Toshio Kawato

Photoisomerization and thermoisomerization I: Unusual photochromism of N-(3,5-di-tert-butyl-salicylidene) amines

Abstract Unusually photosensitive Schiff bases were prepared from 3,5-di-tert-butylsalicylaldehyde and amines; the aniline derivative exhibits both normal and reverse photochromism on irradiation with UV light followed by either storage in the dark or irradiation with visible light. From a consistent kinetics explanation of the thermal back reaction, two courses for the photo-bleaching and the thermal fading of the photochromer, which is assigned to a quinoid amine form, are illustrated.

Crystalline photochromism of N-salicylidene-2,6-dialkylanilines: advantage of 2,6-dialkyl substituents of aniline for preparation of photochromic Schiff base crystals

N-(3,5-Dihalosalicylidene)-2,6-dialkylaniline derivatives were prepared and their structure and photochromic properties were investigated. From the X-ray crystallography, it was revealed that steric repulsion between the azomethine hydrogen atom and the alkyl groups at the 2,6-positions of the aniline ring lead to non-planar molecular structure, which was effective for the crystals to exhibit photochromism. The relationship between photochromicity and crystal packing of N-(3,5-dichlorosalicylidene)-2,6-dialkylanilines series was also discussed. The 2,6-dialkylaniline method was suggested to be applicable to the preparation of photochromic Schiff bases with various substituents in the salicylidene rings.

Photochromism of polymorphic 4,4′-methylenebis(N-salicylidene-2,6-diisopropylaniline) crystals

4,4[prime or minute]-Methylenebis(N-salicylidene-2,6-dialkylaniline) derivatives were prepared and their structures were determined by (1)H NMR, IR, DSC and X-ray crystallographic analyses. The 2,6-diisopropylaniline derivative yielded definite polymorphic crystals: the space groups of the crystals were C2/c and P2(1)/n, respectively. It was found that both polymorphs were similarly photochromic but the thermal stability of the photochrome was different due to the variance of the shape of molecule and cavity in each crystal.

Photoisomerization and thermoisomerization. III: tert-butyl method of selective preparation of photochromic crystalline salicylideneanilines and elucidation of substituent effects on the kinetics of the colour-change process

Abstract Salicylideneanilines possessing tert -butyl and other groups as ring substituents were synthesized and their photochemical properties were studied. The introduction of the bulky- tert -butyl substituent enabled photochromic Schiff base crystals to be prepared. Substituent effects on the photochromic phenomenon were determined by the kinetic measurement of the thermal bleaching reaction of the photocoloured species.

Photochromism of Guest N-Salicylideneaniline in the Rooms of Host Bile Acid Derivatives

Abstract Definite clathrate crystals of deoxycholic acid and its amide and alcohol derivatives as host molecules with N-salicylideneaniline as a guest molecule were prepared to investigate their photochromic properties. The photocoloration study was done by irradiating the crystal powder with 365 nm light; the thermal fading reaction of the photocolored species was followed by reflectance spectrophotometry at 303 K. From the sharp difference in the first-order rate constants of the thermal bleaching of the photochromes, it was found that the thermal unimolecular motion of photo-colored species was strongly influenced by the neighboring environments in the crystal state.

Trinuclear complexation of 2,6-bis(acetylacetoxymethyl)pyridine with Pd(II) and Cu(II) ions

Abstract Treatment of [PdCl 2 (PhCN) 2 ] with 2,6-disubstituted pyridines (L) gave a new series of trans -[PdCl 2 L 2 ] complexes. β-Ketoester substituents in the ligands were found to form OO chelate compounds with a Cu(II) ion. The Pd(II) complex of 2,6-bis(acetylacetoxymethyl)pyridine reacted with copper(II) acetate in dioxane to yield a (Cu(II), Pd(II), Cu(II)) trinuclear complex, which incorporated dioxane in the crystals. NMR, IR and reflectance spectra of the products were examined.

Deuterium isotope effect on the solid-state thermal isomerization of photo-coloured cis-keto species of N-salicylideneaniline

Deuterium isotope kinetic effect in the solid state was observed by using thermal fading reaction of photo-coloured species derived from N-salicylideneaniline deuterohydroxyl derivative; thus, the existence of a cis-keto form in the photo-coloured Schiff base crystals was suggested experimentally along with 6-methyl-substitution effect on the stability of the photoproduct.

Syntheses of new ferrocenylphosphinecopper(I) complexes and their application to the valence isomerization of norbornadiene to quadricyclene

Abstract Copper(I) chloride and bromide reacted with an equimolar amount of ferrocenyldiphenylphosphine (PFcPh 2 ) in refluxing benzene, affording the new tetrameric complexes [CuX(PFcPh 2 )] 4 ( 1 , X= Cl; 2, X = Br) as yellow microcrystals. Their bipyridyl (bpy) derivatives [CuX(bpy)(PFcPh 2 )] (3, X=Cl; 4, X=Br) were prepared also. When copper(I) chloride was allowed to react with abundant PFcPh 2 , only the mononuclear complex [CuCl(PFcPh 2 ) 2 ] (5) was isolated. THF solutions of the copper(I) complexes and 2,5-norbornadiene (Nbd) were irradiated at 366 nm, and the valence isomerization of Nbd to quadricyclene (Q) was observed. Quantum yields with 1 and 2 were about 0.011 and 0.008, respectively, and those with other complexes were very small. 31 P NMR studies were performed for the complexes in the presence of Nbd or norbornene, and the key photoactive species in the isomerization with 1 and 2 were determined to be their ground state copper-Nbd adducts, i.e. ‘CuX(PFcPh 2 )(Nbd)’. Photoexcitation of the adducts was assumed to give rise to the valence isomerization and to release Q.

Utilization of crystal lattice cavities of host deoxycholic acid for achieving photochromism of guest salicylideneanilines in the crystal state

Salicylideneanilines have been easily incorporated in the crystal lattice cacities formed by deoxycholic acid molecules to yield clathrate compounds, which exhibit photochromism irrespective of the photosensitivity of the starting Schiff bases in the crystal state.

Synthesis and properties of fullerene (C70) complexes of 2,6-bis(porphyrin)-substituted pyrazine derivatives bound to a Pd(II) ion

2,6-Bis(porphyrin)-substituted 3,5-dimethylpyrazine and its zinc complex bound C70 to yield 1:1 inclusion complexes, which were characterised by ESI-MS, UV–vis, fluorescence and NMR spectroscopies. Association constants of the C70 complexes were determined by fluorescence and NMR spectral analyses. A decrease in absorbance of the Soret band of the pyrazine derivative by the effect of C70 was observed, suggesting the existence of a charge transfer interaction between C70 and porphyrin. Experimentally reliable values for the association constants were obtained by the NMR method and were about six times larger than those of the corresponding C60 complexes. Palladium complexation of the porphyrin–pyrazine ligand was found to enhance the association with fullerene. The association constant of 2,6-bis(porphyrin-Zn)-substituted 3,5-dimethylpyrazine-Pd(II) complex with C70 was determined to be 8400 ± 900 M− 1. From the comparison of the association constants, it was found that inclusion room for C70 in the Pd(II) complex was maintained, juxtaposed between porphyrins attached to the opposite sides of the pyrazine ligands.