Three bits eight states photochromic recording and nondestructive readout by using IR light

A photochromic polymer film containing three different diarylethene derivatives, that is, 1,2-bis(3,5-dimethyl-2-thienyl)perfluorocyclopentene (1), 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene (2), and 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene (3) was prepared. Upon UV irradiation, the three derivatives changed to their closed-ring isomers having different colors, yellow, red, and blue. They showed different spectra not only in UV/Vis region but also in the IR spectral region. Upon irradiation with visible light of appropriate wavelengths, each closed-ring isomer was selectively bleached, and three bits eight states recording was performed. The eight states could be read out nondestructively by using IR light of appropriate wavenumbers.     

Polymorphism of 1,2-Bis(2-methyl-5-p-methoxyphenyl-3-thienyl)perfluorocyclopentene and Photochromic Reactivity of the Single Crystals

Four polymorphic crystals were obtained by recrystallization of 1,2-bis(2-methyl-5-p-methoxyphenyl-3-thienyl)perfluorocyclopentene (1 a) from hexane. All crystals underwent photochromic reactions upon alternate irradiation with ultraviolet (lambda=370 nm) and visible light (lambda>500 nm). The photocyclization quantum yields were found to be close to unity irrespective of the crystal types, while the photocycloreversion quantum yields were different as much as four times depending on the conformation of the closed-ring isomers in the crystals.     

Development of highly fluorescent photochromic material with high fatigue resistance

Efficient and reversible fluorescence modulation with excellent photo-stability was achieved from a sulfone form of diacetyl diarylethene, 1,2-bis(6-acetyl-2-methyl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentene (DABTFO4). The DABTFO4 emits strong fluorescence in the closed-ring isomer even in the absence of extra fluorophores. The fluorescence quantum yield, fatigue resistance, and photo-cyclization yield of DABTFO4 were significantly improved compared with the unsubstituted 1,2-bis(2-methyl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentene (BTFO4) and the sulfide analogue, 1,2-bis(6-acetyl-2-methyl-1-benzothiophene-3-yl)perfluorocyclopentene (DABTF6).     

Multicolor photochromism of two- and three-component diarylethene crystals

Novel photochromic single crystals composed of three different kinds of diarylethenes, 1,2-bis(3,5-dimethyl-2-thienyl)perfluorocyclopentene (1a), 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene (2a), and 1,2-bis(2-methyl-5-p-methoxyphenyl-3-thienyl)perfluorocyclopentene (3a), have been prepared. The three-component crystals turned yellow, orange, red, purple, blue, green, or black upon irradiation with light of appropriate wavelengths. The colors of the crystals were thermally stable in the dark and completely bleached by irradiation with visible light. Such multicolored photochromic crystals have potential for the application to optoelectronic devices, such as multifrequency three-dimensional optical memory media or full-color displays.     

Syntheses and optoelectronic properties of four photochromic dithienylethenes

Four photochromic dithienylethene compounds, 1,2-bis(2-methyl-5-naphthalene-3-thienyl)perfluorocyclopentene 1a, 1,2-bis[2-methyl-5(p-fluorophenyl)-3-thienyl]perfluorocyclopentene 2a, 1,2-bis[2-methyl-5(p-ethoxyphenyl)-3-thienyl]perfluorocyclopentene 3a, and 1,2-bis[2-methyl-5(p-N,N-dimethylaminophenyl)-3-thienyl]perfluorocyclopentene 4a were synthesized, and their optoelectronic properties, such as photochromism in solution as well as in poly-methylmethacrylate (PMMA) amorphous films, fluorescences and electrochemical properties were investigated in detail. These dithienylethenes have shown good photochromic behavior both in solution and in PMMA amorphous film. All of them exhibited relatively strong fluorescence and gave a bathochromic shift upon increasing concentration in THF. The irreversible anodic oxidation of 1a, 2a and 4a was observed by performing cyclic voltammetry experiments.     

Photochromic reactions of diarylethenes in single crystals with intermolecular O--H...N hydrogen-bonding networks

The crystal structures and photochromic performance of a single crystal of a diarylethene derivative possessing carboxyl groups, 1,2-bis(5-carboxyl-2-methyl-3-thienyl)perfluorocyclopentene (1 a), and cocrystals of 1 a with 4,4'-, 2,4'-, and 2,2'-bipyridines were examined. In crystal 1 a, a discrete cyclic structure was observed, in which four 1 a molecules are linked through hydrogen bonds between the carboxyl groups. In the homocrystal, photoreactive and photoinactive conformers of 1 a exist in the ratio of 1:1. In the cocrystals of 1 a with bipyridines, O--HN-type hydrogen bonds between 1 a and pyridyl groups were formed, and all 1 a molecules are fixed in a photoreactive conformation. Both the homocrystal 1 a and the cocrystals showed photochromic performances, and color variation from bluish-violet to cyan was observed, depending on the conformation of the packed diarylethene molecules.     

Crystal structure-reactivity correlation in single-crystalline photochromism of 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene

Single-crystalline photochromism of 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene 1a was followed in situ by X-ray crystallographic analysis. The crystal of 1a has two molecules with different conformations in the crystallographic asymmetric unit. The X-ray analysis of the photoirradiated crystal showed that the photocyclization reaction of the molecule with the shorter distance between the reactive carbons prevails over the reaction of the other molecule. The mechanism has been discussed based on the calculation of the electronic transitions of the two molecules in the different conformations. The photocyclization quantum yield was determined to be 1 (100%) in the crystal.     

Highly fluorescent photochromic diarylethene in the closed-ring form

A highly fluorescent diarylethene in the closed-ring form was synthesized by the oxidation of 1,2-bis(2-methyl-1-benzothiophene-3-yl)perfluorocyclopentene (BTF6).     

Light-driven bending of diarylethene mixed crystals

Mixed crystals composed of 1,2-bis(2-methyl-5-(p-methoxyphenyl)-3-thienyl)perfluorocyclopentene (1a) and 1,2-bis(5-methyl-2-(p-methoxyphenyl)-4-thiazolyl)perfluorocyclopentene (2a) were prepared, and their photochromic as well as light-driven bending performance was studied to reveal how shape changes of individual molecules cause the bending response. 1a and 2a molecules, having similar geometrical structures, randomly mix with each other in a single crystal. The absorption spectra of the closed-ring isomers 1b and 2b were, however, distinctly different. The difference of the spectra made it possible to discriminate the cycloreversion reactions of 1b and 2b in the mixed crystals by irradiation with 750 nm light. The bending response of the mixed crystals by the selective photoisomerization revealed that the local shape change of each molecule is additively linked to the macroscopic deformation of the crystals.     

Substituent position effect on the properties of new unsymmetrical isomeric diarylethenes having a chlorine atom

Three new unsymmetrical photochromic diarylethenes bearing a chlorine atom at para-, meta- and ortho-position of one terminal benzene ring, namely {1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(4-chlorophenyl)-3-thienyl]}perfluorocyclopentene (para 1o), {1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(3-chlorophenyl)-3-thienyl]}perfluorocyclopentene (meta 2o), and {1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(2-chlorophenyl) -3-thienyl]}perfluorocyclopentene (ortho 3o), have been synthesized. The substituent position effect on their properties, including photochromism, fluorescence both in solution and in PMMA amorphous film and their electrochemical properties were investigated in detail. The results elucidated that the chlorine atom and its substituent position had a remarkable effect on the absorption characteristics, photochromic reactivity, fluorescence, as well as the electrochemical performances of these diarylethene compounds. For diarylethenes 1, 2 and 3, the cycloreversion quantum yields were gradually increased when the chlorine atom was attached to the para-, meta- and ortho-positions of the one terminal benzene rings; but their molar absorption coefficients both of their open-ring and closed-ring isomers were remarkably decreased. The fluorescent properties of para-substituted diarylethene embedded in poly(methyl methacylate) (PMMA) amorphous film showed good fluorescent switches (quenched to 28%). Furthermore, the cyclic voltammograms experiments elucidated that the electrochemical properties of these diarylethene derivatives were also remarkably dependent on the chlorine atom position effect, which may be attributed to the different electron-inducing ability and steric effect when the chlorine atom was substituted on the different position of the terminal benzene ring.     

Characterization of cationic diarylethene by electron spin resonance and absorption spectra-ratio of open/closed-ring isomers

Electrochemical cyclization/cycloreversion reactions of a diarylethene, 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene, are examined experimentally by electron spin resonance (ESR) and absorption spectra. To understand the ESR spectrum, the hyperfine coupling constants are calculated by the density functional theory (DFT) with the B3LYP exchange-correlation functional. The averaged values of the hyperfine coupling constants are approximated by imposing the C(2) symmetry on the structure of the diarylethene. We found that the spectral width of the ESR is significantly different between the open- and closed-ring isomers. This is due to the difference in the pi-conjugation between two isomers. The ESR spectral width analysis could, thus, be used to identify the isomerization of the radical species, which involve the change of the pi-conjugation. The experimentally observed spectrum is found to be the mixture of the open- and closed-ring isomers of the diarylethene. The excitation energies of the cationic diarylethenes are further identified by the SAC-CI calculations.     

多波长存储材料的合成与存储实验研究

报道了用有机光致变色的二芳基乙烯化合物作为多波长光存储记录材料的合成、膜片制作和多波长存储实验。结果显示,分别用1,2-双(2,5-二甲基噻吩-3-基)全氟环戊烯、1,2-双(2-甲基-5-醛基噻吩-3-基)全氟环戊烯和1,2-双(2-甲基-5-(2,2-二氰基乙烯基)噻吩-3-基)全氟环戊烯作为多波长光存储的记录材料,采用旋涂法(spin-coating)制成存储膜片,对应的读写激光器的波长分别532、650和780nm,实现了三波长光存储的信息记录和读出。     

Photochromism of metal complexes composed of diarylethene ligands and Zn(II), Mn(II), and Cu(II) hexafluoroacetylacetonates

Metal complexes composed of bidentate 1,2-bis(2-methyl-5-(4-pyridyl)-3-thienyl)perfluorocyclopentene (1a) and monodentate 1-(2-methyl-5-phenyl-3-thienyl)-2-(2-methyl-5-(4-pyridyl)-3-thienyl)perfluorocyclopentene (2a) photochromic ligands and M(hfac)(2) (M = Zn(II), Mn(II), and Cu(II)) were prepared, and their photoinduced coordination structural changes were studied. X-ray crystallographic analyses showed the formation of coordination polymers and discrete 1:2 complexes for bidentate and monodentate ligands, respectively. The complexes underwent reversible photochromic reactions by alternate irradiation with UV and visible lights in solution as well as in the single-crystalline phase. Upon photoirradiation with UV and visible light, the ESR spectra of the copper complexes of 1a reversibly changed. While the open-ring isomer gave an axial-type spectrum, the photogenerated closed-ring isomer showed a rhombic-type spectrum. This indicates that the photoisomerization induced the change in the coordination structure.     

Photochromism of metal complexes composed of diarylethene ligands and ZnCl2

Metal complexes composed of ZnCl(2) and bidentate 1,2-bis(2-methyl-5-(4-pyridyl)-3-thienyl)perfluorocyclopentene (1a) and monodentate 1-(2-methyl-5-phenyl-3-thienyl)-2-(2-methyl-5-(4-pyridyl)-3-thienyl)perfluorocyclopentene (2a) photochromic ligands were prepared. X-ray crystallographic analyses showed the formation of a coordination polymer and a discrete 2:1 complex for 1a.ZnCl(2) and 2a(2).ZnCl(2), respectively. While the 2a(2).ZnCl(2) crystal underwent photochromic reaction in the crystalline state by alternate irradiation with UV and visible light, the 1a.ZnCl(2) crystal did not show any photoreactivity. The difference in the photochromic behavior was explained by the difference in the conformation of the diarylethenes in the crystals.     

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.     

A proton and optic dual-control molecular switch based on photochromic diarylethene bearing a rhodamine unit

A novel fluorescent switch based on rhodamine B and photochromic diarylethene, 1-[2-methyl-5-(4-methoxylphenyl)-3-thienyl]-2-[2-methyl-5-(4-rhodamine B hydrazine-Schiff base-phenyl)-3-thienyl]perfluorocyclopentene (1), has been successfully synthesized through the condensation of rhodamine B hydrazine and 1-[2-methyl-5-(4-methoxylphenyl)-3-thienyl]-2-[2-methyl-5-(4-formylphenyl)-3-thienyl]perfluorocyclopentene. UV and FL measurements reveal that the compound exhibits good photochromic properties responsive to proton and optic dual inputs. Upon irradiation with 297 nm light, the colorless solution of compound 1 turns blue, while the blue solution becomes colorless after irradiated with visible light (λ>450 nm). Furthermore, upon an addition of H⁺, the fluorescence resonance energy transfers from the rhodamine unit (FRET donor) to the closed-ring diarylethene unit (FRET acceptor), although no energy transfer occurs when the diarylethene is in the open-ring form. The emission intensity of the rhodamine can be modulated with proton and UV/vis light and molecular-level signal communication has been constructed, indicating high potentials of the compound in molecular switches or naked eye recognition systems.     

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.     

Photochromic dihetarylethenes

A series of new photochromic compounds were obtained for the first time from 1,2-bis(2-ethylthio-3-thienyl)perfluorocyclopentene by substituting bromine atoms or carboxy, alkoxycarbonyl, and carbamoyl groups for hydrogen atoms in positions 4 and 4′. Introduction of these substituents causes a slight bathochromic shift (by 20–30 nm) of a long-wavelength absorption band for the cyclic form and significantly increases the quantum yields of photocyclization Ф_A→B and ring opening Ф_B→A. Depending on the nature of a substituent, Ф_A→B decreases in the order COOH>COOMe>CONHAr. The quantum yields are markedly reduced when the ethylthio groups in positions 5 and 5′ are replaced by ethylsulfonyl groups (a tenfold reduction in Ф_A→B and a four- to fivefold reduction in Ф_B→A) The most considerable bathochromic shift of a long-wavelength band and the highest quantum yields of forward and reverse photoreactions were observed for 1,2-bis(4-bromo-2-ethylthio-3-thienyl) perfluorocyclopentene. 1,2- Bis (2-ethyl-5-ethylthio-4-methoxycarbonyl-3-thienyl)perfluorocyclopentene was structurally characterized by X-ray diffraction analysis.     

Synthesis, crystal structure and optoelectronic properties of a new unsymmetrical photochromic diarylethene

A new unsymmetrical photochromic diarylethene, 1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(3-trifluoromethylphenyl)-3-thienyl]perfluorocyclopentene (1a), was synthesized and its structure was determined by single-crystal X-ray diffraction analysis. Its optical and electrochemical properties, including photochromic reactivity both in solution and in the solid state (PMMA film and the single-crystalline phase), fluorescence and electrochemical properties were investigated in detail. The compound showed excellent photochromism even in the single-crystalline phase by photo-irradiation. In acetonitrile, the open-ring isomer of diarylethene 1 exhibited relatively strong fluorescence at 470nm when excited at 300nm, and its emission intensity decreased along with the photochromism upon irradiation with 313nm light. Its closed-ring isomer showed almost no fluorescence. The electrochemical properties of diarylethene were investigated by performing cyclic voltammetry experiment and its HOMO and LUMO energy level were calculated.     

New photoswitching unit for magnetic interaction: diarylethene with 2,5-bis(arylethynyl)-3-thienyl group

Photoswitching of the intramolecular magnetic interaction was demonstrated using diarylethenes with 2,5-bis(arylethynyl)-4-methyl-3-thienyl side group. Two nitroxide radicals were placed at each end of the 2,5-bis(arylethynyl)-4-methyl-3-thienyl group. Three kinds of aryl groups, 2,5-thienylene, p-phenylene, and m-phenylene groups, were used in the arylethynyl moiety. The diarylethene photoswitching units have an extended pi-conjugated chain on one side of the diarylethene. The photochromic reactivity was dependent on the arylethynyl group. Diarylethenes with m-phenylene group showed an efficient photochromic reactivity. Along with the photochromic reaction the diarylethenes showed photoswitching of an ESR spectrum originating from the change in the magnetic interaction between two unpaired electrons. The open-ring isomer showed stronger exchange interaction than the photogenerated closed-ring isomer. The magnetic interaction between two radicals via the pi-conjugated chain was altered by photocyclization due to the change of the hybrid orbital at the 2-position of the thiophene ring from sp(2) to sp(3).