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.     

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.     

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.     

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.     

E-2-benzylidenebenzocyclanones. II. IR and mass spectrometric investigations

A series of E-2-benzylideneindanones (a) -tetralones (b) and -benzosuberones (c) with OCH₃ (2–4), NO₂ (5–7) and F (8–10) substituents in ortho, meta or para position was studied by IR and mass spectrometry. The most important IR bands were assigned and stated correlations between some frequencies and the stereostructure or conjugation feature of the molecules investigated. IR spectra were also analyzed in order to find frequencies characteristic of the size of the alkanone ring. The mass spectrometric investigation aimed at determining fragmentation pathways and finding correlations between them and the ring size of the alkanone ring or the position of the substituents.     

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.     

含典型氟-氢邻近与远程耦合的混合物的核磁共振氢谱示例

Two serials of tetrasubstituted benzene compounds containing fluoro group were designed and synthesized. The other three substitutes are sequentially the para, meta, and ortho to fluoro group. The obtained compounds were all mixtures as confirmed by ¹H NMR spectroscopies. The spectra clearly show the proximity and remote interaction between fluorine atom and hydrogen atom. In addition, the two spectra, one showing the overlapping peaks, one not, can be used as the simple and typical example of ¹H NMR spectra of mixtures.     

A rationalization of orientation and reactivity in the nucleophilic replacement reactions of aromatic polyhalo-compounds

C₆F₅X compounds react with nucleophiles at the position para to X in some cases (X = H, CH₃, NMe₂, SMe, CF₃), meta in others (X = NH₂, O⁻) and occasionally at both meta and para in comparable amounts (X = OMe, NHME); significant amounts of ortho-replacement also occur (X = Cl, OMe). These orientations, and those in polychloro-aromatics and polyfluoro-polynuclear aromatics, can be rationalized by considering the relative stabilities of the Wheland-type intermediates involved (I, II, III), provided the halogens are taken as electron-repelling in π-systems. Reactivities can be rationalized if ground state stabilities are considered as well. A number of predictions have been made on the basis of these arguments.     

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.     

Systematic study on the thermal cycloreversion reactivity of diarylethenes with alkoxy and alkyl groups at the reactive carbons

The relationship between the thermal cycloreversion reactivity of diarylethenes and the bulkiness of the substituents at the reactive carbons was systematically investigated. Two photochromic diarylethenes, 1,2-bis(2-isobutoxy-5-phenyl-3-thienyl)perfluorocyclopentene (1a) and 1,2-bis(2-neopentoxy-5-phenyl-3-thienyl)perfluorocyclopentene (2a), were newly synthesized and their optical properties and thermal cycloreversion reactivity were examined, because there is insufficient data for diarylethenes with alkoxy groups at the reactive carbons. The steric substituent constant was employed to correlate the relationship between the thermal cycloreversion reactivity of diarylethenes with alkyl and alkoxy groups at the reactive carbons and the bulkiness of the substituent. A good correlation was obtained for the substituent constant using CH₂ instead of oxygen in the alkoxy groups. The results indicate that this is a very useful strategy for the design of novel diarylethenes with desired thermal cycloreversion reactivity.     

Dynamic, electrooptical and energetic nonequivalency of NH bonds in 1:1 and 1:2 complexes of aminopyridines with proton acceptors

The influence of the –NH₂ group position in the pyridine ring on the proton donor ability of N–H groups in hydrogen bonding as well as on the spectral behaviour of stretching and bending vibrations of aminopyridines has been studied. The proton donor ability was shown to increase in the row: meta-, ortho-, and para-aminopyridines. It was established tha N–H bonds in ortho-aminopyridine were not equivalent, and the evaluation of their dynamic nonequivalence was made.

The influence of temperature on the spectral characteristics of the absorption bands of the stretching vibrations of amine groups in the free and hydrogen bonded molecules in CCl₄ has been studied (in temperature range 290–330 K), the formation constants of the complexes have been determined, enthalpy of the 1:1 complexes formation (−ΔH₁) between ortho- and meta-aminopyridines with dimethylformamide, dimethylsulphoxide and hexamethylphosphoramide has been calculated in temperature range 290–330 K. The 1:2 complexes of ortho-, meta- and para-aminopyridines with acetonitrile, tetrahydrofurane, dimethylsulphoxide, hexamethylphosphoramide were studied at the indoor temperature. Enthalpy of the 1:2 complex (−ΔH₂) was estimated on the basis of ‘intensity rule’; −ΔH₁=ΔB^1/2 assuming that parameter does not depend on the composition of a complex.

The vibrational and electrooptical tasks were solved for the free and H-bounded molecules of aminopyridines as well as its complexes of the 1:1 and 1:2 compositions. Dynamic, electrooptical and energetic nonequivalency of NH bonds of aminogroups in aminopyridines was studied quantitatively. The independent calculations of dynamic constants proved mentioned above nonequivalency of NH bonds.

Correlations between spectral characteristics of the absorption bands, geometric, dynamic and electrooptical parameters of –NH₂ group in aminopyridines in the free and hydrogen bonded molecules have been established. Those correlations allow to determine the most important molecular characteristics obtained on the basis of spectral measurements in the range of the absorption bands of the stretching vibrations of aminogroup.     

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 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.     

The suppressed reactivity of pyridine towards electrophiles as a result of an interplay between intra- and intermolecular interactions

A new accounting is suggested for the suppressed relative reactivity of all carbon atoms of pyridine as compared to benzene in the bimolecular electrophilic substitution (S_E2) processes in terms of an interplay between intra- and intermolecular interactions. Introduction of a nitrogen atom is shown to be accompanied by emergence of intramolecular interactions between the usual molecular orbitals of benzene that, in turn, give birth to definite mixed terms containing products of intra- and intermolecular interactions in the perturbative expansions for populations transferred between orbitals of the aromatic ring and those of electrophile. For ortho and para directions of the electrophilic attack, all the principal intramolecular interactions are shown to yield negative contributions to the intermolecular charge transfer in accordance with the dramatically reduced reactivities of these positions in pyridine. By contrast, contributions of different signs are shown to emerge in the relevant expressions referring to the meta attack. In this connection, conditions are revealed and analyzed that ensure the reduced intermolecular charge transfer for the meta position as well. Electrophiles of sufficiently high electron-accepting ability are shown to meet these conditions.     

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.     

The stability of columns comprising alternating triphenylene and hexaphenyltriphenylene molecules: variations in the structure of the hexaphenyltriphenylene component

Previous investigations of complementary polytopic interaction (CPI) columnar mesophases, in which the columns are built up of alternating hexaalkoxytriphenylene (HAT) and hexaphenyltriphenylene (PTP) molecules, concentrated mainly on the effect of variations in the structure of the HAT component. This investigation is concerned with the effect of variations in the structure of the PTP component and, in particular, variations in the position of an alkoxy side chain in the phenyl ring. Stable columnar mesophases are obtained when a hexyloxy substituent is placed in the meta- or para-position but not in the ortho-position. In the case of the meta- and para-substituted systems, the two-component CPI columnar phases are stable over a considerably larger temperature range than the one-component HAT systems. The evidence suggests that unfavourable PTP/PTP stacking is as much a driving force for the formation of these mixed stacks as is favourable PTP/HAT stacking, but both need to be explained in terms of the sum of atomically dispersed van der Waals and coulombic interactions. On cooling from the isotropic into the Col_h phase, the columnar phase based on a 1:1 mixture of hexakis(hexyloxy)tripenylene and the meta-hexyloxy-substituted PTP gives an unusual texture consisting of 'viking-axe'-shaped structures.     

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.     

Chloromethylphenylcarbamate derivatives of cellulose as chiral stationary phases for high-performance liquid chromatography

A new class of eight chloromethylphenylcarbamate derivatives of cellulose was prepared by introducing both an electron-donating methyl group and an electron-withdrawing chloro group on to the phenyl moieties and their chiral recognition abilities were evaluated as chiral stationary phases (CSPs) for high-performance liquid chromatography. The superiority of these derivatives over dichloro- and dimethylphenylcarbamates of cellulose as CSPs was demonstrated for some racemic compounds. The elution order and enantioselectivity were greatly dependent on the positions of the substituents. Meta- and para-disubstituted derivatives showed higher chiral recognition than ortho- and meta- or para- disubstituted derivatives. The correlation between the chemical shifts of the N---H protons of the carbamate moieties and the enantiomer-resolving abilities of the derivatives is discussed. Some of the derivatives were effective CSPs in both normal- and reversed- phase conditions and could efficiently separate some chiral drug enantiomers.     

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).