Interestingly, the emission (ML) intensity from a nanoparticle was approximately proportional to the load, the phenomena is similar to the macroscopic ML emission properties.

Raman study of a liquid crystalline gel consisting of photochromic 4‐methyl‐N‐(4‐n‐heptyloxysalicylidene)aniline and a gelling agent (R,R′)‐1,2‐bis(dodecanoylamino)cyclohexane

A liquid crystalline physical gel has been prepared from the mixture of a nematic liquid crystal and a low molecular mass gelling agent containing a hydrogen‐bonding moiety. The newly synthesized liquid crystalline compound exhibited photochromism in the crystalline solid phase. Although photochromism was not observed in the nematic gel state of the mixture, the lifetime of photochromism in the solid phase became longer, compared with that of a single liquid crystalline compound. Some Raman bands of the mixture showed a marked change in both intensity and frequency through the phase transitions. These bands have been assigned to the vibrational modes related to the core part of molecule.