Photochromic Switches Research Articles

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 10K. 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 80min 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.

Dual-Responsive Thermally Activated Delayed Fluorescence of Spiropyran Derivatives

Dual-Responsive Thermally Activated Delayed Fluorescence of Spiropyran Derivatives

The Unusual Photochromic and Hydrochromic Switching Behavior of Cellulose-Embedded 1,8-Naphthalimide-Viologen Derivatives in the Solid-State.

Stimuli-responsive chromic materials such as photochromics, hydrochromics, thermochromics, and electrochromics have a long history of capturing the attention of scientists due to their potential industrial applications and novelty in popular culture. However, hybrid chromic materials that combine two or more stimuli-triggered color changing properties are not so well known. Herein, we report a design strategy that has led to a series of emissive 1,8-naphthalimide-viologen dyads which exhibit unusual dual photochromic and hydrochromic switching behavior in the solid-state when embedded in a cellulose matrix. This behavior manifests as reversible solid state fluorescence hydrochromism upon changes in atmospheric relative humidity (RH), and reversible solid state photochromism upon generation of a cellulose-stabilized viologen radical cation. In this design strategy, the bipyridinium unit serves as both a water-sensitive receptor for the hydrochromic fluorophore-receptor system, and a photochromic group, capable of eliciting its own visible colorimetric response, generating a fluorescence quenching radical cation with prolonged exposure to ultraviolet (UV) light. These dyes can be inkjet-printed onto cellulose paper or drop-cast as cellulose powder-based films and can be unidirectionally cycled between three different states which can be characteristically visualized under UV light or visible light. The material's photochromism, hydrochromism, and underlying mechanism of action was investigated using computational analysis, dynamic vapor sorption/desorption isotherms, electron paramagnetic resonance spectroscopy, and variable humidity UV-Vis adsorption and fluorescence spectroscopies.

Dithienylethenes functionalized by triphenylethene and difluoroboron β-diketonate fragments: Synthesis, optical switching behavior and fluorescent turn-on sensing for volatile organic amines

Two novel dithienylethenes were obtained by appending triphenylethene and BF2bdk moieties at the termini of dithienylethene unit (TDBB and TDTB), in which BF2bdk group not only functions as electron acceptor (A) but also responds to volatile organic amines. Only TDBB displayed excellent visible light-triggered photochromism and fluorescent switching behavior in toluene and in the PMMA film upon alternating irradiation with blue light (460–470 nm) and near-infrared light (760–770 nm). More importantly, they displayed a distinct fluorescent turn-on and colorimetric sensing performance for volatile n-propylamine in THF. Specially, the addition of excessive n-propylamine can effectively modulate their photochromic properties in THF. And their PMMA films showed the fluorescent turn-off and colorimetric sensory behavior towards n-propylamine vapor. Consequently, they would be utilized as novel dual sensory materials for volatile primary or secondary amine vapors in the environment and biological systems.

Photochromism of Sm3+-doped perovskite oxide: Ultrahigh-contrast optical switching and erasable optical recording

Inorganic photochromic materials, exhibiting great potential for optical switcher and erasable optical recording, have attracted more and more attention due to their robust fatigue resistance and excellent stability. However, the optical switching contrast of downshifting emission-based photochromic materials is still inferior. To address this issue, in this work we report a Sm3+-doped perovskite oxide (BaZrO3) photochromic material with good fatigue resistance. With the combination of red emission and photochromism properties, optical switching with the highest contrast value of 90.05% for the downshifting emission-based photochromic material till now is achieved. The good reproducibility is demonstrated. The mechanisms of photoluminescence, photochromism and optical switching are discussed in detail. Finally, as a proof-of-concept, the implementation of erasable optical recording is also realized through the fabrication of photochromic discs and flexible films using the as-obtained BaZrO3: Sm3+.

A QM/MM study of the conformation stability and electronic structure of the photochromic switches derivatives of DHA/VHF in acetonitrile solution

We present a detailed theoretical study of the electronic absorption spectra and thermochemistry of molecular photoswitches composed of one and two photochromic units of dihydroazulene (DHA)/vinylheptafulvene (VHF) molecules. Six different isomers are considered depending on the ring opening/closure forms of the DHA units. The solvent effect of acetonitrile is investigated using a sequential Molecular Mechanics/Quantum Mechanics approach. The thermochemical investigations of these photochromic molecules were performed using the Free Energy Perturbation method, and the simulations were performed using Configurational Bias Monte Carlo. We show that to open the 5-member ring of the DHA, there is no significant gain in thermal release of energy for the back reaction when a unit or two DHA units are considered. Overall, we found agreement between the solvation free energy based on Monte Carlo simulations and the continuum solvent model. However, the cavitation term in the continuum model is shown to be a source of disagreement when the non-electrostatic terms are compared. The electronic absorption spectra are calculated using TDDFT CAM-B3LYP/cc-pVDZ. Agreement with experiment is obtained within 0.1 eV, considering statistically uncorrelated configurations from the simulations. Inhomogeneous broadening is also considered and found to be well described in all cases.

Wavelength-dependent multicolor photochromism and fluorescence switching based on an AIE-active skeleton by regulating the conjugation of the photoactive unit

We proposed a general design strategy to achieve multicolor photochromic systems with dual-signaling color and fluorescence modes using a group of colorful photochromic compounds based on an AIE-active molecular skeleton.

An AIE-active dual fluorescent switch with negative photochromism for information display and encryption

A negative photochromic molecular switch with AIE and two-color fluorescence conversion properties was synthesized.

High-contrast photochromic Eu-doped K0.5Na0.5NbO3 ceramics with prominent pellucidity.

The Eu-doped K0.5Na0.5NbO3 pellucid ceramics were first prepared via a conventional solid-state reaction, and they exhibited light illumination-induced high-contrast photochromism of both optical transmittance and photoluminescence behaviors. Through thermal treatment, the optical performances could return to their initial states and displayed excellent reversibility. Eu3+ ions were selected as the luminescent activator for detecting the local environment of the K0.5Na0.5NbO3 host. Meanwhile, the effects of the amount of Eu3+ present on phase structures, microstructures, optical transmittance and photoluminescence intensities were systematically investigated. The results suggest that Eu-doped K0.5Na0.5NbO3 transparent ceramics possess multifunctionality including photochromism, photoluminescence and optical switching properties, and that they exhibit promising potential for non-destructive optical data storage application.

D–π–A type ferrocene-substituted azobenzene photochromic switches: synthesis, structures, and electrochemical and photoisomerization studies

A series of D–π–A type azobenzenes with a ferrocenyl/ferrocenylethynyl electron donor at thepara/meta-position have been synthesized and characterized by electrochemistry and UV-vis spectroscopy.

A novel water-soluble multicolor halo- and photochromic switching system based on a nitrile-rich acceptor

The first example of a multicolor nitrile-rich dye exhibiting pH-tunable negative photochromism and photoacidity in aqueous media under irradiation using visible light was described.

Mechanism of 2, 3-difurylmaleic anhydride photochromic molecular switch

The photochromic switching mechanism of 2,3-difurylmaleic anhydride (DFMA) is investigated by first-principles calculations. Based on the stable structures of the open-ring (O-DFMA) and closed-ring (C-DFMA) of the DFMA, the minimum energy path (MEP) and the configuration of transition states (TS-DFMA) between the O-DFMA and C-DFMA are found by using the nudged elastic band (NEB) method, the potential barriers of O-DFMA and C-DFMA are 24959 cm<sup>–1</sup>(3.0945 eV) and 23328 cm<sup>–1</sup>(2.8923 eV), respectively, indicating that the DFMA molecule may be a thermally bistable molecule. Along the molecular configuration corresponding to the MEP curve (i.e. ground state S<sub>0</sub>), the potential energy curves of the lowest 8 singlet excited states of DFMA are calculated. Among these energy curves, only the first electronic excited state (i.e. S<sub>1</sub> state) has a minimum value in the transition state (TS-DFMA) configuration. Combined with the molecular orbital transitions and orbital images, the photochromic mechanism of DFMA can be described as follows (1) From C-DFMA to O-DFMA process: under the action of the laser with S<sub>1</sub>–S<sub>0</sub> resonance transition wavelength, the C-DFMA transits from S<sub>0</sub> to S<sub>1</sub> state, and then deactivates along the S<sub>1</sub> potential energy curve, until a cross jumping transition occurs at the TS-DFMA structure from S<sub>1</sub> to S<sub>0</sub> and finally the molecule along the S<sub>0</sub> potentioal energy curve returns to the O-DFMA configuration, then the switching action from closed-ring to open-ring is completed. The S<sub>1</sub> state potential energy curve drops monotonically in this switching process, implying that there will be no fluorescent radiation in this process. (2) From O-DFMA to C-DFMA process: under the action of the laser with S<sub>1</sub>–S<sub>0</sub> resonance transition wavelength, O-DFMA transits from S<sub>0</sub> to S<sub>1</sub> state. From the O-DFMA to TS-DFMA structure, there is a relatively “flat” area in the potential energy curve of the S<sub>1</sub> state, and it decreases significantly only when it is close to the TS-DFMA. This means that O-DFMA needs to be excited with some vibrational modes to pass through the “flat” region of S<sub>1</sub> and approaching to the TS-DFMA configuration, and then DFMA de-excites from the S<sub>1</sub> state potential energy curve along a monotonic decline and a cross jumping transition from S<sub>1</sub> to S<sub>0</sub> occurs in the TS-DFMA configuration, completing the switching action from open-ring to closed-ring. It is also precisely because of the flat region of the potential energy curve of the initial S<sub>1</sub> state that this excitation and switching process is accompanied by fluorescent radiations. The photochromic mechanism of DFMA indicates that it is suitable for making fluorescent molecular switches.

New Insight on Photoisomerization Kinetics of Photo-Switchable Thin Films Based on Azobenzene/Graphene Hybrid Additives in Polyethylene Oxide

In this work, we reported a new insight on the kinetics of photoisomerization and time evolution of hybrid thin films considering the azo-dye methyl red (MR) incorporated with graphene accommodated in polyethylene oxide (PEO). The kinetics of photoisomerization and time-evolution of hybrid thin films were investigated using UV-Vis s and FTIR spectroscopies, as well as appropriate models developed with new analytical methods. The existence of azo-dye MR in the complex is crucial for the resource action of the trans cis cycles through UV-illumination Visible-illumination relaxations. The results of the UV–Vis and the FTIR investigations prove the cyclical trans cis-states. Consequently, PEO-(MR-Graphene) hybrid composite thin films can be introduced as possible applicants for photochromic molecular switches, light-gated transistors, and molecular solar thermal energy storage media.

Fluorescent Photochromic α‐Cyanodiarylethene Molecular Switches: An Emerging and Promising Class of Functional Diarylethene

AbstractFluorescent photochromic molecules that exhibit distinct light‐triggered changes in their emission colors are highly desirable for the fabrication of smart soft materials and advanced photonic devices. α‐Cyanodiarylethenes, that is, α‐cyano‐functionalized diarylethenes, as alternative “non‐azo” Z/E photochromic molecular switches, are popular choices due to their unique characteristics such as their aggregation‐induced emission or aggregation‐induced‐enhanced emission behavior in their self‐assembled states, and visible changes in fluorescence colors during Z/E photoisomerization. In recent years, the development of fluorescent photochromic α‐cyanodiarylethene‐based compounds including α‐cyanostilbenes, dicyanodistyrylbenzenes, and diaryldicyanoethenes, has mainly focused on molecular design, photochemical and photophysical behavior in solution, and smart soft matter technologies. In this review, recent significant achievements in light‐responsive systems based on the Z/E photoisomerization of fluorescent photochromic α‐cyanodiarylethene switches that span the range from liquid crystals to gels and finally to self‐assembled nanostructures, are highlighted. The smart soft materials constructed from α‐cyanodiarylethene molecular switches find use in a plethora of areas, including display, sensing, encrypting, actuating, and biomedical imaging applications, among others. The review concludes with a brief perspective on some major challenges and opportunities for the future development of light‐responsive smart soft photonic materials.

Using Active Surface Plasmons in a Multibit Optical Storage Device to Emulate Long‐Term Synaptic Plasticity

Artificial intelligence takes inspiration from the functionalities and structure of the brain to solve complex tasks and allow learning. Yet, hardware realization that simulates the synaptic activities realized with electrical devices still lags behind computer software implementation, which has improved significantly during the past decade. Herein, the capability to emulate synaptic functionalities by exploiting surface plasmon polaritons (SPPs) is shown. By depositing photochromic switching molecules (diarylethene) on a thin film of gold, it is possible to reliably control the electronic configuration of the molecules upon illumination cycles with UV and visible light. These reversible changes modulate the dielectric function of the photochromic film and thus enable the effective control of the SPP dispersion relation at the molecule/gold interface. The plasmonic device displays fundamental functions of a synapse such as potentiation, depression, and long‐term plasticity. The integration of such plasmonic devices in an artificial neural network is deployed in plasmonic neuroinspired circuits for optical computing and data transmission.

Spiro-conjugated indenodiarylethenes: enabling steric-induced electronic tuning of photochromic and photoluminescent properties by spiro-conjugation

Light-operated excited-state photochemical reactions and the resulting photochromic materials have gained significant attention for their promising technological applications in molecular electronic and photonic devices. To obtain photochromic materials (e.g., diarylethenes) with desired properties, the way to tune energy processes of the excited state is essentially important, from both fundamental and practical viewpoints. The modified diarylethenes mostly focused on structural improvements to achieve efficient photochromism. We report here two new spiro-conjugated indenodiarylethenes (named, SFI-Th and SFI-Sul) with an orthogonally arranged spiro π-scaffold. The spiro fluorene sterically constrains the free volume of photoactive side aromatic rings, while the spiro-conjugation points toward modulation of the decaying channels of excited-state energy, thus allowing for tuning photochromic performances. These spirodiarylethenes SFI-Th and SFI-Sul are readily accessible with low cost and show distinct photochromic and photoluminescent properties. On one hand, the SFI-Th bearing bisthienyl side rings, is an excellent photochromic switch showing high thermal stability and high fatigue resistance in both solution and amorphous state, likely benefited from steric-induced excited-state energy transfer into reversible photochemical reactions, owing to higher π-orbital spiro-conjugation between the two molecular halves. On the other hand, the SFI-Sul with bissulfonyl side rings, most notably, displays quantitative photocyclization to yield SFI-Sulc upon excitation. However, the ring-closed SFI-Sulc has an extremely slow photocycloreversion, and meanwhile immediately switches on emissive state with a strong fluorescence (Φf=0.57 in amorphous powder state). We study the modulated roles of spiro π-scaffold in both cases computationally and experimentally, and attribute the facilitated photochemical reaction to the positively electronic effects of spiro-conjugation, and the photo-responsive radiative transition to the negatively electronic effects of spiro-conjugation, respectively. In all, this work demonstrates that the spiro-conjugation is a new and efficient strategy to deliver excitation energy transfer (EET) for featured photochromic properties, due to its advantage in steric-induced electronic modulation.

Photochromism and Fluorescence Switch of Furan-Containing Tetraarylethene Luminogens with Aggregation-Induced Emission for Photocontrolled Interface-Involved Applications.

It is extremely challenging to design photocontrolled molecular switches with absorption and fluorescence dual-mode outputs that are suited for a solid surface and interface. Herein, we report a group of furan-containing tetraarylethene derivatives with unique photophysical behavior of aggregation-induced emission (AIE) and distinct photochemical reaction-triggered photochromic behaviors by combining a photoactive furan or benzofuran group and an AIE-active triphenylethene molecule. The introduction of a furyl or benzofuryl group into the AIE luminogen endows the molecules with significant reversible photochromism and solid-state fluorescence. The coloration and decoloration of these molecules can be switched by respective irradiation of UV and visible light in a reversible way, and the photochromic changes are accompanied by a switch-on and switch-off of the solid-state fluorescence. It is revealed that the photocontrolled cyclization and cycloreversion reactions are responsible for the reversible photochromism and fluorescence switching based on experimental data and theoretical analysis. Both the position and conjugation of the introduced photoactive units have significant influence on the color and strength of the photochromism, and the simultaneous occurrence of photoinduced fluorescence change in the solid state is perfectly suited for surface-involved applications. The demonstrations of dual-mode signaling in photoswitchable patterning on a filter paper and anti-counterfeiting of an anti-falsification paper strongly highlight the unique advantage of these photochromic molecules with an aggregation-induced emission characteristic in various practical applications. This work proposes a general strategy to design photochromic molecules with AIE activity by introducing photoactive functionals into an AIEgen and demonstrates incomparable advantage in dual-mode signaling and multifunctional applications of these molecules.

A novel diarylethene‐based fluorescence sensor with a benzohydrazide unit for the detection of Zn2+

AbstractA novel fluorescent sensor on the basis of diarylethene and benzohydrazide unit was successfully synthesized. Its photochromic and fluorescent switching properties have been studied in detail by the irradiation of UV‐visible (UV‐Vis) lights and the stimulus of Zn2+/EDTA. The sensor exhibited high sensitivity and selectivity toward Zn2+ in tetrahydrofuran, which is not interfered by other cations, especially of congener Cd2+. The fluorescence intensity enhanced 84 times along with a 44‐nm blue shift of the emission peak after adding Zn2+. The stoichiometric ratio between the sensor and Zn2+ was 1:1, and the limit of detection (LOD) was calculated as 5.60 × 10−9 mol L−1. Besides, the sensor was applied in the detection of practical water samples with high accuracy.

Cooperative and fully reversible color switching activation in hybrid graphene decorated nanocages and copper-TiO2 nanoparticles

Nanostructured systems showing reversible color switching are envisaged to play a significant role in photo-switches, photo-optical sensors, smart windows, displays, optical storage memories. Most of the materials exhibiting reversible color switching are organic molecules. However, their UV-light activation, low thermal and chemical stability, as well as harmful synthesis methods, limit their extensive use. In this research, we have created an inorganic switchable photochromic material exploiting TiO2 ability of creating an exciton upon excitation, copper as the chromophore, and graphene's extraordinarily high electron mobility. Spatially-resolved electron energy-loss spectroscopy and aberration-corrected transmission electron microscopy imaging highlight the high sp2 content of the graphene flakes as well as the presence of few-layers nanocage graphene decorating the surface of the flakes. Our material showed itself to be able to work under visible-light, its photochromic property being three times faster than conventional titania based photochromic materials, reaching a stable change in coloration after only 30 min of visible-light irradiation (vs. > 120 min in conventional Cu–TiO2). With the addition of just 1 wt% graphene, the material exhibited a staggeringly stable photochromic switching over repeated cycles. These results relate to the best previously reported values for any form of TiO2-based photochromic material. This is therefore an excellent candidate for smart-windows, light-sensitive information and energy storage devices, and other chromic devices and applications.

Solid-state photochromic molecular switches based on axially chiral and helical spiropyrans

Solid-state photochromic switches with reversible luminescence modulation property have wide applications in optical data storage, anticounterfeiting, sensing, and bioimaging, however, it is a significant challenge to design and prepare such materials. In the present work, a novel class of chiral and helical binaphthyl-substituted spiropyrans has been synthesized and characterized. The introduction of binaphthyl can not only promote the solid-state luminescence but also achieve the interesting chiroptical switching properties for the potential applications in chiral recognition and circularly polarized luminescence. The single-crystal structures and density functional theory calculations reveal that the presence of strong electron-withdrawing nitro groups can promote photoswitch efficiency by stabilizing the electron-rich conjugated merocyanine with the lower electron cloud density and LUMO/HOMO levels. For charge transfer in excited states, π → π* transition would enhance emission, but n → π* transition and intramolecular charge transfer show the opposite effect. Therefore, these photochromic switches provide a novel paradigm in the design of multiple-responsive, chiral, and luminescent materials.