Cycloreversion Process Research Articles

Beyond Photochromism: Alternative Stimuli to Trigger Diarylethenes Switching.

Diarylethenes (DAEs) are typical photochemically reversible type (P-type) photochromic materials with excellent thermal stability and high fatigue resistance and are widely exploited as photo-switches for various applications in molecular devices, data storage, photoresponsive materials, and bioimaging, etc. In recent years, there is an increasing number of reports using heat, acid, electrochemistry, etc. to drive the isomerization reaction of DAEs. The response to two or more different stimuli enables multi-functionality within a single DAE molecule, which would facilitate complex logic-gate operations, multimode data storage, and increased information density. Herein, the recent advances in DAE systems utilizing stimuli "beyond photo" to trigger the isomerization processes from three perspectives: acidochromism, thermochromism, and electrochromism are reviewed. Emphasis is placed on the molecule design strategies and the underlying mechanisms for cyclization and cycloreversion processes addressed by the alternative stimulus. Then the noticeable applications made in multi-stimuli responsive DAE systems are summarized. Additionally, the challenges and opportunities of DAE switches driven by stimuli "beyond photo" in the future are also discussed.

Reversible Transformations of Polymer Topologies through Visible Light and Darkness.

A fundamentally important characteristic of a macromolecule is its shape. Herein, visible light and darkness are used as the only stimuli to reversibly alter the topology of well-defined polymers in a one-pot procedure. For this, linear naphthalene-containing polyacrylates are used as scaffolds for the visible light-induced cycloaddition with various substituted triazolinediones (i.e., butyl, stearyl, perfluoro, and polymeric), resulting in differently shaped graft polymers, including brushes and combs. The thus-formed cycloadduct linkages dissociate in the dark, resulting in the regeneration of the parent linear polymer at ambient temperature, establishing a dual-topology transformation by only switching green light on and off. By applying different temperatures during the cycloreversion process, the dissociation rate of the cycloadducts can be tuned in a facile manner, thus allowing for time control over the regeneration of the parent polymer. By engineering a polymer that consists of differently substituted naphthalenes at the chain ends and on the side chains, the inherently different cycloreversion rates of the formed cycloadducts are leveraged to achieve in situ multi-topology transformations without external stimuli. The shape transformations have been repeated up to 4 times sequentially in one pot without the need of any purification. The topological alterations are microscopically depicted through reversible self-assembly, with the polymers adopting different morphologies upon visible light or darkness. The versatile yet practical nature of this polymer "reshaping" strategy provides facile access to multifaceted polymer systems and, consequently, to a plethora of potential applications thereof.

Halogen Bond Catalysis on Carbonyl–OlefinRing‐ClosingMetathesis Reaction: Comparison with Lewis Acid Catalysis

Comprehensive SummaryThe carbonyl–olefin ring‐closing metathesis reactions have become a powerful tool for carbon‐carbon bond formation. In this work, the halogen bond catalysis and classical Lewis acid catalysis on the carbonyl–olefin ring‐closing metathesis reaction were investigated by density function theory. For both the halogen bond catalysis and classical Lewis acid catalysis, the carbonyl–olefin ring‐closing metathesis reaction occurs by [2 + 2]‐cycloaddition process and [2 + 2]‐cycloreversion process, the reaction energy barriers are low, therefore, it can be performed easily at room temperature. The essential difference of the two kinds of catalysts is that the catalytic mechanism of halogen bond catalysis is mainly contribution of electrostatic interaction, while that of classical Lewis acid catalysis is mainly catalyzed by orbital interaction. The halogen bond donor catalysts (ICl3, IF3) are expected to be efficient catalysts for the reaction and further promote the chemical synthesis of carbonyl–olefin ring‐closing metathesis reaction.

Theoretical study on the photocyclization reactivity mechanism in a diarylethene derivative with multicolour fluorescence modulation

For a photochromic spiro-diarylethene derivative (Spiro-DAE), its photocyclization reaction and multicolour fluorescence modulation performances were investigated based on a series of density functionals calculations in this work. Some elementary properties such as geometric and electronic structures at ground and the first excited state (S1), absorption and emission spectra in respective open-ring and closed-ring structures were compared, which indicate the cyclization reaction may occur at S1. It is further verified by the lower activation barrier (3.4 kcal/mol) of the transition state at S1 potential energy surface. The photochromic reaction rates for both cyclization and cycloreversion processes were quantitatively estimated, which suggests the much smaller radiative and internal conversion rates contribute to the higher photocyclization rate and thus efficiency. Furthermore, we suspect that the dihydroacridine fragment may make important contribution to the cyclization reaction occurring at S1 considering its contribution to electronic structure.

A dominant factor of the cycloreversion reactivity of diarylethene derivatives as revealed by femtosecond time-resolved absorption spectroscopy.

Dynamics of the cycloreversion reaction of a photochromic diarylethene derivative with a small ring-opening reaction yield (∼1%) was investigated by using femtosecond transient absorption spectroscopy. The reaction rate constant and activation barrier on the reaction coordinate were quantitatively analyzed on the basis of the temperature and excitation wavelength dependencies of the reaction yield and excited state dynamics. From the comparison of the present results with those in a more reactive derivative, we concluded that a key factor regulating the overall reaction yield is the branching ratio at the conical intersection where the excited state population is split into the product and the initial reactant. The excitation wavelength dependence of the dynamics indicated that the geometrical relaxation and vibrational cooling proceed in a few picosecond time scale behind the cycloreversion process, and the vibrational excess energy assists the molecule to climb up the energy barrier.

Synthesis and Application of 1‐(3,5‐dimethyl‐4‐isoxazolyl)‐2‐[2‐ methyl‐5‐bromomethyl‐3‐thienyl]perfluorocyclopentene

A new unsymmetrical photochromic diarylethene 1‐(3,5‐dimethyl‐4‐isoxazolyl)‐2‐ [2‐methyl‐5‐bromomethyl‐3‐thienyl] has been synthesized. Its properties have been discussed systematically in acetonitrile, such as photochromic, fluorescence switch, kinetics experiments and its optoelectronic properties. The results showed the compound exhibited reversible photochromism and undergo reversible cyclization and cycloreversion reactions upon alternating irradiation with UV and visible light. The kinetic experiments showed that the cyclization and cycloreversion processes were zeroth and first order reaction, respectively. The fluorescence had a remarkable initial increase with subsequent dramatic decrease with increasing concentration. Its fluorescence intensity decreased along with the photochromism from open‐ring isomers to closed‐ring isomers.

Synthesis and Photochromism studies of 1-(2-methyl-3- benzothiophene)-2-[2-methyl-5-pyrenyl-3-thienyl] perfluorocyclopentene

A new unsymmetrical photochromic diarylethene 1o, which contains condensed nucleus was synthesized. Its photochromic both in hexane solution and in PMMA film and kinetics experiment were investigated in detail. The result indicated that this diarylethene had reversible photochromism, changing the color from colorless to purple both in hexane solution and in PMMA film upon appropriate irradiation with 297 nm UV light. What’s more, the kinetic experiments showed that the cyclization and cycloreversion processes were zeroth and first order reaction, respectively. This new photochromic system also exhibited fluorescence switching in hexane solution and in PMMA film.

Synthesis and Photochromic Properties of Diarylethene 1‐[2‐ methyl‐5‐phenyl‐3‐thienyl]‐2‐[2‐methyl‐5‐(3‐fluoro‐4‐chloro) phenyl‐3‐thienyl]perfluorocyclopentene

A novel unsymmetrical photochromic diarylethene, 1‐[2‐methyl‐5‐phenyl‐3‐ thienyl]‐2‐[2‐methyl‐5‐(3‐fluoro‐4‐chloro)phenyl‐3‐thienyl]perfluorocyclo‐pentene, was designed and constructed successfully. Its photochemical properties, including photochromic, fluorescence behavior and kinetics, have been investigated systematically. The results indicated that its photochromic behavior could be modulated by UV/V is light, changing from colorless to blue in hexane. What is more, the kinetic experiments illustrated that the cyclization/ cycloreversion process of this diarylethene were determined to be the zeroth/first reaction.

Chemically reprogrammable metal organic frameworks (MOFs) based on Diels-Alder chemistry.

We present the reversible Diels-Alder functionalization of metal organic frameworks (MOFs). Cyclopentadiene (Cp) functional MOFs are ligated with dienophiles to fabricate functional MOFs with a reprogrammable chemical nature. Our strategy thus constitutes an unprecedented concept for chemically dynamic MOFs able to be recoded.

Solvent Polarity Dependence of Photochromic Reactions of a Diarylethene Derivative As Revealed by Steady-State and Transient Spectroscopies

Solvent polarity dependence of photochromic reactions such as cyclization and cycloreversion of a photochromic diarylethene derivative, 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene, was investigated by steady-state spectroscopic and femtosecond laser photolysis methods. For the cyclization reaction, it was revealed that the quantum yield decreased with an increase in solvent polarities, mainly due to the decrease in the fraction of the conformer with C2 symmetry favorable for the cyclization. This result indicated that the branching ratio for the cyclization and the deactivation to the open-ring isomer at the conical intersection was almost independent of the solvent polarity. On the other hand, it was found for the cycloreversion process that the closed-ring isomer in the S1 state rapidly deactivated into the ground state in competition with the activated process leading to the conical intersection providing a pathway toward both open- and closed-ring minima in the ground state. The cycloreversi...

Multistate and Multicolor Photochromism through Selective Cycloreversion in Asymmetric Platinum(II) Complexes with Two Different Dithienylethene-Acetylides.

Four asymmetric bis(dithienylethene-acetylide) platinum(II) complexes trans-Pt(PEt3)2(L1o)(L5o) (1oo), trans-Pt(PEt3)2(L2o)(L5o) (2oo), trans-Pt(PEt3)2(L3o)(L5o) (3oo), and trans-Pt(PEt3)2(L4o)(L5o) (4oo) with two different dithienylethene-acetylides (L1o-L5o) were designed to modulate stepwise, multistate, and multicolor photochromism by modifying ring-closure absorption wavelengths. Upon irradiation under UV light, 1oo converts only to 1oc without the observation of 1co and dually ring-closed species 1cc. In contrast, both mixed ring-open/closed species oc and co as well as dually ring-closed species cc are observed upon UV light irradiation of 2oo-4oo, implying that a substantial stepwise photochromic process occurs following 2oo-4oo → 2oc-4oc/2co-4co → 2cc-4cc. The conversion percentage of dually ring-closed species at the photostationary state (PSS) is progressively increased following 1cc (0%) → 2cc (40%) → 3cc (86%) → 4cc (>95%), coinciding with the progressive red-shift of ring-closure absorption bands in free L1c (441 nm) → L2c (510 nm) → L3c (556 nm) → L4c (591 nm). Particularly, compound 2 affords four states (2oo, 2co, 2oc, and 2cc) with different colors (colorless, purple, blue, and dark blue, respectively) through a selective photochemical cycloreversion process upon irradiation with appropriate wavelengths of light. Although stepwise photocyclization reactions 3oo → 3co/3oc → 3cc and 4oo → 4co/4oc → 4cc are observed, multicolor photochromism of 3oo and 4oo could not be achieved because ring-closure absorption bands between L3c/L4c and L5c are significantly overlapped. The stepwise photochemical processes are well demonstrated by NMR, UV-vis, and infrared (IR) spectroscopy and time-dependent density functional theory (TD-DFT) computational studies.

Synthesis of carbon doped WO3·0.33H2O hierarchical photocatalyst with improved photocatalytic activity

A carbon doping method is developed to overcome the drawback of conventional carbon doping method. The carbon dopant is synthesized by treating carbon with dilute nitric acid through hydrothermal process. Carbon-doped WO3·0.33H2O (CWO3·0.33H2O) is obtained by adding the carbon dopant solution, and then through an additional hydrothermal process. Based on XRD, Raman and XPS, carbon have been incorporated into the interstitial position of WO3·0.33H2O unit cell rather than substitution of oxygen in lattice of WO3·0.33H2O, which induces distortion of WO6 octahedron and lattice defect. In addition, carbon doping also induces the emergence of new level above the valence band. The new level increases the migration pathway of photo-generated carriers, which reduces the recombination rate of photo-generated carriers. The changes of band structure, distortion of WO6 octahedron and lattice defect are beneficial to improve the photocatalytic performance of WO3·0.33H2O. Compared with pristine WO3·0.33H2O, CWO3·0.33H2O display better photocatalytic performance on degradation of rhodamine B (RhB), which include the faster de-ethylation process and cycloreversion process. Moreover, the experiments of radical quenchers confirmed that the h+ display the main influence on degradation of RhB. This study implies that carbon can be doped into some metal oxide hydrates through a mild preparation process, which provides a possible way for the synthesis of carbon doped thermal unstable materials.

Photocatalytic activity of β-MnO2 nanotubes grown on PET fibre under visible light irradiation

ABSTRACTDevelopment of visible light response semiconductor photocatalysts in degradation of organic compounds (pollutants) is one of the current research focuses due to the severe environmental pollution from various industrial and agricultural pollutants in water bodies. In this work, β-MnO2 particles were successfully prepared by sol-gel method with potassium permanganate and manganese (II) sulphate as precursors. The transmission electron microscope/selected area electron diffraction analysis indicates that the particles were polycrystals with tubular structure. The photodegradation of Rhodamine B (RhB) solution using β-MnO2 nanotubes under visible irradiation followed 1st order kinetic with rate constant of 0.022 ± 0.003 min−1 and photodegradation efficiency of 90.3% after 120 min under visible light irradiation. The N-deethylation was the dominant process in photodegradation of RhB dye by β-MnO2 nanotubes as compared to cycloreversion process. By applying similar synthesis condition, the β-MnO2 nanotubes were successfully synthesised on PET fibre. The photodegradation efficiency of RhB dye under circulation condition by β-MnO2 nanotubes grown on PET fibre under visible light irradiation was 1.23 h−1. The result suggests that β-MnO2 nanotubes grown on PET fibre could be used as visible light-driven photocatalysts for wastewater purifier application.

Synthesis and Properties of 1-(2-Methyl-3-benzothiophene)-2-[2-methyl-5-(3-fluoro-4-chloro)phenyl-3-thienyl]perfluorocyclopentene

An asymmetrical photochromic diarylethene1-(2-Methyl-3-benzothiophene)-2-[2-methyl-5-(3-fluoro-4-chloro) phenyl-3-thienyl] perfluorocyclopentene (1o) was synthesized and its phtochromic, fluorescent properties were investigated in detail. This compound exhibited remarkable photochromism, upon irradiation with 297 nm UV light, the colorless solution of 1o turned to violetred with a new visible absorption band centered at 538 nm (ε = 1.17 × 104 L mol-1 cm-1) attributable to the closed-ring isomer 1c. The kinetic experiments showed that the cyclization and cycloreversion processes were zeroth and first order reaction, respectively. Moreover, diarylethene 1o also exhibited obviously fluorescence switches along with the photochromism.The emission intensity of diarylethene 1o in a photostationary state was quenched to ca. 27% in hexane.

Synthesis and Properties of 1-(3,5-dimethyl-4-isoxazole)-2-(2-methyl-(5-ethynyl)-3-thienyl)perfluorocyclopentene

A new photochromic diarylethene of 1-(3,5-dimethyl-4-isoxazole)-2- (2-methyl-(5-ethynyl)-3-thienyl) perfluorocyclopentene (1o) was synthesized. Its photochromic and fluorescence properties were investigated systematically. Upon irradiation with UV light with the extended response time, the diarylethene underwent a ring opening reaction to produce closed forms and color change in solution. The results showed the compound exhibited good photochromism in hexane solution. The kinetic experiments showed that the cyclization and cycloreversion processes were zeroth and first order reaction, respectively. Moreover, diarylethene1oalso exhibited obviously fluorescence switches along with the photochromism.

Synthesis and Properties of [1-(3,5-dimethyl-4-iodoisoxazole)-2-(2-methyl-(5-ethynyl)trimethylsilane-3-thienyl)perfluorocyclopentene

A photochromic diarylethene of [1-(3,5-dimethyl-4-iodoisoxazole)-2-(2-methyl-(5-ethynyl) trimethylsilane-3-thienyl) perfluorocyclopentene (1o) was synthesized and characterized. Its properties, including photochromic behavior and fluorescent properties have been investigated. Upon irradiation with UV light with the extended response time, the diarylethene underwent a ring opening reaction to produce closed forms and color change in solution. The results showed the compound exhibited good photochromism in acetonitrile solution. The kinetic experiments showed that the cyclization and cycloreversion processes were zeroth and first order reaction, respectively. Moreover, diarylethene1oalso exhibited obviously fluorescence switches along with the photochromism.

Synthesis and Photochromism Studies of 1-(2-methyl-3-benzofuran)-2-[2-methyl-5-naphthyl-3-thienyl]perfluorocyclopentene

A novel photochromic diarylethene was synthesized and its photochromic and fluorescent properties were investigated. The results showed that this compound exhibited reversible photochromism, changing from colorless to amaranth after irradiation with UV light both in solution and PMMA amorphous film. In hexane, compound 1a exhibited an absorption peak at 266 nm, upon irradiation with 297 nm light, a new visible absorption band centered at 530 nm emerged while the original peak at 266 nm decreased. In PMMA amorphous film, diarylethene 1a also showed good photochromism as similar to that in solution. The photochromic reaction kinetics indicated that the cyclization processes of 1a belong to the zeroth order reaction and the cycloreversion process belong to the first order reaction. Diarylethene 1a also exhibited good fluorescent switching both in solution and in PMMA film upon alternating irradiation with UV and visible light.

Synthesis and Properties of 1-(2-Cyano-1,5-Dimethyl-4-Pyrryl)-2-{2-Methyl-[5-(4-Methylene-Hydroxyl)Phenyl]-3-Thienyl}Perfluorocyclopentene

A new asymmetrical photochromic diarylethene 1-(2-cyano-1,5-dimethyl-4-pyrryl)-2-{2-methyl-[5-(4-methylene-hydroxyl) phenyl]-3-thienyl} perflu-orocyclopentene (1o) was synthesized and its photochromic properties were investigated systematically. Upon irradiation with 297 nm UV light, 1o exhibited photochromism in acetonitrile solution and in a PMMA amorphous film. The kinetic experiments showed that the cyclization and cycloreversion processes were zeroth and first order reaction, respectively. In addition, diarylethene 1o also exhibited obvious fluorescence switches along with the photochromism.

Synthesis and Photochromism Studies of 1-(2,5-Dimethyl-3-Thienyl)-2-[2-Methyl-5- Pyrenyl-3-Thienyl]Perfluorocyclopentene

A new unsymmetrical photochromic diarylethene1o, which contains condensed nucleus was synthesized. Its photochromic both in hexane solution and in PMMA film and kinetics experiment were investigated in detail. The result indicated that this diarylethene had reversible photochromism, changing the color from colorless to purple in hexane solution upon appropriate irradiation with 297 nm UV light, respectively. What’s more, The kinetic experiments showed that the cyclization and cycloreversion processes were zeroth and first order reaction, respectively. This new photochromic system also exhibited fluorescence switching in acetonitrile solution.

Research on Photochromic Materials with Synthesis and Properties of 1-(3,5-Dimethyl-4-isoxazolyl)-2-[2-methyl-5-(<i>p</i>-ethoxyphenyl)-3-thienyl]perfluorocyclopentene

An asymmetrical photochromic diarylethene 1-(3,5-Dimethyl-4-isoxazolyl)-2-[2-methyl-5-(p-ethoxyphenyl)-3-thienyl] perfluorocyclopentene (1o) was synthesized and its photochromic properties were investigated. Upon irradiation with 297 nm UV light, 1o exhibited photochromism in hexane solution. The kinetic experiments showed that the cyclization and cycloreversion processes were zeroth and first order reaction, respectively. Moreover, diarylethene 1o also exhibited obviously fluorescence switches along with the photochromism.