Koushi Fukunishi

Fluorescence quenching by intermolecular π–π interactions of 2,5-bis(N,N-dialkylamino)-3,6-dicyanopyrazines

Abstract The fluorescence properties of 2,5-bis( N,N -dialkylamino)-3,6-dicyanopyrazine dyes in the solid state were correlated with their molecular stacking behavior. The optimized molecular structures were evaluated by using MOPAC PM3 and AM1 methods and their stacking behaviors of the π -chromophoric system were simulated from their three dimensional molecular structures and 1 H NMR spectra. The steric requirements of the substituents in the parent chromophoric system were the main cause of the spectral changes in the absorption and fluorescence maxima and fluorescence intensity in the solid state. Intermolecular π–π interactions effectively quenched the solid state fluorescence and, consequently, the degree of fluorescence quenching can be used as an indicator of intermolecular π–π interactions of fluorescence dyes chromophores. ©

New syntheses and solid state fluorescence of azomethine dyes derived from diaminomaleonitrile and 2,5-diamino-3,6-dicyanopyrazine

New fluorescent dyes of interest as red light emitters for electroluminescence devices were synthesized by the condensation of diaminomaleonitrile and 2,5-diamino-3,6-dicyanopyrazine with arylaldehydes. Substituent effects on their absorption and fluorescence spectra in the solution were determined by comparison with the parent chromophoric system. Their solid state absorption and fluorescence properties were evaluated with respect to their optimized molecular structures obtained by MOPAC methods.

Syntheses and fluorescent properties of 2,5-diamino-3,6-dicyanopyrazine dyes

Abstract 2,5-Diamino-3,6-dicyanopyrazine (2), a new fluorescent chromophore for functional dye materials, was synthesized by an oxidative coupling reaction of 2,3-diamino-3-(phenylthio)acrylonitrile (1). Compound 2 has a symmetrical structure and a strong intramolecular charge-transfer chromophoric system. It shows strong yellowish-green fluorescence in solution, and thus has good potential as a synthetic intermediate for fluorescent dye chromophores. Alkylation of the amino groups of 2 produced a bathochromic shift of λmax and resulted in red fluorescence in high quantum yield. On the contrary, acylation of the amino groups produced a hypsochromic shift of λmax, with blue fluorescence in high quantum yield. Modifications of the amino and cyano groups in 2 were studied in detail and many new fluorescent dyes were obtained. The absorption and fluorescent properties, together with fluorescence quantum yield of the substituted amino-3,6-dicyanopyrazines were correlated with their chemical structures.

Syntheses and properties of new styryl dyes derived from 2,3-dicyano-5-methylpyrazines

Abstract Reaction of 2,3-dicyano-5-methylpyrazine derivatives ( 3a-e ) with arylaldehydes gave new fluorescent styryl dyes ( 4–8 ). These styryl dyes have extended π-conjugated systems and are strong intramolecular charge-transfer chromophoric systems. They are of interest as non-linear optical materials, which should produce a large dipole moment in the excited state, and consequently induce large dipole moment differences accompanying laser irradiation. The styryl dyes derived from 2,3-dicyano-6-hydroxy-5-methylpyrazine showed large solvatochromism, depending on the polarity of the solvent, due to tautomerism between the hydroxypyrazine and the pyridone forms. The fluorescence and solvatochromism properties of dyes 4–8 were also studied, and structure-property relationships in solution and in the solid state were evaluated on the basis of molecular stacking in the solid state.

INTERCALATION CHARACTERISTICS OF 1,1′-DIETHYL-2,2′-CYANINE AND OTHER CATIONIC DYES IN SYNTHETIC SAPONITE: ORIENTATION IN THE INTERLAYER

The basal spacings of complexes of saponite with five cationic dyes, 1,1′-diethyl-2,2′-cyanine, crystal violet, methylene blue, 1,1′-diethyl-2,2′-carbocyanine, and 1,1′-diethyl-2,2′-dicarbocyanine, varied with degree of saturation of each dye. At low loading of dye to saponite, each cationic dye showed nearly the same absorption spectrum in the UV-visible region as that of its dilute aqueous solution, whereas the spectrum changed distinctly at high loading. With increasing degree of dye loading, the absorption band shifted to longer wavelength for 1,1′-diethyl-2,2′-cyanine (J band) and to shorter wavelength for the others (D, H bands). On the basis of the basal spacing of each respective dye-clay complex, the orientation of the intercalated dye molecules is proposed as follows: the major plane of the cationic dye lies horizontal to the 2:1 layer surface at low loading. With increasing loading, the dye molecules interact with adjacent dye molecules and orient vertically to the 2:1 layer at high loading near the cation-exchange capacity.

Self-assembling of aminopyrazine fluorescent dyes and their solid state spectra, Part 2

2,5-Diamino-3,6-dicyanopyrazine has strong yellowish-green fluorescence in spite of its small chromophoric system. Substitution at the amino groups, and hydrolysis followed by esterification of the cyano groups gave many types of fluorescent dyes. Their absorption and fluorescent spectra both in solution and solid state were correlated with their molecular stacking on vapor deposited thin film. Steric hindrances of the substitutents largely affected their solid state absorption and fluorescent spectra. Structural optimization by means of MOPAC PM3 method was conducted, and these results well indicated their molecular stacking behaviors.

Syntheses and characterization of new styryl fluorescent dyes from DAMN. Part II

Abstract 2,3-Bis(bromomethyl)-5,6-dicyanopyrazine ( 3 ) can be prepared more readily by the condensation of DAMN ( 1 ) and 1,4-dibromobutane-2,3-dione ( 2 ) than by direct bromination of 2,3-dimethyl-5,6-dicyanopyrazine. The Wittig reaction of 3 with arylaldehydes gave a new type of fluorescent styryl dyes ( 6–8 ). These styryl dyes have extended π-conjugation systems and strong intramolecular charge-transfer chromophoric systems. They have strong fluorescence in solution and some have fluorescence even in the solid state, which is very important to evaluate their electroluminescence (EL) property as the emitter for EL devices. Calculation of excitation energies using the PPP-MO method, and optimization of their structures using the MOPAC with the PM 3 method were conducted, and their spectral properties are discussed to correlate their functionalities with chemical structures.

Three dimensional molecular stacking and functionalities of aminonaphthoquinone by intermolecular hydrogen bondings and interlayer π–π interactions

Abstract Three dimensional molecular stacking of aminonaphthoquinones affecting largely on their 3rd order nonlinear optical property was evaluated by X-ray crystal analysis. It was found that the intermolecular hydrogen bondings and the interlayer π–π interactions played a significant role in producing large bathochromic shifts of absorption maximum in solid state, and gave large 3rd order nonlinear optical susceptibility. Molecular symmetry and substituent effects on their physical properties were also correlated with their molecular stacking in crystals.

Structure and molecular motion changes in poly(ethylene terephthalate) induced by annealing under dry and wet conditions

Abstract Structural changes in poly(ethylene terephthalate) (PET) induced by annealing under dry nitrogen gas flow (dry annealing) and in water (wet annealing) were investigated using small- and wide-angle X-ray diffraction methods, density measurements, differential scanning calorimetry and dynamic viscoelastic measurements. The degree of crystallinity of PET was evaluated by wide-angle X-ray diffraction patterns and by heat of fusion measured using differential scanning calorimetry. Based on the two-phase concept, the amorphous density of PET was calculated from the observed density and degree of crystallinity. The amorphous density decreased as crystallization increased for both the dry and wet conditions. The glass transition temperature and activation energy of the glass transition of PET based on dynamic viscoelastic measurements decreased as crystallization proceeded. Since the amorphous density decreased with annealing in the late phases of crystallization, molecular motion in the amorphous region easily occurred as crystallization proceeded. Water molecules enhanced the structural changes during the crystallization of PET.

Introduction of two benzyl groups to C60 by using the collman reagent

Abstract Addition of C 60 to a suspension of the Collman reagent in THF gave a strongly colored but almost transparent solution. Treatment of the resulting solution with benzyl bromide gave a C 60 derivative possessing two benzyl groups. The 1 H-NMR as well as the 13 C-NMR of the product indicated that the reaction site was 1,4-position.