Closed-ring Isomer Research Articles

Efficient Cycloreversion Reaction of a Diarylethene Derivative in Higher Excited States Attained by Off-Resonant Simultaneous Two-Photon Absorption.

Off-resonant excitation of the closed-ring isomer of a photochromic diarylethene derivative at 730 nm induced the efficient cycloreversion reaction with a yield of ∼20%, while the reaction yield was only 2% under one-photon excitation at 365 nm. Excitation wavelength dependence of the one-photon cycloreversion reaction yield under steady-state irradiation in a wide wavelength range showed that the specific electronic state leading to the large cycloreversion reaction yield, which is originally forbidden in the optical transition but partially allowed owing to the low symmetry of the molecule, is spectrally overlapped with the electronic state accessible by the allowed one-photon optical transition in the UV region. Femtosecond transient absorption spectroscopy also revealed that the off-resonant two-photon excitation preferentially pumped the molecule into the specific state, leading to the 10-fold enhancement of the cycloreversion reaction.

A Perspective on Reagent Diversity and Non-covalent Binding of Reactive Carbonyl Species (RCS) and Effector Reagents in Non-enzymatic Glycation (NEG): Mechanistic Considerations and Implications for Future Research.

This perspective focuses on illustrating the underappreciated connections between reactive carbonyl species (RCS), initial binding in the nonenzymatic glycation (NEG) process, and nonenzymatic covalent protein modification (here termed NECPM). While glucose is the central species involved in NEG, recent studies indicate that the initially-bound glucose species in the NEG of human hemoglobin (HbA) and human serum albumin (HSA) are non-RCS ring-closed isomers. The ring-opened glucose, an RCS structure that reacts in the NEG process, is most likely generated from previously-bound ring-closed isomers undergoing concerted acid/base reactions while bound to protein. The generation of the glucose RCS can involve concomitantly-bound physiological species (e.g., inorganic phosphate, water, etc.); here termed effector reagents. Extant NEG schemes do not account for these recent findings. In addition, effector reagent reactions with glucose in the serum and erythrocyte cytosol can generate RCS (e.g., glyoxal, glyceraldehyde, etc.). Recent research has shown that these RCS covalently modify proteins in vivo via NECPM mechanisms. A general scheme that reflects both the reagent and mechanistic diversity that can lead to NEG and NECPM is presented here. A perspective that accounts for the relationships between RCS, NEG, and NECPM can facilitate the understanding of site selectivity, may help explain overall glycation rates, and may have implications for the clinical assessment/control of diabetes mellitus. In view of this perspective, concentrations of ribose, fructose, Pi, bicarbonate, counter ions, and the resulting RCS generated within intracellular and extracellular compartments may be of importance and of clinical relevance. Future research is also proposed.

Photochromism of new unsymmetrical diarylethenes with a quinoline moiety

Three unsymmetrical diarylethenes with a 6-membered quinoline moiety were synthesized to investigate the effects of the substituents on their photochromism, and fluorescence, and the structure of one diarylethene was determined by single crystal X-ray diffraction analysis. Quinoline was connected directly to the central perfluorocyclopentene ring as an aryl moiety and available to participate in photoisomerization reaction in solution, amorphous films, and crystalline phase. These diarylethenes exhibited good photochromism with excellent thermal stability and obvious fatigue resistance. The electron-donating methoxy group could enhance the absorption maxima of closed-ring isomers and the quantum yields of cyclization and cycloreversion, but the electron-withdrawing trifluoromethyl had an opposite effect. In addition, they functioned as notable fluorescence switches in both solution and polymethylmethacrylate films, and the trifluoromethyl group and the methoxy group both increased the emission intensity. The results revealed that the quinoline moiety and substituents played a vital role in the process of photoisomerization reactions for these diarylethenes.

Synthesis and Application of 1-[2-methyl-5-(4-chlorophenyl)-3- thienyl]-2-[2-methyl-5-formyl-3- thienyl]perfluorocyclopentene

A new unsymmetrical photochromic diarylethene 1-[2-methyl-5-(4-chlorophenyl)- 3-thienyl]-2-[2-methyl-5-formyl-3-thienyl]perfluorocyclopentene (1o) has been synthesized . In the meantime, its photochromic, kinetics and fluorescence properties were investigated in detail. This diarylethene had good thermal stability and exhibited reversible photochromism. What is more, the kinetic experiments illustrated that the cyclization/cycloreversion process of this compound was determined to be the zeroth/first reaction. The fluorescence intensity of diarylethene decreased dramatically along with the photochromism from open-ring isomer to closed-ring isomer upon irradiation with UV light in acetonitrile solution.

Discrimination between Conglomerates and Pseudoracemates Using Surface Coverage Plots in 2D Self-Assemblies at the Liquid-Graphite Interface.

The two-dimensional (2D) molecular ordering of two photochromic diarylethenes was investigated using scanning tunneling microscopy at the liquid-graphite interface. The racemic mixture of the closed-ring isomer of one of the diarylethenes showed spontaneous separation of its enantiomers upon 2D crystallization, whereas that of the other diarylethene formed a pseudoracemic crystal in which two enantiomers coexist in a 2D ordering domain. The mixing of enantiomers in 2D assemblies can be analyzed by the dependence of the surface coverage on the concentration of enantiomers at different enantiomeric ratios.

Light-Activated Sensitive Probes for Amine Detection.

Our new, simple, and accurate colorimetric method is based on diarylethenes (DAEs) for the rapid detection of a wide range of primary and secondary amines. The probes consist of aldehyde- or ketone-substituted diarylethenes, which undergo an amine-induced decoloration reaction, selectively to give the ring-closed isomer. Thus, these probes can be activated at the desired moment by light irradiation, with a sensitivity that allows the detection of amines at concentrations as low as 10-6 m in solution. In addition, the practical immobilization of DAEs on paper makes it possible to detect biogenic amines, such as cadaverine, in the gas phase above a threshold of 12 ppbv within 30 seconds.

Theoretical analysis of electrochromism under redox of bis(3-thienyl)/(2-thienyl)hexafluorocyclopentene: effects of charged and substituted systems.

Electrochromism with the ring-closing or ring-opening isomerization of substituted and unsubstituted bis(3-thienyl)/(2-thienyl)hexafluorocyclopentene is discussed using the DFT method. In the neutral ground state, bond making and breaking between two reactive C atoms on thienyls are thermodynamically forbidden. Under redox conditions, the gain or loss of electrons can have a significant effect on the frontier molecular orbital distribution of both open- and closed-ring isomers, particularly in reactive sites. Corresponding structural changes show a trend toward isomerization. The reaction energy barrier shows greater reduction for dication than monocation and even becomes barrierless for dianion. During the isomerization in different states, the conjugated system switches distinctively, which is attributed to the special redistribution of molecular orbitals and spin population in each state. In monocation and monoanion, for the involvement of a single electron, isomerization is inclined to proceed sequentially between right and left thienyls, whereas it becomes synchronous in dication. The direction depends on the stabilization achieved by the formation of a global conjugated system and more average spin population on the molecule. The effect of substituents on thienyls is demonstrated in the promotion of the extent of conjugation and the determination of the spin population level on the reactive C atoms. Moreover, according to their electron-donating and withdrawing abilities, they can kinetically support or suppress the electron transfer pattern in the process from isomer to transition state, which leads to the control of reaction efficiency.

Study on the Synthesis and Application of a Material 1-[2-Methyl-5-Phenyl-3-Thienyl]-2-[2-Methyl-5-(3-Aldehyde-4-Methoxy)-3-Thienyl] Perfluorocyclopentene

A novel photochromic diarylethene was successfully synthesized, which is named 1-[2-methyl-5-phenyl-3-thienyl]-2-[2-methyl-5-(3-aldehyde-4-methoxy)-3-thienyl] perfluorocyclopentene. The compound showed good photochromic behavior. Upon irradiated with UV/vis lights, the color of the compound could be changed between colorless and blue, accompanied by a fluorescence switch between the open-ring isomer and closed-ring isomer.

Cysteine and homocysteine chemosensor based on photochromic diarylethene with fluorine

A new photochromic diarylethene with formyl and fluorene groups, 1-[2-methyl-5-(9,9-diethyl-fluoren-2-yl)-3-thienyl]-2-[(2-methyl-5-formyl)-3-thienyl]perfluorocyclopentene, has been synthesized and characterized with single-crystal X-ray diffraction. Due to the interaction between the formyl group in its ring-closed isomer with cysteine/homocysteine, there was an evident color change in its absorption spectrum from blue to pale yellow and light brick-red upon addition of cysteine and homocysteine, respectively. Moreover, it was revealed that no obvious interference was observed during the titrations with the mixtures of cysteine/homocysteine and other amino acids. These results indicated that the diarylethene could be used as a colorimetric sensor to recognize cysteine/homocysteine with high selectivity.

Diastereoselective photocyclization of a photochromic diarylethene having a benzo[b]phosphole P-oxide group

A photochromic diarylethene derivative 1 having a chiral benzo[b]phosphole P-oxide at the aryl moiety underwent a diastereoselective photocyclization reaction in acetonitrile upon irradiation with ultraviolet (UV) light. It was found that the diastereomeric excess (d.e.) value changes depending on the conversion ratio from the open- to closed-ring isomer as well as the irradiation wavelength. This is attributed to the difference in the photocycloreversion quantum yields of diastereomers of the closed-ring isomer. The diarylethene showed a high photocyclization quantum yield owing to a high population of photoreactive conformers of the open-ring isomer by the steric effect of the benzo[b]phosphole P-oxide group.

ChemInform Abstract: Strategy for Molecular Design of Photochromic Diarylethenes Having Thermal Functionality

AbstractReview: [31 refs.

A new fluorescence probe based on fluorescein-diarylethene fluorescence resonance energy transfer system for rapid detection of Cd2+

A novel diarylethene derivative 1O with fluorescein-quinoline unit was designed and synthesized successfully. Under the stimulation of light and chemical, the diarylethene molecule exhibited multi-responsive photoswitchable properties. Moreover, the compound was a potential ‘naked eye’ chemosensor with significant color and fluorescence changes in the recognition of Cd2+ in tetrahydrofuran (THF). When the fluorescein spirolactam ring-opened form was triggered with Cd2+, an obvious red shift from 459 nm to 560 nm (101 nm) was observed in complex 1O′, and the emission intensity was enhanced by 8 fold with a concomitant fluorescence color change from dark to bright yellow. Significantly fluorescent quenching was observed in ring-closed isomer 1C′ due to the FRET (fluorescence resonance energy transfer) processes between fluorescein moiety and the ring-closed diarylethene moiety. The interference from other effective metal ions, particularly Zn2+, had not been observed. Finally, a molecular logic circuit was constructed with both light and chemical stimuli as inputs and fluorescence intensity at 560 nm as output.

Photochromism of novel [1]benzothien-2-yl fulgides

Novel [1]benzothien-2-yl fulgides were synthesized and their structures established based on analysis by 1H, 13C NMR and IR spectroscopy, mass-spectrometry and X-ray diffraction. All the compounds exist in the ring-opened Z-isomeric forms. Under UV-irradiation fulgides with no substituent at the methylidene bridge undergo thermally or photochemically reversible Z/E-photoisomerization, but do not convert to the cyclic isomeric forms. Under the same conditions, 3-(1-(3-methyl[1]benzothien-2-yl)ethylidene)-4-(1-methylethylidene)-dihydrofuran-2,5-dione with a methyl group at the methylidene bridge rearranges into the thermally stable colored 1,3-cyclohexadiene ring-closed isomer which possesses improved spectral characteristics as compared with 2-thienyl and [1]benzothien-3-yl analogues. Irradiation with visible light results in the fast backward isomerization into the initial colorless hexatriene ring-opened form.

Photosalient Effect of a Diarylethene with a Perfluorocyclohexene Ring.

Crystals of a diarylethene with a perfluorocyclohexene ring exhibit a remarkable photosalient effect upon UV light irradiation that is attributed to the structural changes that occur when going from open- to closed-ring isomers in the crystalline state, together with the existence of two conformers with different photoconversions compared with those of a perfluorocyclopentene derivative. Our current results give a design principle for molecular structures so as to achieve the photosalient effect for photochromic crystals.

Strategy for Molecular Design of Photochromic Diarylethenes Having Thermal Functionality.

Thermal reactivities of photochromic diarylethene closed-ring isomers can be controlled by the introduction of substituents at the reactive positions. Diarylethenes having bulky alkyl groups undergo thermal cycloreversion reactions. When bulky alkoxy groups are introduced, the diarylethenes have both thermal cycloreversion reactivities and low photocycloreversion quantum yields. Such photochromic compounds can be applied to thermally reusable photoresponsive-image recordings. The thermal cycloreversion reactivity of the closed-ring isomers can be evaluated using specific steric substituent constants and be correlated with the parameters. By introduction of trimethylsilyl or methoxymethyl groups at the reactive positions, the diarylethene closed-ring isomers undergo thermal irreversible reactions to produce by-products at high temperatures. These diarylethenes may be useful for secret-image recordings. Furthermore, thiophene-S,S-dioxidized diarylethenes having secondary alkyl groups at the reactive positions undergo thermal by-product formation reactions, in addition to the photostability of the colored closed-ring isomers. Such materials may be used for light-starting thermosensors. The thermal by-product formation reactivity can be evaluated by the specific substituent constants and theoretical calculations of quantum chemistry. These results supply the strategy for the molecular design of the photochromic diarylethenes having thermal functionality.

A novel Br-substituted diarylethene: Synthesis, crystal structure, and solvent dependent acidichromism

A novel Br-substituted diarylethene was synthesized, and its structure has been determined by single-crystal X-ray diffraction analysis. Its photochemical property in solution, a PMMA film, and single crystalline phase was studied. In solution, the absorption maximum of its closed-ring isomer shifted dramatically to shorter wavelengths with notable color change from violet to yellow upon the stimulation of trifluoroacetic acid. Moreover, the acidichromism showed obviously solvent-dependence. With enhancement of solvent polarity, the protonation-induced absorption maxima (Δλmax) and the response time became longer.

Rational Design of Highly Photoresponsive Surface-Confined Self-Assembly of Diarylethenes: Reversible Three-State Photoswitching at the Liquid/Solid Interface

Photoresponsive behavior of systems in equilibrium at the liquid/solid interface can be modulated through the design of photochromic core structures and the process of self-assembly. In this study, we investigated the effects of altering the substitution position of a thienyl group on two-dimensional (2-D) molecular ordering composed of photochromic diarylethenes (DAEs) at a liquid/highly oriented pyrolytic graphite (HOPG) interface using scanning tunneling microscopy (STM). We found that both the open- and the closed-ring isomers of a 3-thienyl-type DAE formed stripe-patterned orderings on a HOPG substrate at similar concentrations and that the process of self-assembly on a 2-D surface was highly cooperative for both isomers. In the case of 2-thienyl-type DAE, similar stripe-patterned ordering was observed only for the open-ring isomer, but no ordering was observed for the closed-ring isomer. Upon irradiation with UV and visible light, reversible three-state photoswitching over the formation/disappearanc...

A novel sensitive sensor for Cu2+ and multi-switch based on a diarylethene with a 2-(2′-hydroxyphenyl)benzothiazole unit

A new asymmetrical photochromic diarylethene with a 2-(2′-hydroxyphenyl)benzothiazole unit has been synthesized. It underwent reversible cyclization and cycloreversion reactions upon alternating irradiation with lower energy UV (297 nm, 25 μW/cm2) and visible light, while it could induce intramolecular proton transfer reaction upon irradiation with higher energy UV light (254 nm, 92 μW/cm2) with distinct color change. The absorption maximum of the closed-ring isomer was redshifted from 539 nm to 660 nm and the color changed from purple to cyan when the diarylethene was stimulated with base. Furthermore, addition of acid enhanced its fluorescence intensity by 5.5 fold and the emission peak was blueshifted from 596 nm to 570 nm with a concomitant color change from light orange to bright green, while base could efficiently quench its fluorescence intensity. Finally, the diarylethene was highly selective towards Cu2+ with significant absorption and fluorescence changes, which makes the ‘naked-eye’ detection of Cu2+ possible.

Photochromic reaction behavior and thermal stability of thiophene-S,S-dioxidized diarylethenes having a benzofuryl group

Diarylethenes having a benzofuryl group and their thiophene-S,S-dioxidized diarylethenes were synthesized and their optical properties and thermal stability were investigated. Upon oxidation of the thiophene ring, the optical properties such as absorption maxima, photocycloreversion quantum yields, and conversion from the open-ring isomer to the closed-ring isomer have changed. On the other hand, the thermal stability of the closed-ring isomers of the S,S-dioxidized diarylethenes is significantly higher than those of thiophene-S,S-dioxidized diarylethenes having a phenylthienyl group instead of a benzofuryl group. The high thermal stability of the closed-ring isomer was quantitatively discussed based on ground state energies obtained by quantum chemical calculations.

A new multi-addressable molecular switch based on a photochromic diarylethene with a thieno-imidazole unit

A novel photochromic diarylethene has been synthesized using dithieno-benzo-imidazole as a functional group and perfluorodiarylethene as photon-controlled unit via a benzene linkage. The diarylethene could be used as a multi-addressable fluorescence switch upon triggering by acid/base, light, and Al3+ in acetonitrile. When stimulated by base, the absorption maximum of its closed-ring isomer was red-shifted from 560nm to 594nm with an evident color change from purple to blue. When induced by acid, the emission intensity of its open-ring isomer was enhanced by 109 fold with a notable fluorescence color change from dark to bright cyan. Moreover, its fluorescence intensity was dramatically increased when triggered by Al3+ and its emission peak was red-shifted from 460nm to 476nm due to the formation of a 1:2 metal/ligand complex. In addition, its light and metal-responsive fluorescence behavior was applied to the construction of a molecular logic circuit with three inputs and one output.