Supramolecular Complex of Photochromic Diarylethene and Cucurbit[7]uril: Fluorescent Photoswitching System for Biolabeling and Imaging

Photoswitchable WO3-x QD/Cu NC composite films for efficient UV detection and dual-mode anticounterfeiting

Photoswitchable fluorescent materials (PFMs) have attracted considerable attention owing to their intrinsic advantages of non-contact operation, cleanliness, and non-invasiveness. Conventional PFMs always require complicated preparation processes with poor fluorescence switching properties, which are affected by the Föster resonance energy transfer (FRET) or photoinduced electron transfer (PET) mechanism. Herein, WO3-x QD/Cu NC composite films were prepared on different substrates via a solution casting method and display outstanding fluorescence switching properties owing to the super photochromic performance of WO3-x QDs and aggregation-induced fluorescence of Cu NCs. The composite film exhibits reversible on/off switchable fluorescence under UV light irradiation and heat treatment based on the inner filter effect (IFE) mechanism. The composite film shows dynamic variations in dual-mode signals, and the applications of UV sensing and anti-counterfeiting are analyzed. Sensitive dual-mode detection is achieved in UV sensing, particularly for UVB. The composite film exhibits a dual-modal imaging capability with good reproducibility and high resolution for security information encryption and anti-counterfeiting. This work provides a novel strategy for fabricating advanced PFMs for multiple optical applications.

Supramolecular Synthesis of Dithienylethene-Albumin Complexes for Enhanced Photoswitching In Photoacoustic Imaging-Guided Near-Infrared Photothermal Therapy

Photoswitchable molecules can transit between two distinct isomers, enabling them to perform highly controllable imaging and therapeutic functions under certain laser irradiation. Dithienylethenes (DTEs), a class of photoswitchable molecules, exhibit strong thermal stability and high fluorescence quantum yield. However, the short excitation wavelength poses a significant challenge for the application of DTEs in photocontrolled imaging and therapy. Therefore, the development of DTE-based derivatives or hybrid materials with near-infrared (NIR) excitation is of great importance. In this study, two novel DTE derivatives are synthesized, whose closed-ring isomers exhibit strong absorption in the NIR region. Compared with a DTE derivative previously reported and commercially available ones, these two DTE derivatives show higher photoswitching efficiency and extended absorption wavelength. Notably, the supramolecular assembly between DTE derivatives and albumin confers NIR-activated photothermal switching ability on DTE molecules in aqueous solution. In addition, DTE-albumin nanoparticles are further developed to enable photoswitchable photoacoustic imaging (PAI) and photothermal therapy (PTT) for in vivo antitumor applications. Finally, by integrating a thermo-responsive free radical initiator into DTE-albumin nanoparticles, photoswitchable PTT and chemodynamic therapy (CDT) are achieved, effectively inhibiting tumor growth and preventing tumor metastasis.

Tale of Three Dithienylethenes: Following the Photocycloreversion with Ultrafast Spectroscopy and Quantum Dynamics Simulations

Photocycloreversion reactions of three diarylethene derivatives whose structures differ only in the placement of two sulfur atoms in the cyclopentene rings are investigated. Despite the minuscule differences between the molecules, both the yields and times of the photoreactions vary considerably. Using UV-vis and infrared femtosecond spectroscopy and quantum chemical dynamics simulations, we elucidate the relationships among the quantum yield, electronic and vibrational relaxation time, and structural properties of the dithienylethene photoswitches. We show that the local aromaticity of the molecule's central ring could be one of the predictors of the quantum yield and the rate of cycloreversion. While from the perspective of electronic dynamics, the cycloreversion is completed within a few picoseconds at most, all three derivatives exhibit much longer (10-25 ps) nuclear rearrangement times that determine the actual times of stable photoproduct formation.

Effect of substitution position of aryl groups on the thermal back reactivity of aza-diarylethene photoswitches and prediction by density functional theory

Aza-diarylethene has been developed as a new family of photochromic compounds. This study explores the photochromic properties and thermal back reactivities of various aza-diarylethene regioisomers (N1-N4 and I1-I4) in n-hexane. These molecules exhibit fast thermally reversible photochromic reactions driven by 6π aza-electrocyclization. Kinetic analysis of the thermal back reaction revealed activation parameters, highlighting how the substitution position of the aryl group affects the thermal stability. Additionally, density functional theory calculations identified M06 and MPW1PW91 as the most accurate functionals for predicting the thermal back reactivity, closely matching the experimental data. These findings offer valuable insights for the design of advanced photochromic materials with tailored thermal and photophysical characteristics.

Asymmetric Donor-Acceptor 2,7-Disubstituted Fluorenes and Their 9-Diazoderivatives: Synthesis, Optical Spectra and Photolysis

In a search for dyes photoactivatable with visible light, fluorenes with substituents at positions 2 and 7 were prepared, and their absorption and emission spectra were studied. In particular, the synthesis route to 9-diazofluorenes with 2-(N,N-dialkylamino) and N-modified 7-(4-pyridyl) substituents was established. These compounds are initially non-fluorescent, undergo photolysis with UV or blue light, and-in non-polar media-provide orange- to red-emitting products with a large separation between absorption and emission bands. Irradiation of non-fluorescent 9-diazoderivative 20 in dioxane with the light of 365 nm or 470 nm was accompanied by strong fluorescence gain (10 to 20 times), orange-red emission, and a large Stokes shift of photoproducts, which structurally relate to fluorescent betaine 13 (model compound without diazo group). Photolysis of 20 in protic solvents (ROH = MeOH, H2O) provided clean transformation to C9-OR derivatives, though the emission gain in protic solvents was low.

Diazocines as Guests of Cucurbituril Macrocycles: Light-Responsive Binding and Supramolecular Catalysis of Thermal Isomerization

The photoswitching of supramolecular host-guest complexes is the basis of numerous molecularly controlled macroscopic functions, such as sol-gel transition, photopharmacology, the active transport of ions or molecules, light-powered molecular machines, and much more. The most commonly used systems employ photoactive azobenzene guests and synthetic host molecules, which bind as the stable E isomers and dissociate as the Z forms after exposure to UV light. We present a new, extraordinarily efficient cucurbit[7]uril (CB7)/diazocine host/guest complex with inverted stability that self-assembles under UV irradiation and dissociates in the dark. The association constants of the Z and E isomers in water differ by more than 104-fold. We also show that the thermally activated E → Z isomerization is significantly accelerated by CB7, which is a rare case of enzyme-like catalysis by transition state stabilization without product inhibition. In contrast to CB7, cucurbit[8]uril (CB8) binds both isomers with high affinity, showing good selectivity (∼1000-fold) toward the Z isomer. Notably, this isomer preferentially binds CB8 relative to CB7 by a factor greater than 1 × 106. We also use the system to introduce a supramolecular photoacid that builds on the increased basicity of a guest bound to CB7 and on the extremely high affinity of the E isomer, which is utilized to displace the acid from CB7, thereby switching the pH of the solution.

Supramolecular Control of the Photoisomerization of a Coumarin-Based Photoswitch

The complex formation of the cationic stilbene-type photoswitch CP with the anionic macrocycles carboxylato-pillar[5]arene (WP5) and carboxylato-pillar[6]arene (WP6) has been investigated in aqueous solution by optical spectroscopic, NMR and isothermal calorimetric experiments and theoretical calculations. Subsequently, the photoisomerization reactions of the supramolecular complexes formed have been studied. CP consists of a 7-diethylamino-coumarin fluorophore and an N-methylpyridinium unit, which are connected via an ethene bridge. The trans isomer of CP is fluorescent, and its cis isomer is dark. The binding constants of the WP6 complexes of the two photoisomers of CP are larger by 2 orders of magnitude than those of the respective complexes with WP5, and trans-CP forms more stable complexes with the individual pillararenes than the cis isomer. As shown by NMR spectroscopic measurements and theoretical calculations, the two isomers of CP form external complexes with WP5 and inclusion complexes with WP6. On complexation with WP6, the quantum yields of both the trans-to-cis and cis-to-trans photoisomerization reactions of CP increase significantly, and the fluorescence quantum yield of trans-CP is also enhanced. These changes are due to the suppression of the TICT deactivation process, which is characteristic of 7-dialkylamino-coumarin derivatives.

Supramolecular nanotherapeutics based on cucurbiturils

Polymeric biomaterials have important applications in aiding clinical disease treatment, including drug delivery, bioimaging, and tissue engineering. Currently, conventional tumor chemotherapy faces obstacles such as poor solubility/stability, inability to target, and uncontrolled drug release in clinical trials, for which the emergence of supramolecular material therapeutics combining non-covalent interactions with conventional therapies is a very promising candidate. Due to their molecular recognition abilities with a range of biomolecules, cucurbit[n]uril (CB[n]), a type of macrocyclic receptors with robust backbones, hydrophobic cavities, and carbonyl-binding channels, have garnered a lot of attention. Therefore, this paper reviews recent advances in CB[n] material-based supramolecular therapeutics for clinical treatments, including targeted delivery applications and related imaging and sensing systems. This study also covers the distinctive benefits of CB materials for biological applications, as well as the trends and prospects of this interdisciplinary subject, based on numerous state-of-the-art research findings.

A Visible-Light-Responsive Fluorescent Diarylethene Having a Betaine Structure

As a new molecular scaffold of photoswitchable fluorophore, we developed a photochromic diarylethene containing a betaine structure based on pyridinium N-enolate. A facile reaction of a pyridyl-substituted dithienylperfluorocyclopentene derivative with octafluorocyclopentene constructed the betaine structure. The introduction of the betaine moiety provided the diarylethene molecule with bathochromically shifted optical absorption and fluorescing ability, thus enabling the molecule to function as a visible-light-responsive turn-off mode photoswitchable fluorophore. The molecule in the open-ring form emitted bright bluish green fluorescence. Upon irradiation with 405 nm light, the molecule underwent cyclization isomerization to form the closed-ring isomer and the fluorescence intensity significantly decreased. The turn-off mode fluorescence photoswitching was observed not only in solution but also in polymer films.

Recent Progress of Photoswitchable Fluorescent Diarylethenes for Bioimaging

Photochromic diarylethene has attracted broad research interest in optical applications owing to its excellent fatigue resistance and unique bistability. Photoswitchable fluorescent diarylethene become a powerful molecular tool for fluorescence imaging recently. Herein, the recent progress on photoswitchable fluorescent diarylethenes in bioimaging is reviewed. We summarize the structures and properties of diarylethene fluorescence probes and emphatically introduce their applications in bioimaging as well as super-resolution imaging. Additionally, we highlight the current challenges in practical applications and provide the prospects of the future development directions of photoswitchable fluorescent diarylethene in the field of bioimaging. This comprehensive review aims to stimulate further research into higher-performance photoswitchable fluorescent molecules and advance their progress in biological application.

Fluorescence Turn-ON Displacement Assays with Cucurbit[7]uril-Thiophenylpyridinium Complexes as Host-Dye Reporter Pairs

The N-methyl-4-thiophenylpyridinium cation (ThioPy) is a high affinity (Kd ca. 5 nM), fast-exchanging fluorescent probe for cucurbit[7]uril (CB7). The CB7/ThioPy complex shows a unique fluorescence turn-ON response upon displacement by an analyte in sensing application. This enabled the development of a real-time fluorescence assay with the MRFA peptide for the protease thermolysin, which is also suitable for the cancer biomarker cathepsin B. Moreover, liposome encapsulation of CB7/ThioPy in large unilamellar vesicles (LUVs) provided mechanistic insight into intravesicular dye displacement reactions.

Synthesis, Characterization, and Photochemistry of a Ga2L3 Coordination Cage with Dithienylethene-Catecholate Ligands

Two new photoswitchable dithienylethene (DTE)-catechol ligands, specifically designed for group 13 metal coordination, were synthesized via Suzuki coupling reactions from a dichloro-DTE building block, each with varying longitudinal extensions. The shorter DTE-catechol ligand did not efficiently assemble with Ga3+ metal ions; however, elongation with a phenylene-amide spacer group enabled the successful formation of a novel triply DTE-functionalized coordination [Ga2L3]6- cage. This cage represents a unique example of integrating DTE photoswitches with main group metals in a supramolecular coordination framework. The [Ga2L3]6- cage was thoroughly characterized by NMR spectroscopy, including DOSY hydrodynamic volumetric analyses, high-resolution mass spectrometry, computational DFT, and photochemical analyses. The DFT studies highlighted the structural integrity and dynamic interplay within the helicate and mesocate isomeric forms of the [Ga2L3]6- cage upon photoswitching. While the free ligands exhibited all-photonic reversible switching at up to mM concentrations upon alternating irradiation at 365 and >495 nm, the [Ga2L3]6- cage demonstrated these capabilities under dilute μM conditions, albeit with lower efficiency and fatigue resistance. This behavior highlights the intricate relationship between rigid coordination with main group metals and the flexibility of the photoswitchable DTE ligands within the [Ga2L3]6- cage.

Synthesis, Structural Characterization, and Theoretical Analysis of Nonconventional Bonding in Dinuclear Zinc(II) Complexes with Tridentate Schiff Bases

Two tridentate N,N,O-donor ligands, HL1 = 4-chloro-2-(((2-(methylamino)ethyl)amino)methyl)phenol and HL2 = 4-chloro-2-(((2-(dimethylamino)ethyl)amino)methyl)phenol, have been used to synthesize phenolate-bridged dinuclear complexes [Zn2(L1)2Cl2] (1) and [Zn2(L2)2(N3)2] (2). Single-crystal X-ray diffraction analysis confirmed their structures. Both complexes form assemblies in the solid state. Moreover, the existence of nonconventional spodium bonds in 1 and tetrel bonds in 2 has been explored using theoretical calculations, including MEP surface plots and QTAIM and NCIplot analyses.

Transient cucurbit[7]uril-mediated host-guest complexes for time-dependent fluorescence and information-self-erasing hydrogel

A non-equilibrium cucurbit[7]uril-mediated supramolecular host-guest system is fabricated by using urea/urease to control aqueous solution pH on time dimension, showing transient assembly behavior and time-dependent fluorescence. The dynamic assembly can be also achieved in hydrogel network, resulting in a time-dependent fluorescent hydrogel for information encryption.

A Supramolecular Fluorescent Sensor Array Composed of Conjugated Fluorophores and Cucurbit[7]uril for Bacterial Recognition

Bacterial infections have emerged as a significant contributor to global mortality and morbidity rates. Herein, we introduce a dual fluorescence "turn-on" supramolecular sensor array composed of three assembled complexes (C1-C3), formed from three positively charged fluorophores (A1-A3) and one cucurbit[7]uril (CB[7]). The ability of this three-element array to simultaneously recognize 10 bacterial species within just 30 s was remarkable, boasting an impressive 100% accuracy. Additionally, the array excelled at distinguishing among various bacterial mixtures and enabled the quantitative detection of common bacterial strains. Notably, it has been skillfully applied to differentiate 10 bacterial samples in urine, achieving excellent differentiation and showcasing promising potential for medical diagnostic applications.

Supramolecular Complex of Cucurbit[7]uril with Diketopyrrolopyrole Dye: Fluorescence Boost, Biolabeling and Optical Microscopy

New photostable and bright supramolecular complexes based on cucurbit[7]uril (CB7) host and diketopyrrolopyrole (DPP) guest dyes having two positively charged 4-(trimethylammonio)phenyl groups were prepared and characterized. The dye core displays large Stokes shift (in H2O, abs./emission max. 480/550 nm; ϵ~19 000, τfl>4 ns), strong binding with the host (~560 nM Kd) and a linker affording fluorescence detection of bioconjugates with antibody and nanobody. Combination of protein-functionalized DPP dye with CB7 improves photostability and affords up to 12-fold emission gain. Two-color confocal and stimulated emission depletion (STED) microscopy with 595 nm or 655 nm STED depletion lasers shows that the presence of CB7 not only leads to improved brightness and image quality, but also results in DPP becoming cell-permeable.

Photochromism, Thermochromism, and Electrochromism in Solid-State Host-Guest Inclusion Complexes of β-Cyclodextrin with Dialkylcarboxyl-Substituted Viologens

Multi-stimuli-responsive chromic materials have immense potential for utilization. Herein, two supramolecular inclusion complexes were prepared by self-assembly of β-cyclodextrin (β-CD) with dialkylcarboxyl-substituted viologens, N,N'-di(3-carboxy-propyl)-4,4'-bipyridinium dichloride (CPV·Cl2) and N,N'-di(6-carboxy-hexyl)-4,4'-bipyridinium dibromide (CHV·Br2). The self-assembled inclusion complexes CPV2+@β-CD and CHV2+@β-CD2 in the solid-state exhibited naked-eye photochromism, thermochromism, and electrochromism in response to multiple external stimuli including light, temperature, and electric field, respectively. Solid-state UV-vis diffuse reflectance and electron spin resonance (ESR) spectroscopy revealed that the observed photochromism, thermochromism and electrochromism are attributed to the formation of viologen free radicals induced by electron transfer under external stimuli. The excellent stimuli-response chromic properties of the title inclusion complexes support their practical utility in visual display, multiple anticounterfeiting, and multilevel information encryption.

Multi Stimuli Responsive Dual Aggregation-Induced Emission and Photochromic Behavior of a Tetraphenyl Substituted Triphenylamine Derivative and its Application as Anti-counterfeiting Agent

A multi-stimuli responsive tetraphenyl substituted tripehnylamine-based aggregation induced emissive (AIE) material coupled with spiropyran was prepared. Owing to the presence of AIE and photochromic moiety, the molecule exhibits emissive aggregates, photochromism, and acidochromism. The multiple stimuli sensitive behavior of the molecule was explored for anti-counterfeiting behavior on TLC plate and commercial banknotes. The fluorogenic and photogenic response under UV and visible light established the potential of the candidate as a new generation encryption material.

A visible-light regulated luminescent switch based on a spiropyran-derived Pt(II) complex for advanced anti-counterfeiting materials

A dual optical switch regulated by visible light has been developed through an integrated strategy, including luminescent Pt(II) and photochromic spiropyran (SP) as a triplet-sensitizer and photo-regulator building block, respectively. An efficient Förster resonance energy transfer (FRET) process is achieved, along with apparent and emissive color changes under visible light irradiation and temperature stimuli, which was utilized to develop advanced anti-counterfeiting materials.

Cucurbit[7]uril as the host of adamantane-modified dyes for fluorescence enhancement in aqueous environments

Taking advantage of the excellent host-guest complexation ability between an auxochrome (adamantane group) and CB[7], the fluorescence emission performance of dyes in water was effectively improved with the addition of two equivalents of CB[7], which provided an efficient method for increasing fluorescence intensity in aqueous environments. Furthermore, these dyes with the host were successfully used in cell imaging.

Pyrene Functionalized Norbornadiene-Quadricyclane Fluorescent Photoswitches: Characterization of their Spectral Properties and Application in Imaging of Amyloid Beta Plaques

This study presents the synthesis and characterization of two fluorescent norbornadiene (NBD) photoswitches, each incorporating two conjugated pyrene units. Expanding on the limited repertoire of reported photoswitchable fluorescent NBDs, we explore their properties with a focus on applications in bioimaging of amyloid beta (Aβ) plaques. While the fluorescence emission of the NBD decreases upon photoisomerization, aligning with what has been previously reported, for the first time we observed luminescence after irradiation of the quadricyclane (QC) isomer. We deduce how the observed emission is induced by photoisomerization to the excited state of the parent isomer (NBD) which is then the emitting species. Thorough characterizations including NMR, UV-Vis, fluorescence, X-ray structural analysis and density functional theory (DFT) calculations provide a comprehensive understanding of these systems. Notably, one NBD-QC system exhibits exceptional durability. Additionally, these molecules serve as effective fluorescent stains targeting Aβ plaques in situ, with observed NBD/QC switching within the plaques. Molecular docking simulations explore NBD interactions with amyloid, unveiling novel binding modes. These insights mark a crucial advancement in the comprehension and design of future photochromic NBDs for bioimaging applications and beyond, emphasizing their potential in studying and addressing protein aggregates.

Precise Regulation the Multiemission Based on Soft Double Salt for Information Encryption

Manipulation of multiemissive luminophores is meaningful for exploring luminescent materials. Herein, we report a soft double salt assembly strategy that could result in well-organized nanostructures and different luminescence based on multiple weak intermolecular interactions thanks to the existence of electrostatic attraction between the anionic and cationic platinum(II) complexes. The cationic complexes B1 and B2 can coassemble with anionic complex A, respectively, and the emission switches from monomeric and excimeric emission to the triplet metal-metal-to-ligand charge transfer (3MMLCT) along with morphology changes from 0-dimensional (0-D) nanospheres to 3-dimensional (3-D) nanostructures. It is demonstrated that an isodesmic growth mechanism is adopted during the spontaneous self-assembly process, and the relative negative ΔG values make the anionic and cationic complex molecules prefer to form aggregates based on π-π stacking, Pt···Pt interactions, and electrostatic interactions. The coassembly strategy between anionic and cationic complexes endows them with multicolor luminescent and apparent color as optical materials for advanced information encryption.

Recent Development of Photochromic Polymer Systems: Mechanism, Materials, and Applications

Photochromic polymer is defined as a series of materials based on photochromic units in polymer chains, which produces reversible color changes under irradiation with a particular wavelength. Currently, as the research progresses, it shows increasing potential applications in various fields, such as anti-counterfeiting, information storage, super-resolution imaging, and logic gates. However, there is a paucity of published reviews on the topic of photochromic polymers. Herein, this review discusses and summarizes the research progress and prospects of such materials, mainly summarizing the basic mechanisms, classification, and applications of azobenzene, spiropyran, and diarylethene photochromic polymers. Moreover, 3-dimensional (3D) printable photochromic polymers are worthy to be summarized specifically because of its innovative approach for practical application; meanwhile, the developing 3D printing technology has shown increasing potential opportunities for better applications. Finally, the current challenges and future directions of photochromic polymer materials are summarized.

Recent Advances on Diarylethene-Based Photoswitching Materials: Applications in Bioimaging, Controlled Singlet Oxygen Generation for Photodynamic Therapy and Catalysis

Photoswitching materials have emerged as a promising class of compounds that possess manifold interesting properties rendering their widespread use from photoswitches, regulators to optoelectronic devices, security technologies and biochemical assays. Diarylethenes (DAE) constitute one such category of photoswitchable compounds, where the key features of stability, photoisomerization wavelengths, quantum yield and variability in the photoisomers significantly depend on their derivatization. The last decade has witnessed a surge in the engagement of DAEs in different areas of chemical and biological sciences, like biomarkers, controlled generation of singlet oxygen, photo-dynamic therapy, chemosensing, catalysis, etc. In all the cases, the photoswitchability of DAE is the principal regulating factor along with its emission properties according to the appended groups. Previous reviews on applications of DAE-based systems did not predominantly cover all the aspects of biological and industrial implementations. They have covered only one field of application either in the biological science or in the synthetic aspect or photochromic aspects only. This review is a coalition of all those aspects in last six years. Here the variation of properties of the DAE systems with respect to structural diversifications have been discussed in detail along with their potential applications in bioimaging of cells, regulating singlet oxygen generation for photodynamic therapy and catalysis of organic reactions, and their future prospects. A tabular presentation of the photophysical properties of DAE derivatives adds to the basic understanding of this subject at a glance. We hope that this cumulative collection of contemporary research on DAE, as presented in this review, will enhance the knowledge of the readers about synthetic design anticipating their properties well in advance, and will certainly motivate researchers to generate new DAE architectures with superior chemical and biological properties in future.

Recent Advances in Photoswitchable Fluorescent and Colorimetric Probes

In recent years, significant advancements have been made in the research of photoswitchable probes. These probes undergo reversible structural and electronic changes upon light exposure, thus exhibiting vast potential in molecular detection, biological imaging, material science, and information storage. Through precisely engineered molecular structures, the photoswitchable probes can toggle between "on" and "off" states at specific wavelengths, enabling highly sensitive and selective detection of targeted analytes. This review systematically presents photoswitchable fluorescent and colorimetric probes built on various molecular photoswitches, primarily focusing on the types involving photoswitching in their detection and/or signal response processes. It begins with an analysis of various molecular photoswitches, including their photophysical properties, photoisomerization and photochromic mechanisms, and fundamental design concepts for constructing photoswitchable probes. The article then elaborates on the applications of these probes in detecting diverse targets, including cations, anions, small molecules, and biomacromolecules. Finally, it offers perspectives on the current state and future development of photoswitchable probes. This review aims to provide a clear introduction for researchers in the field and guidance for the design and application of new, efficient fluorescent and colorimetric probes.

Effect of photoconversion conditions on the spectral and cytotoxic properties of photoconvertible fluorescent polymer markers

Fluorescence labeling of cells is a versatile tool used to study cell behavior, which is of significant importance in biomedical sciences. Fluorescent photoconvertible markers based on polymer microcapsules have been recently considered as efficient and perspective ones for long-term tracking of individual cells. However, the dependence of photoconversion conditions on the polymeric capsule structure is still not sufficiently clear. Here, we have studied the structural and spectral properties of fluorescent photoconvertible polymeric microcapsules doped with Rhodamine B and irradiated using a pulsed laser in various regimes, and shown the dependence between the photoconversion degree and laser irradiation intensity. The effect of microcapsule composition on the photoconversion process was studied by monitoring structural changes in the initial and photoconverted microcapsules using X-ray diffraction analysis with synchrotron radiation source, and Fourier transform infrared, Raman and fluorescence spectroscopy. We demonstrated good biocompatibility of free-administered initial and photoconverted microcapsules through long-term monitoring of the RAW 264.7 monocyte/macrophage cells with unchanged viability. These data open new perspectives for using the developed markers as safe and precise cell labels with switchable fluorescent properties.

Photoswitching the fluorescence of nanoparticles for advanced optical applications

The dynamic optical response properties and the distinct features of nanomaterials make photoswitchable fluorescent nanoparticles (PF NPs) attractive candidates for advanced optical applications. Over the past few decades, the design of PF NPs by coupling photochromic and fluorescent motifs at the nanoscale has been actively pursued, and substantial efforts have been made to exploit their potential applications. In this perspective, we critically summarize various design principles for fabricating these PF NPs. Then, we discuss their distinct optical properties from different aspects by highlighting the capability of NPs in fabricating new, robust photoswitch systems. Afterwards, we introduce the pivotal role of PF NPs in advanced optical applications, including sensing, anti-counterfeiting and imaging. Finally, current challenges and future development of PF NPs are briefly discussed.

Amplifying dual-visible-light photoswitching in aqueous media via confinement promoted triplet-triplet energy transfer

Achieving visible-light photochromism is a long-term goal of chemists keen to exploit the opportunities of molecular photoswitches in multi-disciplinary research studies. Triplet-sensitization offers a flexible approach to building diverse visible-light photoswitches using existing photochromic scaffolds, circumventing the need for sophisticated molecular design and synthesis. Unfortunately, distance-dependence and environment-sensitivity of triplet-excited species remain as key challenges that severely impair sensitization efficiency and limit their practical availability. We present herein a nature-inspired nanoconfinement strategy in which a triplet-sensitized visible-light photoswitch/sensitizer system is assembled into nanoconfined micelles (d ∼ 40 nm). A ca. 10-fold efficiency increase of triplet-triplet energy transfer for photochromism as well as an amplified fluorescence on/off contrast upon bi-directional visible-light excitation (470/560 nm) was achieved in full aqueous media. By virtue of this, the hybrid photoswitchable system is successfully applied for both flash information encryption and multiple dynamic cell imaging assays, further proving its versatility in materials and life science.

Origin of Octafluorocyclopentene Polyelectrophilicity

Octafluorocyclopentene (OFCP) has found utility as a polyelectrophile in substitution cascades that form complex macrocyclic compounds. The Harran group synthesis of macrocyclic polypeptides depends on OFCP as a linker, combining with four different nucleophilic units of a polypeptide. We report a computational investigation of the origins of OFCP reactivity and a rationale for controlled mono-, di-, tri-, and tetrasubstitution of fluoride ions by heteroatomic nucleophiles. The roles of inductive, negative hyperconjugative, and resonance electron-donation by fluoride substituents are explored for the reaction of OFCP, less-fluorinated analogues, and common electrophilic alkenes with several different nucleophiles.

No-wash fluorogenic labeling of proteins for reversible photoswitching in live cells

Photoswitchable fluorescent molecules (PSFMs) are positioned as valuable tools for biomolecule localization tracking and super-resolution imaging technologies due to their unique ability to reversibly control fluorescence intensity upon light irradiation. Despite the high demand for PSFMs that are suitable for live-cell imaging, no general method has been reported that enables reversible fluorescence control on proteins of interest in living cells. Herein, we have established a platform to realize reversible fluorescence switching in living cells by adapting a protein labeling system. We have developed a new PSFM, named HTL-Trp-BODIPY-FF, which exhibits strong fluorogenicity upon recognition of Halo-tag protein and reversible fluorescence photoswitching in living cells. This is the first example of a PSFM that can be applicable to a general-purpose Halo-tag protein labeling system for no-wash live-cell imaging.

Aromatic Bridged Bis(triphenylamine) Cascade Assembly Achieved Tunable Nanosupramolecular Morphology and NIR Targeted Cell Imaging

Possessing four cationic pyridium groups, phenyl-bridged bis(triphenylamine) derivatives (G1, G2) were encapsulated by cucurbit[8]uril (CB[8]) at a 1:2 stoichiometry to form the network-like organic two-dimensional nanosheet, which could efficiently enhance the near-infrared (NIR) luminescence and companies with a red-shift from 750 to 810 nm for G1. Benefiting from the supramolecular multivalent interaction, α-cyclodextrin modified hyaluronic acid (HACD) and G1/CB[8] formed nanoparticles to further enhance NIR luminescence behaviors. Compared with the short rigid aromatic bridged bis(triphenylamine) derivative (G2), the supramolecular assembly derived from G1 with long flexible cationic arms gives a larger Stokes shift, which further coassembles with the phosphorescent bromophenylpyridinium derivative/CB[8] pseudorotaxane, leading to efficient phosphorescent resonance energy transfer (PRET). Especially, the nanoparticle showed delayed NIR fluorescence under 308 nm light excitation with an ultralarge Stokes shift up to 502 nm, which was successfully applied in targeted NIR cell imaging.

2,3-Diarylmaleate salts as a versatile class of diarylethenes with a full spectrum of photoactivity in water

There is incessant interest in the transfer of common chemical processes from organic solvents to water, which is vital for the development of bioinspired and green chemical technologies. Diarylethenes feature a rich photochemistry, including both irreversible and reversible reactions that are in demand in organic synthesis, materials chemistry, and photopharmacology. Herein, we introduce the first versatile class of diarylethenes, namely, potassium 2,3-diarylmaleates (DAMs), that show excellent solubility in water. DAMs obtained from highly available precursors feature a full spectrum of photoactivity in water and undergo irreversible reactions (oxidative cyclization or rearrangement) or reversible photocyclization (switching), depending on their structure. This finding paves a way towards wider application of diarylethenes in photopharmacology and bioinspired technologies that require aqueous media for photochemical reactions.

Ligand-protected nanocluster-mediated photoswitchable fluorescent nanoprobes towards dual-color cellular imaging

Development of robust multi-color photoswitchable fluorescent probes is critical for many optical applications, but it remains a challenge to rationally design these probes. Here, we report a new design of Förster resonance energy transfer-based dual-color photoswitchable fluorescent nanoparticles (DPF NPs) by taking advantage of the distinct properties of ligand-protected gold nanoclusters (AuNCs). Detailed photophysical studies revealed that ultrasmall-sized AuNCs not only act as the FRET donors due to their intrinsic fluorescence properties, but also play a significant role in regulating the photochromic and aggregate properties of spiropyran through ligand-spiropyran interactions. These DPF NPs exhibit a high fluorescence on/off ratio (∼90%) for both green and red fluorescence emission, and good reversibility during cycled photo-stimulation. Cell imaging experiments showed that DPF NPs could specifically accumulate in lipid droplets, and enable photoswitchable dual-color imaging in living cells. Moreover, by labeling mitochondria with a green-emitting marker, we demonstrated that DPF NPs can distinguish different targets based on dynamic and static fluorescence signals at the sub-cellular level in two emission channels reliably. This study provides a new strategy for designing robust photoswitchable fluorescent probes by modulating the properties of photochromic dyes through ligand-protected nanoclusters, which can be generalized for the development of other photoswitch systems towards advanced optical applications.

Phototransduction in a supramolecular cascade: a mimic for essential features of the vision process

The tailored design of a light-triggered supramolecular cascade results in an artificial machinery that assimilates the transduction of photons into chemical communication and the final release of a neurotransmitter. This is reminiscent of key steps in the natural vision process.

Current Trends in Nanotheranostics: A Concise Review on Bioimaging and Smart Wearable Technology

The area of interventional nanotheranostics combines the use of interventional procedures with nanotechnology for the detection and treatment of physiological disorders. Using catheters or endoscopes, for example, interventional techniques make use of minimally invasive approaches to diagnose and treat medical disorders. It is feasible to increase the precision of these approaches and potency by integrating nanotechnology. To visualize and target various parts of the body, such as tumors or obstructed blood veins, one can utilize nanoscale probes or therapeutic delivery systems. Interventional nanotheranostics offers targeted, minimally invasive therapies that can reduce side effects and enhance patient outcomes, and it has the potential to alter the way that many medical illnesses are handled. Clinical enrollment and implementation of such laboratory scale theranostics approach in medical practice is promising for the patients where the user can benefit by tracking its physiological state. This review aims to introduce the most recent advancements in the field of clinical imaging and diagnostic techniques as well as newly developed on-body wearable devices to deliver therapeutics and monitor its due alleviation in the biological milieu.

Tunable Photochromism of Spirooxazine in the Solid State: A New Design Strategy Based on the Hypochromic Effect

As an important organic photofunctional material, spirooxazine (SO) usually does not exhibit photochromism in the solid state since the intermolecular π-π stacking impedes photoisomerization. Developing photochromic SO in the solid state is crucial for practical applications but is still full of challenges. Here, a series of spirooxazine derivatives (SO1-SO4) with bulky aromatic substituents at the 4- and 7-positions of the skeleton, which provide them with a large volume with which to undergo solid-state photochromism under mild conditions, is designed and synthesized. All the compounds SO1-SO4 exhibit tunable solid photochromism without ground colors, excellent fatigue resistance, and high thermal stability. Notably, it takes only 15 s for SO4 to reach the saturation of absorption intensity, thought to represent the fastest solid-state photoresponse of spirooxazines. X-ray crystal structures of the intermediate compound SO0 and the products SO1-SO2 as well as computational studies suggest that the bulky aromatic groups can lead to a hypochromic effect, allowing for the photochromism of SO in the solid state. The ideal photochromic properties of these spirooxazines open a new avenue for their applications in UV printing, quick response code, and related fields.

Small-molecule photoswitches for fluorescence bioimaging: engineering and applications

Fluorescence microscopy has revolutionised our understanding of biological systems, enabling the visualisation of biomolecular structures and dynamics in complex systems. The possibility to reversibly control the optical or biochemical properties of fluorophores can unlock advanced applications ranging from super-resolution microscopy to the design of multi-stimuli responsive and functional biosensors. In this Highlight, we review recent progress in small-molecule photoswitches applied to biological imaging with an emphasis on molecular engineering strategies and promising applications, while underlining the main challenges in their design and implementation.

Cucurbituril Enhanced Electrochemiluminescence of Gold Nanoclusters via Host-Guest Recognition for Sensitive D-Dimer Sensing

Gold nanoclusters (AuNCs) are promising electrochemiluminescence (ECL) signal probes for their outstanding biocompatibility, unusual molecule-like structures, and versatile optical and electrochemical properties. Nevertheless, their relatively low ECL efficiency and poor stability in aqueous solutions hindered their application in the ECL sensing field. Herein, a facile host-guest recognition strategy was proposed to enhance the ECL efficiency and stability of Au NCs by rigidifying the surface of ligand-stabilized AuNCs via supramolecular self-assembly between cucurbiturils[7] (CB[7]) and l-phenylalanine (l-Phe). Meanwhile, mercaptopropionic acid (MPA) was introduced as a ligand in order to cooperatively enhance the performance of the AuNCs and facilitate the link between AuNCs and bioactive substances. The prepared CB[7]/l-Phe/MPA-AuNCs had a higher ECL emission efficiency, achieving about 2-fold stronger ECL intensity than that of l-Phe/MPA-AuNCs. In addition, after non-covalent modification with CB[7], the finite stability of the papered AuNCs was significantly improved. The prepared CB[7]/l-Phe/MPA-AuNCs showed excellent D-dimer sensing results, exhibiting a linear range from 50.00 fg/mL to 100.0 ng/mL and a detection limit of 29.20 fg/mL (S/N = 3). Our work demonstrated that the host-guest self-assembly strategy provided a universal approach for strengthening the ECL efficiency and stability of nanostructures on an ultra-small scale.

Long-Wavelength Photoconvertible Dimeric BODIPYs for Super-Resolution Single-Molecule Localization Imaging in Near-Infrared Emission

Sulfoxide-bridged dimeric BODIPYs were developed as a new class of long-wavelength photoconvertible fluorophores. Upon visible-light irradiation, a sulfoxide moiety was released to generate the corresponding α,α-directly linked dimeric BODIPYs. The extrusion of SO from sulfoxides was mainly through an intramolecular fashion involving reactive triplet states. By this photoconversion, not only were more than 100 nm red shifts of absorption and emission maxima (up to 648/714 nm) achieved but also stable products with bright fluorescence were produced with high efficiency. The combination of photoactivation and red-shifted excitation/emission offered optimal contrast and eliminated the interference from biological autofluorescence. More importantly, the in situ products of these visible-light-induced reactions demonstrated ideal single-molecule fluorescence properties in the near-infrared region. Therefore, this new photoconversion could be a powerful photoactivation method achieving super-resolution single-molecule localization imaging in a living cell without using UV illumination and cell-toxic additives.