A trident dithienylethene-perylenemonoimide dyad with super fluorescence switching speed and ratio

Biomimetic Exploration and Reflection on Switchable Coordination and Narrow-Band Electrofluorochromic Devices

Electrofluorochromic (EFC) materials and devices with controllable fluorescence properties show great application potential in advanced anticounterfeiting, information storage and display. However, the low color purity caused by the broad emission spectra and underperforming switching time of the existing EFC materials limit their application. Through biomimetic exploration and the study of reversible electrochemical responsive coordination reactions, boron-nitrogen embedded polyaromatics (B,N-PAHs) with narrow-band emission and high color purity have been successfully integrated into EFC systems, which also help to better understand the role of boron in biological activity. The EFC device achieve good performance containing quenching efficiency greater than 90% within short switching time (ton: 0.6 s, toff: 2.4 s), and nearly no performance change after 200 cycles test. Three primary color (red, green, and blue) EFC devices are successfully prepared. In addition, new phenomena are obtained and discussed in this biomimetic exploration of related boron reactions. The success and harvest of this exploration are expected to provide new ideas for optimizing properties and broadening applications of EFC materials. Moreover, it may provide ideas and reference significance for further exploring and understanding the function of boron compounds in biological systems.

Towards Optical Information Recording: A Robust Visible-Light-Driven Molecular Photoswitch with the Ring-Closure Reaction Yield Exceeding 96.3

Diarylethene molecular photoswitches hold great fascination as optical information materials due to their unique bistability and exceptional reversible photoswitching properties. Conventional diarylethenes, however, rely on UV light for ring-closure reactions, typically with modest yields. For practical application, diarylethenes driven by visible lights are preferred but achieving high ring-closure reaction yield remains a significant challenge. Herein, we synthesized a novel all-visible-light-driven photoswitch, TPAP-DTE, by facilely endcapping the dithienylethene (DTE) core with triphenylamine phenyl (TPAP) groups. Owing to the electron-donating conjugation effect of TPAP, the open-form TPAP-DTE responds strongly to short-wavelength visible lights with considerable photocyclization quantum yields and molar absorption coefficient. Upon 405 nm visible-light irradiation, TPAP-DTE achieves a ring-closure reaction yield exceeding 96.3 % (confirmed by both nuclear magnetic resonance spectroscopy and high-performance liquid chromatography). Its ring-opening reaction yield is 100 % upon irradiation with long-wavelength visible light. TPAP-DTE could be regarded as a bidirectional "quasi"-quantitative conversion molecular switch. Furthermore, TPAP-DTE exhibits robust fatigue resistance over 100 full photoswitching cycles and great anti-aging property under 85 °C and 85 % humidity for at least 1000 h. Consequently, its rewritable QR-code, multilevel data storage, and anti-counterfeiting/encryption applications are successfully demonstrated exclusively using visible lights, positioning TPAP-DTE as a highly promising medium for information recording.

Highly stretchable and self-healing photoswitchable supramolecular fluorescent polymers for underwater anti-counterfeiting

Thanks to the non-destructiveness and spatial-controllability of light, photoswitchable fluorescent polymers (PFPs) have been successfully applied in advanced anti-counterfeiting and information encryption. However, most of them are not suitable for use in harsh underwater environments, including high salinity seawater. In this study, by integrating photochromic molecules into a hydrophobic polymer matrix with the fluorine elastomer, including dipole-dipole interactions, we describe a class of novel photoswitchable supramolecular fluorescent polymers (PSFPs) that can adaptively change their fluorescence between none, green and red by the irradiation of different light. The PSFPs not only exhibited excellent photoswitchable properties, including fast photo-responsibility, prominent photo-reversibility, and photostability, but also exhibited some desired properties, including exceptional stretchability, hydrophobicity, antifouling, self-healing ability, simple preparation process, and processability. We thus demonstrated their applications in underwater data encryption and anti-counterfeiting labels.

Non-Conjugated Bis-(Dithienylethene)-Naphthalenediimide as a Dynamic Anti-Counterfeiting Agent: Driving the Wheel of Photoswitching Enactment

Photochromic fluorescent molecules dramatically extend their fields of applications ranging from optical memories, bioimaging, photoswitches, photonic devices, anti-counterfeiting technology and many more. Here, we have logically designed and synthesized a triazole appended bis-(dithienylethene)-naphthalenediimide based photo-responsive material, 5, which demonstrated fluorescence enhancement property upon photocyclization (ΦF =0.42), with high photocyclization (44 s, ksolution =0.0355 s-1 , ksolid =0.0135 s-1 ) and photocycloreversion (160 s, ksolution =0.0181 s-1 , ksolid =0.0085 s-1 ) rate and decent photoreaction quantum yield (Φo→c =0.93 and Φc→o =0.11). The open isomer almost converted to the closed isomer at photo-stationary state (PSS) with distinct color change from colorless to blue with 92.85 % conversion yield. A reversible noninvasive modulation of fluorescence through efficient photoinduced electron transfer (PET) process was observed both in solution as well as in solid state. The fluorescence modulation through PET process was further corroborated with thermodynamic calculations using the Rehm-Weller equation and quantum chemical studies (DFT). The thermally stable compound 5 exhibits high fatigue resistance property (up to 50 cycles) both in solution and solid state. Furthermore, the compound 5 was successfully applied as erasable ink and in deciphering secret codes (Quick Response/bar code) portending potential promising application in anti-counterfeiting.

Kinetic Analysis of the Photochemical Paths in Asymmetric Diarylethene Dimer

An asymmetric diarylethene dimer composed of 2- and 3-thienylethene units linked by m-phenylene developed various colors upon UV irradiation via an independent photochromic reaction on each unit. The change in contents and the other photoresponses of the photogenerated four isomers were analyzed using quantum yield for all the possible photochemical paths, i. e., photoisomerization, fluorescence, energy transfer, and the other non-radiative paths. Almost all the rate constants of photochemical paths were calculated using measurable quantum yields and lifetimes. It was found that a significant contribution on photoresponse was the competition between photoisomerization and intramolecular energy transfer. The clear difference was observed in the photoresponses of the dimer and the 1 : 1 mixture solution of the model compounds. The m-phenylene spacer appropriately regulated the rate of energy transfer in the asymmetric dimer, and the spacer enabled isolation of the excited state of the dimer, making the above quantitative analysis possible.

Diestervinyl-functionalized acceptor-acceptor type dithienylethenes with efficient photochromic performance

Exploring novel dithienylethenes (DTEs) with efficient photochromism has drawn increasing attention in virtue of the potential applications for photoelectric functional materials. In this contribution, we presented two novel acceptor-acceptor (A-A) type DTE derivatives (4a and 4b) by incorporating the diestervinyl moieties with strong electron-withdrawing capacity into two sides of DTE skeleton. The corresponding structures were well confirmed by the NMR (¹H and ¹³C) and HRMS. When irradiated alternately with ultraviolet and visible light, 4a and 4b showed efficient photochromism in toluene, chloroform and DMSO, clearly implying a solvent-dependence feature. Moreover, excellent photoswitching behaviors were also observed in the poly(methyl methacrylate) (PMMA) film. The density functional theory (DFT) calculations suggested that strong Acceptor-Acceptor effect plays a dominative role in the efficient photochromic performance. Hence, this study will provide a useful guidance for developing high-performance DTE derivatives in multi-media.

Photoresponsive Diarylethene-Containing Polymers: Recent Advances and Future Challenges

Photoresponsive polymers have attracted increasing interest owing to their potential applications in anticounterfeiting, information encryption, adhesives, etc. Among them, diarylethene (DAE)-containing polymers are one of the most promising photoresponsive polymers and have unique thermal stability and fatigue resistance compared to azobenzene- and spiropyran-containing polymers. Herein, the design of DAE-containing polymers based on different types of structures, including main chain polymers, side-chain polymers, and crosslinked polymers, is introduced. The mechanism and applications of DAE-containing polymers in anti-counterfeiting, information encryption, light-controllable adhesives, and photoinduced healable materials are reviewed. In addition, the remaining challenges of DAE-containing polymers are also discussed.

Recent Advances in Applications of Fluorescent Perylenediimide and Perylenemonoimide Dyes in Bioimaging, Photothermal and Photodynamic Therapy

The emblematic perylenediimide (PDI) motif which was initially used as a simple dye has undergone incredible development in recent decades. The increasing power of synthetic organic chemistry has allowed it to decorate PDIs to achieve highly functional dyes. As these PDI derivatives combine thermal, chemical and photostability, with an additional high absorption coefficient and near-unity fluorescence quantum yield, they have been widely studied for applications in materials science, particularly in photovoltaics. Although PDIs have always been in the spotlight, their asymmetric counterparts, perylenemonoimide (PMI) analogues, are now experiencing a resurgence of interest with new efforts to create architectures with equally exciting properties. Namely, their exceptional fluorescence properties have recently been used to develop novel systems for applications in bioimaging, biosensing and photodynamic therapy. This review covers the state of the art in the synthesis, photophysical characterizations and recently reported applications demonstrating the versatility of these two sister PDI and PMI compounds. The objective is to show that after well-known applications in materials science, the emerging trends in the use of PDI- and PMI-based derivatives concern very specific biomedicinal applications including drug delivery, diagnostics and theranostics.

Dynamics of the energy transfer involved in a diarylethene-perylenebisimide dyad: comparison between the molecule and the nanoparticle level

Photochromic materials are widely used to achieve fluorescence photoswitching. Understanding the energy transfer processes occurring in these systems would be an advantage for their use and better optimization of their properties. In this scope, we studied a diarylethene-perylenebisimide (DAE-PBI) dyad that presents a bright red emission and a large ON-OFF contrast, both in solution and in an aqueous suspension of nanoparticles (NPs). Using ultrafast transient absorption spectroscopy, the excited state dynamics was characterized for this dyad in THF solution and compared to its behavior in NPs state. An efficient energy transfer process between the PBI fluorophore and the DAE photochromic unit in its closed form was demonstrated, occurring in a few hundreds of femtoseconds.

Small-molecule fluorogenic probes for mitochondrial nanoscale imaging

Mitochondria are inextricably linked to the development of diseases and cell metabolism disorders. Super-resolution imaging (SRI) is crucial in enhancing our understanding of mitochondrial ultrafine structures and functions. In addition to high-precision instruments, super-resolution microscopy relies heavily on fluorescent materials with unique photophysical properties. Small-molecule fluorogenic probes (SMFPs) have excellent properties that make them ideal for mitochondrial SRI. This paper summarizes recent advances in the field of SMFPs, with a focus on the chemical and spectroscopic properties required for mitochondrial SRI. Finally, we discuss future challenges in this field, including the design principles of SMFPs and nanoscopic techniques.

Emission modulation of fluorescent turn-on mode dibenzothienyl sulfonyl ethene photoswitches embedded in a polymer film

For decades photochromic molecules have attracted attention for their potential in using light as an external stimulus to change their photophysical properties. Here we report the spectroscopic characterization of two emissive photochromic molecules that are intrinsically fluorescent and that undergo a photocyclization/cycloreversion reaction upon illumination with light in the UV and VIS spectral ranges. For appropriately adjusted illumination intensities the emission can be modulated between the high- and the low-level with a contrast ratio exceeding 80%. The data are in reasonable agreement with the predictions from a simple kinetic model.

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.

Future-Oriented Advanced Diarylethene Photoswitches: From Molecular Design to Spontaneous Assembly Systems

Diarylethene (DAE) photoswitch is a new and promising family of photochromic molecules and has shown superior performance as a smart trigger in stimulus-responsive materials. During the past few decades, the DAE family has achieved a leap from simple molecules to functional molecules and developed toward validity as a universal switching building block. In recent years, the introduction of DAE into an assembly system has been an attractive strategy that enables the photochromic behavior of the building blocks to be manifested at the level of the entire system, beyond the DAE unit itself. This assembly-based strategy will bring many unexpected results that promote the design and manufacture of a new generation of advanced materials. Here, recent advances in the design and fabrication of diarylethene as a trigger in materials science, chemistry, and biomedicine are reviewed.

A DNA-Based Two-Component Excitonic Switch Utilizing High-Performance Diarylethenes

Nucleosidic diarylethenes (DAEs) are an emerging class of photochromes but have rarely been used in materials science. Here, we have developed doubly methylated DAEs derived from 2'-deoxyuridine with high thermal stability and fatigue resistance. These new photoswitches not only outperform their predecessors but also rival classical non-nucleosidic DAEs. To demonstrate the utility of these new DAEs, we have designed an all-optical excitonic switch consisting of two oligonucleotides: one strand containing a fluorogenic double-methylated 2'-deoxyuridine as a fluorescence donor and the other a tricyclic cytidine (tC) as acceptor, which together form a highly efficient conditional Förster-Resonance-Energy-Transfer (FRET) pair. The system was operated in liquid and solid phases and showed both strong distance- and orientation-dependent photochromic FRET. The superior ON/OFF contrast was maintained over up to 100 switching cycles, with no detectable fatigue.

Photopatterning of Carbon Dots in Poly(vinyl alcohol) with Photoacid Generators

Carbon dots (CDs) have drawn considerable attention owing to their attractive photoluminescence, advantageous chemical tolerance, good biocompatibility, and so on. However, it remains challenging to tune their photoluminescence spatially and temporally due to their high photostability. Herein, a viable approach to in-situ dialing the photoluminescence of CDs by using light in the presence of a photoacid generator (PAG, e.g., diphenyliodonium hexafluorophosphate) is demonstrated. Fluorescence quenching occurs upon light irradiation due to the protonation of pyridine and amino nitrogen atoms of CDs according to X-ray photoelectron spectroscopy and cyclic voltammetry. As such, blue, green, and red color fluorescent patterns of CDs are ready to form in poly(vinyl alcohol) by light irradiation under photomask. These patterns not only show a controlled preservation time under room light, but also can be erased on demand by flood UV irradiation, which are promising for advanced anti-counterfeiting such as shelf-life based security and erasable encryption.

Conformationally flexible heterohelicenes as stimuli-controlled soft molecular springs

Structurally engineered molecules which can behave as stimuli-controlled mechanical nanomachines such as molecular shuttles, rotors, ratchets, and springs are important in several research areas, including molecular robotics, actuation, sensing, cargo transportation, etc. Helicenes, by virtue of their unique screw-type structures, were proposed as functional models for molecular springs; however, experimental realization has remained an elusive and unmet task until now, because of the lack of appropriate helicene molecules consisting of backbone-decorated dynamic architectures. Aiming to explore this unearthed direction, we present herein a novel class of modular flexible heterohelicenes with a stimuli (acid/base and light)-responsive core and peripheral modules. By applying pH (at core-embedded free imidazole sites) and light (at backbone-tethered dithienylethene units) stimuli, we demonstrate that these flexible heterohelicenes exhibit spring-like movement, with the reversible contraction/extension of the helical pitch. The uniquely functionalized structure of these molecules played a critical role in bestowing such capability, as revealed by crystallographic, spectroscopic and computational data. Careful assessment disclosed that the protonation/deprotonation-induced reversible generation and delocalization of positive charge throughout the π-conjugated helical rim switch the operative interactions between the π clouds of the terminal overlapping arene rings of the helicenes between repulsive and attractive, leading to extension/contraction of the helical pitch. On the other hand, in the case of the light stimulus, it was analyzed that the light-induced ring-closure of the photoactive dithienylethene units created a geometric distortion causing the helicenic wings to bend outward from the helicene rim, which resulted in extension of the helical pitch. The photo-assisted (or thermal) reverse ring-opening reaction converted the system to its original conformation, thus enabling the helicene molecule to display spring-like reversible extension/contraction motion. The new insights on the reversible dynamic features of this class of heterohelicenes under the influence of external stress would guide crucial design principles of helicene-based molecular springs for potential applications.

Sub-expanded flexible heterohelicenes were configured through a modular synthetic approach to experimentally demonstrate their capability of stimuli-controlled soft molecular spring-like behavior.

Green-/NIR-Light-Controlled Rapid Photochromism Featuring Reversible Thermally Activated Delayed Fluorescence and Photoelectronic Switching

Fluorescent dithienylethene based photochromic materials have been attracting considerable attention owing to their wide applications in biological and material sciences. However, limitations of detrimental UV irradiation for photocyclization, short emission...

Photofluorochromic water-dispersible nanoparticles for single-photon-absorption upconversion cell imaging

Photofluorochromic diarylethene (DAE) molecules have been widely investigated due to their excellent fatigue resistance and thermal stability. However, the poor water solubility of DAEs limits their biological applications to some extent. Herein, we reported two kinds of water-dispersible DAE nanoparticles (DAEI-NPs and DAEB-NPs), in which DAE molecules were stabilized by the amphiphilic polymer DSPE-mPEG2000 using the nanoprecipitation approach. The fabricated nanoparticles retain well-controlled luminescence and fluorescence photoswitching properties in aqueous solution, which could be reversibly switched on and off under the alternating irradiation of ultraviolet (UV) and visible light. In addition, the closed-ring isomers of DAEB-NPs performed hot-band-absorption-based photon upconversion when excited by a 593.5 nm laser. Bearing excellent photophysical properties and low cytotoxicity, DAEB-NPs were applicable for upconversion cell imaging without high-excitation power density and free from oxygen removal. Additionally, the imaging process could be switched on by regulating the photofluorochromic nanoparticles.

Developing Anisotropy in Self-Assembled Block Copolymers: Methods, Properties, and Applications

Block copolymers (BCPs) self-assembly has continually attracted interest as a means to provide bottom-up control over nanostructures. While various methods have been demonstrated for efficiently ordering BCP nanodomains, most of them do not generically afford control of nanostructural orientation. For many applications of BCPs, such as energy storage, microelectronics, and separation membranes, alignment of nanodomains is a key requirement for enabling their practical use or enhancing materials performance. This review focuses on summarizing research progress on the development of anisotropy in BCP systems, covering a variety of topics from established aligning techniques, resultant material properties, and the associated applications. Specifically, the significance of aligning nanostructures and the anisotropic properties of BCPs is discussed and highlighted by demonstrating a few promising applications. Finally, the challenges and outlook are presented to further implement aligned BCPs into practical nanotechnological applications, where exciting opportunities exist.

Long-term switching of single photochromic triads based on dithienylcyclopentene and fluorophores at cryogenic temperatures

Photochromic molecules can be reversibly converted between two bistable forms by light. These systems have been intensively studied for applications as molecular memories, sensing devices, or super-resolution optical microscopy. Here, we study the long-term switching behavior of single photochromic triads under oxygen-free conditions at 10 K. The triads consist of a photochromic unit that is covalently linked to two strong fluorophores that were employed for monitoring the light-induced conversions of the switch via changes in the fluorescence intensity from the fluorophores. As dyes we use either perylene bisimide or boron-dipyrromethen, and as photochromic switch we use dithienylcyclopentene (DCP). Both types of triads showed high fatigue resistance allowing for up to 6000 switching cycles of a single triad corresponding to time durations in the order of 80 min without deterioration. Long-term analysis of the switching cycles reveals that the probability that an intensity change in the emission from the dyes can be assigned to an externally stimulated conversion of the DCP (rather than to stochastic blinking of the dye molecules) amounts to 0.7 ± 0.1 for both types of triads. This number is far too low for optical data storage using single triads and implications concerning the miniaturization of optical memories based on such systems will be discussed. Yet, together with the high fatigue resistance, this number is encouraging for applications in super-resolution optical microscopy on frozen biological samples.

Correlative dual-alternating-color photoswitching fluorescence imaging and AFM enable ultrastructural analyses of complex structures with nanoscale resolution

There is a practical motivation for correlating different types of microscopy for revealing complementary information of ultrastructures with resolution beyond the diffraction limit. The correlative microscopy strategy based on the combination of super-resolution fluorescence imaging with atomic force microscopy (AFM) is expected to provide both the specificity and three-dimensional structural information of nanomaterials. Herein we synthesized a dual-alternating-color photoswitchable fluorescent probe based on a naphthalimide-spiropyran dyad (NI-SP) and explored the capability of such correlative microscopy for visualizing nanostructures with complex structural hierarchy. NI-SP underwent reversible photoswitching between green and red fluorescence based on a reversible photochemical reaction and such reaction-linked correlation between two distinct types of fluorescence signals intrinsically enabled mutual authentication in super-resolution fluorescence imaging. Additionally, such correlative microscopy also demonstrated mutual complementation between different pieces of structural information of the target acquired via fluorescence imaging and AFM, respectively, in which the former reveals spatial distribution of fluorescent dyes in the nanoscale polymer fibroid micelles while the latter maps the topographical structure of the target with complex structural hierarchy. The results obtained in this work proclaimed that the combination of such correlative microscopy with our NI-SP probe is an effective modality for ultrastructural analysis and has future applications in various complex systems such as tissue/organ imaging.

Super-resolution RESOLFT microscopy of lipid bilayers using a fluorophore-switch dyad

Dyads consisting of a photochromic switch covalently linked to a fluorescent dye allow the emission from the dye to be controlled by reversible photoisomerization of the switch; one form of the switch quenches fluorescence by accepting energy from the dye. Here we investigate the use of dyads of this type for super-resolution imaging of lipid bilayers. Giant unilamellar vesicles stained with the dyads were imaged with about a two-fold resolution-enhancement compared with conventional confocal microscopy. This was achieved by exciting the fluorophore at 594 nm, using a switch activated by violet and red light (405/640 nm).

Reversible Emitting Anti-Counterfeiting Ink Prepared by Anthraquinone-Modified β-Cyclodextrin Supramolecular Polymer

Intelligent fluorescent materials have been paid more and more attention due to their wide application in information encryption and anti-counterfeiting materials. Herein, a supramolecular polymer is constructed through the host-guest interaction of anthraquinone-modified β-cyclodextrin (AQ-β-CD) in aqueous solution. Thanks to the hydrophobic microenvironment of the cyclodextrin cavity and the shielding effect on oxygen molecules, the anthraquinone group, as the guest molecule, can rapidly produce 9,10-anthracenediol (QH2) with strong fluorescence by photoreduction. Interestingly, the generated anthracenediol group is still sensitive to oxygen and can be converted to anthraquinone by oxygen. Significantly, aqueous solution of AQ-β-CD supermolecular polymer is used as emitting ink, which decrypts the information by ultraviolet light and encrypts the information in the air.

Visible-Light-Driven Photoswitching of Aggregated-Induced Emission-Active Diarylethenes for Super-Resolution Imaging

Photoswitchable fluorescent diarylethenes are promisingly widely applied in the fields of optical memory, all-optical transistors, bioimaging, and super-resolution imaging, and so on. However, they face the problems of fluorescence quenching in an aggregated/solid state, the inadequate fluorescence ON/OFF switching ratio, and the necessity of UV-light irradiation. Herein, we report a novel kind of high-performance diarylethenes with aggregated-induced emission (AIE) by conjugating two diarylethene groups on one AIE-gen (i.e., TPE-2DTE (blue-green fluorescent) and OTPE-2DTE (orange fluorescence)). Their open forms show enhanced fluorescence in the aggregated and solid states. The closed form of TPE-2DTE/OTPE-2DTE was effectively generated upon short-wavelength visible-light (400 nm-450 nm) irradiation, whose fluorescence was dramatically quenched by intra- and inter-molecular energy transfer. Remarkably, 405 nm purple irradiation gives fluorescence ON/OFF ratios of 1196:1 and 1983:1 for TPE-2DTE and OTPE-2DTE, respectively. The reverse process can be accomplished after another longer wavelength irradiation such as 621 nm and shows considerable fatigue resistance. Taking advantage of superior photoswitching properties under visible-light irradiation, TPE-2DTE and OTPE-2DTE were used for super-resolution imaging with a high resolution of sub 50 nm. This work offers guidance to design bright-emitting and high-performance visible-light-controlled diarylethene photoswitches for practical applications.

Quinoline-containing diarylethenes: bridging between turn-on fluorescence, RGB switching and room temperature phosphorescence

Simple structural modifications using oxidation and methylation of a quinoline-containing diarylethene result in dramatic variation of photophysical properties. Turn-on fluorescence, room temperature phosphorescence (RTP) and red-green-blue (RGB) switching were achieved in three different related compounds. Photoswitchable diarylethenes (DAEs) that exhibit turn-on fluorescence are in high demand for super-resolution microscopy, and the development of purely organic phosphorescent materials in the amorphous state is attractive but challenging. The findings reported here provide a novel toolkit for designing turn-on fluorescence DAEs for super-resolution microscopy and extending the scope of amorphous RTP materials. More importantly, we bridge between these two fundamentally significant photochemical and photophysical phenomena, and reveal structure-property relationships between DAE photochromism and RTP.

Non-Oxido-Vanadium(IV) Metalloradical Complexes with Bidentate 1,2-Dithienylethene Ligands: Observation of Reversible Cyclization of the Ligand Scaffold in Solution

Derivatives of 1,2‐dithienylethene (DTE) have superb photochromic properties due to an efficient reversible photocyclization reaction of their hexatriene structure and, thus, have application potential in materials for optoelectronics and (multi‐responsive) molecular switches. Transition‐metal complexes bearing switchable DTE motifs commonly incorporate their coordination site rather distant from the hexatriene system. In this work the redox active ligand 1,2‐bis(2,5‐dimethylthiophen‐3‐yl)ethane‐1,2‐dione is described, which reacts with [V(TMEDA)₂Cl₂] to give a rare non‐oxido vanadium(IV) species 3(M,M/P,P). This blue complex has two bidentate en‐diolato ligands which chelate the V^IV center and give rise to two five‐membered metallacycles with the adjacent hexatriene DTE backbone bearing axial chirality. Upon irradiation with UVA light or prolonged heating in solution, the blue compound 3(M,M/P,P) converts into the purple atropisomer 4(para,M/para,P). Both complexes were isolated and structurally characterized by single‐crystal X‐ray diffraction analysis (using lab source and synchrotron radiation). The antiparallel configuration (M or P helicity) present in both 3(M,M/P,P) and 4(para,M/para,P) is a prerequisite for (reversible) 6π cyclization reactions. A CW EPR spectroscopic study reveals the metalloradical character for 3(M,M/P,P) and 4(para,M/para,P) and indicates dynamic reversible cyclization of the DTE backbone in complex 3(M,M/P,P) at ambient temperature in solution.

Imidazole diarylethene switches: an alternative to acid-gated photochromism

Improving the photoactivity of imidazole diarylethenes by modifying their response sites in imidazole instead of appended aryl units is accomplished.

Quantitative Comparison of Dye and Ultrasmall Fluorescent Silica Core-Shell Nanoparticle Probes for Optical Super-Resolution Imaging of Model Block Copolymer Thin Film Surfaces

In recent years, high-resolution optical imaging in the far field has provided opportunities for alternative approaches to nanocharacterization traditionally dominated by electron and scanning probe microscopies. Here, we report the optical super-resolution imaging of model block copolymer (BCP) thin film surface nanostructures through stochastic optical reconstruction microscopy (STORM). We compare a set of surface-functionalized fluorescent core-shell silica nanoparticles encapsulating two different organic dyes, Cy3 and Cy5, with the corresponding free dyes in STORM. Using various click-type chemistries, these probes are covalently attached to the surface of specific blocks of BCP thin films, enabling selective block labeling and optical visualization. We demonstrate that the enhanced brightness of these particle probes offers distinct advantages over conventional dye labeling, outperforming one of the best STORM dyes available (Cy5).

Deciphering Erasing/Writing/Reading of Near-Infrared Fluorophore for Nonvolatile Optical Memory

A near-infrared fluorescence-switchable molecule, dithienylethene-terrylenediimide (TDI-4DTE) exhibits high near-infrared fluorescence and on/off ratio, decent reversibility, and fatigue resistance upon alternating UV/vis (305/621 nm) irradiation. Photoinduced electron transfer mainly contributes to the fluorescence quenching of TDI-4DTE. As an information storage unit, single molecular TDI-4DTE in the polymer film can be written by red light (621 nm) and erased by UV light (305 nm), while nondestructive fluorescence readout (750 nm) of a single molecular memory has been obtained upon excitation with near-infrared light (720 nm). The fluorescence patterning of TDI-4DTE in the polymer film demonstrates that the erasing/writing/reading wavelengths are deciphered to minimize the signal crosstalk in nonvolatile fluorescent molecular memories.

Photoplastic Transformation Based on Dynamic Covalent Chemistry

The magical fantasy of decades-old transformer characters is becoming closer to scientific reality, as transformable materials can change their shapes in response to thermal, mechanical, electrical, and chemical stimuli. However, precise and prompt control of plastic shaping remains to be wanted. Photoresponsive materials provide a promising alternative for rapid optomechanical shaping with limited success. Here, we report a new class of photoplastic transformation based on dynamic covalently crosslinked polytriazole (PTA) networks, in which crosslinking points are comprised of photocleaveable hexaarylbiimidazole (HABI). Upon sub-500 nm light irradiation, HABI is dissociated into two triphenylimidazole radicals (TPIRs) followed by spontaneous recombination back to the initial state. This photoswitching effect is demonstrated to generate nonthermal shape change in the PTA-HABI gel network at will upon light stimulus. A unique photoalignment phenomenon has also been discovered which can form oriented nanoscale patterning in the PTA-HABI gel network upon laser irradiation. The solvent-free PTA-HABI elastomer exhibits photoenhanced automatic self-healing properties at temperatures ranging from 25 °C to freezing points, which is attributed to the dynamic equilibrium between TPIRs and HABI. A photoplastic spring is fabricated and exhibits photoswitchable plastic behavior, i.e., a reversible transformation between plastic strain and elastic strain upon light irradiation. HABI-based polymer networks, including solvated gel and solvent-free elastomer, are promising as smart materials for nonthermal photoactivated shape changing, transformation, and self-healing applications.

Post-Modification of the Ethene Bridge in the Rational Design of Photochromic Diarylethenes

Fine-tuning of the molecular structure of organic bistable compounds to improve their photochromic performance or to introduce additional functions remains an important issue in the development of photoresponsive materials. Diarylethenes bearing heterocyclic moieties belong to the most intensively studied class of organic photochromes due to their excellent photochemical properties. A huge number of diarylethenes have been synthesized so far. Analysis of the literature data shows that there are very worthy examples of diarylethenes developed by the Irie and Feringa groups, which can be the common starting material for a number of diarylethenes functionalized in hetaryl moieties. We refer to these structures as photochromic diarylethene precursors. These diarylethenes have proved to be very useful in the construction of functional molecules with desired properties. On the other hand, in our groups, we have elaborated on diarylethene precursors with modifiable ethene bridges. In this review, we have collected examples of such structures and their chemical modifications, leading to the improvement or fine-tuning of photochromic switching.

A colorimetric and fluorescent dual-modal displacement probe based on host-assisted modulation of intramolecular charge transfer and deaggregation

A new colorimetric and fluorescent dual-modal displacement probe based on a supramolecular host–guest complex involving macrocycle encapsulation that modulated intramolecular charge transfer and deaggregation.

A single-stranded coordination copolymer affords heterostructure observation and photoluminescence intensification

Few artificial systems can be exfoliated into, and observed as, single wires with lengths of more than several micrometers, and no previous example features a copolymer structure; this is in contrast with biopolymers such as single-strand DNAs. Here, we create a set of one-dimensional coordination copolymers featuring bis(dipyrrinato)zinc complex motifs in the main chain. A series of random copolymers is synthesized from two types of bridging dipyrrin proligand and zinc acetate, with various molar ratios between the proligands. Sonication of the bulk solid copolymer in organic solvent exfoliates single strands with lengths of 1.4 to 3.0 μm. Atomic force microscopy at ambient conditions visualizes the copolymer structure as height distributions. The copolymer structure improves its photoluminescence (up to 32%) relative to that of the corresponding homopolymers (3 and 10%). Numerical simulation based on a restricted random walk model reproduces the photoluminescence intensification, suggesting at the same time the existence of fast intrawire exciton hopping.

Photoswitchable Self-Assembly/Disassembly of Near-Infrared Fluorophores

A new photoswitchable near-infrared fluorophore (TDI-4DTE) with a symmetric structure exhibited reversible photo-controllable self-assembly and disassembly. The modification of π-conjugated terrylenediimide with four dithienylethene groups not only induced photoswitchable near-infrared fluorescence, but also photoregulated reversible precipitation-dissolution with microscopic and macroscopic polymorphism. Upon 302 nm UV-light irradiation, a noticeable precipitation was observed within seconds. The precipitate was gradually dissolved again in half an hour upon visible light irradiation. Different microscopic morphologies of the precipitates, including nanoparticles, nanofibrils and nanosheets, were observed when altering the intensity of the 302 nm light irradiation, indicating the dynamic control process of self-assembly. Upon UV-light irradiation, TDI-4DTE nanosheets were also obtained as a solid polymeric film, whereas well-defined nanoribbons with molecular monolayer thickness formed at the oil/water interface with slower assembly dynamics.

A Molecular Level Approach To Elucidate the Supramolecular Packing of Light-Harvesting Antenna Systems

The molecular geometry and supramolecular packing of two bichromophoric prototypic light harvesting compounds D1A2 and D2A2, consisting of two naphthylimide energy donors that were attached to the 1,7 bay positions of a perylene monoimide diester energy acceptor, have been determined by a hybrid approach using magic angle spinning NMR spectroscopy and electron nano-crystallography (ENC), followed by modelling. NMR shift constraints, combined with the P 1 ‾ space group obtained from ENC, were used to generate a centrosymmetric dimer of truncated perylene fragments. This racemic packing motif is used in a biased molecular replacement approach to generate a partial 3D electrostatic scattering potential map. Resolving the structure of the bay substituents is guided by the inversion symmetry, and the distance constraints obtained from heteronuclear correlation spectra. The antenna molecules form a pseudocrystalline lattice of antiparallel centrosymmetric dimers with pockets of partially disordered bay substituents. The two molecules in a unit cell form a butterfly-type arrangement. The hybrid methodology that has been developed is robust and widely applicable for critical structural underpinning of self-assembling structures of large organic molecules.

Switchable Fluorophores for Single-Molecule Localization Microscopy

The past decade has witnessed an explosion in the use of super-resolution fluorescence microscopy methods in biology and other fields. Single-molecule localization microscopy (SMLM) is one of the most widespread of these methods and owes its success in large part to the ability to control the on-off state of fluorophores through various chemical, photochemical, or binding-unbinding mechanisms. We provide here a comprehensive overview of switchable fluorophores in SMLM including a detailed review of all major classes of SMLM fluorophores, and we also address strategies for labeling specimens, considerations for multichannel and live-cell imaging, potential pitfalls, and areas for future development.

Near Infrared Boron Dipyrromethene Nanoparticles for Optotheranostics

Boron dipyrromethene (BODIPY) is a class of important emerging fluorescent dyes. Due to their unique chemical and optical properties, near infrared (NIR)-emitting BODIPY dyes containing nanoparticles have recently been developed for a wide array of cutting-edge cancer optotheranostic applications. These nanoparticles not only have robust photostability and tunable photophysical properties, but they can also be flexibly tailored to a multitude of functional uses. Based on these outstanding characteristics, such nanoparticles have shown great promise in diagnosis as biological sensors, as well as in their utilization in advanced imaging and photomedicine for cancer treatment. In particular, here, this study first discusses their use as photoswitchable fluorescence probes toward in vitro single-molecule imaging. Second, this study takes a look at their opportunities for photoacoustic imaging utilization. Third, approaches are discussed to construct new NIR-absorbing BODIPY nanoparticles for photodynamic therapy (PDT). Fourth, this study delves into the new approach to use such nanoparticles as an emerging version of triplet-triplet annihilation upconversion (TTA-UC) and their biological uses, such as their photoactivation prodrug therapy (PAPT) for cancer. Finally, new biological sensors based on NIR BODIPY nanoparticles are introduced.

Controlled Photoerasable Fluorescent Behaviors with Dithienylethene-Based Molecular Turnstile

The precise control of molecular interaction and motion is a powerful strategy in the creation and development of intelligent materials. We demonstrate here a simple concept and approach to integrate intramolecular photochromic property with intermolecular aggregation-induced emission behaviors, with the aim to construct a new type of photoswitchable luminescent materials. This strategy is realized by the dithienylethene-bridged bispyridinium salt as photochromic molecular turnstile, and their subsequent fabrication into optically functional materials is reported. By restricting the rotation of central chemical bonds, the obtained molecular turnstile not only exhibits photocontrolled fluorescence emission through solvent exchange but is also capable of transforming into photowritable and photoerasable films in polymeric matrix with good recyclability. This functional molecular turnstile provides convenient routes to construct photochromic nanomaterials with controlled photophysical behaviors.