Synthesis and photochromism of photochromic spiro compounds having a reactive pendant group

The photochromic spiropyrans and spirooxazines having a reactive pendant group, including carboxyl, halide, succinimidyl ester and isothiocyanate, were synthesized. Their photochromic behaviors in solution and solid state were studied.     

Syntheses and properties of new photochromic diarylethene derivatives having a pyrazole unit

New photochromic diarylethenes 1a, 2a and 3a bearing a pyrazole unit have been synthesized. Their properties, including photochromic reactivity, fluorescence and electrochemical properties were investigated. These compounds showed good photochromic properties, high cycloreversion quantum yield and relatively strong fluorescence. The cycloreversion quantum yields of 1a, 2a and 3a are 0.46, 0.53 and 0.57, respectively, which are larger than those of their cyclization quantum yields (0.43, 0.45 and 0.47, respectively). The oxidations of diarylethenes 1a, 2a and 3a were initiated at 0.73, 1.11 and 0.79 V, respectively. Moreover, the position of the methoxyl substituent had remarkable impacts on the above optical and electrochemical properties.     

Synthesis and properties of widely conjugated polyacetylenes having anthryl and phenanthryl pendant groups

The metathesis polymerization of 1- and 2-ethynylanthracenes (1-EA and 2-EA) and 2- and 3-ethynylphenanthrenes (2-EP and 3-EP) in the presence of various WCl₆-based catalysts produced widely conjugated soluble polymers with relatively high molecular weights. The highest weight-average molecular weights of poly(1-EA) and poly(2-EA) reached 61,000 and 26,000, respectively, when Ph₄Sn was used as cocatalyst, while those of poly(2-EP) and poly(3-EP) reached 23,000 and 65,000, respectively, with Ph₃Bi as cocatalyst. In contrast, MoCl₅-based catalysts were hardly or not effective for these monomers. A large red-shifted peak was observed centering at 570 nm (the cutoff at 750 nm) in the absorption spectrum of poly(1-EA), while the red-shifted peaks were seen around 500 nm (the cutoffs near 700 nm) in the spectra of other polymers, indicating wide conjugations of the polymer chains. The configurational structures of all the polymers confirmed by DSC and ¹H-NMR were trans structures. However, poly(1-EA) and poly(3-EP) appeared to consist partly of cis structures in their main chains. All of the present polymers showed relatively high thermal stability in air compared with poly(phenylacetylene). © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3131–3137, 1998     

The allomorphism of a photochromic diarylethene

The photochromic diarylethene, 1,2-bis(2-methyl-5-(2,2′-dicyanovinyl)-thien-3-yl)perfluorocyclopentene (1a), was synthesized by a novel method. Two kinds of single crystals of the compound were obtained depending on the different recrystallization conditions and their structures were determined by X-ray crystallographic analysis. Allomorphism of the photochromic diarylethene was discovered. The compound underwent a photochromic reaction both in solution and in the single crystalline phase of the anti-parallel conformer.     

Synthesis and positive‐imaging photosensitivity of soluble polyimides having pendant carboxyl groups

Polyimides having pendant carboxyl groups were prepared by a direct one‐pot polycondensation of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 3,5‐diaminobenzoic acid (DABz) and bis[4‐(3‐aminophenoxy)phenyl]sulfone (m‐BAPS) in the presence of a γ‐valerolactone/pyridine catalyst system using N‐methyl‐2‐pyrrolidone (NMP)/toluene mixture as a solvent at 180 °C. The obtained polyimides were soluble in dipolar aprotic solvents such as dimethylformamide, dimethyl sulfoxide, and NMP as well as in tetrahydrofuran and aqueous basic solution. The solubility of the polyimides was dependent on the diamine composition. Photosensitve polyimide (PSPI) systems composed of the polyimides and diazonaphthoquinone compound as a photosensitive material gave positive‐tone behavior by UV irradiation, followed by development with aqueous tetramethylammonium hydroxide (TMAH) solution. The scanning electron microscopic photograph of the resulting image showed 10‐μm line/space resolution with about 15 μm of film thickness. The PSPIs baked at 350 °C for a short time had excellent thermal resistance comparable to the original polyimides. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 934–946, 2001     

Photoswitching of an alcohol-sensitive photochromic diarylethene

The closed-ring isomer of diarylethene 1a, 1-(2-methyl-5-(4-N,N-diethylaminophenyl)thien-3-yl)-2-(2-methyl-5-phenylthien-3-yl)perfluorocyclopentene was found to cause the substitution reaction with primary alcohols at room temperature. The open-ring isomer 1a was stable in the alcohols. The product obtained in methanol was isolated by HPLC, and the structure was identified by ¹H NMR, mass spectrometry, and X-ray crystallographic analysis. It was revealed that two fluorine atoms were replaced with methoxy groups. The substitution reaction was also caused with ethylene glycol to form the five-membered ring. Both the products also showed photochromism, and had absorption maxima and photocycloreversion quantum yields different from those of 1a.     

Synthesis of photochromic diarylethene polymers for a write-by-light/erase-by-heat recording system

A functionalized styrene monomer (1a) having a photochromic diarylethene chromophore with functional properties of photocoloration, photostability of the colored state, and thermal erasion by heating was synthesized, and the polymer and copolymers of 1a were prepared by radical polymerization and copolymerization. Their polymers exhibited excellent photocoloration and rapid thermal bleaching above 150 °C in solution and in the solid state as well as the performance of the monomeric diarylethene chromophore. In addition, the colored state has a high photostability under visible room light. The diarylethene homopolymer had a glass transition temperature (T_g) as high as polystyrene. The copolymer of 1a with N-1-adamantylmaleimide exhibited extremely high T_g above 200 °C with keeping the photofunctional performance. Such photochromic polymer and copolymers with high T_g can be potentially applied to rewritable display materials and image recordings by a write-by-light/erase-by-heat system.     

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.     

Polyimides based on new diamines having pendant imide groups

New aromatic diamines were prepared in two steps from 4,5‐dichlorophthalic anhydride and primary amines. The resulting 4,5‐dichlorophthalimide was reacted with 4‐mercaptoaniline, so that the chloroatoms were substituted by the mercapto groups (via the sulfide anions). The new diamines were polycondensed either with the diphenyl ether 3,3′,4,4′‐tetracarboxylic anhydride or with bicyclooctane tetracarboxylic anhydride. These polycondensations were conducted in boiling m‐cresol with azeotropic removal of water. The isolated polyimides were characterized by viscosity measurement, IR‐spectroscopy, elemental analyses, and MALDI‐TOF mass spectrometry. The mass spectra evidenced a high content of cyclic polyimides, indicating nearly perfect reaction conditions. The mass spectra also proved the formation of copolymers containing one diamine with a trialkylamine group in the side chain. High glass transition temperatures but a low crystallization tendency were found by DSC measurements. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6272–6281, 2005     

Synthesis and photochromic properties of functional diarylethene with a 2,5-dihydrothiophene bridging unit

A novel synthetic route to symmetric and nonsymmetric dithienylethene derivatives with a 2,5-dihydrothiophene bridging unit was described. A class of new functional photochromic compounds was prepared and showed photochromic properties similar to those of known diarylethenes. [reaction: see text]     

Synthesis and photochromic reactivity of diarylethene trimers bridged by ethenyl and ethynyl unit

Two diarylethene trimers bridged by ethenyl and ethynyl groups were synthesized and their photochromic behaviors were examined. Upon irradiation of the trimers 2 and 4 with UV light, one-three photoinduced cyclization reactions occur. Each isomer was isolated and analyzed by ¹H NMR spectrum. The quantum yield of 2 and 4 is 0.52 and 0.311, respectively.     

Synthesis of aromatic polyesters having pendant carboxyl groups in the side chains and conversion of the carboxyl groups to other reactive groups

Aromatic polyester, copolyester, and poly(ester-amide-thioester) having pendant carboxyl groups are directly synthesized by the organic phase/water phase interfacial polyconden-sation using low-molecular and polymeric phase transfer catalysts. Spectral analysis of the resulting polymers indicates that the nucleophilicity of salts of phenols to diacid chloride is far higher than that of salts of carboxylic acids and chemoselective esterification occurs in a 100% yield. Even if the polymeric catalyst having amino acid moiety as a nucleophilic group is used in the polycondensation, the polymers do not contain anhydride groups. The polyester can be almost quantitatively converted to polymers with different reactive groups by reacting the pendant carboxyl groups with alkyl halides in a DMA_c-H₂O mixture con-taining K₂CO₃. A bifunctional catalytic mechanism is proposed for the chemical modification of the polyesters. © 1995 John Wiley & Sons, Inc.     

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.     

Synthesis and photochromic reactivity of a diarylethene dimer linked by a phenyl group

A diarylethene dimer linked by a phenyl group was synthesized and the photochromic behavior was examined. Upon irradiation with ultraviolet light (λ=313 nm), a hexane solution of the diarylethene dimer (1a) turned purple blue. Upon further prolonged irradiation the color changed to blue. The purple-blue and blue colors are due to the formation of a dimer having one open- and one closed-ring forms (1b) and a dimer having two closed-ring forms (1c), respectively. Both 1b and 1c returned to 1a by irradiation with visible light (λ>500 nm). The photochromic reactivity was evaluated by measuring quantum yields of the photocyclization and photocycloreversion reactions. The photocyclization quantum yield was 0.50. The cycloreversion quantum yield from 1c to 1b (0.0026) was lower than that from 1b to 1a (0.0094).     

Recent progresses on diarylethene based photochromic switches

Organic photochromic materials have received considerable attention because of their potential for photonic applications, especially for fast and high density data storage. In 2000, Chemical Reviews published a special issue on photochromic materials including a review about the properties and applications of diarylethene photochromic compounds. Since then much impressive progress has been made in this area. Various new diarylethene derivatives have been prepared and examined. The tutorial review presented herein describes developments in diarylethene-based molecular switches made in the last three years. In addition, the synthetic aspects of diarylethene photochromic compounds, which are important issues and neglected in most previous reviews, have been included.     

Switching mechanism of photochromic diarylethene derivatives molecular junctions

The electronic transport properties and switching mechanism of single photochromic diarylethene derivatives sandwiched between two gold surfaces with closed and open configurations are investigated by a fully self-consistent nonequilibrium Green's function method combined with density functional theory. The calculated transmission spectra of two configurations are strikingly distinctive. The open form lacks any significant transmission peak within a wide energy window, while the closed structure has two significant transmission peaks on both sides of the Fermi level. The electronic transport properties of the molecular junction with closed structure under a small bias voltage are mainly determined by the tail of the transmission peak contributed unusually by the perturbed lowest perturbed unoccupied molecular orbital. The calculated on-off ratio of currents between the closed and open configurations is about two orders of magnitude, which reproduces the essential features of the experimental measured results. Moreover, we find that the switching behavior within a wide bias voltage window is extremely robust to both substituting F or S for H or O and varying end anchoring atoms from S to Se and Te.     

Synthesis and the effect of alkyl chain length on photochromic properties of diarylethene derivatives

A new class of photochromic diarylethenes bearing pyrrole and thiophene units with different length of alkyl chains at 2-position of thiophene rings have been synthesized. Their characteristics, including photochromism and fatigue resistance were investigated systematically, and each diarylethene derivative showed good photochromic properties whether in solution or in PMMA films. The alkyl group moiety was connected directly to the central cyclopentene ring as a heteroaryl unit and availably participated in photoisomerization reaction. And some properties, for example, the conversion ratio in the photostationary state(PSS) and the absorption coefficient of the ring-closed isomers in acetonitrile were significantly affected by the alkyl chain length. The results revealed that substituents of alkyl chain played an important role in the photoisomerization process of diarylethenes.     

Synthesis of reactive aromatic polyesters having pendant chlorohydrin moieties

A monomer containing a chlorohydrin moiety, propyl chlorohydrin diphenolate (PCHDP), was synthesized. Reactive polyesters having these pendant chlorohydrin moieties were prepared by the interfacial polycondensation of isophthaloyl chloride with PCHDP or with PCHDP and diphenolic acid using phase transfer catalyst. The molar ratio of reactants and the phase ratio of water to organic solvent strongly affect the molecular weight of resulting polymers and polymers with high molecular weight are obtained at the molar ratio of 1.0–1.15 and the phase ratio of 2.0–3.5. Swelling of the growing polymers is dependent on the molar ratio of the reactants and the phase ratio because of the hydrophilic and hydrophobic nature of the pendant chlorhydrin moiety. The resulting polymers are not soluble in any solvent except water in which hydrolysis occurs. Thus so, the structure of polymers was confirmed by ¹³C CP/MAS NMR. © 1996 John Wiley & Sons, Inc.     

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).     

Synthesis, characterization, thermal and optical properties of styrene derivatives having pendant p-substituted benzylic ether groups

The derivatives of styrene monomer, 4-chlorophenyl-4-vinylbenzyl ether (M1), 4-methoxyphenyl-4-vinylbenzyl ether (M2), 4-ethylphenyl-4-vinylbenzyl ether (M3) and 1-naphtylphenyl-4-vinylbenzyl ether (M4) were synthesized. The normal free radical polymerization of monomers in 1,4-dioxane were performed by using 2,2′-azobisisobutyronitrile as an initiator at 65 °C. The monomers and their homopolymers were characterized by FT-IR, NMR and elemental analyses measurements. The thermal stability of polymers was investigated by thermogravimetric and differential scanning calorimetric analysis. Thermal degradation activation energies of the polymers were calculated by the Ozawa and Kissinger methods. In addition, photo-stability tests of the polymers under near-UV irradiation were performed.