Closed-ring Isomer 1b Research Articles

Photochromic Performance of 5-Heteroaryl-4-vinyl-2-phenylthiazole Derivatives

Abstract Compounds 5-(5-methyl-2-phenyl-4-thiazolyl)-4-(5-methyl-1-phenyl-1-propenyl)-2-phenylthiazole 1a and 5-(2-methyl-5-phenyl-3-thienyl)-4-(2-methyl-1-phenyl-1-propenyl)-2-phenylthiazole 2a having an S-N heteroatom-contact interaction and a CH-N hydrogen bonding were synthesized in an attempt to obtain new photochromic compounds having terarylene and 1-aryl-2-vinylcyclopentene backbones. The S-N interaction and CH-N hydrogen bonding of 1a and 2a can be explained by DFT calculation and temperature dependent 1H NMR spectra. The tethering interactions are expected to stabilize the reactive conformation of 1a and 2a, and to increase the photocyclization quantum yield. Two 5-heteroaryl-4-vinyl-2-phenylthiazoles 1 and 2 underwent reversible photocyclization reactions from the open-ring isomers 1a and 2a to the closed-ring isomers 1b and 2b, respectively. The photocyclization quantum yields of 1a and 2a are 0.57 and 0.63, which are 3 times larger than that of 1-thiazolyl-2-vinylcyclopentene derivatives (0.20). The number of photochromic cycles exhibited by 1b was 50 in the presence of air, which is higher than that of 2b.

A turn-on mode fluorescent diarylethene: Solvatochromism of fluorescence

Environment-sensitive fluorophores have been used as molecular probes to acquire physical and chemical information in microstructures. Here, we report on solvatochromism of a fluorescent diarylethene, which is switched by photoirradiation. A turn-on mode photoswitchable fluorescent diarylethene derivative, 1,2-bis(2-ethyl-6-(5-methylthiophen-2-yl)-1-benzothiophen-1,1-dioxide-3-yl)perfluorocyclopentene (1a), underwent a cyclization reaction upon irradiation with ultraviolet (UV) light to form fluorescent closed-ring isomer 1b. 1b dramatically changed the fluorescent color in response to solvent polarity, such as green in n-hexane, yellow in tetrachloromethane (CCl4), orange in dichloromethane (CH2Cl2), and red in dimethyl sulfoxide (DMSO), and showed high fluorescence quantum yields of 0.6–0.8 in these solvents. The fluorescent solvatochromism is ascribed to the intramolecular charge-transfer (ICT) character of 1b, which consists of electron-donating thiophene rings at both ends and central electron-accepting benzothiophene 1,1-dioxide groups. The analysis based on the Mataga-Lippert plot revealed that the difference in the dipole moments between the excited and ground states of 1b is as large as 12 D. Such a solvatochromic fluorophore with photoswitching ability can find potential applications in super-resolution fluorescence imaging of microscopic polarity in biological cells and materials.

Fluorescence Photoswitching of a Diarylethene by Irradiation with Single-Wavelength Visible Light.

Photoswitchable turn-on mode fluorescent molecules have been so far successfully used in super-resolution fluorescence microscopies. Here, we report on fluorescence photoswitching of 1,2-bis(2-ethyl-6-phenyl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentene (1) by irradiation with single-wavelength visible (420 nm < λ < 470 nm) light, the wavelength of which is longer than the 0-0 transition of open-ring isomer 1a, without UV light excitation. By absorbing very weak hot bands or Urbach tails 1a underwent a cyclization reaction to produce fluorescent closed-ring isomer 1b. Both cyclization and cycloreversion reactions of 1 took place with the visible light in the far off-resonance region of the absorption edge. Based on numerical simulations of the formation process of 1b from 1a by irradiation with 450 nm light, weak absorption coefficients at 450 nm in n-hexane and CCl4 were estimated to be 0.084 and 0.19 M-1 cm-1, respectively. The reversible fluorescence photoswitching with the single visible light is advantageously applicable to super-resolution fluorescence imaging in biological systems.

Synthesis and Photochromism of a Novel Diarylethene Bearing Xylosyltriazolyl Groups

A new unsymmetrical photochromic diarylethene, 1-{2-methyl-5-[5-(2,3,5-trihydroxyl-β-D-xylosyl)-3-(1,2,3-triazolyl)] methylene-3-thienyl}-2-[2-methyl-5-(4-methoxylphenyl) methyl-3-thienyl] perfluorocyclopentene (1a), was synthesized, and its photochromic properties were investigated in detail. The compound exhibited good photochromism both in acetonitrile solution and in PMMA film with alternating irradiation by UV/vis light, and the maxima absorption of its closed-ring isomer 1b are 556 and 560 nm, respectively. There almost no fluorescence switches of 1a in acetonitrile solution and PMMA amorphous film. The diarylethene 1a has promising application for photo-switching, which can use for data storage.

Synthesis, Photochromism and Optical Recording Properties of a Diarylethene Materials Bearing an Isoxazole Unit

A new unsymmetrical photochromic diarylethene, 1-(3,5-dimethyl-4-isoxazolyl)-2-[2-methyl-5-(4-formylphenyl)-3- thienyl]perfluorocyclopentene(1a) were synthesized, and its properties, such as photochromism and fluorescence properties, were investigated in detail. The results showed that this compound had good thermal stability and exhibited reversible photochromism, changing from colorless to darkred after irradiation with UV light both in solution and in PMMA amorphous film, the maxima absorption of its closed-ring isomer 1b are 529 nm and 541 nm respectively. The open-ring isomer of the diarylethene 1a exhibited relatively strong fluorescence at 492 nm in hexane solution (2 × 10-5 mol/L) when excited at 418 nm. The fluorescence intensity decreased along with the photochromism upon irradiation with 297 nm light. This new photochromic system also exhibited remarkable optical storage character.

Photoinduced Anisotropy in a New Diarylethene Bearing Five and Six-Membered Aryl

A new symmetrical photochromic diarylethene, 1-(2-methyl-5-formyl)-2-(2- cyanophenyl) perfluorocyclopentene(1a), was synthesized, and its photochromic properties were investigated in detail. The compound exhibited good photochromism both in solution and in PMMA film with alternating irradiation by UV/VIS light, and the maxima absorption of its closed-ring isomer 1b are 544 and 549 nm, respectively. The photochromism properties of 1a diarylethene show good photochromism in hexane and in PMMA amorphous film. Steady state fluorescence studies indicated that 1a diarylethene is higher fluorescent in the open-ring isomer, but there almost no fluorescence in the closed-ring isomer in PMMA amorphous film. The diarylethene 1a has promising application for photo-switching, fluorescence-switching which can use for data storage.

Synthesis and the optoelectronic properties of diarylethene derivatives having benzothiophene and n-alkyl thiophene units

Six new unsymmetrical diarylethenes having both benzothiophene and n-alkylthiophene units have been synthesized. The structures of diarylethenes 2a– 6a were determined by single-crystal X-ray diffraction analysis. The results showed that the alkyl chain length had a significant effect on the optoelectronic properties of these diarylethenes, including photochromism, fatigue resistance, fluorescence and electrochemical properties. The long alkyl chains can increase the cyclization/cycloreversion quantum yields but decrease the absorption maxima of diarylethenes 1– 6. The long alkyl chains can also induce a remarkable bathochromic shift for the absorption maxima of the closed-ring isomers 1b– 6b both in solution and in PMMA film. All these diarylethene derivatives showed good fluorescent switching (quench to ca. 10%) in hexane. The emission intensities and the fluorescent quantum yields of diarylethenes 1– 6 decreased gradually with the alkyl chain length becoming longer. In addition, cyclic voltammetry tests showed that the alkyl chain length had a remarkable effect on the electrochemical behaviors of these diarylethenes.

Photochromic properties of diarylethenes having 2,4-diphenylphenyl substituents in the amorphous and PMMA films

1,2-Bis[5-methyl-2-(2,4-diphenyl)phenyl-4-thiazolyl]perfluorocyclopentene 1a and 1,2-bis-[2-methyl-5-(2,4-diphenyl)phenyl-3-thienyl]perfluorocyclopentene 2a were synthesized and their photochromic performance was examined in the bulk amorphous states. Compounds 1a and 2a formed stable amorphous bulk solid at room temperature and the glass transition temperatures ( T gs) of them were observed at 77 °C. The conversions in the photostationary states were evaluated to be 88% and 90% in the amorphous films prepared from the closed-ring isomers 1b and 2b. The values are higher than that of 1,2-bis[2,4-dimethyl-5-(2,4-diphenyl)phenyl-3-thienyl]perfluorocyclopentene 3 (74%). Photochromic reactions of these compounds were also examined in poly(methyl methacrylate) (PMMA) films. The conversion ratios of 1 and 2 (91% for both compounds) in the PMMA films are also higher than that observed in 3 (80%). The photocyclization quantum yields of 1a, 2a, and 3a are the same, while the photocycloreversion quantum yields of 1b and 2b are lower than that of 3b. The higher conversions of 1 and 2 are attributed to the lower photocycloreversion quantum yields, which were caused by the decrease in the steric hindrance between 4-position of the aryl groups and perfluorocyclopentene ring.

Photochemically Stable Novel Yellow Developing Photochromic Compounds Having a Thiazole Group

ABSTRACT Diarylethene derivatives having a thiazole ring as the aryl group 1a , 2a , and 3a have been synthesized in an attempt to obtain photochromic compounds which change the color from colorless to yellow, and have low photocycloreversion quantum yields and high absorption coefficients of the colored isomers. Compounds 1 and 3 exhibited reversible photochromic reactions in hexane solution. The closed-ring isomers 1b and 3b showed orange and yellow colors, respectively. The ϵ value of 3b at the absorption maximum is 18400 M−1cm−1, which is much larger than those of 1b (ϵ = 10000 M−1cm−1) and 2b (ϵ = 11400 M−1cm−1). The photocyclization/cycloreversion quantum yields of 3 were determined to be 0.19 and 0.0014, respectively. The yellow color was sufficiently photochemically stable under room light.

Fluorescence Property of Photochromic Diarylethenes with Indole Groups

Abstract Diarylethenes having a fluorescent indole ring as the aryl group 1a and 2a were synthesized. Upon alternate irradiation with 366 nm and visible (λ &amp;gt; 480 nm) light, 1a underwent reversible photocyclization reactions to produce closed-ring isomer 1b. The fluorescence intensity also reversibly changed along with the reactions. The fluorescence quantum yields of the open-ring isomers 1a and 2a were 4.6 and 6.3% respectively, while the yields of the closed-ring isomers 1b and 2b were almost zero. The fluorescence quantum yields decreased with the increase in the photocyclization quantum yields.

Photochromism of 1,2-Bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene in a Single-Crystalline Phase. Conrotatory Thermal Cycloreversion of the Closed-Ring Isomer

1,2-Bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene (1a) was found to undergo a thermally reversible photochromic reaction in solution as well as in the single-crystalline phase. Upon irradiation with ultraviolet light the hexane or toluene solution containing 1a and single-crystal 1a turned blue along with the formation of closed-ring isomer (1b). The blue solution and single crystal returned colorless by irradiation with visible light (λ > 500 nm) or heating above 100 °C. The bleaching is due to the cycloreversion of 1b to 1a. The thermal cycloreversion activation energies were measured in the toluene solution and in the single-crystalline phase above 100 °C. The activation energy from photogenerated 1b to 1a in the solution was 128 kJ mol-1, while it decreased to 120 kJ mol-1 in the crystal of the open-ring isomer 1a. In the crystal of the closed-ring isomer 1b the energy increased to 137 kJ mol-1. The cycloreversion reaction was found to be controlled by the environmental conditions. The thermal cycloreversion reaction in the crystal was directly followed by X-ray crystallography and revealed to proceed in a conrotatory mode, which is opposed to the general Woodward−Hoffmann rules.