Ring-closed Form Research Articles

Excitation-Dependent Circularly Polarized Luminescence Inversion Driven by Dichroic Competition of Achiral Dyes in Cholesteric Liquid Crystals.

The development of stimuli-responsive chiral cholesteric liquid crystals (CLCs) materials holds significant potential for achieving three-dimensional (3D) anti-counterfeiting and multi-level information encryption. However, constructing phototunable CLCs systems with easy fabrication and fast response remains a great challenge. Herein, we exploit an excitation-dependent CLCs (ExD-CLCs) material by establishing dynamically photoresponsive dichroic competition between two achiral dyes: a negative dichroic dye (SP-COOH) and a positive dichroic dye (Nile Red, NR) within a CLCs medium. The ExD-CLCs exhibits a negative CPL signal (glum = -0.16) at 650 nm when excited at 365 nm. Remarkably, under excitation at 430 nm, the CPL signal is inverted, and the glum value increases to +0.26. Notably, the helical superstructure and handedness of the ExD-CLCs remain unchanged during this reversal process. The CPL signal reversal is driven by the dichroic competition between the SP-COOH dimer, which displays strong negative dichroism in its open-ring isomer form and silent negative dichroism in its closed-ring isomer form, and the NR dye, which exhibits static positive dichroism. Leveraging these excitation-dependent CPL properties, the quadruplex numerical anti-counterfeiting using ExD-CLCs is achieved.

Rational Design of High-Performance Photocontrolled Molecular Switches Based on Chiroptical Dimethylcethrene: A Theoretical Study.

The reversible photo-induced conformation transition of a single molecule with a [5]helicene backbone has garnered considerable interest in recent studies. Based on such a switching process, one can build molecular photo-driven switches for potential applications of nanoelectronics. But the achievement of high-performance reversible single-molecule photoswitches is still rare. Here, we theoretically propose a 13,14-dimethylcethrene switch whose photoisomerization between the ring-closed and ring-open forms can be triggered by ultraviolet (UV) and visible light irradiation. The electronic structure transitions and charge transport characteristics, concurrent with the photo-driven electrocyclization of the molecule, are calculated by the non-equilibrium Green's function (NEGF) in combination with density functional theory (DFT). The electrical conductivity bears great diversity between the closed and open configurations, certifying the switching behavior and leading to a maximum on-off ratio of up to 103, which is considerable in organic junctions. Further analysis confirms the evident switching behaviors affected by the molecule-electrode interfaces in molecular junctions. Our findings are helpful for the rational design of organic photoswitches at the single-molecule level based on cethrene and analogous organic molecules.

Predictive Guidelines for Electrocyclization of Dithienylethenes.

Molecular photoswitches undergo a structural transformation upon photoexcitation to interconvert between two or more stable forms. In some cases, the structural rearrangement involves the transition between ring-open and ring-closed forms. In this work, we develop simple guidelines for the design of organic molecules able to undergo photochemical electrocyclization, using electronic structure calculations on dithienylethene (DTE)-based compounds. We conclude that the ability to photocyclize can be predicted from the localization and symmetry of frontier molecular orbitals. These ideas are based on the Woodward-Hoffmann rules but go beyond them, allowing us to address a more general family of chromophores. Our methodology has been experimentally validated in a novel series of quinoline-based DTEs, where the ability for photocyclization depends on specific chemical modifications. We use the DTE scaffold as the workhorse model in our study; however, these simple yet powerful guidelines are expected to be generally valid to guide the design of other diarylethenes.

Black phosphorus quantum dots functionalized with photochromic poly(vinylspiropyran)-grafted polydopamine for transient digital-type memristors

Abstract The covalent functionalization of black phosphorus quantum dots (BPQDs) with organic species or polymers will inevitably change or damage their electronic structure and intrinsic structure. To address this problem and explore the application of BPQDs in transient digital-type memristors, a polydopamine (PDA) thin film is first synthesized in situ onto the surface of BPQDs to produce a donor–acceptor-type BPQDs@PDA composite that is directly used to react with 2-bromoisobutyryl bromide to give BPQDs@PDA-Br. By using BPQDs@PDA-Br as an atom transfer radical polymerization agent, a large number of polyvinylspiropyran (PSP) chains are in situ grown from the PDA surface to yield BPQDs@PDA-PSP. Upon ultraviolet (UV)–visible light illumination, the 2 isomers of the spiropyran (ring-closed spiropyran form and ring-opened merocyanine) in the PSP moieties will interconvert into each other rapidly. As expected, the as-fabricated indium tin oxide (ITO)/BPQDs@PDA-PSP/ITO device exhibits typical nonvolatile digital-type memristive performance under visible irradiation, with a small turn-on voltage of −1.52 V, a turn-off voltage of +1.16 V, and an ON/OFF ratio current ratio of 1.02 × 104. Upon UV illumination, the information stored in the device is quickly and completely erased within 6 s. By utilizing a simple memristor-based convolutional neural network, one can easily realize handwritten digit recognition. After 10 epochs of training, numeral recognition accuracy can reach up to 96.21%.

A Hexaarylbiimidazole-Terarylene Hybrid: Visible-to-NIR-II Absorption via Sequential Photochromic Reactions.

A synergetic interaction between two or more photochromic chromophores has a potential to achieve advanced photochemical properties beyond conventional photochromic molecules and to realize photochemical control of complex systems using only a single molecule. Herein, we report a hybrid photochromic molecule consisting of hexaarylbiimidazole (HABI) and terarylene that exhibits multi-state photochromism. The biphotochrome hybrid shows four-state photochromic reaction involving sequentially proceeding photoreactions. The UV or visible light irradiation to the biphotochrome leads to the C-N bond breaking reaction of the HABI in preference to the ring-closing reaction of the 6π-electron system in the terarylene unit, leading to two terarylene radical molecules. The photogenerated terarylene radical further exhibits the 6π-electrocyclization reaction by UV irradiation. The delocalized π-radical on the closed-ring form of the terarylene is efficient to enhance the photosensitivity to the NIR-I and -II region. Furthermore, a recombination reaction of radicals between the open- and closed-ring isomers of terarylene affords an unprecedented photochromic dimer as a structural isomer of the initial molecule. This is a consequence of the sequential hybrid photochromic system involving the HABI and terarylene units.

Fast tumor imaging using pH-responsive aggregation of cyanine dyes with rapid clearance

Rapid and selective tumor detection using conventional pH-activatable chemical probes as contrast agents is challenging. Moreover, a large proportion of the contrast agent is usually retained in the body long-term, which causes potential toxicity risks. In this study, we developed a fluorescent sensor, CypH2S, with a pH-sensitive cyclic substructure for detection of acidic tumor microenvironment. Upon pH variation, the sensor underwent structural changes: the closed-ring form, CypH2S-C, exhibited suppressed dye aggregation, while the open-ring form, CypH2S-O, tended to aggregate in aqueous solutions under slightly acidic conditions. Importantly, CypH2S facilitated rapid and selective tumor visualization in a living mouse model via fluorescence imaging of its pH-responsive aggregation with a 1.9-fold tumor/background ratio (< 1 h). Furthermore, prompt clearance of CypH2S from the bloodstream post-tumor detection occurred because of the relatively small size of the aggregates and cell impermeability. These properties would make CypH2S a promising candidate for clinical tumor diagnosis.

Harnessing the Conformer/Atropisomer-Dependent Photochromism of Diarylethene Photoswitches and Forcing a Diarylethene Atropisomer to Its Configurational Diastereomers with Polymer Mechanochemistry

AbstractDiarylethenes are an important class of photoswitches that usually exist in interconvertible parallel (photoinert) and antiparallel (photochromic) conformational states. Recent research afforded sterically congested diarylethenes that exist as stable and separable configurational atropisomers. Rational manipulation of stereochemistry is a robust strategy for regulating diarylethene photochemistry. Here, we present a brief account of the conformer/atropisomer-dependent photochromism of diarylethene photoswitches, and we discuss a recent advance at the interface of diarylethene photochemistry and polymer mechanochemistry: our group recently introduced a mechanical approach for converting a parallel diarylbenzothiadiazole into its antiparallel configurational diastereomers, thereby turning on its photochromic reactivity. After mechanical activation, UV light changes the converted diarylethene molecule into a colored ring-closed form by a 6π-electrocyclization reaction that permits the visualization of the mechanical activation event. Besides the fundamentally new mechanism of converting a molecule into its configurational diastereomers through force–stereochemistry coupling, the conversion of atropisomer stereochemistry is a noncovalent process and features high mechanical reactivity in comparison to conventional mechanophores, which require covalent bond scission. This new type of configurational mechanophore holds promise for various applications, such as high-sensitivity stress sensing, lithography, and information storage.1 Diarylethene Conformers and Atropisomers2 Polymer Mechanochemistry and Configurational Mechanophores3 Regulating the Stereochemistry and Reactivity of a Diarylethene Atropisomer with Mechanical Force4 Summary and Future Outlook

UV-Light-Induced Morphological Transformation of Spiropyran Assemblies from Irregular Sheet-like Structures to Nanospheres.

Studies on self-assembling systems with a controllable morphology responding to light stimulation are significant for revealing the process and mechanism of assembly. Here, a molecule of spiropyran derivative (SP) possessing photoresponsive assembly morphology is constructed. SP self-assembles into irregular sheet-like structures whose morphology can be significantly transformed into regular nanospheres under continuous ultraviolet light stimulation. The UV-vis absorption spectra indicate that 56% of SP are isomerized from closed-ring form (SPC) to open-ring form (SPO) with color changes from colorless to magenta. Furthermore, theoretical calculations demonstrate that SPO-SPO aggregates possess stronger van der Waals forces than do SPC-SPC aggregates and tend to form stable intermediates combined with SPO isomers. Therefore, the isomerization of SP from SPC to SPO and the differences in intermolecular interactions are important factors in the morphological transition. Our study provides an efficient strategy to modulate the assembled morphology, which holds great promise to be applied in the field of smart materials.

Regulation of replication origin licensing by ORC phosphorylation reveals a two-step mechanism for Mcm2-7 ring closing

Eukaryotic DNA replication must occur exactly once per cell cycle to maintain cell ploidy. This outcome is ensured by temporally separating replicative helicase loading (G1 phase) and activation (S phase). In budding yeast, helicase loading is prevented outside of G1 by cyclin-dependent kinase (CDK) phosphorylation of three helicase-loading proteins: Cdc6, the Mcm2-7 helicase, and the origin recognition complex (ORC). CDK inhibition of Cdc6 and Mcm2-7 is well understood. Here we use single-molecule assays for multiple events during origin licensing to determine how CDK phosphorylation of ORC suppresses helicase loading. We find that phosphorylated ORC recruits a first Mcm2-7 to origins but prevents second Mcm2-7 recruitment. The phosphorylation of the Orc6, but not of the Orc2 subunit, increases the fraction of first Mcm2-7 recruitment events that are unsuccessful due to the rapid and simultaneous release of the helicase and its associated Cdt1 helicase-loading protein. Real-time monitoring of first Mcm2-7 ring closing reveals that either Orc2 or Orc6 phosphorylation prevents Mcm2-7 from stably encircling origin DNA. Consequently, we assessed formation of the MO complex, an intermediate that requires the closed-ring form of Mcm2-7. We found that ORC phosphorylation fully inhibits MO complex formation and we provide evidence that this event is required for stable closing of the first Mcm2-7. Our studies show that multiple steps of helicase loading are impacted by ORC phosphorylation and reveal that closing of the first Mcm2-7 ring is a two-step process started by Cdt1 release and completed by MO complex formation.

Photoresponsive Spiropyran and DEGMA-Based Copolymers with Photo-Switchable Glass Transition Temperatures.

Herein, novel photoresponsive spiropyran (SP)-based P(DEGMA-co-SpMA) copolymers with variable percentages of SP fractions are synthesized. The SP group present in these polymers exhibited the abilities of reversible photoisomerism. Their photoresponsive, structural, and thermal properties have been investigated and compared using various characterization techniques. These light-responsive copolymers are found to exhibit photoswitchable glass transition temperature (Tg ), high thermal stability (Td > 250°C), instant photochromism as well as fluorescence upon exposure to UV light. It is demonstrated that the Tg of these synthesized polymers increased when irradiated with UV light (λ = 365nm), as a consequence of the photoisomerization of incorporated SP groups into their merocyanine form. This increase in Tg is attributed to an increase in polarity and a decrease in the overall entropy of the polymeric system when it switches from the ring-closed SP form (less-ordered state) to the ring-opened merocyanine form (more-ordered state). Therefore, such polymers with a unique feature of phototunable glass transition temperatures provide the possibility to be integrated into functional materials for various photoresponsive applications.

Photo-Induced Fluorochromism of a Star-Shaped Photochromic Dye with 2,4-Dimethylthiazole Attaching to Triangle Terthiophene.

A photochrmic triangle terthiophene dye with 2,4-dimethylthiazole attached was synthesized and shows regular photochromic properties when irradiated with UV/Vis light alternately. It was found that the attaching of 2,4-dimethylthiazole has a significant effect on both the photochromism and fluorescence of triangle terthiophene. During the photocyclizatioin prcess, not only the color but also the fluorescence of the dye in THF can be toggled between ring-open and ring-closed forms of the dye. Additionally, the absolute quantum yields (AQY) of ring-open and ring-closed forms of the dye (0.32/0.58) were greatly larger than the literature report. Along with the 254nm light irradiation, the fluorescence color changed from deep blue (428nm) to sky blue (486nm) in THF. A fluorochromism cycle could be established based on the UV/visible light irradiation cycle, which provides a strategy for the design of new type fluorescent diarylethene derivatives for biological application.

Smart One-for-All Agent with Adaptive Functions for Improving Photoacoustic /Fluorescence Imaging-Guided Photodynamic Immunotherapy.

Multifunctional phototheranostics that integrate several diagnostic and therapeutic strategies into one platform hold great promise for precision medicine. However, it is really difficult for one molecule to possess multimodality optical imaging and therapy properties that all functions are in the optimized mode because the absorbed photoenergy is fixed. Herein, a smart one-for-all nanoagent that the photophysical energy transformation processes can be facilely tuned by external light stimuli is developed for precise multifunctional image-guided therapy. A dithienylethene-based molecule is designed and synthesized because it has two light-switchable forms. In the ring-closed form, most of the absorbed energy dissipates via nonradiative thermal deactivation for photoacoustic (PA) imaging. In the ring-open form, the molecule possesses obvious aggregation-induced emission features with excellent fluorescence and photodynamic therapy properties. In vivo experiments demonstrate that preoperative PA and fluorescence imaging help to delineate tumors in a high-contrast manner, and intraoperative fluorescence imaging is able to sensitively detect tiny residual tumors. Furthermore, the nanoagent can induce immunogenic cell death to elicit antitumor immunity and significantly suppress solid tumors. This work develops a smart one-for-all agent that the photophysical energy transformation and related phototheranostic properties can be optimized by light-driven structure switch, which is promising for multifunctional biomedical applications.

Spirocyclic rhodamine B benzoisothiazole derivative: a multi-stimuli fluorescent switch manifesting ethanol-responsiveness, photo responsiveness, and acidochromism.

Multi-stimuli fluorescent switching materials have been extensively employed in chemistry, biochemistry, physics, and materials science. Although rhodamine-based spirolactams have been specifically considered for metal ion sensing by photoluminescence, only some of them manifest photochromic behavior, and further development of rhodamine B (RHB)-based photochromic materials is required. RHB and its cyclic amides are advantageous in various sensing applications owing to their colorimetric responses to external stimulation. Hence, the current work reports a novel multifunctional active molecular material (3',6'-bis(diethylamino))-2-(5-nitrobenzo[c]isothiazol-3-yl)spiro[isoindoline-1,9'-xanthen]-3-one (RHBIT) by linking rhodamine B with 3-amino,5-nitro[2,1]benzoisothiazole (ANB) in a facile synthetic pathway; that perceives both emission color change and switching between off-on states. RHBIT shows acidochromism, photochromism, and pH sensitivity accompanied by unique ethanol responsiveness, with potential applications in anti-counterfeiting and drug delivery. Notably, RHBIT is highly acid sensitive and reverts to the ring-closed form on treatment with triethylamine (base), visible with the naked eye amidst colorless-pink-colorless transformations. On short UV irradiation, RHBIT provides a two-fold rise in the lifetime for the ring-open form in CHCl3 and DCM compared to the spirolactam (closed form). DFT and TDDFT studies provide electronic characterization for the absorption spectra of the open and closed forms. Using the photoresponsive feature of RHBIT, an information protection application has been enacted via a rewritable platform.

Thermostably photoswitchable red fluorescent polymeric nanoparticles for rewritable fluorescence patterning and zebrafish imaging

Photoswitchable fluorescent nanomaterials (PFNs) are gaining popularity in a variety of applications including bioimaging, information encryption and anti-counterfeiting. However, the photoswitching properties of traditional PFNs are still far from application, due to the complex background fluorescence interference, the lower brightness and contrast, the poor thermal and light stability. To tackle this question, we developed new thermostably photoswitchable red fluorescent polymer nanoparticles (TPFPNs) through a facile miniemulsion polymerization in this study. TPFPNs contained a high quantum yield of red fluorescence dye, 1,6,7,12-tetra(p-tBu-phenoxy)-3,4,9,10-di(anhydride) perylene (TBPDI) as donor and a thermostably photochromic diarylethene derivative (DTEDA) as acceptor. When DTEDA changed from its opened-ring state (DTEDA-o) to its closed-ring form (DTEDA-c) after UV irradiation, fluorescence resonance energy transfer (FRET) process occurred from TBPDI to DTEDA-c, which induced the transition from red fluorescence to quenching state. In addition, TPFPNs showed adjustable FRET efficiency, outstanding thermal stability, prominent long-term stability, superior photoreversibility, as well as high contrast of on/off fluorescence. Moreover, TPFPNs were successfully used for photo-rewritable patterning and reversible fluorescence bioimaging in Zebrafish.

Multicolor Photochromism of Two-Component Diarylethene Crystals Containing Oxidized and Unoxidized Benzothiophene Groups

Preparing mixed crystals composed of two or more components is one of the useful approaches to not only modifying the physical properties and chemical reactivity of molecular crystals but also creating their novel functionality. Here we report preparation and photoresponsive properties of two-component mixed crystals containing photochromic bis(benzothienyl)ethene derivatives that show different colors in the closed-ring forms depending on the oxidation state of the benzothiophene groups. The similarity in the molecular structures of the two diarylethenes, which are different from each other only in the oxidation state of the benzothiophene groups, allowed the formation of two-component mixed crystals by recrystallization from mixed solutions containing the two compounds. Irradiating the mixed crystals with light of appropriate wavelengths induced the selective photoisomerizaion of the two diarylethenes, leading to multicolor photochromic performance, such as colorless, orange, yellow, and red. Such molecular crystals with multiresponsive functions can find potential applications in multistate optical recording and multicolor displays. The present results demonstrate that combining differently oxidized diarylethene derivatives is an effective strategy for preparing multicomponent mixed crystals with finely tuned composition and desired photoresponsive properties.

Steric Control in Activator-Induced Nucleophilic Quencher Detachment-Based Probes: High-Contrast Imaging of Aldehyde Dehydrogenase 1A1 in Cancer Stem Cells.

Turn-on fluorescence probes can visualize the enzyme activity with high contrast. We have established a new turn-on mechanism, activator-induced nucleophilic quencher detachment (AiQd), and developed AiQd-based turn-on fluorescence probes for the detection of enzymes. Herein, we demonstrate that the precise steric control efficiently quenches the fluorescence of AiQd-based turn-on probes before the enzymatic transformation. Theoretical calculation appropriately predicted the ratio of the fluorescence-quenched closed-ring form of probes. βC5S-A, which has a sterically demanding methyl group at the β-position of a fluorescence-quenching nucleophilic mercapto group, showed a low background signal. βC5S-A responded to aldehyde dehydrogenase 1A1 (ALDH1A1) with high selectivity, thereby enabling high-contrast live imaging of cancer stem cells (signal-to-noise ratio >10). The ALDH1A1-responsiveness of βC5S-A was not significantly affected by amino acids and biological thiols, such as cysteine and glutathione.

Light-Stimulated Luminescence Control of Lead Halide-Based Perovskite Nanocrystals Coupled with Photochromic Molecules via Electron and Energy Transfer.

Photoswitchable nanomaterials are key materials in the development of advanced imaging techniques, such as super-resolution fluorescence microscopy. The combination of perovskite CsPbBr3 nanocrystals (NCs) with bright photoluminescence (PL) emission and diarylethenes (DAEs) with structural changes in response to ultraviolet (UV) and visible light is a promising candidate system. Herein, CsPbBr3 NCs are coupled with photochromic DAE molecules to control the PL emission from the NCs by light stimulation. The PL emission is successfully switched ON and OFF by alternating UV and visible light irradiation. Time-resolved PL emission studies suggest that Förster resonance energy transfer from CsPbBr3 NCs to the closed-ring form of DAE occurs after UV irradiation, and the PL emission is quenched. Upon visible-light irradiation, DAE is converted to the open-ring isomer, and the PL emission is restored. Femtosecond pump-probe spectroscopy reveals that light stimulation induces not only energy transfer but also photoinduced electron transfer in the NC-DAE pair on the picosecond timescale to form DAE radicals. Thus, it is suggested that the holes residing in the NCs react with the NCs, degrading the PL emission. Stable PL switching is realized using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) as a hole scavenger to avoid the reaction between the holes and NCs.

Structure Identification for Force-Induced Reaction Using Single-Molecule Conductance Measurement

Structure Identification for Force-Induced Reaction Using Single-Molecule Conductance Measurement

Merocyanine Complexes Coupled with Plasmonic Au Nanoparticles for Inhibiting Tau Aggregation

Singlet oxygen (1O2) has been recently identified as the key mechanism for depressing β-amyloid (Aβ) accumulation and neurofibrillary tangles (NFTs). Slow cell internalization and short half-life of photosensitizing effects still impede the application of nanophotosensitizers for photodynamic therapy (PDT). The current major challenge of using spiropyran for PDT is the extremely short half-life of its ring-opened isomer, merocyanine. Merocyanine is the center of generation of 1O2. Here, we report that the complexation of spiropyran onto Au nanoparticles greatly enhances the stability of merocyanine (half-life is 91.6 h). Additionally, Au nanoparticles sharply decelerate the reversion of merocyanine back to spiropyran (a ring-closed form) by modifying the energy configuration of merocyanine, resulting in generation of a long-lived 1O2 phototherapy response (24 h) in the intracellular environment for depressing tau aggregation (a 32% reduction of NFT formation).

Optically Switchable NIR Photoluminescence of PbS Semiconducting Nanocrystals using Diarylethene Photoswitches.

Precisely modulated photoluminescence (PL) with external control is highly demanded in material and biological sciences. However, it is challenging to switch the PL on and off in the NIR region with a high modulation contrast. Here, we demonstrate that reversible on and off switching of the PL in the NIR region can be achieved in a bicomponent system comprised of PbS semiconducting nanocrystals (NCs) and diarylethene (DAE) photoswitches. Photoisomerization of DAE to the ring-closed form upon UV light irradiation causes substantial quenching of the NIR PL of PbS NCs due to efficient triplet energy transfer. The NIR PL fully recovers to an on state upon reversing the photoisomerization of DAE to the ring-open form with green light irradiation. Importantly, fully reversible switching occurs without obvious fatigue, and the high PL on/off ratio (>100) outperforms all previously reported assemblies of NCs and photoswitches.