Invisible photochromism of diarylethene derivatives

Diarylethene derivatives with oxidized thiophene rings shift their absorption band to a shorter wavelength in the UV region upon photocyclization; no color change was observed during the photochromic reaction, and the invisible photochromism is advantageous for devices used under room light.     

Two-photon photochromism of diarylethene dimer derivatives.

Photochromic diarylethene dimer derivatives with large two-photon absorption (TPA) cross-sections have been designed and synthesized. The derivatives have a D-pi-D structure in which indole rings are used as donor units (D) and 1,4-bis(ethynyl)benzene or 1,4-bis(ethenyl)benzene as a pi-conjugated chain unit (pi). Compound 5 a, which has oxazole rings as one of the aryl groups, showed a TPA cross-section of 23 GM at 820 nm and exhibited efficient two-photon photochromic reactivity.     

Study on photochromic diarylethene with phenolic Schiff base: preparation and photochromism of diarylethene with benzoxazole

A photochromic diarylethene with phenolic Schiff base 1a can be easily transformed to photochromic diarylethene with benzoxazole 3a in the conditions of base and phototrigger. Both of their photochromic properties are investigated. They show that the conversions of ring-open form to ring-closed form at photostationary equilibrium are ca. 20% and 10% for 3a and 1a, respectively, and the backconversions are in nearly quantitative yield for both compounds. They also show that the response time for photostationary equilibrium is ca. 0.5 and 5 min for 3a and 1a, respectively, in the solution. In addition, a general preparation of 2-arylbenzoxazole from phenolic Schiff base in the conditions of base and phototrigger is demonstrated by employing phenolic Schiff bases with different substituted groups as template, and other conditions (solvents, in the presence and absence of oxygen) for preparation of benzoxazole from phenolic Schiff base are explored as well.     

Preparation and photochromism of diarylethene covalently bonded onto layered sodium-magadiite surfaces

Diarylethene derivatives (DE) covalently bonded to silanol oxygens of layered silicate surfaces, i.e., magadiite (Mag), were synthesized and investigated for their photochromic behavior. The DE-Mag layered hybrids were found to undergo reversible color change by alternating UV and visible light irradiation. A more highly efficient, reproducible photochromic behavior was realized with DE-Mag than with a corresponding DE-Si possessing silyl substituents on DE in place of the Mag surface. Moreover, the present covalently bonded DE exhibited an improvement over DE hybrids incorporated in layered double hydroxide (LDH) clays, in which the repetitive photochromic behavior decreased during alternating irradiation, due to the accumulation of the photochemically inert parallel isomers of DE.     

Chiral helicenoid diarylethene with large change in specific optical rotation by photochromism

A diarylethene possessing one [4]thiaheterohelicene and one benzothiophene, the latter with a chiral methoxymethoxyethyl group on its C-3 position, was proved to work as a switch of specific optical rotation at a wavelength at which both colored and colorless forms have no absorption in solution. The difference of the specific optical rotation was 1300 degrees between the open form and the photostationary state. The specific optical rotation of one of the isolated optically active major colored forms was -4680 degrees. The conversion to the colored form was 64%, and the diastereomeric excess of photocyclization was 47%.     

Crystal engineering of photochromic diarylethene single crystals

Photochromic performance of diarylethene single crystals was controlled by crystal engineering using non-covalent aromatic-aromatic interactions as the directional intermolecular force. A diarylethene derivative with two pentafluorophenyl groups, 1,2-bis(2-methyl-5-pentafluorophenyl-3-thienyl)perfluorocyclopentene (1a), formed stoichiometric co-crystals with benzene (Bz) and naphthalene (Np) by aryl-perfluoroaryl interactions. Face-to-face pi-stacking interactions between the pentafluorophenyl groups of 1a and the aromatic molecules are responsible for 2:1 and 1:1 stoichiometric compositions in 1a/Bz and 1a/Np co-crystals, respectively. The diarylethene underwent thermally stable and photoreversible photochromic reactions in a homo-crystal of 1a and co-crystals 1a/Bz and 1a/Np. The absorption spectra of the photogenerated closed-ring isomers varied depending on the conformation of the diarylethene molecules packed in the crystals. The diarylethene 1a also formed 1:1 stoichiometric co-crystals with different kinds of diarylethenes, 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene (2a) and 1,2-bis[2-methyl-5-(1-naphthyl)-3-thienyl]perfluorocyclopentene (3a). Both co-crystals 1a/2a and 1a/3a showed photochromism. Although 1a, 2a, and 3a underwent efficient photocyclization reactions in their homo-crystals, highly selective photocyclization reactions of 2a or 3a were observed in the co-crystals. The selective reactions were confirmed by HPLC and X-ray crystallography. Excited energy transfers from 1a to 2a and from 1a to 3a are considered to occur and cause the selective reactions.     

Digital photoswitching of fluorescence based on the photochromism of diarylethene derivatives at a single-molecule level

Photochromic reactions of diarylethene derivatives were detected at a single-molecule level by using a fluorescence technique. Fluorescent photoswitching molecules in which photochromic diarylethene and fluorescent bis(phenylethynyl)anthracene units are linked through an adamantyl spacer were synthesized, and switching of fluorescence upon irradiation with UV and visible light was followed in solution as well as on polymer films at the single-molecule level. Although in solution the fluorescence intensity gradually changed upon irradiation with UV and visible light, digital on/off switching between two discrete states was observed at the single-molecule level. The "on"- and "off"-times were dependent on the power of UV and visible light. When the power of UV and visible light was increased, the average on- and off-times became short in proportion to the reciprocal power of the light. The response-times were found to show distribution. The distribution of the on- and off-times is considered to reflect the difference in the micro-environment as well as conformation of the molecules.     

Cholesteric mixture containing chiral‐photochromic and diarylethene dopants as novel material with dual photochromism

New cholesteric polymeric mixture containing nematic side‐chain homopolymer, 2 wt% of photochromic diarylethene dopant and 5 wt% of chiral‐photochromic dopant based on cinnamic acid and isosorbide was prepared. Upon UV irradiation of planarly‐oriented mixture films at room temperature, a transformation of open colorless form of diarylethene dopant into a closed colored form takes place, which is followed by the appearance of an intense absorption maximum in the visible spectral region and decreasing selective light reflection intensity. This process is photo‐ and thermo‐reversible and many cycles ‘recording‐erasing’ can be realized. UV irradiation and subsequent annealing of the films lead to untwisting of the cholesteric helix and cause an irreversible shift of selective light reflection to the long‐wavelength region. This process is explained by the E‐Z isomerization of chiral photochromic groups of the dopant relative to a C?C bond accompanied by a decrease in their twisting ability. It has been shown, that the use of the material prepared in this work provides an opportunity to record two images at the same time: one image is due to a change in the helical pitch and another (second) image is due to the photochromism of diarylethene dopant. It is pertinent to note that using the approach developed in this work allows one to widely vary the range of materials exhibiting dual photochromism. It was demonstrated that the mixture under study shows advantage as new photosensitive material for optics, optoelectronics and data recording. Copyright © 2002 John Wiley & Sons, Ltd.     

Diastereoselective cyclization in chiral diarylethene crystals: polymorphism and selectivity

[structure: see text] An optically active photochromic diarylethene, (S)-1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(4-(3-methyl-1-penten-1-yl)phenyl)-3-thienyl]perfluorocyclopentene ((S)-1a), was synthesized. (S)-1a formed two crystalline phases, alpha- and beta-phases. The diarylethene underwent a photochromic reaction in solution and even in the single-crystalline phase. In solution, no diastereoselection was observed. On the other hand, in the beta-crystalline phase, only one diastereomer (S,R,R)-1b was produced. No such diastereoselection was observed in the alpha-crystalline phase.     

Spectroscopic studies of the photochromism of N-salicylideneaniline mixed crystals and glasses

The reaction mechanism of the photochromism of N-salicylideneaniline (SA) in crystalline and glass matrices has been investigated at low temperatures. The structures of the initial E and final QC states as well as those of the intermediates QA and QB have been analyzed by optical absorption and emission spectroscopy. The potential barriers involved in the photochromic activity have been deduced from the temperature-dependent kinetics of the absorption spectra. An energy-level scheme of the forward and back reactions is presented.     

Photochromism of diarylethene single crystals: crystal structures and photochromic performance

Diarylethenes undergo thermally irreversible and fatigue-resistant photochromic reactions not only in solution but also in the single-crystalline phase. This article describes recent development of the single-crystalline photochromism of diarylethene derivatives. We focused on the relationship between their crystal structures and the photochromic performance. Photocyclization/cycloreversion quantum yields, absorption spectra, the absorption anisotropies, and surface morphology changes are strongly dependent on the conformations and packing structures of the molecules in the crystals.     

Crosslinked polydiacetylene and its two- and three-component interpenetrating polymer networks (IPNs)

The synthesis of crosslinked polydiacetylene [poly4ECMU (a polydiacetylene with ethoxy carbonyl methylene urethane substitution): where R = ? (CH₂)₄OCONHCH₂COOCH₂CH₃] was carried out utilizing its polar and flexible substituent groups. Polydiacetylene was crosslinked by the formation of allophanate linkages utilizing urethane groups in the substituent groups of the polydiacetylene. Two-component IPNs of polydiacetylene [poly4BCMU (a polydiacetylene with butoxy carbonyl methylene urethane substitution): where R = ? (CH₂)₄OCONHCH₂COO(CH₂)₃CH₃] and an epoxy resin (diglycidyl ether of Bisphenol A) were synthesized. Two-component IPNs of poly4ECMU with the above epoxy resin were also synthesized. For the first time, two-component stiff-backbone IPNs of two different kinds of polydiacetylene (poly4BCMU and polyECMU) and a three-component IPN of poly4BCMU, poly4ECMU, and the epoxy resin were synthesized. IPNs with fewer allophanate linkages were also made in order to examine morphological differences between them. The glass transition behavior of these networks was studied using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) by means of a Rheovibron.     

Simultaneous two- and three-component determinations in multicomponent mixtures by extraction-spectrophotometry and thermochromism of ion-association complexes

A selective method of determination of amines and quaternary ammonium salts by solvent extraction and thermochromism of ion-association complexes has been established. The method is based on the formation of ion-association species with tetrabromophenolphthalein ethyl ester and the thermochromism effect in the organic phase at low temperature. The absorbance of the red amine charge-transfer complexes decreases quantitatively (DeltaA) with increase in temperature (DeltaT), and Delta A Delta T is characteristic of a particular species. This characteristic has been applied for the sensitive and selective determination of amines. The absorbance of the blue quaternary ammonium ion-association complexes does not vary with temperature, however, and the quaternary ammonium compounds can be determined without interference by amines because of the disappearance of the red species at 60 degrees . Methylephedrine, diphenhydramine, ephedrine (amines), benzethonium and/or berberine (quaternary ammonium compounds) in two- and three-component mixtures can be determined by using the thermochromism effect. The method is highly selective, sensitive and reproducible.     

Kinetic spectrophotometric method for the simultaneous quantitation of amino acids in two- and three-component mixtures

The development and evaluation of a kinetic method for the simultaneous quantitation of two- and three-component mixtures of amino acids are described. The method is based on reaction with ninhydrin. Multipoint kinetic data collected during one or more half-lives of the slower-reacting component are processed with a nonlinear regression program to resolve the data into the concentrations of the individual components in the mixture. Results demonstrate good linearity between prepared and calculated concentrations of each component and total amino acid in the mixture (10–50 μM). Slopes of least-squares fits of calculated vs. prepared concentrations vary from 0.98 to 1.13 and intercepts vary from ?0.1 to 2.9 μM with standard errors of the estimate (S_yx) between 0.67 and 1.7 μM.     

In-situ crystal structure analysis and control of photochromism with dual-mode photoreactive soft crystals

Photochromic compounds are of great interest currently owing to their potential applications. Their three-dimensional structure must be clarified to understand the photochromism mechanism. In-situ X-ray crystal structure analysis is a powerful tool for determining the structure directly after the photochromic reaction. In this review, I discuss about solid-state photochromic compounds, their direct X-ray observation in the crystal form, and in-situ control of photochromism in “dual photoreactive soft crystals”, which is a novel approach.     

Free radical-mediated aryl amination: convergent two- and three-component couplings to chiral 2,3-disubstituted indolines

5-exo-trig Cyclization of an aryl radical to the nitrogen of an azomethine is used as the key annulating step in a modular preparation of 2,3-cis- and trans-disubstituted indolines. The precursors are readily prepared by phase-transfer-catalyzed Michael addition of a glycine Schiff base to a variety of acceptors. When the more reactive alkylidene malonate Michael acceptors are implemented, a one-pot three-component coupling is possible. The net result is a convergent [3 + 2] coupling strategy for the construction of highly functionalized indolines, a substructure occurring in numerous biologically active natural products.     

Nonstationary evolution of the size,composition, and temperature of microdroplets of nonideal two- and three-component aqueous solutions

Results of numerical solution have been presented for a set of equations describing the nonstationary and nonisothermal growth or evaporation of microdroplets consisting of ethanol and water, sulfuric acid and water, and sulfuric and nitric acids and water. Time dependences of droplet size, temperature, and composition have been determined at low concentrations of a condensable vapor, as compared with the concentration of a carrier gas in an ambient vapor–gas mixture. The calculations have been performed using different initial conditions and approximations for the dependences of saturation vapor pressures, activity coefficients, and partial heats of condensation of the components, as well as average volumes per molecule on droplet composition and temperature. By the examples of ethanol–water and sulfuric acid–water droplets, it has been shown that nonmonotonic variations in the droplet radius are possible. Regimes of nonmonotonic variations in the temperature of a droplet that precede the onset of its stationary growth or evaporation have been revealed for all systems under consideration.     

Photochromism of diarylethene derivatives having cyclohexyl and cyclohexenyl groups in single-component crystals and a two-component mixed crystal

Diarylethene derivatives 1a having two cyclohexyl groups and 2a having a cyclohexyl and a cyclohexenyl group formed a mixed crystal composed of almost equal amounts of the two components, and underwent photochromism in the mixed crystal as well as in the single-component crystals.