One-step synthesis and photochromic properties of a stable triangle terthiophene

A new photochromic compound based on the hexatriene backbone was prepared by one-step coupling. The photochromic backbone, composed of three thiophene ring, undergoes reversible ring-opening and ring-closing photoisomerization reactions when irradiated with ultraviolet and visible light, respectively. It exhibited fatigue resistance and thermally irreversible photochromic properties. The ring-open form exhibits appreciable fluorescence, while quenched by the ring-closed form.     

Photochromism of single crystals of arylhydrazide derivatives

Photochromic transformations in single crystals of hydrazides due to trans—cis-isomerization were found. The presence of the hydroxyl group in the ortho-position of the benzylidene fragment completely precludes photoinduced isomerization in the crystalline state.     

Photochromism of diarylethene derivatives having an indene unit

Photochromic indene derivatives, 1-(2-methyl-1-inden-3-yl)-2-(2-methyl-1-benzothien-3-yl)perfluorocyclopentene and 1-(2-methyl-1-inden-3-yl)-2-(2-methyl-1-benzofuran-3-yl)perfluorocyclopentene, were synthesized and their photochromic performance was examined.     

Photochromism of dinaphthylethene derivatives. Stability of the closed-ring forms

Stability of various types of closed-ring forms of dinaphthylperfluorocyclopentenes was investigated from both experimental as well as theoretical points of view. The stability was dependent on the energy differences between the open-ring and the closed-ring forms. When the energy difference was small, the closed-ring form became stabler.     

Photochromism of cis(z)-1,2-bispyrryl-substituted ethene derivatives

Photochromism of two bispyrryl-substituted ethenes, 2, 3-bis-(1-p-methoxyphenyl-5-phenyl-2-methyl-3-pyrryl)-2-butene (BPE1) and 2,3-bis(1-p-bromophenyl-4-phenyl-2-methyl-3-pyrryl)-2-butene (BPE2), was studied by laser flash photolysis technique. The results indicate that photocyclization of these compounds proceeds mainly via the excited triplet state, and the cis-trans isomerization proceeds mainly via the excited singlet state. After UV laser pulse irradiation, both photocylization and cis-trans isomerization of BPEl occur, but photocydization is the main reaction. On the other hand, laser photolysis of BPE2 leads mainly to photocydization. The effects of the substituents on the photochromic mechanism are also discussed.     

Helix triangle: unique peptide-based molecular architecture

We here report a unique cyclic peptide structure, "helix triangle", as a unique example of peptide-based molecular architecture. The cyclic peptide is designed to have a triangular shape in which three 9mer helical peptide units make the sides and three pyrene derivatives make the apexes. The helical peptide units are ideally linear, and the pyrene units are ideal 60 degrees angular components. The yield of the cyclic peptide was relatively high despite its large cycle size. Absorption and fluorescence spectroscopy revealed that the three pyrene units do not interact with each other electronically, and circular dichroism spectroscopy indicated that the helical peptide units take 3(10)-helical conformation. Geometry optimization by the semi-empirical molecular orbital method gave a triangular structure with 3(10)-helices as the plausible molecular structure. To gain more information on the geometry and demonstrate one example of its self-assemblies, the monolayer of the cyclic peptide was prepared at the air/water interface, and its surface pressure-molecular area isotherm was studied. The isotherm indicated formation of a stable monolayer and suggested that the cyclic peptide actually takes the triangular structure predicted by the geometry optimization. The monolayer was then transferred onto a substrate and characterized by various methods. Ellipsometry and infrared reflection-absorption spectroscopy confirmed that the cyclic peptide has horizontal orientation to the surface in the monolayer. Furthermore, absorption and fluorescence spectroscopy showed that the isolated electronic properties of the pyrene units are intact even in a condensed state in the monolayer.     

Photochromism of mixed crystals containing bisthienyl-, bisthiazolyl-, and bisoxazolylethene derivatives

Single crystals composed of two or three different kinds of diarylethenes, having similar geometrical structures but different colors in the closed-ring isomers, 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene (1a), 1,2-bis(5-methyl-2-phenyl- 4-thiazolyl)perfluorocyclopentene (2a), and 1,2-bis(5-methyl-2-phenyl-4-oxazolyl)perfluorocyclopentene (3a) have been prepared in an attempt to form single crystals which exhibit different colors, depending on illumination wavelengths. When 1a and 2a are mixed in ethanol and the content of 2a in the feed is higher than that of 1a, only a needle-shaped crystal is obtained. The crystal shape is similar to that of 2a. On the other hand, high content of 1a in the feed leads to formation of a block-shaped crystal, of which the shape is similar to that of 1a. At a feed ratio of 1:1 for 1a and 2a, two types of crystals such as needle- and block-shapes are obtained from the same batch. Mixed crystals composed of three kinds of derivatives 1a/2a/3a have also been prepared. A crystal composed of the three derivatives in the molar ratio of 32 (1a):53 (2a):15 (3a) was obtained. X-ray analysis proved that 1a and 3a are packed in the crystal lattice of 2a. The mixed crystal 1a/2a/3a changed color from colorless to yellow, red, and blue upon irradiation with light of appropriate wavelengths.     

Chromatographic resolution of molecular species of phosphatidylethanolamine as n-acyl-o-methyl derivatives

Phosphatidylethanolamines were converted into the N-acetyl-O-methyl or N-benzoyl-O-methyl derivatives by treatment with acetic anhydride/benzoyl chloride and diazomethane. Methods for the separation of these derivatives by argentation thin-layer chromatography and reversed-phase partition thin-layer chromatography are described. The procedure is especially advantageous for the analysis of phosphatidylethanolamines that are radioactively labelled in the ethanolamine moiety.     

Photochromism of 2-benzyl-3-benzoyl-4(1H)-quinolone derivatives

A series of 2-benzyl-3-benzoyl-4(1H)-quinolone derivatives was investigated. The UV–vis spectra of all photochromic derivatives and the corresponding colored photoenols are similar and almost solvent independent. In contrast, the stability of the photoenols depends strongly on the substituents at the quinolone moiety and solvent. We conclude that conversion of the photoinduced forms into the initial quinolones occurs through ionization rather than usual for photochromic compounds thermal relaxation or sigmatropic H-shift. The experimental observations are in good agreement with the results of quantum mechanical calculations.     

Photochromism of bis(2-alkyl-1-benzofuran-3-yl)perfluorocyclopentene derivatives

[reaction: see text] Photochromic diarylethene derivatives having benzofuran heteroaryl groups, bis(2-methyl-1-benzofuran-3-yl)perfluorocyclopentene and bis(2-butyl-1-benzofuran-3-yl)perfluorocyclopentene, were synthesized, and their photochromic performance was examined in hexane solution as well as in the single-crystalline phase. The compounds exhibited photochromic reactivity even in the single-crystalline phase.     

Photochromism of spirofluorenylindolizines

The decoloration kinetics of three spirofluorenylindolizines have been followed in solution and in polymer matrix. They are the 5′-methyl-spiro[9H-fluorene-9.1′(1′H)-indolizine]-2′-3′-bis-methoxycarbonyl ( I ), its methacryloyl oxymethyl ( II ) derivative, and the copolymers of ( II ) with ethyl acrylate. In solution the reactions follow first-order kinetics and show pronounced negative solvatochromism. In solid polymer film, the incorporation of the photochrome as side group of polyethylacrylate affects strongly the decoloration below T_g of the film. Above T_g the decoloration was interpreted on the basis of the WLF equation.     

Photochromism of diarylethene derivatives bearing a benzo[b]silole unit

Photochromic benzo[b]silole derivatives, 1-(1,1-dimethyl-2-phenylbenzo[b]silol-3-yl)-2-(2-phenylbenzo[b]thien-3-yl)perfluorocyclopentene and 1-(1,1-dimethyl-2-phenylbenzo[b]silol-3-yl)-2-(2-phenyl-1-benzofuran-3-yl)perfluorocyclopentene, were synthesized and their photochromic performance was examined in solution.     

Photochromism of new 3,5-position hybrid diarylethene derivatives bearing both thiophene and thiazole moieties

Five new diarylethenes based on a hybrid structure of bis(5-thiazolyl)ethene and bis(3-thienyl)ethene were synthesized, and the structures of the four compounds were determined by single-crystal X-ray diffraction analysis. The properties of these diarylethenes, such as photochromism, fluorescence, and electrochemical properties were investigated in detail. All of these compounds showed good photochromism and fluorescence both in solution and in PMMA films. The electron-donating substituents could effectively increase the cyclization and cycloreversion quantum yields, and the fluorescence emission peaks, whereas the electron-withdrawing groups functionalized an inverse action for these diarylethene derivatives. Cyclic voltammetry revealed that great differences existed amongst the electrochemical behaviors of these compounds. The oxidation potentials and the band gaps of these diarylethenes increased remarkably with the increase in electron-withdrawing ability. All results suggested that the effects of substitution have a significant effect on the photochemical and electrochemical behaviors of these diarylethene derivatives.     

Phase transition equilibrium of terthiophene isomers

The thermodynamic study of the phase transition (fusion and sublimation) of 2,2′:5′,2″-terthiophene and 3,2′:5′,3″-terthiophene is presented. The obtained data is used to evaluate the (solid + liquid) and (solid + gas) phase equilibrium, and draw the phase diagrams of the pure compounds near the triple point coordinates. For each compound the vapour pressures at different temperatures were measured by a combined Knudsen effusion method with a vacuum quartz crystal microbalance. Based on the previous results, the standard molar enthalpies, entropies and Gibbs energies of sublimation were derived at T = 298.15 K. For the two terthiophenes and for 3,3′-bithiophene, the temperature, and the molar enthalpies of fusion were measured in a power compensated differential scanning calorimetry. The relationship between structure and energetics is discussed based on the experimental results, ab initio calculations and previous literature data for 2,2′-bithiophene and 3,3′-bithiophene. The 3,2′:5′,3″-terthiophene shows a higher solid phase stability than the 2,2′:5′,2″-terthiophene isomer arising from the higher cohesive energy due to positioning of the sulphur atom in the thiophene ring. The higher phase stability of 3,3′-bithiophene relative to 2,2′-bithiophene isomer is also related to its higher absolute entropy in the solid phase associated with the ring positional degeneracy observed in the crystal structure of this isomer. A significant differentiation in the crystal phase stability between isomers was found.     

Photochromism of dihydroindolizines. Part XVI: first attempts toward molecular wires comprising photochromic dihydro 5-azaindolizines and π-extended ethynyl and butadiynyl oxadiazole derivatives

Eight new photochromic dihydro 5-azaindolizines (DHAIs) linked with 2,5-diaryl-1,3,4-oxadiazole (OXD) derivatives containing terminal ethynes and butadiyne substituents on the fluorene part of the DHAI skeleton are synthesized via palladium-mediated coupling reaction pathways. Irradiation of the DHAI-OXD derivatives with polychromatic light affords red- and green-colored betaines.     

Platinum(II) molecular triangle with a deep intramolecular cavity

Depending on the conditions, the reaction of K 2PtCl 4 with 1,3-bis( N-pyrazolyl)benzene (bpzphH) yields either Pt(bpzph)Cl, [Pt(mu-bpzph)Cl] 3, or a mixture of these products. In the case of the C 3-symmetric trimer, each bpzph (-) ligand is bidentate with the metal bonded to a pyrazolyl group and to the phenyl group at the 6 position; the remaining pyrazolyl group bridges to an adjacent platinum center. The crystal structure confirms that each complex is chiral with an unusually deep (approximately 8 A) intramolecular cavity; enantiomeric pairs of trimers encapsulate the diethyl ether solvate. NMR studies establish that the trimer exhibits excellent thermal and kinetic stability. Substitution of the chloride ligands provides a strategy for elaborating the macrocycle.     

Photochromism, anomalous multi-banded fluorescence and laser properties of some amino- and tosyl-amino derivatives of oxadiazole

The multi-banded fluorescence and laser properties of 11 new amino- and tosylamino derivatives of 2,5-di(phenyl)-1,3,4-oxadiazole and oxadiazole in various solvents at 293 K are reported. All the compounds investigated possess intra-molecular hydrogen quasi-bond (IHB) of 4.6-5.2 kcal mol(-1) in the ground state. In the excited state they can undergo protolytic dissociation or intra-molecular photon-initiated transfer of proton and reveal anomalous fluorescence which cannot be explained within the framework of the Kasha and Kasha-Vavilov rules. Depending upon the excitation wavelength, solvent, concentration and pH of the medium, the compounds studied show a single, double, triple or even a four-banded fluorescence, which has not been reported earlier. The nature of multi-banded fluorescence is explained in terms of the possible photochromic processes in excited states. Quantum yields and decay times of the different fluorescence bands are reported. Anomalous dependence of quantum yield upon concentration of the solution is observed. Laser properties of the compounds studied are carefully tested. Laser action based on the fluorescence of the so-called bi-radical molecules is reported. Various possible arrangements of singlet and triplet levels of compounds investigated are discussed.     

Synthesis and molecular docking studies of some new thiosemicarbazone derivatives as HCV polymeraseinhibitors

Series of new thiosemicarbazones was prepared and molecular studied as inhibitors of HCV 4WTG polymerase. Thus, the thiosemicarbazone derivatives (3a–k) were synthesized by two different ways, from reacting thiosemicarbazides with aldehydes and by one-pot three component reaction using ZnCl₂/SiO₂ as a catalyst under solvent free conditions. Molecular docking analysis of the synthesized products predicted that the thiosemicarbazone derivatives 3c, 3g, and 3k were the most promised as a highly inhibitors for HCV 4WTG polymerase in comparison with Sofosbuvir drug.     

A QSAR study and molecular design of benzothiazole derivatives as potent anticancer agents

A quantitative structure-activity relationship (QSAR) of a series of benzothiazole derivatives showing a potent and selective cytotoxicity against a tumorigenic cell line has been studied by using the density functional theory (DFT), molecular mechanics (MM ) and statistical methods, and the QSAR equation was established via a correlation analysis and a stepwise regression analysis. A new scheme determining outliers by "leave-one-out" (LOO) cross-validation coefficient (q2n-i) was suggested and successfully used. In the established optimal equation (excluding two outliers), the steric parameter (MRR) and the net charge (QFR) of the first atom of the substituent (R), as well as the square of hydrophobic parameter (lgP)2 of the whole molecule, are the main independent factors contributing to the anticancer activities of the compounds. The fitting correlation coefficient (R2) and the cross-validation coefficient (q2) values are 0.883 and 0.797, respectively. It indicates that this model has a significantly statistical quality and an excellent prediction ability. Based on the QSAR studies, 4 new compounds with high predicted anticancer activities have been theoretically designed and they are expected to be confirmed experimentally.