Hiroyuki Nakazumi

Photoinduced pitch changes in chiral nematic liquid crystals formed by doping with chiral diarylethene

Chiral binaphthyl derivatives having two photochromic diarylethene units were synthesized in an attempt to use them as dopants for photoresponsive liquid crystals. These compounds showed thermally irreversible photochromic reactions. The circular dichroism (CD) spectra and the optical rotation values of the derivatives reversibly changed in methanol upon alternate irradiation with ultraviolet and visible light. Large photostimulated pitch changes of chiral nematic K-15 liquid crystals were observed on addition of the derivatives as dopants. The relation between the optical rotation and the twisting power force was discussed.

Phase Transition of a Liquid Crystal Induced by Chiral Photochromic Dopants

Abstract A chiral cyclohexane having two photochromic diarylethene unit was synthesized in an attempt to use it as a dopant for a photoresponsive liquid crystal. A stable photoswitching between nematic and cholesteric phases could be induced by the addition of a small amount of the chiral cyclohexane to a nematic liquid crystal 4-cyano-4′-penthylbiphenyl (K-15).

Synthesis of novel unsymmetrical squarylium dyes absorbing in the near-infrared region

Novel unsymmetrical squarylium dyes which absorb in the near-infrared region were synthesized by a stepwise procedure via intermediate 4-substituted 3-hydroxycyclobut-3-ene-1,2-diones. By introducing benz[c,d]indoline or benzo[b]pyran moieties at one end as an electron-donating component, the SQ dyes exhibited their absorption maxima at 739–821 nm with large molar absorption coefficients (log exa0=xa04.96–5.18) in CHCl3. The X-ray analysis for one of these dyes was also examined to confirm the overall structure of the unsymmetrical SQ dye.

New sol-gel photochromic thin films made by super-fine particles of organic photochromic compounds

New photochromic thin gel films have been prepared by the dipping method from a sol-gel coating solution containing Malachite Green Leucocyanide soluble in sol and super-fine dispersed solution of spiropyran or spironaphthooxazine, which was effective to increase the concentration of photochromic compounds in gel film. Photochromism of these gel films is compared with that in sol under the conditions of acid catalysis. Though in sols using spiropyran and Malachite Green Leucocyanide normal photochromism was not observed, photochromism in thin gel films prepared from the same sol was confirmed. Normal photochromism of spironaphthooxazine in thin gel films was similar to that in solution. The reaction rate from the colored form to the spiro form of spiropyran and spironaphthooxazine in thin gel film is dependent on the gel matrix, which is influenced by the reaction time of the sol.

Metal–semiconductor structural phase transitions and antiferromagnetic orderings in (Benzo-TTFVO)2·MX4 (M = Fe, Ga; X = Cl, Br) salts

Crystals of the 2 : 1 salts of a new donor molecule, benzotetrathiafulvalenoquinone-1,3-dithiolemethide (4, Benzo-TTFVO) with magnetic FeX4− and non-magnetic GaX4− (X = Cl, Br) ions, 42·FeX4 and 42·GaX4, are isostructural to each other and showed a β-type packing of the donor molecules where they form a uniform-stacked structure with an interplanar distance of 3.50 A. These salts exhibited metallic behavior down to 140–170 K, but at these temperatures (∼TM−I) an abrupt increase in the resistivities (ρ) occurred and thereafter semiconducting behavior with an activation energy of 40–100 meV was observed. A structural change in the donor column from uniform to tetramer-unit stacks was observed in the 42·FeBr4 crystal before and after TM−I. By application of pressures up to 1.0 GPa, the metallic behavior in the higher temperature region was gradually strengthened and TM−I gradually became lower with increasing pressure, but the transitions could not be suppressed at all. In response to the metal–semiconductor transition at TM−I, there was a sharp decrease in the paramagnetic susceptibility of the π electron system, where the transition from Pauli paramagnetism due to the metal-conducting behavior to the spin singlet state caused by tetramer formation of the donor molecules was observed. In addition, the FeX4− (X = Cl, Br) salts showed comparatively strong antiferromagnetic interactions between the Fe(III) d spins of the FeCl4− and FeBr4− ions (Weiss temperature: −11 K for 42·FeCl4 and −37 K for 42·FeBr4), giving rise to antiferromagnetic orderings at 1.6 K for 42·FeCl4 and 9.3 K for 42·FeBr4. The magnitudes of the d–d and π–d interactions in 42·FeBr4 are calculated to be Jdd = 2.06 K and Jπd = 2.32 K, respectively. The comparison of these J values with the other magnetic conductors based on our system suggests that the d–d interaction of 42·FeBr4 is stronger than the π–d interaction. Since the three-dimensional antiferromagnetic ordering appears at the comparatively high temperature of 9.3 K, there is an important contribution of the π electrons to the antiferromagnetic ordering of the Fe(III) d spins in order to mediate the magnetic interaction between two-dimensional magnetic anion layers.

N-(2,4,7-trinitrofluorenylidene)anilines—new electron transport materials in positive charge electrophotography

New electron transport materials, N-(2,4,7-trinitrofluorenylidene)-2,6-dialkylanilines, show excellent properties in positive charge electrophotography. Single-crystal X-ray diffraction analyses of two of these compounds are reported. The high solubility of N-(2,4,7-trinitrofluorenylidene)-2,6-diethylanilines could be mainly attributed to the loss of overlap between intermolecular fluorene rings due to the bulkiness of the ethyl groups.

Photochromic glass thin film formed by the sol-gel coating method

The photochromic gel thin films using 1-butyl-3,3-dimethyl-6-nitro-spiro[2H-1- benzopyran-2,2-indoline] (1) and 1-butyl-spiro[2H-indole-2,3- [3H]naphtho[2,1-b][1,4]oxazine] (2) dispersed in sol in the sol-gel processing were prepared and photochromic behaviors of these films were investigated. A good transparent coating layer on glass surface was formed in the range of ca. 6 - 10 wt% of 1 or 2 to alkoxysilane, and was colored by UV irradiation. The absorption band formed by UV-irradiation disappeared by thermal decay and also by Vis irradiation for 1. The thermal fading of the colored form to the spiro form 1 or 2 is dependent on a matrix of the gels, the colored forms in the film starting from methyltriethoxysilane (MTES), which is expected to include larger pores than in the film starting from tetraethoxysilane (TEOS) or silane oligomer, show faster thermal fading which roughly follows the first order kinetics. The colored form in the gel is stabilized, compared with that in solution or bulk gel, and it is suggested that there are some kinds of colored species in thin gel films containing spiropyran 1, which may be some aggregates, whereas only a colored species from spironaphthooxazine 2 is suggested. Photochromic behavior of 2 in sol was also examined.

Fluorescent thin gel films using organic dyes and pigments

New organic-inorganic fluorescent thin gel films included with laser dyes or fluorescent organic pigments have been prepared for display application. The florescent dyes (benzoxazolium, pyrromethene, and rhodamine dyes) and super-fine particles of fluorescent pigments (coumarin and perylene) were successfully incorporated into thin silicate gel films prepared from tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), and methoxysilane oligomer (MTSO) under acid catalyzed hydrolysis. The blue, green, and red luminescence were observed from these thin films (thickness: 100 - 400 nm), respectively. Fluorescence spectra, fluorescent quantum yield and lifetime of thin gel films are examined. Fluorescent peaks for most of dyes and pigments used in gel films were similar to those in solution, and fluorescent lifetime for dyes and pigments used in gel films were 2.9 - 4.5 ns. Photostability of fluorescent gel films is dependent on fluorescent organic dyes and pigments used and/or silicate gel matrixes. Coumarin and perylene pigments have higher fluorescent quantum yield in gel film prepared from MTSO. The large Stokes shift was observed in fluorescent gel film using coumarin and benzoxazolium dyes. The coumarin and perylene pigments are significantly photo- stable in gel film prepared from MTSO, and photodegradation of perylene red after irradiation of 500 W Xi-lamp for 30 min is below 20%.

Light-controlled gas permeability of mesoporous silica glass bearing photochromic spironaphthoxazine on its surface

N2 and CO2 gas permeability of mesoporous silica glass bearing photochromic indolinospironaphth[2,1-b][1,4]oxazine through a covalent linkage was controlled by photo-irradiation: the photo-isomerization of the spironaphthoxazine to the photomerocyanine form suppressed the gas permeation of the glass.