Reversible Photoswitching Research Articles

BTDAzo: A Photoswitchable TRPC5 Channel Activator**

Photoswitchable reagents can be powerful tools for high-precision biological control. TRPC5 is a Ca2+-permeable cation channel with distinct tissue-specific roles, from synaptic function to hormone regulation. Reagents giving spatiotemporally-resolved control over TRPC5 activity may be key to understanding and harnessing its biology. Here we develop the first photoswitchable TRPC5-modulator, BTDAzo, to address this goal. BTDAzo can photocontrol TRPC5 currents in cell culture, as well as controlling endogenous TRPC5-based neuronal Ca2+ responses in mouse brain slices. BTDAzos are also the first reported azo-benzothiadiazines, an accessible and conveniently derivatised azoheteroarene with strong two-colour photoswitching. BTDAzo′s ability to control TRPC5 across relevant channel biology settings makes it suitable for a range of dynamically reversible photoswitching studies in TRP channel biology, with the aim to decipher the various biological roles of this centrally important ion channel.

Photoswitching of Local (Anti)Aromaticity in Biphenylene-Based Diarylethene Molecular Switches.

Photoinduced tuning of (anti)aromaticity and associated molecular properties is currently in the focus of attention for both tailoring photochemical reactivity and designing new materials. Here, we report on the synthesis and spectroscopic characterization of diarylethene-based molecular switches embedded in a biphenylene structure composed of rings with different levels of local (anti)aromaticity. We show that it is possible to modulate and control the (anti)aromatic character of each ring through reversible photoswitching of the aryl units of the system between open and closed forms. Remarkably, it is shown that the irreversible formation of an annulated bis(dihydro-thiopyran) side-product that hampers the photoswitching can be efficiently suppressed when the aryl core formed by thienyl groups in one switch is replaced by thiazolyl groups in another.

Aptamer functionalization and high-contrast reversible dual-color photoswitching fluorescence of polymeric nanoparticles for latent fingerprints imaging

Exploiting the intelligent stimuli-responsive fluorescent materials, which can selectively recognize lysozyme in fingerprints and enable high-contrast imaging, is still a challenge in latent fingerprints (LFPs) detection. Herein, based on Fluorescence Resonance Energy Transfer (FRET) mechanism, aptamer functionalization and high-contrast reversible dual-color photoswitching fluorescence of polymeric nanoparticles (LBA-RPFPNs) have been successfully constructed for efficient imaging of LFPs. Experiments results showed that LBA-RPFPNs displayed good water dispersibility, fast photo-responsiveness, favorable photoreversibility and good long-term stability. Of note, the aptamer possessed the ability of LBA-RPFPNs to target lysozyme in LFPs, thus realizing the selectivity of LFPs. Furthermore, the fluorescence of LBA-RPFPNs was reversibly switched between green and red through UV/visible light, achieving for high-contrast imaging of LFPs. This strategy provides good potential in disclosing the valuable information within LFPs.

First biphotochromic fluorescent protein moxSAASoti stabilized for oxidizing environment

Biphotochromic proteins simultaneously possess reversible photoswitching (on-to-off) and irreversible photoconversion (green-to-red). High photochemical reactivity of cysteine residues is one of the reasons for the development of “mox”-monomeric and oxidation resistant proteins. Based on site-saturated simultaneous two-point C105 and C117 mutagenesis, we chose C21N/C71G/C105G/C117T/C175A as the moxSAASoti variant. Since its on-to-off photoswitching rate is higher, off-to-on recovery is more complete and photoconversion rates are higher than those of mSAASoti. We analyzed the conformational behavior of the F177 side chain by classical MD simulations. The conformational flexibility of the F177 side chain is mainly responsible for the off-to-on conversion rate changes and can be further utilized as a measure of the conversion rate. Point mutations in mSAASoti mainly affect the pKa values of the red form and off-to-on switching. We demonstrate that the microscopic measure of the observed pKa value is the C–O bond length in the phenyl fragment of the neutral chromophore. According to molecular dynamics simulations with QM/MM potentials, larger C–O bond lengths are found for proteins with larger pKa. This feature can be utilized for prediction of the pKa values of red fluorescent proteins.

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.

Reversible photoswitching of spiropyran in biomolecular interfaces: A combined spectroscopy and computational study

The reversible photoswitching of nonactivated spiropyran viz., 1,3,3 Trimethylindolinobenzopyrylospiran (SP) is studied by employing UV–Vis spectroscopy and computational based calculations (DFT and MD simulation) under various environmental conditions. When SP resides at Histone (H1) interfaces, upon photoirradiation with UV 254 nm, it readily isomerizes to its merocyanine (MC) trans conformer which on exposure to visible light, reversibly cyclizes back to its original ring closure (SP) state with a rate constant of 2.8 min−1. Furthermore, in the presence of negatively charged nucleic acid DNA, positively charged H1 protein form H1-DNA condensates. Noncovalently bound MC molecule, sandwiched between H1 protein and DNA at H1-DNA interfaces, with associated free energy of binding −8.3 kcal/mol, reveals very rigid attachment at the recognition sides. We believe that the significant structural isomerization of the non-substituted spiropyran at room temperature depending on its microenvironmental stimuli may find potential use in target-oriented drug delivery applications.

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.

Fabricating and Modulating Robust Multi-Photoaddressable Systems with the Derivatives of Diarylethylene and Donor–Acceptor Stenhouse Adducts

Multi-photoaddressable systems (MPSs) belong to complex systems, which are comprised of more than one photoswitching molecule and can respond to different wavelengths of light simultaneously. While MPSs have been extensively applied in various fields, there are also some challenges, such as the deficiency of the wavelength-selective control and the interference from the poor thermodynamic stability of used photoswitching molecules. Herein, we reported two robust MPSs (MPS1/2) consisting of diarylethylene derivative (DAE) and different donor-acceptor Stenhouse adducts (DASAs), in which both opened and closed forms of DAE and opened forms of DASAs are thermodynamically stable. MPS1/2 enable fully reversible cyclic photoswitching with improved thermal interference resistance. Moreover, MPS2 also shows a favorable property in PMMA films and has been applied in multicolor display. It is expected that the prepared MPSs could be used in more fields such as information storage and reading and encoding light.

Dynamic Control of Microbial Movement by Photoswitchable ATP Antagonists

Adenosine triphosphate (ATP) is the energy source for various biochemical processes and biomolecular motors in living things. Development of ATP antagonists and their stimuli-controlled actions offer a novel approach to regulate biological processes. Herein, we developed azobenzene-based photoswitchable ATP antagonists for controlling the activity of motor proteins; cytoplasmic and axonemal dyneins. The new ATP antagonists showed reversible photoswitching of cytoplasmic dynein activity in an in vitro dynein-microtubule system due to the trans and cis photoisomerization of their azobenzene segment. Importantly, our ATP antagonists reversibly regulated the axonemal dynein motor activity for the force generation in a demembranated model of Chlamydomonas reinhardtii. We found that the trans and cis isomers of ATP antagonists significantly differ in their affinity to the ATP binding site.

Unexpected Acid-Triggered Formation of Reversibly Photoswitchable Stenhouse Salts from Donor-Acceptor Stenhouse Adducts.

Donor-acceptor Stenhouse adducts (DASAs) are reversibly photoswitchable dyes, which are able to interconvert between a red/NIR absorbing triene-like state and a colorless cyclic state. Although optically attractive for multiple applications, their low solubility and lack of photoswitching in water impede their use in aqueous environments. We developed water-soluble DASAs based on indoline as donor and methyl, or trifluoromethyl, pyrazolone-based acceptors. In acetonitrile, photophysical analysis and photochemical studies, accounted with a three-state kinetic model, confirmed the reversible photoswitching mechanism previously proposed. In water, the colorless cyclic state is a thermodynamic sink at neutral pH values. In contrast, in acidic conditions, we observed a fast scrambling of DASAs' end-group resulting in the in situ formation of Stenhouse salts (StS), which are in turn capable of reversible photoswitching. We believe that this unexpected result is of interest not only for the future design of DASAs with improved stability, but also for further development and applications of StS as photoswitchable probes.

S-Tetrazine-Bridged Photochromic Aromatic Framework Material.

Integrating fluorescent chromophores in aromatic frameworks could not only prevent aggregation-induced quenching caused by the π–π stacking interaction between the chromophore components but also confer new fluorescence properties. Herein, we report the fabrication of s-tetrazine-bridged aromatic frameworks TzAF by the incorporation of the smallest aromatic fluorophore, s-tetrazine (Tz), into the skeleton of a tetrahedrally connected lattice of aromatic frameworks. The thin films of TzAF coated on silica gel plates were found to exhibit reversible photoswitching fluorescence characteristics under alternate UV and visible-light irradiations with excellent fluorescence stability and high on/off contrast. The repeatable “on/off”fluorescence photoswitchability of the TzAF thin films was mechanistically attributed to light-induced reversible transformation between TzAF’s neutral and radical states.

Is it possible to maintain photomechanical properties of crystalline diarylethenes after thermal amorphization?

The photomechanical properties of the photochromic 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene (DTE) crystals, largely documented since the discovery by Irie et al. of its reversible photoswitching of crystallographic plane morphology, is renewed with a novel approach consisting on suppressing gradually dynamical effects through thermal amorphization. In the crystalline case, the reversibility of UV/Visible induced plastic deformations have been observed as expected. In addition, a number of large jumps for both cycles are reported for the first time for this molecule in contrast to being observed only during the first UV irradiation cycle for other DTEs. In the amorphous case, several striking results have been obtained: (i) the still present reversible photoinduced plastic deformations mimicking the crystalline case are interpreted in terms of apparent polyamorphism; (ii) the total vanishing of the jumps brings the evidence of the crucial role of the crystallinity for the propelling surface in contact with the substrate; (iii) the discovery of a never reported material jump during the first visible cycle. This last result is rationalized combining two features –a thermal one, a glass transition temperature very close to the room temperature (Tg ≈ 34°C) and –a photochemical one, an inefficient photoreversion allowing the other vibrational relaxation pathway to proceed inducing the required temperature rise to overpass the phase transition (Solid → Liquid) responsible for the jump.

Dual-gated single-molecule field-effect transistors beyond Moore\u2019s law

As conventional silicon-based transistors are fast approaching the physical limit, it is essential to seek alternative candidates, which should be compatible with or even replace microelectronics in the future. Here, we report a robust solid-state single-molecule field-effect transistor architecture using graphene source/drain electrodes and a metal back-gate electrode. The transistor is constructed by a single dinuclear ruthenium-diarylethene (Ru-DAE) complex, acting as the conducting channel, connecting covalently with nanogapped graphene electrodes, providing field-effect behaviors with a maximum on/off ratio exceeding three orders of magnitude. Use of ultrathin high-k metal oxides as the dielectric layers is key in successfully achieving such a high performance. Additionally, Ru-DAE preserves its intrinsic photoisomerisation property, which enables a reversible photoswitching function. Both experimental and theoretical results demonstrate these distinct dual-gated behaviors consistently at the single-molecule level, which helps to develop the different technology for creation of practical ultraminiaturised functional electrical circuits beyond Moore’s law.

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.

Stimuli-Modulated Metal Oxidation States in Photochromic MOFs.

Tuning metal oxidation states in metal-organic framework (MOF) nodes by switching between two discrete linker photoisomers via an external stimulus was probed for the first time. On the examples of three novel photochromic copper-based frameworks, we demonstrated the capability of switching between +2 and +1 oxidation states, on demand. In addition to crystallographic methods used for material characterization, the role of the photochromic moieties for tuning the oxidation state was probed via conductivity measurements, cyclic voltammetry, and electron paramagnetic resonance, X-ray photoelectron, and diffuse reflectance spectroscopies. We confirmed the reversible photoswitching activity including photoisomerization rate determination of spiropyran- and diarylethene-containing linkers in extended frameworks, resulting in changes in metal oxidation states as a function of alternating excitation wavelengths. To elucidate the switching process between two states, the photoisomerization quantum yield of photochromic MOFs was determined for the first time. Overall, the introduced noninvasive concept of metal oxidation state modulation on the examples of stimuli-responsive MOFs foreshadows a new pathway for alternation of material properties toward targeted applications.

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.

Reversible Photoswitching between Fluorescence and Room Temperature Phosphorescence by Manipulating Excited State Dynamics in Molecular Aggregates

AbstractRegulation of fluorescence–phosphorescence pathways in organic molecular aggregate remains a challenge due to the complicated singlet–triplet excited state dynamics process. Herein, we demonstrated a successful example (o‐BFT) to realize photoreversible fluorescence and room temperature phosphorescence (RTP) switching based on an effective strategy of integrating a phosphor (dibenzofuran) with a photoswitch (dithienylbenzothiophene). o‐BFT exhibited dual emission of fluorescence and RTP in both powder and doping polymer film. Notably, the long‐lived RTP of o‐BFT could be repeatedly erased and restored through reversible photocyclization and decyclization under alternate ultraviolet and visible photoirradiation. In‐depth theoretical and spectroscopic investigations revealed that the triplet inactivation was dominated by a photo‐controlled triplet‐to‐singlet Förster resonance energy transfer from light‐activated o‐BFT to photoisomer c‐BFT. Yet, the initial fluorescence could be preserved in this process to afford a photoreversible fluorescence‐RTP switching.

Reversible Photoswitching between Fluorescence and Room Temperature Phosphorescence by Manipulating Excited State Dynamics in Molecular Aggregates.

Regulation of fluorescence-phosphorescence pathways in organic molecular aggregate remains a challenge due to the complicated singlet-triplet excited state dynamics process. Herein, we demonstrated a successful example (o-BFT) to realize photoreversible fluorescence and room temperature phosphorescence (RTP) switching based on an effective strategy of integrating a phosphor (dibenzofuran) with a photoswitch (dithienylbenzothiophene). o-BFT exhibited dual emission of fluorescence and RTP in both powder and doping polymer film. Notably, the long-lived RTP of o-BFT could be repeatedly erased and restored through reversible photocyclization and decyclization under alternate ultraviolet and visible photoirradiation. In-depth theoretical and spectroscopic investigations revealed that the triplet inactivation was dominated by a photo-controlled triplet-to-singlet Förster resonance energy transfer from light-activated o-BFT to photoisomer c-BFT. Yet, the initial fluorescence could be preserved in this process to afford a photoreversible fluorescence-RTP switching.

The role of cysteine residues in the allosteric modulation of the chromophore phototransformations of biphotochromic fluorescent protein SAASoti

Biphotochromic fluorescent protein SAASoti contains five cysteine residues in its sequence and a V127T point mutation transforms it to the monomeric form, mSAASoti. These cysteine residues are located far from the chromophore and might control its properties only allosterically. The influence of individual, double and triple cysteine substitutions of mSAASoti on fluorescent parameters and phototransformation reactions (irreversible green-to-red photoconversion and reversible photoswitching) is studied. A set of mSAASoti mutant forms (C21N, C117S, C71V, C105V, C175A, C21N/C71V, C21N/C175A, C21N/C71G/C175A) is obtained by site-directed mutagenesis. We demonstrate that the C21N variant exists in a monomeric form up to high concentrations, the C71V substitution accelerates photoconversion to the red form and the C105V variant has the maximum photoswitching rate. All C175A-containing variants demonstrate different photoswitching kinetics and decreased photostability during subsequent switching cycles compared with other considered systems. Classical molecular dynamic simulations reveal that the F177 side chain located in the vicinity of the chromophore is considerably more flexible in the mSAASoti compared with its C175A variant. This might be the explanation of the experimentally observed slowdown the thermal relaxation rate, i.e., trans–cis isomerization of the chromophore in mSAASoti upon C175A substitution.

Multiple anti-counterfeiting guarantees from simple spiropyran derivatives with solid photochromism and mechanochromism

Stimuli-responsive materials have gained a lot of attention recently because of their promising use in data storage, drug release, sensing, and anti-counterfeiting. Herein, we report spiropyran-silane derivatives with dual reversible characteristics as photo- and mechanochromic materials. These molecules are susceptible to ultraviolet (UV) light and exhibit efficient and reversible solid-state photoswitching under alternating UV light and heat/visible light treatment for at least 100 cycles. Meanwhile, they can change colors under slight grinding. Additionally, they have the following advantages as anti-counterfeiting materials: (1) they show high contrast and reversibility to design complex anti-counterfeit patterns; (2) the response and recovery is fast, and the validations can be realized in a short time; (3) they can achieve multiple stimuli responses of both fluorescence and color changes controlled by either UV light or mechanical force. In particular, based on mechanochromism, handwriting can be used as another guarantee to strengthen anti-counterfeiting. The multiple guarantees will greatly improve the reliability of anti-counterfeiting measures, making counterfeiting more difficult.