Fluorescence Photoswitching Research Articles

Fluorophore unit controlled photoswitching of hydrazone derivatives: reversible and irreversible off–on/dual-color fluorescence photoswitches

Photo-responsive hydrazone functionalized fluorophores displayed structure-dependent reversible and irreversible fluorescence photoswitching and mechanofluorochromism.

Recent advances in small-molecule fluorescent photoswitches with photochromism in diverse states

This review summarizes recent advances in small-molecule fluorescent photoswitches based on classic photochromic molecules in diverse states, and provides some existing problems and challenges to promote follow-up development in this field.

Photoisomerization, assembling and fluorescence photoswitching behaviors of a water-soluble stiff-stilbene with cucurbit[7]uril

Photoresponsive supramolecular systems have merited extensive attention for their applications in materials science and life science. Here, we synthesized a water-soluble stiff-stilbene molecular photoswitch, exhibiting outstanding photoisomerization reaction between its (E)- and (Z)-configurations upon irradiation at distinct light. The photoswitch can assemble with cucurbit[7]uril (CB[7]) to form a superior fluorescent supramolecular complex (compared to the only guest) with excellent water solubility, which manifested dramatic photoluminescence enhancement caused by restriction of intramolecular rotation and remained good photochromic characteristics. Furthermore, introduction of CB[7] influence photoreaction quantum yield (Φ) of the stiff-stilbene, leading to reduction of ΦE→Z and increase of ΦZ→E of the stiff-stilbene. Importantly, the photoadjustable supramolecular assembly can act as a fluorescence switch, and the phototunable guest further selectively modulate G-quadruplex structure of Tel22 upon light irradiation or with addition of CB[7]. The study provides a new simple way for accurately regulating photochromic properties of molecular switches and developing smart materials with potential applications in controlled modulation of G-quadruplex, targeted biological imaging and so on.

Supramolecular Polymers with Photoswitchable Multistate Fluorescence for Anti-Counterfeiting and Encryption.

Photoswitchable fluorescent materials are desirable for many applications because their emission signals can be easily modulated on demand. In this study, novel photoswitchable multistate fluorescent supramolecular polymers (PMFSPs) were prepared via host-guest interactions under a facile ultrasonication strategy. In the system, photochromic fluorescent diarylethylene monomer (SDTE, donor) and adamantane-containing monomer (BAC) were covalently combined into the backbone of the guest polymer (P1) via radical copolymerization. Meanwhile, the host moiety (CDSP, acceptor) was synthesized by covalent incorporation of photochromic spiropyran dye (SPCOOH) with β-cyclodextrin. By adjusting the stimulation wavelength and utilizing photoinduced fluorescence resonance energy transfer (FRET), the supramolecular polymers can undergo reversible tristate fluorescence switching among none, red, and green. In addition, due to the high contrast, rapid photoresponsiveness and prominent photoreversibility of the prepared PMFSPs, we demonstrated that they have great potential in advanced anti-counterfeiting and multilevel information encryption.

Reconfigurable Fluorescent Liquid Crystal Elastomers for Integrated Visual and Haptic Information Storage.

The rapid advancements in information technology require new information storage and display materials. However, the development of on-demand information storage systems with multiple modes remains a significant challenge. As a pioneering approach, this study designed an integrated visual and haptic information storage and display using a reconfigurable fluorescent liquid crystal elastomer (FLCE) with dynamic covalent bonds. The FLCEs were fabricated in two steps of amine-acrylate aza-Michael addition and photopolymerization, and they simultaneously exhibited phototunable fluorescence caused by the reversible Z/E photoisomerization of the chromophores and a reprogrammable shape owing to the catalyst-free transesterification. In addition, we established various information storage and display modes featuring the characteristics of reversibly photoswitchable fluorescence, shape memory, and thermally reconfigurable shape with a reconfigurable FLCE system. Moreover, a strategy to display the information by incorporating both visual and haptic feedback is implemented for fulfilling the needs of the visually impaired and related users. Such reconfigurable FLCE systems will aid in the development of on-demand information storage, display, and protection devices.

A robust photoswitchable dual-color fluorescent poly (vinyl alcohol) composite hydrogel constructed by photo-responsive FRET effect

Stimuli responsive fluorescence characteristics are significant in some fields, such as sensors, information encryption, and bionic camouflage. In this work, a robust poly(vinyl alcohol) (PVA) hydrogel with photoswitchable dynamic fluorescence behaviors was constructed by incorporating dual-color fluorescent nanoparticles (DCFNs). The DCFNs were composed of the spiropyran-modified β-cyclodextrin (β-CD-SP) and nitrobenzoxadiazolyl (NBD) derivatives, which could exist in the PVA network through non-covalent interaction. The SP moiety functioned as an acceptor and realized the photoisomerization to further quench or recover the fluorescence of the NBD moiety based on the fluorescence resonance energy transfer (FRET) effect. Therefore, under the irradiation of ultraviolet light (UV) or visible light (Vis), the hydrogel showed a fluorescence emission peak of merocyanine (MC) at 660 nm (red) or NBD at 550 nm (green), respectively. Additionally, the pH responsive characteristic of the MC chromophore also endowed the hydrogel with pH responsive fluorescence behaviors. Utilizing these advantages, specific patterns can be displayed on the hydrogel in dual mode through a hollowed-out photomask. The hydrogel could also be utilized as dual-color “building blocks” to construct various 2D or 3D structures. This composite hydrogel has potential application in various fields, such as sensors, optical switch, information storage, and biomimetic components.

Ternary host-guest complexes with rapid exchange kinetics and photoswitchable fluorescence

SummaryConfinement within molecular cages can dramatically modify the physicochemical properties of the encapsulated guest molecules, but such host-guest complexes have mainly been studied in a static context. Combining confinement effects with fast guest exchange kinetics could pave the way toward stimuli-responsive supramolecular systems—and ultimately materials—whose desired properties could be tailored “on demand” rapidly and reversibly. Here, we demonstrate rapid guest exchange between inclusion complexes of an open-window coordination cage that can simultaneously accommodate two guest molecules. Working with two types of guests, anthracene derivatives and BODIPY dyes, we show that the former can substantially modify the optical properties of the latter upon noncovalent heterodimer formation. We also studied the light-induced covalent dimerization of encapsulated anthracenes and found large effects of confinement on reaction rates. By coupling the photodimerization with the rapid guest exchange, we developed a new way to modulate fluorescence using external irradiation.

Turn-On Mode Circularly Polarized Luminescence in Self-Organized Cholesteric Superstructure for Active Photonic Applications.

Developing circularly polarized luminescence (CPL)-active materials with a large luminescence dissymmetry factor (glum) or stimulus responses has evoked a lot of interest in the past few years; however, the light-controllable "on/off" CPL still remains a challenge. Here, a novel diarylethene-based chiral fluorescent photoswitch featuring "turn-on" CPL characteristic is developed, designated as (S,S)-switch 6, which can undergo reversible photocyclization/cycloreversion upon irradiation with UV and visible light. (S,S)-Switch 6 shows completely reversible "off-on-off"-responsive CPL behavior in solution. By doping (S,S)-switch 6 into nematic liquid crystals (LCs), the consequent luminescent cholesteric LCs (CLCs) exhibit a larger glum value enhanced 2 orders of magnitude when irradiated with UV light, which can be attributed to the highly ordered helical arrangement of CLCs. The potentials of this turn-on type CPL material for anticounterfeiting and information encryption are illustrated. Furthermore, the visualization of circularly polarized (CP) fluorescent patterns can be successfully achieved by constructing the double-layer CPL system consisting of a CP luminescent layer and a polymer cholesteric reflective layer. The proposed concept establishes a light-controlled off-on-off CPL platform that is of tremendous potential for applications in multi-informational data storage and encryption devices.

Site‐specific fabrication of gold nanocluster‐based fluorescence photoswitch enabled by the dual roles of albumin proteins

AbstractFluorescence photoswitch is becoming increasingly desirable for many applications, but its controllable fabrication still remains challenging yet. In this paper, a new strategy is proposed to fabricate fluorescence photoswitch by harnessing dual roles of albumin proteins as both photochrome carriers and biotemplates of fluorophore. As an example, we demonstrated the successful fabrication of a fluorescence photoswitch by incorporating both the photochromic diarylethene dye (CMTE) and red‐emitting fluorescent gold nanoclusters (AuNCs) into the specific domains of bovine serum albumin (BSA) in a highly controllable manner. Detailed spectral and photophysical characterisation showed that CMTE well‐retains the photochromic properties within the CMTE–BSA–AuNC construct, although its photoconversion rate is slightly retarded. Different from previously reported photoswitches, the fluorescence of the present system is mainly modulated via the inner filter effect (IFE) mechanism, which exhibits high switching efficiency with an on–off ratio up to 90%, reversible fluorescence response and good antifatigue performance. This work provides a new, generable albumin protein‐assisted strategy of fabricating advanced fluorescence photoswitch, which can find wide applications in biological, optical and information fields.

Gated photochromic reactivity of diarylethenes with visible-light-triggered turn-on fluorescence

All visible-light-driven fluorescent photo-switches are essential for high-density optical memories, whereas their gated photochromism remains a great challenge. Herein, we report the synthesis and photochromic properties of 2,3-bis(2-methyl-1-benzothiophene-1,1-dioxide-3-yl)-thiophene (BTTO4) based photochromic diarylethene isomers oDB, mDB, and pDB functionalized with N,N-dimethylaniline at three positions. These compounds all exhibit turn-on fluorescence upon visible light irradiation at 405 nm. Surprisingly, the cycloreversion reaction of para-substituted closed-isomer c-pDB was suppressed. Upon addition of trifluoroacetic acid, the acidic compound c-pDB•H+ was turned active, displaying an unusual gated photochromic property. Moreover, the photochromic reactivity can be suppressed again by neutralizing the acid with Et3N. To the best of our knowledge, this is the first report of gated photochromic diarylethene with visible-light-triggered turn-on fluorescence. This study provides a new type of all-visible-light triggered fluorescent photo-switches, and a novel “lock” and “unlock” system for photocycloreversion reactions.

A diarylethene-based fluorescent chemosensor for highly selective recognition of Zn2+ and its application

A new diarylethene-based fluorescent chemosensor (1o) for highly selective recognition of Zn2+ was synthesized. The good photochromic response of 1o was found by alternately irradiating UV and visible light. Under the excitation of light at 350 nm, 1o emitted a strong blue fluorescence at 495 nm and the fluorescence intensity of 1o' (1o + Zn2+) had 58-fold increasement after adding Zn2+, the limit of detection (LOD) of 1o for Zn2+ was calculated to be only 14 nM. The 1:1 binding mode of 1o and Zn2+ was determined by Job’s plot curves, NMR titration and mass spectrometry data. In addition, the 1o-Zn2+ complex could function as a reversible fluorescence photoswitch in the response to UV/vis light. Further, 1o was also successfully used to design a molecular logic gate, detect Zn2+ in real water samples and used as a test strip.

Multicolor Zinc(II)-Coordinated Hydrazone-Based Bistable Photoswitches for Rewritable Transparent Luminescent Labels.

Repeatable printing of invisible multicolor luminescence patterns with long retention times on transparent substrates is of significant importance, but it remains a formidable challenge. Here, two novel hydrazone-based on/off fluorescent photoswitches with decent emission quantum efficiencies, good reversible photoisomerization properties, and extremely long thermal half-lives, were designed and synthesized. Excitingly, X-ray crystallography data of both Z and E isomers of one hydrazone-based photoswitch were obtained. Multiple emission colors of blue, cyan, green, yellow, and orange can be obtained readily for these two photoswitches upon coordination with various zinc salts. Moreover, the photo-controlled rewritable printing of invisible multicolor images with high resolution was achieved by using these photoswitches. Importantly, the legibility of the printed patterns can last at least over 3 months without detectable emission intensity loss under ambient conditions.

Multicolor Zinc(II)‐Coordinated Hydrazone‐Based Bistable Photoswitches for Rewritable Transparent Luminescent Labels

AbstractRepeatable printing of invisible multicolor luminescence patterns with long retention times on transparent substrates is of significant importance, but it remains a formidable challenge. Here, two novel hydrazone‐based on/off fluorescent photoswitches with decent emission quantum efficiencies, good reversible photoisomerization properties, and extremely long thermal half‐lives, were designed and synthesized. Excitingly, X‐ray crystallography data of both Z and E isomers of one hydrazone‐based photoswitch were obtained. Multiple emission colors of blue, cyan, green, yellow, and orange can be obtained readily for these two photoswitches upon coordination with various zinc salts. Moreover, the photo‐controlled rewritable printing of invisible multicolor images with high resolution was achieved by using these photoswitches. Importantly, the legibility of the printed patterns can last at least over 3 months without detectable emission intensity loss under ambient conditions.

Fluorescence photoswitch of stiff-stilbene derivatives for anti-counterfeiting

Precise improvement of photo-isomerized reaction of molecular photoswitches is a greatly meaningful research topic for the fabrication of high-performance smart materials. Herein, a series of stiff-stilbene derivatives with substituents of different electronic effects were designed and prepared handily through Suzuki coupling reaction. Through studying their photoisomerization properties, we disclosed the influence law of electronic effect on photoisomerization properties of stiff-stilbenes that strong electron-donating and electron-deficient groups located in the counterposition of stiff-stilbenes on the benzene ring were not conducive to photochromism performance of stiff-stilbene skeleton. The (E)-form of these stiff-stilbenes, a new class of fluorescence dyes, showed good photoluminescence performance, and dramatically stronger than their (Z)-isomers. Importantly, we witnessed a fascinating photo-modulating fluorescence behavior for these molecular photoswitches, which were further applied in high-secrecy-level anti-counterfeiting. The study provided a reference for the design of excellent molecular photoswitches with purpose and precision and the development of new intelligent optical materials.

Reversible polymerization of carbon dots based on dynamic covalent imine bond

Carbon dots (CDs), as new type of carbon-based nanoparticles, are considered to be an aggregate with irreversible polymerization. Achieving the reversible tunability of CDs luminescence based on their reversible polymerization is a challenging subject. Herein, we, for the first time, design and construct the blue-emitting CDs with reversible polymerization by a room-temperature Schiff base reaction between tannic acid and ethylenediamine. The formation of CDs is proven to be due to the crosslinking polymerization of precursors caused by imine bond. As a dynamic covalent bond, imine bond endows CDs with controllable structural transformation properties, and the prepared CDs can be depolymerized and polymerized reversibly by pH-controlled imine bond cleavage and re-formation. These properties of reversible fluorescence photoswitching make the CDs have a good application prospect in reversible information encryption.

A Highly Efficient Phosphorescence/Fluorescence Supramolecular Switch Based on a Bromoisoquinoline Cascaded Assembly in Aqueous Solution.

Despite ongoing research into photocontrolled supramolecular switches, reversible photoswitching between room‐temperature phosphorescence (RTP) and delayed fluorescence is rare in the aqueous phase. Herein, an efficient RTP‐fluorescence switch based on a cascaded supramolecular assembly is reported, which is constructed using a 6‐bromoisoquinoline derivative (G3), cucurbit[7]uril (CB[7]), sulfonatocalix[4]arene (SC4A4), and a photochromic spiropyran (SP) derivative. Benefiting from the confinement effect of CB[7], initial complexation with CB[7] arouses an emerging RTP signal at 540 nm for G3. This structure subsequently coassembles with amphiphilic SC4A4 to form tight spherical nanoparticles, thereby further facilitating RTP emission (≈12 times) in addition to a prolonged lifetime (i.e., 1.80 ms c.f., 50.1 µs). Interestingly, following cascaded assembly with a photocontrolled energy acceptor (i.e., SP), the efficient light‐driven RTP energy transfer occurs when SP is transformed to its fluorescent merocyanine (MC) state. Ultimately, this endows the final system with an excellent RTP–fluorescence photoswitching property accompanied by multicolor tunable long‐lived emission. Moreover, this switching process can be reversibly modulated over multiple cycles under alternating UV and visible photoirradiation. Finally, the prepared switch is successfully applied to photocontrolled multicolor cell labeling to offer a new approach for the design and fabrication of novel advanced light‐responsive RTP materials in aqueous environments.

Reversible Three-Color Fluorescence Switching of an Organic Molecule in the Solid State via "Pump-Trigger" Optical Manipulation.

In photoswitches that undergo fluorescence switching upon ultraviolet irradiation, photoluminescence and photoisomerization often occur simultaneously, leading to unstable fluorescence properties. Here, we successfully demonstrated reversible solid-state triple fluorescence switching through "Pump-Trigger" multiphoton manipulation. A novel fluorescence photoswitch, BOSA-SP, achieved green, yellow, and red fluorescence under excitation by pump light and isomerization induced by trigger light. The energy ranges of photoexcitation and photoisomerization did not overlap, enabling appropriate selection of the multiphoton light for "pump" and "trigger" photoswitching, respectively. Additionally, the large free volume of the spiropyran (SP) moiety in the solid state promoted reversible photoisomerization. Switching between "pump" and "trigger" light is useful for three-color tunable switching cell imaging, which can be exploited in programmable fluorescence switching. Furthermore, we exploited reversible dual-fluorescence switching in a single molecular system to successfully achieve two-color super-resolution imaging.

Reversible Three‐Color Fluorescence Switching of an Organic Molecule in the Solid State via “Pump–Trigger” Optical Manipulation

AbstractIn photoswitches that undergo fluorescence switching upon ultraviolet irradiation, photoluminescence and photoisomerization often occur simultaneously, leading to unstable fluorescence properties. Here, we successfully demonstrated reversible solid‐state triple fluorescence switching through “Pump–Trigger” multiphoton manipulation. A novel fluorescence photoswitch, BOSA‐SP, achieved green, yellow, and red fluorescence under excitation by pump light and isomerization induced by trigger light. The energy ranges of photoexcitation and photoisomerization did not overlap, enabling appropriate selection of the multiphoton light for “pump” and “trigger” photoswitching, respectively. Additionally, the large free volume of the spiropyran (SP) moiety in the solid state promoted reversible photoisomerization. Switching between “pump” and “trigger” light is useful for three‐color tunable switching cell imaging, which can be exploited in programmable fluorescence switching. Furthermore, we exploited reversible dual‐fluorescence switching in a single molecular system to successfully achieve two‐color super‐resolution imaging.

Reversible Near-Infrared Fluorescence Photoswitching in Aqueous Media by Diarylethene: Toward High-Accuracy Live Optical Imaging.

Fluorescence imaging is an indispensable tool in modern biological research, allowing simple and inexpensive color-coded visualizations of real-time events in living cells and animals, as well as of fixed states of ex vivo specimens. The accuracy of fluorescence imaging in living systems is, however, impeded by autofluorescence, light scattering, and limited penetration depth of light. Nevertheless, the clinical use of fluorescence imaging is expected to grow along with advances in imaging equipment, and will increasingly demand high-accuracy probes to avoid false-positive results in disease detection. To this end, a water-soluble and relatively safe diarylethene (DAE)-based reversible near-infrared (NIR) fluorescence photoswitch for living systems is prepared here. Furthermore, to facilitate excellent switching performance, the photoirradiation results obtained is compared using three different visible light sources to turn on NIR fluorescence through cycloreversion of DAE. While photoswitching using 589nm light leads to slightly higher cell viability, fluorescence quenching efficiency and fatigue resistance are higher when 532nm light with low photobleaching is used in both aqueous solution and living systems. The authors anticipate that their reversible NIR fluorescence photoswitch mediated by DAE can be beneficial for fluorescence imaging in aqueous media requiring accurate detection, such as in the autofluorescence-rich living environment.

A dual-functional chemical sensor for the detection of Cu2+ and Cd2+ based on the photochromic diarylethene

A dual-functional sensor DTF-o with a photochromic diarylethene moiety has been designed and synthesized. Its structure was confirmed and analyzed by NMR and MS. The photochromism and fluorescence photoswitching properties of DTF-o were studied in acetonitrile/water (9:1, v/v) solution. DTF-o could selectively recognize Cu2+ by changing its color from colorless to yellow which was attributed to the metal-to-ligand charge transfer (MLCT) absorption band of metal-ligand cooperation. Meanwhile, DTF-o could also be used to detect Cd2+ through obvious emission intensity enhancement by inhibition of CN isomerization with chelation enhanced fluorescence (CHEF). Finally, DTF-o was successfully used in practical samples and made into test strips to detect Cu2+/Cd2+ with high accuracy.