dl-Serine Covalently Ornamented and Ln3+-Incorporated Arsenotungstates with Fast-Responsive Photochromic and Photoinduced Luminescent Switchable Behaviors

Three isostructural dl-serine covalently functionalized and multinuclear lanthanide (Ln³⁺)-embedded arsenotungstates, K₂[{As₄W₄₄O₁₃₇(OH)₁₈(H₂O)₂(dl-Ser)₂}{Ln₂(H₂O)₄(dl-Ser)}₂{Ln(H₂O)₇}₂]·70H₂O (Ln = Sm (1), Eu (2), and Gd (3); dl-Ser = C₃H₇NO₃), were prepared, where the centrosymmetric [{As₄W₄₄O₁₃₇(OH)₁₈(H₂O)₂(dl-Ser)₂}{Ln₂(H₂O)₄(dl-Ser)}₂]^8- polyanion consists of two {As₂W₁₉O₅₉(OH)₈(H₂O)}^6- fragments, integrated with a two-dl-serine-ornamented [W₆O₂₃(OH)₂(dl-Ser)₂{Ln₂(H₂O)₄}₂]^8- segment. In addition, the photochromic transformation of solid-state compounds 1-3 was observed from colorless to blue after a UV illumination of 4 min, and the decay process lasted as long as ∼20 h in the dark. The coloration kinetic half-life (t_1/2) values of compounds 1, 2, and 3 were calculated to be 0.597, 0.920, and 0.723 min, respectively. Furthermore, the luminescent properties and energy migration from arsenotungstates and organic chromophores to Sm³⁺ and Eu³⁺ ions in 1 and 2 have been intensively investigated. Further analysis manifests that 1 possesses an effective luminescent switchable behavior, triggered by its fast-responsive photochromism effect.

The Intrinsic Charge Carrier Behaviors and Applications of Polyoxometalate Clusters Based Materials

Polyoxometalates (POMs) are a series of molecular metal oxide clusters, which span the two domains of solutes and solid metal oxides. The unique characters of POMs in structure, geometry, and adjustable redox properties have attracted widespread attention in functional material synthesis, catalysis, electronic devices, and electrochemical energy storage and conversion. This review is focused on the links between the intrinsic charge carrier behaviors of POMs from a chemistry-oriented view and their recent ground-breaking developments in related areas. First, the advantageous charge transfer behaviors of POMs in molecular-level electronic devices are summarized. Solar-driven, thermal-driven, and electrochemical-driven charge carrier behaviors of POMs in energy generation, conversion and storage systems are also discussed. Finally, present challenges and fundamental insights are discussed as to the advanced design of functional systems based upon POM building blocks for their possible emerging application areas.

Self-Rechargeable-Battery-Driven Device for Simultaneous Electrochromic Windows, ROS Biosensing, and Energy Storage

A self-powered electrochromic device (ECD) powered by a self-rechargeable battery is easily fabricated to achieve electrochromic window design, quantitative reactive oxygen species (ROS) sensing, and energy storage. The special design of the battery was composed of Prussian blue (PB) and magnesium metal as the cathode and anode, respectively, which exhibits fast self-charging and high power-density output for continuous and stable energy supply. Benefitting from the fast electrochromic response of PB, it was not only used for structuring self-rechargeable batteries but also used as an electrochromic display for highly sensitive self-powered ROS sensing and visual analysis. We believe that this work provides a solution to self-powered ECDs limited to a single application and could combine the applications in smart windows, ROS sensing, and other fields together, and in the meantime provide a solution for energy supply problems.

In situ reversible color variation of a ready-made upconversion material using the designed component of a three-state fluorescence switching system

In recent years, upconversion materials have attracted considerable attention because of their unique physicochemical features. Numerous studies have focused on the synthesis of upconversion materials with different colors. However, an easier way to vary the upconversion colors without changing the materials' components has not been extensively studied. In this study, we realized the in situ color variation of the designed upconversion material with the help of a three-state fluorescence switching hybrid device. The device was composed of Prussian blue and upconversion materials; the former element functioned as a fluorescence resonance energy transfer acceptor and the latter acted as a donor. Smartly applying the RGB color model guaranteed multicolor of the device. Moreover, the highest fluorescence contrast of the three-state fluorescence switching system was 86% (larger than the result of a previous study), and the three-state reversibility was remarkable; this was probably owing to the unique layer-by-layer dripping/electrodepositing assembly method. To the best of our knowledge, the in situ reversible color variation of the ready-made upconversion material has been demonstrated for the first time.

Electroluminochromic Materials: From Molecules to Polymers

Electroluminochromism is an interesting property found in certain classes of molecules and polymers whose photoluminescence can be modulated through the application of an external electrical bias. Unlike electrochromic materials, electroluminochromic counterparts and their applications are comparatively fewer in quantity and are less established. Nonetheless, there prevails an increasing interest in this class of electro-active materials due to their potential applications in optoelectronics, such as smart-displays, and chemical and biological sensing. This review seeks to showcase the different classes of electroluminochromic materials with focus on (i) organic molecules, (ii) transition metal complexes, and (iii) organic polymers. The mechanisms and electroluminochromic performance of these classes of materials are summarized. This review should allow scientists to have a better and deeper understanding of materials design strategies and, more importantly, structure-property relationships and, thus, develops electroluminochromic materials with desired performance in the future.

Dual electrical switching permeability of vesicles via redox-responsive self-assembly of amphiphilic block copolymers and polyoxometalates

Electro-responsive vesicles were demonstrated based on an amphiphilic block copolymer PEO114-b-P(DCH-Ru)n and an inorganic nanoparticle polyoxometalate H3PMo12O40 (PMo12) via electrostatic interactions. After undergoing electrochemical reactions, vesicle membranes allow the migration of electrolyte ions and release of loaded cargos.

Printable Skin-Driven Mechanoluminescence Devices via Nanodoped Matrix Modification

Mechanically driven light generation is an exciting and under-exploited phenomenon with a variety of possible practical applications. However, the current driving mode of mechanoluminescence (ML) devices needs strong stimuli. Here, a flexible sensitive ML device via nanodopant elasticity modulus modification is introduced. Rigid ZnS:M²⁺ (Mn/Cu)@Al₂ O₃ microparticles are dispersed into soft poly(dimethylsiloxane) (PDMS) film and printed out to form flexible devices. For various flexible and sensitive scenes, SiO₂ nanoparticles are adopted to adjust the elasticity modulus of the PDMS matrix. The doped nanoparticles can concentrate stress to ZnS:M²⁺ (Mn/Cu)@Al₂ O₃ microparticles and achieve intense ML under weak stimuli of the moving skin. The printed nano-/microparticle-doped matrix film can achieve skin-driven ML, which can be adopted to present fetching augmented animations expressions. The printable ML film, amenable to large areas, low-cost manufacturing, and mechanical softness will be versatile on stress visualization, luminescent sensors, and open definitely new functional skin with novel augmented animations expressions, the photonic skin.

A chemical/molecular 4-input/2-output keypad lock with easy resettability based on red-emission carbon dots-Prussian blue composite film electrodes

In this work, a resettable 4-input/2-output keypad lock system based on red-emission carbon dots (rCDs) and Prussian blue (PB) modified electrodes was developed. Electrochromic PB layers were first electrochemically deposited on the indium tin oxide (ITO) electrode surface. An admixture of rCDs and chitosan (Chi) was then cast on the surface of PB layers, forming rCDs-Chi/PB film electrodes. UV-vis absorption of the films was sensitive to the applied potential since the blue PB constituent of the films would be transformed to nearly colorless Prussian white (PW) at the reduction potential of -0.2 V and then from PW back to PB at the oxidation potential of 0.4 V, and the transformation between PB and PW would also influence the fluorescence emission of the rCD constituent in the films. The addition of cysteine (Cys) in the testing solution could reduce the PB in the films into PW and generate an amperometric electrocatalytic current at 0.4 V. Meanwhile, the addition of Fe3+ in solution could greatly quench the fluorescence from the rCD component in the films. Thus, the responses of UV-vis absorbance, fluorescence emission and amperometric current of the rCDs-Chi/PB film electrode system exhibited potential-, Cys- and Fe3+-responsive switching properties. Based on the aforementioned work, a combinational logic gate circuit with 3 inputs and 3 outputs was established. In particular, on the same platform, a novel chemical/molecular 4-input/2-output keypad lock with easy resettability was elaborately designed with amperometric current and fluorescence peak intensity as two different types of outputs, so that a higher security level could be achieved.

Recent advances in spectroelectrochemistry

The integration of two quite different techniques, conventional electrochemistry and spectroscopy, into spectroelectrochemistry (SEC) provides a complete description of chemically driven electron transfer processes and redox events for different kinds of molecules and nanoparticles. SEC possesses interdisciplinary advantages and can further expand the scopes in the fields of analysis and other applications, emphasizing the hot issues of analytical chemistry, materials science, biophysics, chemical biology, and so on. Considering the past and future development of SEC, a review on the recent progress of SEC is presented and selected examples involving surface-enhanced Raman scattering (SERS), ultraviolet-visible (UV-Vis), near-infrared (NIR), Fourier transform infrared (FTIR), fluorescence, as well as other SEC are summarized to fully demonstrate these techniques. In addition, the optically transparent electrodes and SEC cell design, and the typical applications of SEC in mechanism study, electrochromic device fabrication, sensing and protein study are fully introduced. Finally, the key issues, future perspectives and trends in the development of SEC are also discussed.

Highly Efficient, Near-Infrared and Visible Light Modulated Electrochromic Devices Based on Polyoxometalates and W18O49 Nanowires

Over the past years the performance of electrochromic smart windows with the promising potential for significant energy savings has been progressively improved; however, the electrochromic windows have not yet to come into use at scale mainly because the electrochromic materials suffer from some significant drawbacks such as low coloration efficiency, slow switching time, bad durability and poor functionality. Herein, we fabricate the optically modulated electrochromic smart devices through sequential deposition of the crown-type polyoxometalates, K₂₈Li₅H₇P₈W₄₈O₁₈₄·92H₂O (P₈W₄₈), and W₁₈O₄₉ nanowires. Unlike most reported electrochromic smart devices, the resulting P₈W₄₈ and W₁₈O₄₉ nanocomposites allow active and selective manipulation of the transmittance of near-infrared (750-1360 nm) and visible light (400-750 nm) by varying the applied potential. Furthermore, thanks to the stable nature of both P₈W₄₈ and W₁₈O₄₉ and precise structural control over the nanocomposites, the prepared electrochromic smart devices exhibit high efficiency, quick response and excellent stability.

Redox-driven porphyrin based systems for new luminescent molecular switches

This work explores the possibility of controlling the fluorescence of porphyrins via oxidation of a ruthenium acetylide unit. The modulation depends on the nature of the porphyrin unit(s).

Dynamics of field-driven population inversion in a confined colloidal mixture

We study, using Langevin dynamics simulations, the change in composition of a binary colloidal mixture confined in a finite-length channel, induced by an external field. The field-induced transition from a near-bulk composition to an inverted population is studied as a function of time, for different field strengths and system parameters. For state points corresponding to reversible field cycles, the cyclic filling and emptying of the channel by the minority species are compared. Extrapolation of the physical relaxation times to the colloidal regime is performed through a series of simulations at increasing value of the damping parameter. For state points at which the mixture is unstable at zero field, reproducible irreversible cycles are illustrated. For reversible field cycles, the scaling with the particles size of the characteristic cycling time is discussed.

Self-powered fluorescence display devices based on a fast self-charging/recharging battery (Mg/Prussian blue)

Stimuli-responsive (such as voltage and/or light) fluorescence display systems have attracted particular attention in their promising fields of application. However, there are few examples of self-powered fluorescence display devices. Here we designed and fabricated a self-powered fluorescence display device based on a fast-charging/recharging battery. The specially designed battery was composed of a Prussian blue (PB) cathode and a magnesium metal anode with a high theoretical redox potential difference (∼2.8 V). Moreover, smartly adding a trace amount of NaClO in the electrolyte could realize oxidizing PW to PB ∼480 times faster than when oxidizing without NaClO, leading to the fast self-charging and high power density (maximum power density of 13.34 mW cm^-2, about two to three orders of magnitude larger than previous bio-fuel cells) of the Mg/PB battery. Most importantly, PB was used as not only the cathodic catalyst but also as an electrochromic material, making it possible to construct a self-powered and rechargeable electrochromic fluorescence display with only two electrodes. Besides, fluorescent [Ru(bpy)₃]²⁺-doped silica nanoparticles (Ru@SiO₂), were selected as the fluorescence resonance energy transfer (FRET) donor to match PB (FRET acceptor). To the best of our knowledge, we demonstrated a self-powered and rechargeable electrochromic fluorescence display with only two electrodes for the first time.

A high performance fluorescence switching system triggered electrochemically by Prussian blue with upconversion nanoparticles

A high performance fluorescence switching system triggered electrochemically by Prussian blue with upconversion nanoparticles was proposed. We synthesized a kind of hexagonal monodisperse β-NaYF4:Yb(3+),Er(3+),Tm(3+) upconversion nanoparticle and manipulated the intensity ratio of red emission (at 653 nm) and green emission at (523 and 541 nm) around 2 : 1, in order to match well with the absorption spectrum of Prussian blue. Based on the efficient fluorescence resonance energy transfer and inner-filter effect of the as-synthesized upconversion nanoparticles and Prussian blue, the present fluorescence switching system shows obvious behavior with high fluorescence contrast and good stability. To further extend the application of this system in analysis, sulfite, a kind of important anion in environmental and physiological systems, which could also reduce Prussian blue to Prussian white nanoparticles leading to a decrease of the absorption spectrum, was chosen as the target. And we were able to determine the concentration of sulfite in aqueous solution with a low detection limit and a broad linear relationship.

Automatic illumination compensation device based on a photoelectrochemical biofuel cell driven by visible light

Inverted illumination compensation is important in energy-saving projects, artificial photosynthesis and some forms of agriculture, such as hydroponics. However, only a few illumination adjustments based on self-powered biodetectors that quantitatively detect the intensity of visible light have been reported. We constructed an automatic illumination compensation device based on a photoelectrochemical biofuel cell (PBFC) driven by visible light. The PBFC consisted of a glucose dehydrogenase modified bioanode and a p-type semiconductor cuprous oxide photocathode. The PBFC had a high power output of 161.4 μW cm(-2) and an open circuit potential that responded rapidly to visible light. It adjusted the amount of illumination inversely irrespective of how the external illumination was changed. This rational design of utilizing PBFCs provides new insights into automatic light adjustable devices and may be of benefit to intelligent applications.

Preparation of polyoxometalate stabilized gold nanoparticles and composite assembly with graphene oxide: enhanced electrocatalytic performance

P₅W₃₀ stabilized Au nanoparticles and graphene oxide were fabricated to form composite films exhibiting good electrocatalytic activity for H₂O₂ reduction.

A fluorescence molecular switch with high contrast multi-emissions and ON/OFF states

A fluorescence molecular switch of SPTPE is prepared, which can be reversibly switched between blue, cyan, red and dark with external stimuli.

High-contrast electrochromic and electrofluorescent dual-switching materials based on 2-diphenylamine-(9,9-diphenylfluorene)-functionalized semi-aromatic polymers

Two kinds of 2-diphenylamine-(9,9-diphenylfluorene)-functionalized semi-aromatic polymers were prepared and they exhibited stable and high-contrast electroswitching in both coloration and emission.

Enhanced sensitivity of color/emission switching of fluorescein film by incorporation of polyoxometalate using HCl and NH3 gases as in situ stimuli

Highly transparent tricomponent hybrid film agarose–[P₅W₃₀O₁₁₀]¹⁵⁻–fluorescein displays enhanced sensitivity of color/emission switching for HCl and NH₃ gases.

An effective combination of electrodeposition and layer-by-layer assembly to construct composite films with luminescence switching behavior

A novel fabrication strategy for a functional composite film was explored, and the fluorescence performance was studied.

A high fatigue resistant, photoswitchable fluorescent spiropyran–polyoxometalate–BODIPY single-molecule

In the reported spiropyran/polyoxometalate/BODIPY triad, the fluorescence of the BODIPY can be highly reversibly quenched by the activation of the photochromic spiropyran.

Light harvesting of CdSe/CdS quantum dots coated with β-cyclodextrin based host–guest species through resonant energy transfer from the guests

Nano-hybrids based on red emitting QDs covered by β-cyclodextrin hosting a green emitting nitrobenzoxadiazole derivative show emission harvested by the host–guest organic system.