DFT/TDDFT Investigation of the Modulation of Photochromic Properties in an Organoboron‐Based Diarylethene by Fluoride Ions

The diarylethene derivative 1,2‐bis‐(5′‐dimesitylboryl‐2′‐methylthieny‐3′‐yl)‐cyclopentene ( 1 ) containing dimesitylboryl groups is an interesting photochromic material. The dimesitylboryl groups can bind to F^?, which tunes the optical and electronic properties of the diarylethene compound. Hence, the diarylethene derivative 1 containing dimesitylboryl groups is sensitive to both light and F^?, and its photochromic properties can be tuned by a fluoride ion. Herein, we studied the substituent effect of dimesitylboron groups on the optical properties of both the closed‐ring and open‐ring isomers of the diarylethene molecule by DFT/TDDFT calculations and found that these methods are reliable for the determination of the lowest singlet excitation energies of diarylethene compounds. The introduction of dimesitylboron groups to the diarylethene compound can elongate its conjugation length and change the excited‐state properties from π→π* transition to a charge‐transfer state. This explains the modulation of photochromic properties through the introduction of dimesitylboron groups. Furthermore, the photochromic properties can be tuned through the binding of F^? to a boron center and the excited state of the diarylethene compound is changed from a charge‐transfer state to a π→π* transition. Hence, a subtle control of the photochromic spectroscopic properties was realized. In addition, the changes of electronic characteristics by the isomerization reaction of diarylethene compounds were also investigated with theoretical calculations. For the model compound 2 without dimesitylboryl groups, the closed‐ring isomer has better hole‐ and electron‐injection abilities, as well as higher charge‐transport rates, than the open‐ring isomer. The introduction of dimesitylboron groups to diarylethene can dramatically improve the charge‐injection and ‐transport abilities. The closed isomer of compound 1 ( 1 C ) has the best hole‐ and electron‐injection abilities, whereas the charge‐transport rates of the open isomer of compound 1 ( 1 O ) are higher than those of 1 C . Importantly, 1 O is an electron‐accepting and ‐transport material. These results show that the diarylethene compound containing dimesitylboryl groups has promising potential to be applied in optoelectronic devices and thus is worth to be further investigated.     

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.     

Synthesis, structure and fluorescence of a novel diarylethene

The photochromic diarylethene, 1,2-bis(2-methyl-5-(2-(1,3-dithiolpentane))-thien-3-yl)perfluorocyclopentene (BMDTP), has been synthesized in high yield and its structure was determined by X-ray crystallographic analysis. The compound undergoes a photochromic reaction both in solution and in the single crystalline phase. In addition, its fluorescence property in solution is discussed.     

Synthesis and photochromic reactivity of a new class of photochromic diarylethene dimer-containing dithieno[3,2-b:2′3′-d]thiophene

Novel photochromic diarylethene dimers containing dithieno[3,2-b:2′3′-d]thiophene were synthesized and their photochromic properties were studied in solution as well as in the crystalline phase. Only the isomer with the diarylethene units one in open-form and one in closed-form was produced upon irradiation with ultraviolet light because of the intramolecular excitation energy transfer in this isomer. Their electrochemical properties were also investigated associating with computational studies.     

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.     

Photoswitching CO2 Capture and Release in a Photochromic Diarylethene Metal–Organic Framework

We demonstrate herein a promising pathway towards low‐energy CO₂ capture and release triggered by UV and visible light. A photosensitive diarylethene ligand was used to construct a photochromic diarylethene metal–organic framework (DMOF). A local photochromic reaction originating from the framework movement induced by the photoswitchable diarylethene unit resulted in record CO₂‐desorption capacity of 75 % under static irradiation and 76 % under dynamic irradiation.     

Synthesis of a new diarylethene diradical which has extended π-conjugated chains from the 2,5-position of one thiophene ring

A diarylethene diradical having a new switching unit for intramolecular magnetic interaction was synthesized. The photoswitching unit has an extended π-conjugated chain in one aryl unit, and two nitronyl nitroxide radical are placed at both ends of the π-conjugated chain. The diarylethene moiety is located in the middle of the chain. This diarylethene is designed to change the hybrid orbital from sp² to sp³ at the 2-position of the thiophene ring when this diarylethene undergoes a photochromic reaction. But the new diradical compound did not undergo photocyclic reaction upon irradiation with UV light. The photochemical behavior is perturbed by a resonant quinoid structure which stabilizes the open-ring isomer.     

Photochromism of new unsymmetrical isomeric diarylethenes bearing a pyridine group

A new class of unsymmetrical isomeric diarylethenes bearing a terminal pyridine group was synthesized and their structures were determined by single-crystal X-ray diffraction analysis. The effects of the nitrogen atom position in the pyridine group on their properties including photochromism, acidchromism, and fluorescence were investigated systematically. Among the three isomeric derivatives, the cyclization quantum yield and the absorption maxima of the ortho-substituted diarylethene were the biggest, while the fluorescence quantum yield of the para-substituted diarylethene was the biggest. Furthermore, the three isomeric diarylethenes exhibited multi-addressable switching behaviors by the stimulation of acid/base and light. Addition of trifluoroacetic acid to solutions of these diarylethenes produced the protonated derivatives, which also showed excellent photochromic behaviors, but only the para-substituted diarylethene exhibited a notable color change of solution from crimson to violet. The results revealed that the effects of the nitrogen atom position in the terminal pyridine group played a very important role during the process of photoisomerization for these isomeric diarylethene derivatives.     

一种新光致变色二芳基乙烯化合物的合成、光致变色反应动力学、荧光和结构研究

The photochromic diarylethene, 1,2-bis[2-methyl-5-（3-trifluoromethylphenyl）-3-thienyl]perfluorocyclopentene （BMTTP）, was synthesized and its photochromic kinetics, fluorescence and X-ray structure were investigated. This compound underwent a photochromic reaction both in solution and the single crystalline phase. Its cyclization/cycloreversion process was determined to be zeroth/first order reaction, respectively, and this is the first report on the cyclization/cycloreversion reaction order. In addition, its fluorescence property was also discussed.     

A highly selective fluorescence switch for Cu2+ and Fe3+ based on a new diarylethene with a triazole-linked rhodamine 6G unit

A new diarylethene compound with a triazole-linked rhodamine 6G unit attached to the imino group (1O) was designed and synthesized. According to the test results, the solution color and fluorescence color of diarylethene can be modulated by lights and metal ions. The solution color could change from colorless to light purple when irradiated with UV light. When Cu²⁺ was added to the diarylethene solution, the color of diarylethene solution became blue, the fluorescence color turned from dark to bright yellow. Although the solution color did not change by adding Fe³⁺, its fluorescence color varied from dark to yellow. Moreover, it was found that the complex ratio of the diarylethene to Cu²⁺ was 1:1 and the binding stoichiometry of the diarylethene to Fe³⁺ was also 1:1 based on the data of NMR, MS, and other experiments. Based on these findings, photochromic figure of the diarylethene with UV/Vis light, Cu²⁺ and Fe³⁺ was constructed. Furthermore, the logic circuit was designed by input signals (ultraviolet stimulus, visible light stimulus, Cu²⁺ (or Fe³⁺) and EDTA) and an output signal (fluorescent intensity at 566?nm (or 575?nm)).     

A Combination of Selective Light Reflection and Fluorescence Modulation in a Cholesteric Polymer Matrix

Summary: The phase behavior and optical properties of a cholesteric ternary copolymer, containing nematogenic phenylbenzoate, cholesteric, and photochromic diarylethene side groups, and its mixture with 2 wt.‐% fluorescent dopant were studied. The investigation of the kinetics of a photochemical opening‐cycle process of the photochromic groups in the cholesteric mixture proved the energy transfer from the fluorescent dopant to the photochromic diarylethene groups. It was shown that the fluorescence intensity of the fluorescent dopant could be controlled by the portion of the “closed” form of the diarylethene groups. During the photocyclization of the photochromic groups a “degeneration” of the selective light reflection of the cholesteric matrix is observed.

Fluorescence‐resonance energy transfer makes possible the process of photosensitization of the back ring‐opening photoreaction of the photochromic diarylethene groups in the cholesteric polymer matrix.     

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.     

Nonsymmetrical Dithienylethenes Bearing Dithieno[3,2‐b:2′,3′‐d]thiophene Units with Photochromic Performance in the Crystalline Phase

Four novel nonsymmetrical photochromic diarylethene compounds containing dithieno[3,2‐b:2′,3′‐d]thiophene units were designed and synthesized to investigate their photochromic properties. All these molecules adopt a photoactive antiparallel conformation in single crystals, as revealed by X‐ray crystallographic analysis, and exhibit excellent photochromism in solution as well as in the crystalline phase.     

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).     

Investigation on photochromism of 1,2-bis(1,4-dimethyl-2-phenyl)perfluorocyclopentene

The photochromic diarylethene, 1,2-bis(1,4-dimethyl-2-phenyl)perfluorocyclopentene has been synthesized and its single crystal can be obtained in hexane at -4℃. The structure of diphenylperluorocyclopentene bearing C2/c space group and monoclinic crystal system is very different from that of dithienylperfluorocyclopentene derivatives bearing Pī space group and triclinic crystal system by X-ray crystallographic analysis. The compound undergoes the phototchromic reaction in solution but no optical activity in single crystal. In addition, its optimum conformation in solvent is also discussed.     

Characterization and photophysical properties of sulfur-oxidized diarylethenes

Controlled oxidation of sulfur atoms in benzothiophene rings of a photochromic diarylethene, 1,2-bis(2-methyl-1-benzothiophene-3-yl)perfluorocyclopentene (BTF6) by 3-chloroperbenzoic acid afforded various oxidation products such as BTFO1, BTFO2, and BTFO4. Upon irradiation with UV light, colorless o-BTFO1 and o-BTFO2 turned to red color, whereas colorless o-BTFO4 turned to yellow color. Theoretical calculation was performed to understand the absorption spectra of closed-ring isomers. All of those compounds returned back to their open-ring isomers upon irradiation with visible light. The cyclization conversions of BTFOn (n=1, 2, and 4) at the photostationary state are higher than that of BTF6. Interestingly, in the case of BTFO1, because of the unsymmetrical environment around the sulfoxide subunit in the molecule, the diastereoselective photocyclization was observed in 25% de. In addition, c-BTFO2 and c-BTFO4 also exhibited a marked fatigue resistance and strong fluorescence, respectively. Oxidation state of sulfur atom in a diarylethene can play an important role in determining its photophysical and photochromic properties.     

A multi-photo responsive photochromic dithienylethene containing coumarin derivative

A complex photochromic diarylethene derivative containing photo-responsive coumarin groups was synthesized by an efficient method. The dimerization of coumarin groups and photochromism of diarylethene can be controlled respectively to produce the four corresponding states, which were verified by ¹H NMR, fluorescent, UV–vis spectroscopy and mass spectrometry. This compound gives a unique example for the controllable switch of both optical properties and chemical composition by light and chemical stimuli.     

Two-photon absorption of photochromic diarylethene and its application to rewritable holographic recording

A new photochromic diarylethene (1a) has been prepared. Both its photochromic behavior and nonlinear optical properties are investigated. 1a shows excellent ring-opening (λ_max = 386 nm) and ring-closing (λ_max = 652 nm) photoisomerization with UV-Vis light irradiation. With 800 nm femtosecond pulsed laser irradiation, 1a shows two-photon-induced photoisomerization, and a two-photon absorption cross-section (σ = 423×10⁵⁰ cm⁴·s per photon) is obtained by using two-photon induced fluorescence method. The applications of two-photon absorption of 1a to holographic recording has been also investigated. A two-photon induced micro-pattern is recorded on the diarylethene 1a-PMMA film with an femtosecond laser of 800 nm, 100 fs, 1 kHz, 50 mW.     

Polarization holographic optical recording based on a new photochromic diarylethene compound

A new unsymmetrical photochromic diarylethene, namely1-[2-methyl-5-(p-N,N-dimethylaminophenyl)-3-thienyl]-2-[2-methyl-5-(3-methoxylphenyl)-3-thienyl] perfluorocyclopentene (1a), was synthesized. The compound showed good photochromism, high sensitivity and remarkable fatigue-resistance both in solution and in poly(methyl methacrylate) (PMMA) matrix with UV/Vis light irradiation. The absorption maximum of its closed-ring isomer was observed at 624 nm in PMMA amorphous film. It is a nice match for the wavelength of the recording laser (633 nm). Using this target compound as recording medium, four types of polarization holographic optical recordings were performed successfully using a He-Ne laser. The results showed that only the orthogonal circular polarization recording could obtain a hologram with high diffraction efficiency and high signal-to noise-ratio. With multiplexing recording technology, three types of polarization multiplexing holographic optical recordings, including angular multiplexing, polarization multiplexing, and angular plus polarization multiplexing holographic recording, were also carried out perfectly based on its photoinduced anisotropic phenomenon accompanying the photochromic reaction by photoirradiation. The results demonstrate that the multiplexing recording technology is an effective method to improve recording capacity when using diarylethene 1 as recording medium.