Reversible Photochromic System Based on Rhodamine B Salicylaldehyde Hydrazone Metal Complex

Wavelength-Tunable Single-Mode Microlasers Based on Photoresponsive Pitch Modulation of Liquid Crystals for Information Encryption

Information encryption and decryption have attracted particular attention; however, the applications are frequently restricted by limited coding capacity due to the indistinguishable broad photoluminescence band of conventional stimuli-responsive fluorescent materials. Here, we present a concept of confidential information encryption with photoresponsive liquid crystal (LC) lasing materials, which were used to fabricate ordered microlaser arrays through a microtemplate-assisted inkjet printing method. LC microlasers exhibit narrow-bandwidth single-mode emissions, and the wavelength of LC microlasers was reversibly modulated based on the optical isomerization of the chiral dopant in LCs. On this basis, we demonstrate phototunable information authentication on LC microlaser arrays using the wavelength of LC microlasers as primary codes. These results provide enlightenment for the implementation of microlaser-based cryptographic primitives for information encryption and anticounterfeiting applications.

Adsorption Promoted Aggregation-Induced Emission Showing Strong Dye Lateral Interactions

Aggregation-induced emission (AIE) is a powerful method to produce fluorescence for a diverse range of applications. While most previous work induced aggregation by change of solvent, ionic strength, pH, or self-assembly, we herein explored adsorption-induced aggregation using 4,4'-(hydrazine-1,2-diylidene bis(methanylylidene)) bis(3-hydroxybenzoic acid) (HDBB) as an AIE luminogen. HDBB is known to aggregate with AIE at low pH but not at neutral pH, and its aggregation facilitates excited state intramolecular proton transfer for enhanced emission. Using a nonquenching nanomaterial, Y₂O₃ nanoparticles, HDBB showed sevenfold fluorescence increase at pH 7.0. Fluorescence lifetime showed that HDBB was in the aggregated state in the presence of Y₂O₃. For comparison, a fluorescent porphyrin compound showed that adsorption caused quenching after mixing with Y₂O₃, whereas other dyes such as fluorescein, calcein, and rhodamine B failed to be adsorbed by Y₂O₃. Adsorption did not follow a Langmuir isotherm, but it showed strong lateral HDBB interactions because adsorption was only achieved with a high concentration of HDBB. Adsorption was inhibited by salt and by phosphate, indicating the importance of electrostatic and metal-binding interactions. Comparisons were made with other nanomaterials, where graphene oxide and CeO₂ quenched HDBB and a cationic liposome also enhanced its emission, although with a less red-shifted peak wavelength. This study provides a simple method to induce aggregation of an AIE dye and its aggregation in turn-enhanced adsorption.

A multicolour bistable electronic shelf label based on intramolecular proton-coupled electron transfer

Bistable electrochromic materials have been explored as a viable alternative to reduce energy consumption in display applications. However, the development of ideal bistable electrochromic displays (especially multicolour displays) remains challenging due to the intrinsic limitations associated with existing electrochromic processes. Here, a bistable electrochromic device with good overall performance-including bistability (>52 h), reversibility (>12,000 cycles), colouration efficiency (≥1,240 cm² C^-1) and transmittance change (70%) with fast switching (≤1.5 s)-was designed and developed based on concerted intramolecular proton-coupled electron transfer. This approach was used to develop black, magenta, yellow and blue displays as well as a multicolour bistable electrochromic shelf label. The design principles derived from this unconventional exploration of concerted intramolecular proton-coupled electron transfer may also be useful in different optoelectronic applications.

Smart Responsive Luminescent Aptamer-Functionalized Covalent Organic Framework Hydrogel for High-Resolution Visualization and Security Protection of Latent Fingerprints

Covalent organic frameworks (COFs) have been proposed as alternative candidates for "smart" materials due to their ordered π-columnar structures. However, it remains a challenge to develop external-stimuli-responsive luminescent COFs for confidential information protection. Here, we have designed and synthesized a water-dispersible and smart responsive luminescent carboxymethyl cellulose-COF hydrogel encapsulated 5-(dimethylamino)-N,N-bis (pyridin-2-ylmethyl) napthalene-1-sulfonamide, named CMC-COF-LZU1⊃DPYNS, for latent fingerprint imaging and encryption. We show that the fluorescence of CMC-COF-LZU1⊃DPYNS is reversibly switchable upon addition of Cu²⁺/H₂O. This effect endows potential applications of tunable luminescent COFs based hydrogel as an invisible security probe for imaging, recording, storage, and security of latent fingerprint information. It is shown that the latent fingerprint information incubated by the aptamer-functionalized CMC-COF-LZU1⊃DPYNS hydrogel is invisible in the presence of Cu²⁺, but three levels of fingerprint features with high-resolution patterns could be readable upon addition of H₂O under UV light. The design strategy provides a promising platform for the development of smart responsive luminescent COFs and their detection and protection of valuable latent fingerprint information.

Dynamic Covalent Switches and Communicating Networks for Tunable Multicolor Luminescent Systems and Vapor-Responsive Materials

Molecular switches are an intensive area of research, and in particular, the control of multistate switching is challenging. Herein we introduce a general and versatile strategy of dynamic covalent switches and communicating networks, wherein distinct states of reversible covalent systems can induce addressable fluorescence switching. The regulation of intramolecular ring/chain equilibrium, intermolecular dynamic covalent reactions (DCRs) with amines, and both permitted the activation of optical switches. The variation in electron-withdrawing competition between the fluorophore and 2-formylbenzenesulfonyl unit afforded diverse signaling patterns. The combination of switches in situ further enabled the creation of communicating networks for multistate color switching, including white emission, through the delicate control of DCRs in complex mixtures. Finally, reversible and recyclable multiresponsive luminescent materials were achieved with molecular networks on the solid support, allowing visualization of different types of vapors and quantification of primary amine vapors with high sensitivity and wide detection range. The results reported herein should be appealing for future studies of dynamic assemblies, molecular sensing, intelligent materials, and biological labeling.

A new mitochondrion targetable fluorescent probe for carbon monoxide-specific detection and live cell imaging

A new mitochondrion targetable molecular probe for carbon monoxide (CO)-specific detection based on palladium-free mediated opening of spirolactam was designed. The turn-on red fluorescence caused by CO enables a safe and powerful method for unravelling the function of CO in biological systems to be established.

Symmetric-Key Encryption Based on Bioaffinity Interactions

The research presented here shows a bridge between biochemistry and cryptography. Enzyme-based assays were used in a new methodology linked to ciphers and cipher systems. Three separate enzyme assays, alkaline phosphatase (ALP) (E.C. 3.1.3.1), lysozyme (E.C. 3.2.1.17), and horseradish peroxidase (HRP) (E.C. 1.11.1.7), were used to create a cipher key in order to encrypt a message. By choosing certain parameters for one's experiment that are performed in the same way as a person receiving the message, correct encryption and decryption keys would be produced, resulting in a correct encryption and decryption of a message. It is imperative that both parties perform the same experiment under the same conditions in order to correctly interpret the message. Bioaffinity-based assays, in particular enzymatic assays, provide a specific, yet flexible mechanism to use for the encryption of messages. Because of the nature of this process there are a multitude of sets of parameters that may be chosen, each of which would result in a different key being produced, heightening the security and the robustness of the method. This paper shows that by using this concept of forming encryption keys using a bioaffinity-based approach, one is able to properly encrypt and decrypt a message, which could be viable for other biochemically based techniques.

An ensemble of Zn2+ with a rhodamine B-3-allylsalicylaldehyde hydrazone as novel photosensitive material: Photochromism, photopatterning, photoprinting and molecular logic gates

An ensemble of Zn²⁺ with Rhodamine B-3-allylsalicylaldehyde hydrazone (1-Zn²⁺), has been synthesized and fully characterized using spectroscopic techniques. A solution of 1-Zn²⁺ in THF, displays color changes from light yellow to pink color in the presence UV light (λ, 405 nm). The process is reversible and owes to keto-enol tautomerism which allows the opening of spirolactam ring of rhodamine in the presence of UV light. It is corroborated by the appearance of a new peak at λ_max = 554 nm. The ensemble, 1-Zn²⁺ embedded in the matrix of silica gel, displays photo patterning phenomena initiated by the conventional light sources including sunlight. It also displays photoprinting property with a laser pen (λ 405 nm) and has been displayed by a videography. The module 1-Zn²⁺ meets real challenges through a simple synthetic route, fast response, and as a binary data storage system with non-destructive optical identity.

Large-scale synthesis of carbon dots/TiO2 nanocomposites for the photocatalytic color switching system

In view of the easy control and contactless spatial nature of light, the photoreversible color switching system has attracted tremendous attention. Although some progress has been achieved in the past few years, the practical applications have been limited by the complicated preparation process, material toxicity and low reaction yield. Herein, we report a rapid, a one-pot large-scale synthesis approach for the preparation of carbon dots (CDs)/TiO₂ nanocomposites via the thermal condensation at 160 °C, affording high photocatalytic color switching on/off performance. Under ambient conditions and with the introduction of some oxygen gas, MB rapidly changed from blue to colorless in one minute under UV-vis irradiation and recovered (again showed its original blue color) in twenty minutes. We anticipate that the designed low-cost and green carbon dots (CDs)/TiO₂ nanocomposites have much potential in practical applications and represent a solid step toward color switching applications.

A H-bond strategy to develop acid-resistant photoswitchable rhodamine spirolactams for super-resolution single-molecule localization microscopy

Rhodamine spirolactam based photoswitches have been extensively applied in super-resolution single-molecule localization microscopy (SMLM). However, the ring-opening reactions of spirolactams are cross-sensitive to acid, limiting their photoswitch use to neutral pH conditions. In addition, the ring-closing reactions of spirolactams are environment-sensitive and slow (up to hours), virtually making rhodamine spirolactams caged fluorescent dyes instead of reversible photoswitches in SMLM. Herein, by introducing hydrogen bonds to stabilize spirolactams, we report a series of acid-resistant rhodamine spirolactams with accelerated ring-closing reactions from fluorescent xanthyliums to non-fluorescent spirolactams, endowing them with good photoswitchable properties even in acidic environments. By further substitution of 6-phenylethynyl naphthalimide on the spirolactam, we shifted the photoactivation wavelength into the visible region (>400 nm). Subsequently, we have successfully applied these dyes in labeling and imaging the cell surface of Bacillus subtilis at pH 4.5 using SMLM.

Supramolecular catalytic synthesis of a novel bis(salicylaldehyde hydrazone) ligand for ratiometric recognition of AT-DNA

Hydrazone bond formation under physiological conditions remains challenging. In this study, bis(salicylaldehyde hydrazone) was synthesized using supramolecular catalysis under physiological conditions and its AT-DNA ratiometric sensing properties were identified.

Strategy to Lengthen the On-Time of Photochromic Rhodamine Spirolactam for Super-resolution Photoactivated Localization Microscopy

Rhodamine derivatives and analogues have been widely used for different super-resolution imaging techniques, including photoactivated localization microscopy (PALM). Among them, rhodamine spirolactams exhibit great superiority for PALM imaging due to a desirable bright-dark contrast during the photochromic switching process. Although considerable attention has been paid to the chemical modifications on rhodamine spirolactams, the on-time of photochromic switching, one of the key characteristics for PALM imaging, has never been optimized in previous developments. In this study, we proposed that simply installing a carboxyl group close to the lactam site could impose an intramolecular acidic environment, stabilize the photoactivated zwitterionic structure, and thus effectively increase the on-time. On the basis of this idea, we have synthesized a new rhodamine spirolactam, Rh-Gly, that demonstrated considerably longer on-time than the other tested analogues, as well as an enhancement of single-molecule brightness, an improvement on signal-to-noise ratio and an enlargement of total collected photons of a single molecule before photobleaching. Finally, super-resolution images of live cell mitochondria stained with Rh-Gly have been obtained with a good temporal resolution of 10 s, as well as a satisfactory localization precision of ∼25 nm. Through self-labeling protein tags, Rh-Gly modified with a HaloTag ligand enabled super-resolution imaging of histone H2B proteins in live HeLa cells; through immunostaining antibodies labeled with an isothiocyanate-substituted Rh-Gly, super-resolution imaging of microtubules was achieved in fixed cells. Therefore, our simple and effective strategy provides novel insight for developing further enhanced rhodamine spirolactams recommendable for PALM imaging.

A multi stimuli responsive material with rhodamine B and carbazole groups

A facile material with multi stimuli responsive behaviors was developed. The chromic properties of the material can be observed by stimulating it with light, electricity and ions.

Two new cobalt(II) rhodamine 6G hydrazone complexes: structure, fluorescence and magnetism

Two new Co^II complexes, namely bis{N-[(6-bromopyridin-2-yl)methylidene]-2-[6-ethylamino-3-(ethyliminiumyl)-2,7-dimethyl-3H-xanthen-9-yl]benzene-1-carbohydrazonate}cobalt(II) bis(perchlorate)-dichloromethane-methanol (1/1/2), [Co(C₃₂H₃₀BrN₅O₂)₂](ClO₄)₂·CH₂Cl₂·2CH₃OH or [Co^II(L)₂](ClO₄)₂·CH₂Cl₂·2CH₃OH, (1), and the bis(tetrafluoridoborate) salt, [Co(C₃₂H₃₀BrN₅O₂)₂](BF₄)₂·CH₂Cl₂·2CH₃OH or [Co^II(L)₂](BF₄)₂·CH₂Cl₂·2CH₃OH, (2) (L is commonly 6-bromopyridine-2-carbaldehyde rhodamine 6G hydrazone), have been successfully constructed and characterized. The crystal structure analysis revealed that complexes (1) and (2) are mononuclear and have a Co^IIN₄O₂ distorted octahedral structure. The large π-conjugated xanthene moiety of the L ligand causes strong intermolecular π-π stacking interactions, yielding a supramolecular one-dimensional chain. Complexes (1) and (2) display an obvious fluorescence emission near 560 nm in the solid state. Magnetic investigations show that both (1) and (2) are paramagnetic, dominated by the structural distortion and spin-orbit coupling of Co^II.

Multicomponent reactions provide key molecules for secret communication

A convenient and inherently more secure communication channel for encoding messages via specifically designed molecular keys is introduced by combining advanced encryption standard cryptography with molecular steganography. The necessary molecular keys require large structural diversity, thus suggesting the application of multicomponent reactions. Herein, the Ugi four-component reaction of perfluorinated acids is utilized to establish an exemplary database consisting of 130 commercially available components. Considering all permutations, this combinatorial approach can unambiguously provide 500,000 molecular keys in only one synthetic procedure per key. The molecular keys are transferred nondigitally and concealed by either adsorption onto paper, coffee, tea or sugar as well as by dissolution in a perfume or in blood. Re-isolation and purification from these disguises is simplified by the perfluorinated sidechains of the molecular keys. High resolution tandem mass spectrometry can unequivocally determine the molecular structure and thus the identity of the key for a subsequent decryption of an encoded message.

Molecules for security measures: from keypad locks to advanced communication protocols

The idea of using molecules in the context of information security has sparked the interest of researchers from many scientific disciplines. This is clearly manifested in the diversity of the molecular platforms and the analytical techniques used for this purpose, some of which we highlight in this Tutorial Review. Moreover, those molecular systems can be used to emulate a broad spectrum of security measures. For a long time, molecular keypad locks enjoyed a clear preference and the review starts off with a description of how these devices developed. In the last few years, however, the field has evolved into something larger. Examples include more complex authentication protocols (multi-factor authentication and one-time passwords), the recognition of erroneous procedures in data transmission (parity devices), as well as steganographic and cryptographic protection.

Scalable Preparation of Photochromic Composite Foils with Excellent Reversibility for Light Printing

Photochromic inks for repeatable light-printed media have attracted increasing attention owing to the fact that they may be widely applied to reduce the consumption of papers and plastics and conserve the environment. Therefore, it is of practical significance to develop convenient photochromic inks with a low cost and on a large scale. In this study, a simple one-step hydrothermal route was used to prepare tungsten trioxide (WO₃ ) nanoparticles, which were further used to make photochromic inks and transparent photochromic films. The obtained transparent photochromic film could rapidly respond to UV light within tens of seconds, then return to its initial state, with different recovery times at different temperatures, and also exhibit good reversible coloration-bleaching effect. A typical polyethylene terephthalate (PET) foil coated with the photochromic ink could also be repeatedly printed with various patterns and displayed excellent rewritable performance over tens of cycles. This study proposes a simple method for widespread applications of WO₃ -based photochromic inks.

Photoswitchable azobenzene–rhodamine tweezers for biosensing of Al3+ ions

Photoswitchable tweezers: light catalysed enhanced binding of Al³⁺ using an azobenzene–rhodamine dyad by gating the photoisomerization process.

Mixed polymeric micelles as a multifunctional visual thermosensor for the rapid analysis of mixed metal ions with Al3+ and Fe3+

A novel type of responsive mixed double hydrophilic block copolymer (DHBC)-based multifunctional visual thermosensor for the detection of Al³⁺ and Fe³⁺ was designed and synthesized based on reversible addition fragmentation chain transfer (RAFT) polymerization.

Photo-induced free radical production in a tetraphenylethylene ligand-based metal–organic framework

Photo-induced free radical production was observed in an AIE ligand-based MOF, which exhibited a reversible, fast, obvious, and controllable photo-induced color/emission transformation.

Photochromic naphthalene diimide Cd-MOFs based on different second dicarboxylic acid ligands

Three novel 3D calcium-based metal–organic frameworks (FJU-67, FJU-68, and FJU-69) established on naphthalene diimide chromophores have been synthesized, which exhibit unique multiple interpenetrated networks with dia net topologies.

Toward bidirectional photoswitchable colored photochromic molecules with visible light stability

Novel bidirectional photoswitchable colored photochromic [2]rotaxanes were fabricated, whose colored states exhibit considerable visible-light stability and high thermal stability. These features are crucial for photochromic molecules to be applied in information displays and data storage.

Endowing Hydrochromism to Fluorans via Bioinspired Alteration of Molecular Structures and Microenvironments and Expanding Their Potential for Rewritable Paper

Interest and effort toward new materials for rewritable paper have increased dramatically because of the exciting advantages for sustainable development and better nature life cycle. Inspired by how nature works within living systems, herein, we have used fluorans, as a concept verification, to endow original acidochromic, basochromic or photochromic molecules with broader properties, such as switchable with solvent, water, heat, electricity, stress, other force, etc., via simplified methods (i.e., via variation of submolecular structure or microenvironments). The hydrochromic visual change and reversible behavior of selected molecules have been explored, and the primary mechanism at the atomic or subatomic level has been hypothesized. In addition, several newly demonstrated hydrochromic fluorans have been utilized for water-jet rewritable paper (WJRP), which exhibit great photostability, high hydrochromic contrast, and fast responsive rate and which can be reused at least 30 times without significant variation. The water-jet prints have good resolution and various colors and can keep legibility after a few months or years. This improved performance is a major step toward practical applications of WJRP.

Light-Up of Rhodamine Hydrazide to Generate Emissive Initiator for Polymerization and to Afford Photochromic Polypeptide Metal Complex

Ring-opening polymerization (ROP) of cyclic peptide monomer of γ-propargyl-l-glutamate N-carboxyanhydride (PLG⁻NCA) was originally initiated by non-emissive, ring-close rhodamine 6G hydrazide (R-C). However, instantaneously after adding PLG⁻NCA to R-C, the spirolactam ring of R-C was opened by PLG⁻NCA, rendering emissive, ring-open R-O to initiate ROP of PLG⁻NCA. The emissive R-O moiety therefore produced fluorescent R⁻PLG with aggregation-induced emission (AIE) properties. Moreover, R⁻PLG was found to exhibit photochromic properties with good fatigue resistance and long lifetime when forming metal complexes with Sn(II) and Fe(III). In the dark, irradiated metal complexes slowly (~50 min) restored to the initial state. This research provides foundation for the development of new photochromic materials with long lifetime.

A volumetric three-dimensional digital light photoactivatable dye display

Volumetric three-dimensional displays offer spatially accurate representations of images with a 360° view, but have been difficult to implement due to complex fabrication requirements. Herein, a chemically enabled volumetric 3D digital light photoactivatable dye display (3D Light PAD) is reported. The operating principle relies on photoactivatable dyes that become reversibly fluorescent upon illumination with ultraviolet light. Proper tuning of kinetics and emission wavelengths enables the generation of a spatial pattern of fluorescent emission at the intersection of two structured light beams. A first-generation 3D Light PAD was fabricated using the photoactivatable dye N-phenyl spirolactam rhodamine B, a commercial picoprojector, an ultraviolet projector and a custom quartz imaging chamber. The system displays a minimum voxel size of 0.68 mm³, 200 μm resolution and good stability over repeated ‘on-off’ cycles. A range of high-resolution 3D images and animations can be projected, setting the foundation for widely accessible volumetric 3D displays.

Despite living in a three-dimensional world, almost all information in our society is conveyed in a two-dimensional format. Here, the authors provide a technique for the generation of spatially accurate and high-resolution three-dimensional images using fluorescent photoswitch chemistry.

Reversible Bond/Cation-Coupled Electron Transfer on Phenylenediamine-Based Rhodamine B and Its Application on Electrochromism

A biomimetic system on reversible bond-coupled electron transfer (BCET) has been proposed and investigated in a switchable Rh-N molecule with redox active subunits. We discover that energy barrier of C-N bond breaking is reduced dramatically to less than 1/7 (from 40.4 to 5.5 kcal/mol), and 1/3 of the oxidation potential is simultaneously lowered (from 0.67 to 0.43 V) with the oxidation of Rh-N. The concept, cation-coupled electron transfer (CCET), is highly recommended by analyzing existing proton coupled electron transfer (PCET) and metal coupled electron transfer (MCET) along with aforementioned BCET, which have same characteristic of transferring positive charges, such as proton, metal ion, and organic cation. Molecular switch can be controlled directly by electricity through BCET process. Solid electrochromic device was fabricated with extremely high coloration efficiency (720 cm²/C), great reversibility (no degradation for 600 cycles), and quick respond time (30 ms).

Photocatalytic Color Switching of Transition Metal Hexacyanometalate Nanoparticles for High-Performance Light-Printable Rewritable Paper

Developing efficient photoreversible color switching systems for constructing rewritable paper is of significant practical interest owing to the potential environmental benefits including forest conservation, pollution reduction, and resource sustainability. Here we report that the color change associated with the redox chemistry of nanoparticles of Prussian blue and its analogues could be integrated with the photocatalytic activity of TiO₂ nanoparticles to construct a class of new photoreversible color switching systems, which can be conveniently utilized for fabricating ink-free, light printable rewritable paper with various working colors. The current system also addresses the phase separation issue of the previous organic dye-based color switching system so that it can be conveniently applied to the surface of conventional paper to produce an ink-free light printable rewritable paper that has the same feel and appearance as the conventional paper. With its additional advantages such as excellent scalability and outstanding rewriting performance (reversibility >80 times, legible time >5 days, and resolution >5 μm), this novel system can serve as an eco-friendly alternative to regular paper in meeting the increasing global needs for environment protection and resource sustainability.

A Stimuli-Responsive Smart Lanthanide Nanocomposite for Multidimensional Optical Recording and Encryption

A stimuli-responsive lanthanide-based smart nanocomposite has been fabricated by supramolecular assembly and applied as an active material in multidimensional memory materials. Conjugation of the lanthanide complexes with carbon dots provides a stimuli response that is based on the modulation of the energy level of the ligand and affords microsecond-to-nanosecond fluorescence lifetimes, giving rise to intriguing memory performance in the spatial and temporal dimension. The present study points to a new direction for the future development of multidimensional memory materials based on inorganic-organic hybrid nanosystems.

Synthesis and improved photochromic properties of pyrazolones in the solid state by incorporation of halogen

Four novel photochromic pyrazolones have been prepared by introducing halogen atoms as substituents on the benzene ring. All as-synthesized compounds exhibited excellent reversible photochromic performances in the solid state. Upon UV light irradiation, the as-synthesized compounds can change their structures from E-form to K-form with yellow coloration. Further processed by heating, they rapidly reverted to their initial states at 120°С. Their photo-response and thermal bleaching kinetics were detailed investigated by UV absorption spectra. The results showed that the time constants were higher than that of our previously reported compounds at least one order of magnitude and the rate constants of the as-synthesized compounds were significantly influenced by the size and electronegativity of different halogen atoms. The fluorescence emission were modulated in a high degree via photoisomerization of pyrazolones, which might be due to the efficient energy transfer from E-form to K-form isomers for their partly overlaps between their E-form absorption spectra and K-form fluorescence spectra.

Spirolactam capped cyanine dyes for designing NIR probes to target multiple metal ions

This work reports cyanine based spirocyclic metal ion probes, showing a fluorescence turn-on response to various metal ions in the near-infrared spectral region.

Super-resolution imaging of self-assembly of amphiphilic photoswitchable macrocycles

Self-assembly of an amphiphilic photoswitchable fluorescent macrocycle methoxy-tetraethylene glycol-substituted hexaarylbiimidazole-borondipyrromethene can be observed directly under a super-resolution fluorescence microscope, with the nanoscale resolution beyond the optical diffraction limitation.

An electron-transfer photochromic crystalline MOF accompanying photoswitchable luminescence in a host–guest system

A new electron transfer type photoactive host–guest supramolecule was constructed by introducing (CH₃)₂NH₂⁺ cations to the MOF framework. The resulting compound 1 exhibits reversible photochromic property without using photochromic components.