Dithienylethene Unit Research Articles

Easy Processable Photomechanical Thin Film Involving a Photochromic Diarylethene and a Thermoplastic Elastomer in Supramolecular Interaction.

A novel supramolecular photoactuator in the form of a thin film of centimetric size has been developed as an alternative to traditional liquid crystal elastomers (LCE) involving azobenzene (AZO) units or photochromic microcrystals. This thin film is produced through spin coating without the need for alignment or crosslinking. The photoactuator combines a photochromic dithienylethene (DTE) functionalized with ureidopyrimidinone (UPy) units, and a telechelic thermoplastic elastomer, also functionalized with UPy, allowing quadruple hydrogen bonding between the two components. Upon alternating ultraviolet (UV) and visible light exposure, the film exhibits reversible bending and color changes, studied using displacement and absorption tracking setups. For the first time, the photomechanical effect (PME) is quantitatively correlated with photochromism, showing that DTE units drive the movement under both UV (photocyclization) and visible (photoreversion) light. In situ illumination techniques reveal that the PME arises from photoinduced strain within 160 nm UPy-bonded DTE domains, which expand and contract by approximately 50% under UV and visible light, respectively. The semicrystalline nature of the elastomer and a robust supramolecular network connecting both components are critical in converting microscopic photostrain into macroscopic actuation.

A Green-to-Near-Infrared Photoswitch Based on a Blended Subporphyrazine-Dithienylethene System.

A subporphyrazine (SubPz)-dithienylethene (DTE) photochromic device with 1o and 1c states, was developed and characterized. In this device, the DTE unit can reversibly switch the SubPz absorbance from green to near-infrared [λmax (o/c) = 527 nm/740 nm], as well as the SubPz fluorescence and singlet oxygen quantum yields. The core of this design involves using a highly tunable SubPz chromophore that shares its quasi-isolated ethene moiety with a DTE photoswitch.

Ytterbium(III) Complex with Photochromic Ruthenium(II) Acetylide Ligand: All Visible Light Photoswitching of NIR Luminescence.

We report a ruthenium(II) bisacetylide complex bearing a photochromic dithienylethene (DTE) acetylide arm and a coordinating bipyridyl on the trans acetylide unit. Its coordination with Yb(TTA)3 centers (TTA = 2-thenoyltrifluoroacetonate) produces a bimetallic complex in which the dithienylethene isomerization is triggered by both ultraviolet (UV) light absorbed by the DTE unit and 450 nm excitation in a transition of the organometallic moiety. The redox behavior arising from the ruthenium(II) bisacetylide system is fully investigated by cyclic voltammetry and spectroelectrochemistry, revealing a lack of stability of the DTE-closed oxidized state preventing effective redox luminescence switching. On the other hand, the photoswitching of ytterbium(III) near-infrared (NIR) emission triggered by the photochromic reaction is fully operational. The electronic structure of this complex in its different states characterized by strong electronic coupling between the DTE and the ruthenium(II)-based moieties leading to metal-assisted photochromic behavior were rationalized with the help of time-dependent density functional theory (TD-DFT) calculations.

Light-regulating chirality of metallacages featuring dithienylethene switches.

Dynamic chiral superstructures are of vital importance for understanding the organization and function of chirality in biological systems. However, achieving high conversion efficiency for photoswitches in nanoconfined architectures remains challenging but fascinating. Herein, we report a series of dynamic chiral photoswitches based on supramolecular metallacages through the coordination-driven self-assembly of dithienylethene (DTE) units and octahedral zinc ions, thereby successfully achieving an ultrahigh photoconversion yield of 91.3% in nanosized cavities with a stepwise isomerization mechanism. Interestingly, the chiral inequality phenomenon is observed in metallacages, resulting from the intrinsic photoresponsive chirality in the closed form of the dithienylethene unit. Upon hierarchical organization, we establish a dynamic chiral system at the supramolecular level, featuring chiral transfer, amplification, induction, and manipulation. This study provides an intriguing idea to simplify and understand chiral science.

Dual and sequential locked/unlocked photo-switching effects on FRET processes by tightened/loosened nano-loops of diarylethene-based [1]rotaxanes.

The self-trapping nano-loop structures of [1]rotaxanes exhibited multiple Förster resonance energy transfer (FRET) patterns via dual and sequential locking/unlocking of pH-gated and UV exposure processes. As a tightened and constrained nano-loop in the acidic condition, dithienylethene (DTE) unit was locked in the highly bending open form to forbid ring closure upon UV irradiation.

Photoswitchable electron-rich phosphines: using light to modulate the electron-donating ability of phosphines.

The synthesis and properties of photoswitchable electron-rich phosphines containing N-heterocyclic imines equipped with a photochromic dithienylethene unit are reported. Heteronuclear NMR spectroscopy and UV/vis studies reveal that the imine substituents undergo reversible electrocyclic ring-closing and ring-opening reactions upon exposure to UV and visible light, respectively. The photoisomerization alters the electron-donating ability of the phosphines by up to ΔTEP = 8 cm-1.

A New Biphotochromic Fluorescent Switch Based on Dithienylethene and Triphenylethylene: Synthesis, Crystal Structure, and Optical Waveguide

AbstractA novel biphotochromic fluorescent switch molecule N‐2F derived from dithienylethene (DTE) and triphenylethylene (TPE) is reported. Interestingly, different photochromic and fluorescence phenomena of N‐2F are observed in tetrahydrofuran/water mixtures. When fw ≤ 50%, N‐2F shows effective photochromic and fluorescent switch under alternating with 254 and 500 nm light irradiation due to the DTE unit undergoing reversible cyclization and cycloreversion reactions between its open and closed forms. However, when fw ≥ 60%, the strong blue‐green fluorescence of the original solution is almost quenched under 254 nm light irradiation, but becomes red fluorescent emission under 500 nm light irradiation. When further irradiated with 254 nm, the red fluorescent emission disappears, but it reappears upon 500 nm light illumination. The results reveal that DTE and TPE take cyclization and cycloreversion reactions upon alternating with 254 and 500 nm light irradiations, and TPE will take dehydrogenation reaction with further 254 nm irradiation. Moreover, N‐2F can easily obtain long length (about 2 cm) rod single crystal with high fluorescence quantum yield of 68.97%. Impressively, N‐2F shows excellent optical waveguide with very low loss coefficient of 0.171 dB mm−1. Therefore, N‐2F exhibits potential applications in anti‐counterfeiting, multi‐color display, and functional photonic devices.

Intriguing Second‐Order NLO Switches Based on New DTE Compounds

AbstractTwo new photochromic compounds bearing a dithienylethene unit have been designed, synthesized, and well characterized. The first contains a platinum dialkynyl moiety whereas the second bears a simple phenyl‐dimethylamino fragment. Both compounds have demonstrated an excellent photochromic behavior. This efficient photochromism is the springboard for a significant photomodulation of the second‐order nonlinear optical properties, determined in dichloromethane solution by means of the Electric Field Induced Second Harmonic generation technique. The results are of interest for the design of reversible NLO switches as a tool for emerging photonic technologies.

Photoresponsive Covalent Organic Frameworks with Diarylethene Switch for Tunable Singlet Oxygen Generation

Incorporation of molecular switches with light, heat, and electricity responsibility into artificial solids has been developed as a successful strategy to construct stimuli-responsive functional materials. However, precise manipulation of their molecular geometries and electronic structures to control the properties of macroscopic materials still remains a fundamental challenge. Herein, a photoresponsive covalent organic framework (o-COF) with the square lattice was fabricated from the dynamic covalent chemistry reaction of ring-open dithienylethene–dialdehyde with 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (H2TAPP). UV irradiation of the dithienylethene-based units in o-COF afforded its reversible photoisomer (c-COF) in the ring-closed form. In addition to a range of diffraction, microscopic, and gas physical sorption characterizations, spectroscopic investigations with the help of theoretical simulations revealed different photocatalytic activities toward the evolution of singlet oxygen and corresponding photocatalytic oxidation of amines due to the different energy transfer pathways from the porphyrin unit to BBTP photoisomers in these two COFs. Most interestingly, such different photocatalytic behaviors for two COFs could be easily tuned in a reversible manner by adjusting the ring-closed/open form of dithienylethene units by means of UV and visible light.

Stimuli-Responsive Porous Molecular Crystal with Reversible Modulation of Porosity.

Responsive materials have received much attention due to modulated properties under stimuli such as light, heat, and electricity. A photoresponsive porous molecular crystal (1) has been assembled from a racemic dithienylethene-cage (L) by multiple C-F···H-C hydrogen bonds and van der Waals forces according to crystallographic investigation. Electronic absorption spectroscopy reveals reversible photochromic behaviors of the solution and film forms of enantiomeric L upon UV and visible light irradiation due to photoisomerization of dithienylethene units. X-ray photoelectron spectroscopy (XPS), in combination with NMR, discloses the quantitative photoisomerization of photochromic dithienylethene moieties. Moreover, the porosity of 1 is modulated by UV irradiation based on gas sorption data. Interestingly, heating the irradiated sample of 1 in 1,4-dioxane leads to recovered porosity due to the recovered cage molecular structure and maintained periodic frameworks.

Photoswitchable Nitrogen Superbases: Using Light for Reversible Carbon Dioxide Capture.

Using light as an external stimulus to alter the reactivity of Lewis bases is an intriguing tool for controlling chemical reactions. Reversible photoreactions associated with pronounced reactivity changes are particularly valuable in this regard. We herein report the first photoswitchable nitrogen superbases based on guanidines equipped with a photochromic dithienylethene unit. The resulting N‐heterocyclic imines (NHIs) undergo reversible, near quantitative electrocyclic isomerization upon successive exposure to UV and visible irradiation, as demonstrated over multiple cycles. Switching between the ring‐opened and ring‐closed states is accompanied by substantial pK a shifts of the NHIs by up to 8.7 units. Since only the ring‐closed isomers are sufficiently basic to activate CO2 via the formation of zwitterionic Lewis base adducts, cycling between the two isomeric states enables the light‐controlled capture and release of CO2.

Dithienylethene metallodendrimers with high photochromic efficiency

It has been challenging to achieve multi-photochromic systems without affecting the individual photoswitching properties of the constituent units. Herein, we present the design and synthesis of a new family of platinum-acetylide dendrimers containing up to twenty-one photochromic dithienylethene (DTE) units that exhibit both high photochromic efficiency and individual switching properties. Upon irradiation with ultraviolet (UV) and visible (vis) light, the resultant metallodendrimers display high conversion yield and good fatigue resistance. More interestingly, cyclization-cycloreversion kinetics revealed that the photochromic property of each DTE unit in these metallodendrimers is unaffected by its neighbor and the full ring-closure of up to twenty-one DTE units in one single dendrimer has been achieved.

Dithienylethenes functionalized by triphenylethene and difluoroboron β-diketonate fragments: Synthesis, optical switching behavior and fluorescent turn-on sensing for volatile organic amines

Two novel dithienylethenes were obtained by appending triphenylethene and BF2bdk moieties at the termini of dithienylethene unit (TDBB and TDTB), in which BF2bdk group not only functions as electron acceptor (A) but also responds to volatile organic amines. Only TDBB displayed excellent visible light-triggered photochromism and fluorescent switching behavior in toluene and in the PMMA film upon alternating irradiation with blue light (460–470 nm) and near-infrared light (760–770 nm). More importantly, they displayed a distinct fluorescent turn-on and colorimetric sensing performance for volatile n-propylamine in THF. Specially, the addition of excessive n-propylamine can effectively modulate their photochromic properties in THF. And their PMMA films showed the fluorescent turn-off and colorimetric sensory behavior towards n-propylamine vapor. Consequently, they would be utilized as novel dual sensory materials for volatile primary or secondary amine vapors in the environment and biological systems.

A Solid-State Fluorescence Switch Based on Triphenylethene-Functionalized Dithienylethene With Aggregation-Induced Emission.

The development of novel dithienylethene-based fluorescence switches in the aggregated state, and the solid state is highly desirable for potential application in the fields of optoelectronics and photopharmacology. In this contribution, three novel triphenylethene-functionalized dithienylethenes (1–3) have been designed and prepared by appending triphenylethene moieties at one end of dithienylethene unit. Their chemical structures are confirmed by 1H NMR, 13C NMR, and HRMS (ESI). They display good photochromic behaviors with excellent fatigue resistance upon irradiation with UV or visible light in Tetrahydrofuran (THF) solution. Before irradiation with UV light, they exhibit Aggregation Induced Emission (AIE) properties and luminescence behaviors in the solid state. Moreover, upon alternating irradiation with UV/visible light, they display effective fluorescent switching behaviors in the aggregated state and the solid state. The experimental results have been validated by the Density Functional Theory (DFT) calculations. Thus, they can be utilized as novel fluorescence switches integrated in smart, solid-state optoelectronic materials and photopharmacology.

Dithienylethene-bridged gold(I) isocyanide complexes: Synthesis, photochromism and “turn-on” fluorescent switching behavior

Developing novel photochromic complexes based on dithienylethene is highly desirable for potential application in the fields of photoresponsive optoelectronics. In this contribution, four novel dithienylethene-bridged gold(I) isocyanide complexes 1a-1d have been designed and prepared by appending alkynyl-gold(I)-isocyanide triads at the termini of dithienylethene unit. They were fully characterized and confirmed by 1H NMR, 13C NMR, and HRMS (MALDI). Moreover, investigation on photochromic properties indicated that these complexes had good photochromic behavior upon irradiation with UV (302 nm) and green light (530 nm). And the effect of terminal ligands on photochromic properties of these gold(I) complexes was observed. Surprisingly, they displayed an unusual “turn-on” fluorescent switching behavior upon irradiation with UV light, which was mainly attributed to LMCT (ligand-to-metal charge transfer) for ring-closed isomers of these complexes by TD-DFT calculations. Accordingly, these complexes can be utilized as a potential fluorescent switch in smart optoelectronic materials.

Photochromic properties of ruthenium complexes with dithienylethene-ethynylthiophene

In order to extend stepwise photochromism to more metal-coordination systems for multicolors and multistates, a new photochromic dithienylethene-ethynylthiophene (L1o) was synthesized to design head–head coupled symmetric ruthenium(II) complex trans-Ru(dppe)2(L1o)2 (1oo) and head-shoulder coupled asymmetric ruthenium(II) complex trans-Ru(dppe)2(L1o)(L2o) (2oo). However, upon irradiation under UV light, 1oo only converts to 1co without the observation of dually ring-closed species 1cc, and only the dually ring-closed species 2cc is observed without the detection of the mixed ring-open/closed species 2co and 2oc, implying that it is difficult to achieve substantial stepwise photochromic process of 1oo-2oo → 1co-2oc/2co→1cc-2cc due to the rapid intramolecular energy transfer in 1co and the absence of electronic communication between two dithienylethene units in 2oo. The photochemical processes are well demonstrated and explained by NMR, UV–vis, electrochemical, as well as time-dependent density functional theory (TD-DFT) computational studies.

Visible light-activated optical switching behaviors of tetra-/triphenylethene-dithienylethene-BF2bdk triad

Developing new visible light-triggered fluorescent molecular photoswitches is highly desirable for potential application in the fields of photoresponsive optoelectronics and photopharmacology. In this contribution, two novel tetra-/triphenylethene-dithienylethene-BF2bdk triads (TDB1 and TDB2) have been designed and prepared by appending tetra-/triphenylethene and BF2bdk moieties at the termini of dithienylethene unit. Before irradiation with blue light at 460–470 nm, they showed an intense emission in solution and in the PMMA film state, suggesting that the AIE effect of tetra-/triphenylethene was inhibited, and functioned only as electron-donating groups. Moreover, upon alternating irradiation with blue/NIR light, TDB1 and TDB2 displayed effective fluorescent switching behaviors and NIR photochromism in toluene and the PMMA film. Therefore, they would be utilized as novel visible light-triggered switches integrated in smart optoelectronic materials. The DFT calculations further validate the differences for their optical properties in the experiments.

Photoresponsive Dithienylethene-Containing Tris(8-hydroxyquinolinato)aluminum(III) Complexes with Photocontrollable Electron-Transporting Properties for Solution-Processable Optical and Organic Resistive Memory Devices.

The rational design of a new class of photoresponsive tris(8-hydroxyquinolinato)aluminum(III) (Alq3) complexes has been developed. By incorporating the photochromic dithienylethene units with different peripheral heterocycles into the Alq3 framework, the photochromic properties as well as photoswitching efficiency can be readily modulated, through effective photocyclization of the Al(III) complex. Such intrinsic photochromic behavior leads to the unprecedented enhancement in the electron-transporting properties as demonstrated by the as-fabricated electron-only device, rendering the realization of photoswitchable electron mobility. In addition, one of these complexes is capable of serving as an active layer for solution-processable resistive memory devices. Photocontrollable memory performance has been achieved with a binary memory behavior, with high ON/OFF ratio and long retention time. This work represents not only the first example of photoresponsive Alq3-based electron-transporting materials but also the solution-processable Alq3-based optical and resistive memory devices with photocontrollable performance.

Efficient Photomodulation of Visible Eu(III) and Invisible Yb(III) Luminescences using DTE Photochromic Ligands for Optical Encryption

AbstractThis work describes a class of complex combining three dithienylethene units and a lanthanide ion used as an optical system displaying a double encryption method: i) a colorful code, drawn and erased under UV and visible irradiations respectively, due to coloration and discoloration of the photochromic entities, and ii) a concomitant gradual disappearance and progressive restoration of the associated lanthanide ion luminescence triggered with the same stimuli. The innovation of the system stems from the emission color tunability, i.e., with either a lanthanide ion emitting only in the visible range (Eu3+) or with another lanthanide ion emitting only in the near infrared (NIR) range (Yb3+), therefore observable, or not, to the naked eye. This system is the very first one to achieve efficient repeatable modulation of pure NIR luminescence on photochemical command. Furthermore, it is proven to be highly efficient when embedded in a PDMS polymer opening real opportunities for practical applications as anti‐counterfeiting.

Light-driven coordination anions-directed regulation of chromism in three metal complexes assembled by cyano-equipped dithienylethene ligand

Three coordination compounds were self-assembled successfully with Ag(I) ions and photo-responsive ligands featuring a cyano-equipped dithienylethene unit. Anions with different coordinating abilities were selected to construct distinct topologies, which are evidenced by X-ray crystallographic analysis. CF3 COO− and CF3 SO3− are involved into coordination in 1 and 3, respectively, whereas in 2 BF4− present merel y as ionic guests counterbalancing the framework charge. Anions also show their subtle effects on coordinated atoms, interactions, and ligand configurations. The quite different structures of 1–3 indicate an interesting anion-directed structural self-assembly.Followed examinations on photochromism illustrated that the reversible photo-isomerizations of three complexes are all retained after complexzation with Ag(I) center. Various degrees of bathochromic shifts in absorptions were observed as compared with that of the metal-free ligand. Therefore, the photo-switching of these compounds could be modulated conveniently and finely by varying simply the coordination anions and then triggering by light irradiation. The discussions of structure-properties relationship concluded that anions exert their effects on coordination structure through adjusting the configurations of ligands in complexes. Strong coordinating anions facilitate a pronounced conformational change of ligand whereas un-coordinating anion leads to smaller variation. The distinct structural changes of ligand result finally the different perturbation of photochromic behavior.