Photochromic crystalline hybrid materials with switchable properties: Recent advances and potential applications

Immobilization of electrospun alumina nanofiber-embedded nanocomposite into delignified wood toward multifunctional ultraviolet filtering smart windows for energy efficiency of residential buildings

Long-persistent photoluminescent wood with ultraviolet protection, photochromism, mechanical reliability, transparent appearance, and hydrophobic properties was developed. A combination of polylactic acid (PLA; a hosting substrate), alumina/polyvinylpyrrolidone nanofiber (a reinforcement agent), and nanoparticles (NPs) of lanthanide-doped aluminate (LdA; a photoluminescent pigment) was embedded into a delignified Basswood to produce a multifunctional window. The coloration screening and photoluminescence spectra confirmed that the developed wood is transparent under daylight but becomes green under UV light. When the LdA ratio was increased, the UV protection of the hardwoods was enhanced from 43 to 195. The contact and sliding angles increased in the ranges of 147.0°-153.4° and 14°-7°, respectively. A viscous nanocomposite of polyvinylpyrrolidone/AlCl3 was prepared by the sol-gel technology. The electrospun alumina/polyvinylpyrrolidone nanofibers were exposed to calcination. The diameters of the alumina nanofibers were reported in the range of 75-220 nm, and the diameters of the LdA nanoparticles were in the range of 2-5 nm. The luminescent wood showed an emission band at 517 nm upon excitation at 365 nm. The wood sample with a phosphor content of 2 % was set for an optimal fluorescence emission, whereas the wood sample with a phosphor content of 8 % was set for an optimum afterglow emission.

Proton-Mediated ROS Amplification in Hydrazone-Linked Pillararene Microspheres for Photocatalysis

Smart materials that adapt to environmental stimuli have massive technological potential. Translating well-established molecular-level responsiveness to macroscopic systems, particularly complex systems for photocatalysis, remains a significant hurdle. Herein, we introduce a new approach using a hydrazone-linked pillararene microsphere (NP5-TF-HPM) as a smart stimuli-responsive photocatalyst. NP5-TF-HPM showcases unique proton responsiveness owing to electron-rich cavities, resulting in a proton-induced structural rearrangement from the enol-imine to keto-amine form. Experiments and density functional theory calculations reveal that pillararenes in the protonated framework function as activity amplifiers. These molecules donate π-electrons from their cavities to another building unit, not only shifting the framework's conduction band to a more negative potential, which enhances its electron-donating capability, but also inducing a nonuniform charge distribution in the donor-acceptor moiety, thereby resulting in an intramolecular built-in electric field. Consequently, protonated HPM exhibits amplified photo-oxidation activity, efficiently catalyzing sulfide photo-oxidation with high conversions (up to 99%).

Synergistic Photochromism, Fluorescence Switching, and Photomagnetism of Three Mn(II) Complexes Based on a Thiazolothiazole Extended Viologen Derivative

Multifunctional photochromic hybrid materials have attracted great attention due to their wide prospects in information storage, molecular switches, and sensors. Herein, three new photochromic coordination polymers (CPs) with paramagnetic Mn2+ ions, namely [Mn2(TTVP)(m-BDC)2] (1), [Mn3(TTVP)(p-BDC)3(H2O)2]·0.5H2O (2), and [Mn(TTVP)(H2O)4]·(4,4'-BPC)·2H2O (3) have been synthesized (TTVP = 2,5-bis(pyridinium-4-yl)thiazolo[5,4-d]thiazole propionate, m-H2BDC = isophthalic acid, p-H2BDC = terephthalic acid, 4,4'-H2BPC = 4,4'-diphenyldicarboxylic acid). Interestingly, under Ultraviolet (UV) light irradiation, these compounds exhibit distinct photochromic performances due to photoinduced electron transfer (PIET) between aromatic carboxylic acids and TTVP, as validated by spectroscopic and structural analyses. The coloration kinetics and final states are finely tuned by modulating the number and strength of weak interactions between electron donors (EDs) and electron acceptors (EAs). Furthermore, these complexes exhibit photoinduced magnetization enhancement at room temperature, while complexes 2 and 3 exhibit reversible fluorescence modulation during the coloration-decoloration cycles. The introduction of photoregulated fluorescent and magnetism into PIET photochromic compounds presents a promising approach for the development of multifunctional materials, holding potential for a range of applications.

Advances in crystalline metal-organic photochromic materials

Metal-organic materials have undergone rapid advancements due to their unique structural properties and exceptional application potential. As a key branch, crystalline metal-organic photochromic materials (CMOPMs), have attracted significant attention for their ability to modulate physical properties in response to light stimulation, thereby expanding the research landscape of metal-organic materials in areas such as molecular switch, gas adsorption and separation, and sensing applications. Furthermore, light as a renewable and clean energy source significantly enhances its application potential. In this feature article, we review the design and synthesis strategies, classification, and applications of CMOPMs. Finally, we present the opportunities and challenges for the development of CMOPMs.

Anion-π(-π) Interactions in Donor-Acceptor Hybrid Materials to Control Photochromism and Room-Temperature Phosphorescence

Photochromic materials and room-temperature phosphorescence (RTP) are essential for applications in optoelectronics and bioimaging. Organic-inorganic hybrid materials, particularly those exhibiting donor-acceptor (D-A) characteristics through supramolecular interactions, have shown significant potential to integrate both photochromic and RTP properties. Among them, the anion-π and π-π interactions have been extensively studied; however, the role of anion-π-π interactions in hybrid materials remains largely unexplored. This study investigated three naphthalenediimide-polyoxometalate (NDI-POM) hybrids: (H2DMAP-NDI)·(HPW12O40)·(NMP)2 (1), (HDMAP-NDI)2·(HPW12O40)·(NMP)2 (2), and (HDMAP-NDI)2·(HPW12O40)·(NMP)7 (3), focusing on the impact of anion-π-π interactions on their photochromic and RTP properties. The results indicate that hybrid 1 exhibits the fastest photoresponse and highest RTP quantum yield, primarily driven by anion-π interactions. Hybrid 2, which involves anion-π-π interactions, shows slower photochromism and lower RTP yield due to exciton localization and nonradiative decay paths resulting from π-π stacking. Hybrid 3, characterized by excessively strong interactions, is unstable and nonemissive. This study provides valuable insights into the role of anion-π-π interactions in hybrid materials and offers a framework for designing advanced photoresponsive materials with tunable properties for diverse applications.

Hysteresis Photomodulation within Photochromic Assemblies of [Dy(Tp2-py)F]+ Single-Molecule Magnets : Influence of the Supramolecular Magnetic Couplings

A 1D coordination compound made of a photochromic dithienylethene linker and [Dy(Tp2-py)F]+ units (with Tp2-py=tris(3-(2-pyridyl)pyrazolyl)hydroborate) and having tetrakis[3,5-bis(trifluoromethyl)phenyl]borate counterions is reported. Full photoconversion from the closed isomer to the open isomer of the dithienylethene within single crystals allow for monitoring of the transformation by photocrystallography. Magnetic slow relaxation as well as magnetic hysteresis are observed and can be both modulated upon light irradiation. Comparison with previously published structures with similar components highlights the role of the supramolecular organization, and of dipolar couplings within these compounds, in driving the nature of the observed hysteresis photomodulation.

Naphthalenediimide-Based Hybrid Material with Eu-Substituted Polyoxometalate: Photochromism, Near-Infrared Photothermal Conversion, and C-3 Functionalization of Indoles

Designing and developing novel photochromic materials with additional functions such as photothermal conversion and photocatalysis are challenging but meaningful objectives. Crystalline naphthalenediimide (NDI)-based hybrids are an attractive class of multifunctional materials with fast-response photoinduced electron transfer and charge separation properties. They are promising photothermal conversion materials and photocatalysts. Herein, a novel hybrid material, EuPMo11O39(L)1.5(H2O)2]·DMA (EuMo-NDI) (L = N,N'-di(1-oxido-4-pyridyl)-1,4,5,8-naphthalenediimide), was prepared with a solvothermal method, integrating a photoactive NDI derivative and an Eu-substituted polyoxometalate. EuMo-NDI exhibits 0D structure with sensitive photochromic behavior under UV-vis light irradiation due to fast-response photoinduced electron transfer between its components. The colored EuMo-NDI sample demonstrated efficient near-infrared photothermal conversion due to the strong absorption of the photogenerated radical anion NDI•- and mixed valence heteropoly blue in the near-infrared region. Meanwhile, EuMo-NDI is easily excited in the presence of electron donors to form the radical species, which can activate inert O2 to superoxide radical O2•-. EuMo-NDI exhibited high photocatalytic activity for C-3 thiocyanation of indoles under mild conditions using white light as a driving force. This work provides an effective avenue to design novel photothermal conversion materials and photocatalysts using photochromic materials as platforms.

Electrothermochromic Fabrics with a Single-Layer Functional Coating Based on Silver Nanowires/Thermochromic Microcapsules/Waterborne Polyurethane Paints

The Ag NWs/TCMs/WPU/PET fabric was prepared by coating the polyester (PET) fabric with Ag NWs/TCMs/WPU paint. First, an electrothermochromic paint was fabricated by incorporating waterborne polyurethane (WPU) and thermochromic microcapsules (TCMs) into silver nanowire (Ag NW) dispersions, and then the Ag NWs/TCMs/WPU paint was applied to polyester (PET) fabrics via brushing, thereby integrating electrothermal and color-changing properties into a single functional layer. The color change test and DSC data demonstrate that the Ag NWs/TCMs/WPU paint exhibits a reversible color change effect, and the flexibility test data indicate that the coating's resistance remains essentially unchanged after 1000 bending cycles. The sheet resistance of the Ag NWs/TCMs/WPU/PET fabric is 8.62 Ω·sq-1. Electrothermal tests show that the fabric surface temperature reaches 48.9 °C at 4 V, triggering a color change. Varying the type of TCMs yields electrothermochromic fabrics exhibiting two distinct color-changing effects at 4 and 6 V. Following 50 cycles of washing and rubbing, the fabric's resistance remains within the same order of magnitude, and the color change is minimal. The Ag NWs/TCMs/WPU/PET fabric, featuring a straightforward preparation method, a rich color-changing effect, and excellent durability, is poised for application in smart color-changing textiles.

Heterogeneous photocatalytic organic transformation using crystalline naphthalenediimide/perylenediimide-based hybrid materials

The use of light energy to drive photocatalytic organic transformations for the production of high-value-added organic compounds has garnered growing interest as a sustainable strategy for solving environmental problems and addressing the energy crisis. Naphthalenediimide (NDI) and perylenediimide (PDI)-based hybrid materials are highly regarded photocatalysts due to their strong visible-light absorption properties, highly electron-deficient aromatic cores, excellent redox activity, and tunable electrochemical and photochemical properties. However, although the design and preparation of NDI/PDI-based hybrid materials have progressed in the past few years, their application in photocatalytic organic reactions remains in the initial stage. This review highlights the recent research progress in NDI/PDI-based hybrid materials and their crystalline composites for photocatalytic organic transformations. In particular, the synthetic methods, structures, photochemical properties, and catalytic performance of NDI/PDI-based hybrid photocatalysts are illustrated to provide useful guidance for the further development and application of these materials.

Regulating the Topologies and Photoresponsive Properties of Lanthanum-Organic Frameworks

Metal-organic frameworks (MOFs) show potential application in many domains, in which photochromic MOFs (PMOFs) have received enormous attention. Researchers mainly utilize photoactive ligands to build PMOFs. Recently, the mixed electron donating and accepting ligands strategies have also been used to construct PMOFs driven by the electron transfer between nonphotochromic moieties. However, the potential interligand competition inhibits the formation of PMOFs. Therefore, the exploration of single-ligand-guided assembly is conductive for building PMOFs. Considering the existing electron accepting and donating role of pyridyl and carboxyl, the pyridinecarboxyate derived from the fusion of pyridyl and carboxyl units may serve as single ligand to yield PMOFs (Figure 1d). In this work, the coordination assembly of bipyridinedicarboxylate (2,2'-bipyridine-4,4'-dicarboxylic acid, H2bpdc; 1,10-phenanthroline-2,9-dicarboxylic acid, H2pda) and LaCl3 generate two PMOFs, [La(bpdc)(H2O)Cl] (1) and [La(pda)(H2O)2Cl]⋅2H2O (2). Both complexes feature dinuclear lanthanum as building blocks with differences in the connecting number of likers, in which 1 has (4,8)-connected topology and 2 exhibits sql topology. Their structural differences result in the diversities of photoresponsive functionalities. Compared with reported PMOFs built from photoactive ligands and mixed ligands, this study provides new available categories of single ligand for generating PMOFs and tuning the structure and photoresponsive properties via ligand substitution and external photostimulus.

Multi-Stimuli Responsive Viologen-Imprinted Polyvinyl Alcohol and Tricarboxy Cellulose Nanocomposite Hydrogels

Photochromic inks have shown disadvantages, such as poor durability and high cost. Self-healable hydrogels have shown photostability and durability. Herein, a viologen-based covalent polymer was printed onto a paper surface toward the development of a multi-stimuli responsive chromogenic sheet with thermochromic, photochromic, and vapochromic properties. Viologen polymer was created by polymerizing a dialdehyde-based viologen with a hydroxyl-bearing dihydrazide in an acidic aqueous medium. The viologen polymer was well immobilized as a colorimetric agent into a polyvinyl alcohol (PVA)/tricarboxy cellulose (TCC)-based self-healable hydrogel. The viologen/hydrogel nanocomposite films were applied onto a paper surface. The coloration measurements showed that when exposed to ultraviolet light, the orange layer printed on the paper surface switched to green. The photochromic film was used to develop anti-counterfeiting prints using the organic hydrogel composed of a PVA/TCC composite and a viologen polymer. Reversible photochromism with strong photostability was observed when the printed papers were exposed to UV irradiation. A detection limit was monitored in the range of 0.5-300 ppm for NH3(aq). The exposure to heat (70 °C) was found to reversibly initiate a colorimetric change.

The Solid-State Multi-Color Fluorescence Switching from a [2.2]Paracyclophane-Based Triarylborane

The fluorophores, the fluorescence of which can be switched between multi bright colors in the solid state, show promising applications not only in the sophisticated multicolor display but also in the advanced encryption and anti-counterfeiting systems. However, it is very challenging to obtain such fluorophores. Herein, we disclose such an example, g-BPhANMe2-Cp, which contains an electron-donating dimethylamino (NMe2) and an electron-accepting [(2-dimesitylboryl)phenyl]acetyl at the pseudo-gem position of [2.2]paracyclophane skeleton. This molecule can display tricolor mechanochromic luminescence (MCL) due to the different responses of the mechanically ground amorphous state to heating and solvent-fuming. Owing to the absence of intermolecular π-π interactions in the solid state, the fluorescence efficiency is very high irrespective of its morphological state (ΦF=0.60-0.87). Moreover, this molecule also displays reversible acidochromic luminescence (ACL) by protonation and deprotonation of NMe2 with trifluoroacetic acid (TFA) and triethylamine (TEA), respectively. The protonated sample fluoresces (ΦF=0.31) at much shorter wavelength due to the interruption of intramolecular charge transfer process. Therefore, with the combination of tricolor MCL and ACL properties, the solid-state emission of g-BPhANMe2-Cp can be switched among four bright fluorescence colors of yellow, green, cyan and blue via treatment with appropriate stimulus.

A reversible photochromic covalent organic framework

Covalent organic frameworks are a type of crystalline porous materials that linked through covalent bond, and they have numerous potential applications in adsorption, separation, catalysis, and more. However, there are rarely relevant reported on photochromism. Fortunately, a hydrazone-linked DBTB-DETH-COF is rapidly generated through ultrasound method. The DBTB-DETH-COF is found to exhibit reversible photochromism (at least 50 cycles) from yellow to olive in the presence of light and air, and subsequently back to the original color upon heating. In addition, the structure of DBTB-DETH-COF remains unchanged after 15 days of light illumination. Furthermore, the reason of photochromic process is discussed by electron paramagnetic resonance, X-ray photoelectron spectroscopy, electrochemistry characterizations and transient absorption measurements. The reversible photochromic DBTB-DETH-COF can be used as anti-counterfeiting ink and optical switch in the presence of air. This work expands a stable organic photochromic material and broadens the applications of COFs.

Light-Induced Antiferromagnetic to Ferromagnetic Transition in Halogen Substituted 1,4-Bis(imidazolyl)benzene Systems: An Effect of Spin-Orbit Coupling and π-Stacking in Enhanced Photomagnetism

Employing the spin-orbit coupling effect by introducing halogen substituents is an excellent strategy to tune the magnetic behavior of organic or metal-organic materials. Light is an alternative tool to modulate the magnetic behavior of a material through a photoinduced electron transfer process, without changing its chemical identity. In this work, three halogen containing 1,4-bis(4,5-diphenyl-1H-imidazol-2-yl)benzene (F-BDPI, Cl-BDPI and Br-BDPI) systems have been chosen to exploit the role of halogen substituents on solid-state photoinduced phenomena. Through a comprehensive analysis involving various characterization techniques, including UV/vis diffuse reflectance, solid-state photoluminescence, and EPR measurements, it was found that the as-synthesized forms Cl-BDPI-IA and Br-BDPI-IA (IA denotes the hexahydrate form of Cl/Br-BDPI) exhibited fast photochromic response through the generation of photoinduced free radicals in the solid state. Moreover, the SQUID analysis revealed an antiferromagnetic to ferromagnetic transition in Cl-BDPI-IA through photoirradiation, which led to an increase in the magnetic moment value up to 38% at room temperature. This signifies the first occurrence of such a significant level of magnetization amplitude compared with previously reported metal-organic photomagnets. This investigation underscores the significance of halogen substitution in tailoring the magnetic properties of organic photomagnets, where strong halogen-π and π-π interactions facilitate the spin-orbit coupling effect in the solid state.

Electron transport chain-inspired coordination polymers for macroscopic spatiotemporal scales of charge separation and transport in photocatalysis

Classic homogeneous photocatalysis is limited by the temporal transience and the spatial proximity of photoinduced charge separation and transport. The electron transfer chain (ETC) in cellular respiration can mediate unidirectional and long-range electron transfer to isolate the oxidation and reduction centres. Inspired by this, we modified electron-accepting (A) viologen with π-extending thiazolothiazole and electron-donating (D) phenyl carboxylate into a D-A-π-A-D-type ligand and assembled segregated dye stacking in coordination polymer Cd-TzBDP for breaking the spatiotemporal limitation of single-molecule photocatalysis. The offset characteristics of D-A segregated stacking not only allowed the photoinduced-2e- transfer from the D-type carboxylate terminal to the spatially adjacent A-type viologen motif within 1 ps but also permitted the following delocalization of e- and h+ along stacked columns. These advantages endowed Cd-TzBDP with long-lived photochromic visualization of intermittent aerobic photooxidation steps, which enabled the bioinspired ETC-mediated aerobic respiration of mitochondria, achieving the continuous photocatalytic α-C(sp3)-H functionalization of tertiary amines with pharmaceutical interest. Enlightened by ETC-mediated electron leak in hypoxia, the coordination polymer was further employed in a photocatalytic membrane reactor, which visually illustrated the photo-driven cross-membrane long-range transfers of multiple electrons and protons from the hypoxic compartment to normoxic one, benefiting the distal photooxidation and photoreduction with biomimetic compartment selectivity.

Development of gum Arabic/chitosan-infiltrated photoluminescent wooden smart window with multifunctional properties

Photochromic wood materials are very important and appealing for smart windows. Herein, we describe the development of transparent photochromic wood that can change its color under ultraviolet and visible lights. Photoluminescent transparent wood was prepared by delignification of wood followed by infiltration with a combination of gum Arabic/chitosan/acrylic acid (ACA), lanthanide-activated aluminum strontium oxide (LASO) as a photoluminescent, and Genipin as a cross-linking agent. The produced mixture was then infused into the lignin-modified wood substrate. In order to develop a luminescent colorless wood, the LASO phosphor must be well-distributed in the ACA solution without aggregation. According to the colorimetric parameters and photoluminescence spectra, this optically active wooden window switched color from transparent in daylight to green when UV-irradiated. Transmission electron microscopy (TEM) was employed to examine the morphological features of phosphor nanoparticles. The morphological features of the developed smart wooden window were investigated by scanning electron microscopy (SEM), X-ray fluorescent spectroscopy (XRF), and energy-dispersive X-ray analyzer (EDX). The mechanical performance was explored by investigating both hardness and resistance to scratches. The luminescent woods displayed an emission band at 518 nm when excited at 365 nm. The superhydrophobic performance and ultraviolet shielding of woods were improved upon increasing the phosphor content.

Development of strontium aluminate-printed nonwoven fabric from recycled cotton cellulose for smart wearable photochromic applications

Smart photochromic and fluorescent textile refers to garments that alter their colorimetric properties in response to external light stimulus. Cotton fibers have been reported as a main resource for many textile and non-textile industries, such as automobiles, medical devices, and furniture applications. Cotton is a natural fiber that is distinguished with breathability, softness, cheapness, and highly absorbent. However, there have been growing demands to find other resources for cotton textiles at high quality and low cost for various applications, such as sensor for harmful ultraviolet radiation. Herein, we present a novel method toward luminescent and photochromic nonwoven textiles from recycled cotton waste. Using the screen-printing technology, a cotton fabric that is both photochromic and fluorescent was developed using aqueous inorganic phosphor nanoparticles (10-18 nm)-containing printing paste. Both CIE Lab color coordinates and photoluminescence spectra showed that the transparent film printed on the nonwoven fabric develops a reversible green emission (519 nm) under ultraviolet light (365 nm), even at low pigment concentration (2%) in the printing paste. Colorfastness of printed fabrics showed high durability and photostability.

Light and Heat-Driven Flexible Solid Supramolecular Polymer Displaying Phosphorescence and Reversible Photochromism

Herein, a type of light- and heat-driven flexible supramolecular polymer with reversibly long-lived phosphorescence and photochromism is constructed from acrylamide copolymers with 4-phenylpyridinium derivatives containing a cyano group (P-CN, P-oM, P-mM), sulfobutylether-β-cyclodextrin (SBCD), and polyvinyl alcohol (PVA). Compared to their parent solid polymers, these flexible supramolecules based on the non-covalent cross-linking of copolymers, SBCD, and PVA efficiently boost the phosphorescence lifetimes (723.0 ms for P-CN, 623.0 ms for P-oM, 945.8 ms for P-mM) through electrostatic interaction and hydrogen bonds. The phosphorescence intensity/lifetime, showing excellent responsiveness to light and heat, sharply decreased after irradiation with a 275 nm flashlight or sunlight and gradually recovered through heating. This is accompanied by the occurrence and fading of visible photochromism, manifesting as dark green for P-CN and pink for P-oM and P-mM. These reversible photochromism and phosphorescence behaviors are mainly attributed to the generation and disappearance of organic radicals in the 4-phenylpyridinium derivatives with a cyano group, which can guide tunable luminescence and photochromism.

Tunable photo/thermochromic properties of Cd(II)-viologen coordination polymers modulated by coordination modes for flexible imaging films and anti-counterfeiting

Two photochromic Cd(II)-CPs were obtained based on the viologen ligand using different synthetic routes, named {[Cd4(p-BDC)4(CPB)2(H2O)2]·2H2O·EtOH}n (1) and {[Cd(p-BDC)(CPB)(H2O)]·(L)·DMF}n (2) (p-H2BDC = 1,4-benzene-dicarboxylate, HCPB·Cl = 1-(4-carboxyphenyl)-4,4'-bipyridinium·Cl, L = 2,4-dinitrochlorobenzene, and DMF = N,N-dimethylformamide), respectively. Due to different coordination modes, the two Cd(II)-CPs show different structures. Compound 1 exhibits a three-dimensional (3D) framework with bimetallic nodes, while compound 2 displays a 2-fold interpenetrated (4,4) net topology. Notably, the two Cd(II)-CPs exhibit substantial disparities in photo/thermochromism, which can be attributed to variations in donor-acceptor (D-A) distances arising from structural differences. Compound 1 showed visually sensitive photo- and thermochromic behavior due to multi-pathway electron transfer and short D-A distances, which is relatively rare in electron-transfer type photochromic systems. In contrast, 2 only demonstrates insensitive photochromic behavior, with a slight deepening of the color observed after 2 hours of UV light, which is due to the mono-pathway electron transfer and long D-A distance. Moreover, we first combined Cd(II)-viologen CPs with polydimethylsiloxane (PDMS) to prepare a 1@PDMS flexible UV imaging film. 1@PDMS exhibits excellent bendability and stretchability and maintains good photochromic properties after 100 bending cycles. To demonstrate the rapid color response and distinct color contrast of 1, its application in anti-counterfeiting is also demonstrated.

Tuning the Chirality Evolution in Achiral Subnanometer Systems by Judicious Control of Molecule Interactions

Chirality evolution from molecule levels to the nanoscale in an achiral system is a fundamental issue that remains undiscovered. Here, we report the assembly of polyoxometalate (POM) clusters into chiral subnanostructures in achiral systems by programmable single-molecule interactions. Driven by the competing binding of Ca2+ and surface ligands, POM assemblies would twist into helical nanobelts, nanorings, and nanotubes with tunable helicity. Chiral molecules can be used to differentiate the formation energies of chiral isomers and immobilize the homochiral isomer, where strong circular dichroism (CD) signals are obtained in both solutions and films. Chiral helical nanobelts can be used as circularly polarized light (CPL) photodetectors due to their distinct chiroptic responsivity for right and left CPL. By the fine-tuning of interactions at single-molecule levels, the morphology and CD spectra of helical assemblies can be precisely controlled, providing an atomic precision model for investigation of the structure-chirality relationship and chirality manipulation at the nanoscale.

A novel bioresponsive self-immolative spacer based on aza-quinone methide reactivity for the controlled release of thiols, phenols, amines, sulfonamides or amides

A stimuli-sensitive linker is one of the indispensable components of prodrugs for cancer therapy as it covalently binds the drug and releases it upon external stimulation at the tumour site. Quinone methide elimination has been widely used as the key transformation to release drugs based on their nucleofugacity. The usual approach is to bind the drug to the linker as a carbamate and release it as a free amine after a self-immolative 1,6-elimination. Although this approach is very efficient, it is limited to amines (as carbamates), alcohols or phenols (as carbonates) or other acidic functional groups. We report here a self-immolative spacer capable of directly linking and releasing amines, phenols, thiols, sulfonamides and carboxyamides after a reductive stimulus. The spacer is based on the structure of (5-nitro-2-pyrrolyl)methanol (NPYM-OH), which was used for the direct alkylation of the functional groups mentioned above. The spacer is metabolically stable and has three indispensable sites for bioconjugation: the bioresponsive trigger, the conjugated 1,6 self-immolative system and a third arm suitable for conjugation with a carrier or other modifiers. Release was achieved by selective reduction of the nitro group over Fe/Pd nanoparticles (NPs) in a micellar aqueous environment (H2O/TPGS-750-M), or by NADH mediated nitroreductase activation. A DFT study demonstrates that, during the 1,6 elimination, the transition state formed from 5-aminopyrrole has a lower activation energy compared to other 5-membered heterocycles or p-aminobenzyl derivatives. The NPYM scaffold was validated by late-stage functionalisation of approved drugs such as celecoxib, colchicine, vorinostat or ciprofloxacin. A hypoxia-activated NPYM-based prodrug (HAP) derived from HDAC inhibitor ST7612AA1 was also produced, which was active in cancer cells under hypoxic conditions.

Photochromism and single-component white light emission from a metalloviologen complex based on 1,5-naphthyridine

Metalloviologens, as emerging electron-transfer photochromic compounds, have shown intriguing properties such as radiochromism, photochromism and photoconductance. However, only a limited number of them have been reported so far. Exploration of new metalloviologens is strongly desired. Herein, we report a new solvothermally synthesized metalloviologen complex [CdCl2(ND)2]n (1, ND = 1,5-naphthalenes) that exhibits photochromic and intrinsic white light emission properties. Density functional theory calculation results reveal that the photochromism could be assigned to photoinduced electron transfer from chlorine atoms to ND molecules. The photoinduced charge-separated states are heat/air stable, attributed to the delocalization of ND and strong intermolecular π-π interactions. Besides, complex 1 consistently emits intrinsic white light when excited with 340-370 nm UV light, achieving high color rendering index (CRI) values (82.54-94.04). By adjusting the excitation wavelength, both "warm" and "cold" white light emission can be produced, making it suitable for the application of a white light emitting diode (WLED). Thus, this work demonstrates that the ND-based metalloviologen is not only helpful in producing photochromism, but also beneficial for creating white-light emission.

3D-Printed Smartwatch Fabricated via Vat Photopolymerization for UV and Temperature Sensing Applications

Ultraviolet (UV) exposure overdose can cause health issues such as skin burns or other skin damage. In this work, a UV and temperature sensor smartwatch is developed, utilizing a multimaterial 3D printing approach via a vat photopolymerization-digital light processing technique. Photochromic (PC) pigments with different UV sensitivities, UVA (315-400 nm) and UVB (315-280 nm), were utilized to cover a wider range of UV exposure and were mixed in transparent resin, whereas the smartwatch was printed with controlled thickness gradients. A multifunctional sensor was next fabricated by adding a thermochromic (TC) material to PC, which is capable of sensing UV and temperature change. Colorimetric measurements assisted by a smartphone-based application provided instantaneous as well as cumulative UV exposure from sunlight. The mechanical properties of the device were also measured to determine its durability. The prototype of the wearable watch was prepared by fixing the 3D-printed dial to a commercially available silicon wristband suitable for all age groups. The 3D-printed watch is water-resistant and easily removable, allowing for its utilization in multiple outdoor activities. Thus, the developed wearable UV sensor alerts the user to the extent of their UV exposure, which can help protect them against overexposure.

Immobilization of rare-earth doped aluminate nanoparticles encapsulated with silica into polylactic acid-based color-tunable smart plastic window

An inorganic/organic nanocomposite was used to develop an afterglow and color-tunable smart window. A combination of polylactic acid (PLA) plastic waste as an environmentally-friendly hosting agent, and lanthanide-activated strontium aluminum oxide nanoparticles (SAON) encapsulated with silica nanoparticles (SAON@Silica) as a photoluminescent efficient agent resulted in a smart organic/inorganic nanocomposite. In order to prepare SAON-encapsulated silica nanoparticles (SAON@Silica), the SAON nanoparticles were coated with silica using the heterogeneous precipitation method. By using transmission electron microscopy (TEM), SAON showed a diameter range of 5-12 nm, while the SAON@Silica nanoparticles showed a diameter range of 50-100 nm. In order to ensure the development of a colorless plastic film, a homogeneous dispersion of the phosphorescent Phosphor@Silica nanoparticles throughout the plastic bulk was confirmed. CIE Lab coordinates and luminescence spectra were used to study the color shift characteristics. Under visible light conditions, the plastic films were transparent. The photoluminescent films emitted green light at 525 nm when excited at 375 nm. The hydrophobicity and ultraviolet protection were enhanced without altering the fundamental physico-mechanical performance of the plastic sheet. The current color-tunable plastic can be used in many potential applications, such as warning signs, anti-counterfeiting barcodes, smart windows, and protective apparel.

Multi-site isomerization of synergistically regulated stimuli-responsive AIE materials toward multi-level decryption

Stimuli-responsive aggregation-induced emission (AIE) materials are highly sensitive and rapidly responsive to external signals, making them ideal solid materials for anti-counterfeiting encryption. However, the limited conformational and packing variations resulting from regio-isomerization with a single substituent restricts the stimuli-responsive behavior of these materials. In this work, several AIE-active regio-structural isomers based on the salicylaldehyde Schiff base scaffold have been straightforwardly obtained through multiple substitutions with bromide and triphenylamine moieties. Solvent-effect experiments demonstrate their different orders of charge-transfer and excited-state intramolecular proton transfer upon photoexcitation, indicating the regulation of excited-state processes via multi-site isomerization. These isomers also demonstrate mechanochromism and acidichromism, allowing for adjustable stimuli-responsive effects. As a demonstration, p-Br-TPA with both mechanochromism and acidichromism can be synergistically utilized for multi-level decryption. This study successfully regulates the evolution of excited states through multi-site isomerization, offering a general approach for achieving tunable stimuli-responsive properties in AIE-active salicylaldehyde Schiff bases toward multi-level decryption.

Photo-Controllable Ultralong Room-Temperature Phosphorescence: State of the Art

In this concept, we showcase the upsurge in the studies of dynamic ultralong room-temperature phosphorescence (RTP) materials containing inorganic and/or organic components as versatile photo-responsive platforms. The goal is to provide a comprehensive analysis of photo-controllable RTP, and meanwhile delve into the underlying RTP properties of various classes of photochromic materials including metal-organic complexes, organic-inorganic co-crystals, purely organic small molecules and organic polymers. In particular, the design principles governing the integration of the photochromic and RTP moieties within a single material system, and the tuning of dynamic RTP in response to light are emphasized. As such, this concept sheds light on the challenges and opportunities of using these tunable RTP materials for potential applications in optoelectronics, particularly highlighting their use of reversible information encryption, erasable light printing and rewritable smart paper.

Polyoxometalate/s-triazine hybrid heterostructures with ultrafast photochromic properties

As an emerging class of hybrid complexes, donor-acceptor (D-A) hybrid heterostructures, which combine the advantages of both organic and inorganic photoactive components, provide excellent platforms for the fabrication of photochromic materials with enhanced photo-responsive performances. Herein, four novel hybrid heterostructures, namely H3TPT·(PW12O40)·2NMP (1), (H1.5TPT)2·(PW12O40) (2), (H3TPT)2·(SiW12O40)·2Cl·2MeCN (3), and H3TPT·(HPMo12O40)·Cl·3NMP (4) (TPT is tri(4-pyridyl)-s-triazine, NMP is N-methylpyrrolidone), have been synthesized and characterized. Benefitting from the strong interactions (anion-π interactions) and matching electron energy levels between the donors and acceptors, some of them exhibited ultrafast photochromic behaviour even up to 1 second. Furthermore, based on experimental and theoretical calculations, the plausible PIET process and structure-activity relationship have been discussed in detail.

Near infrared emissions from both high efficient quantum cutting (173%) and nearly-pure-color upconversion in NaY(WO4)2:Er3+/Yb3+ with thermal management capability for silicon-based solar cells

Raising photoelectric conversion efficiency and enhancing heat management are two critical concerns for silicon-based solar cells. In this work, efficient Yb3+ infrared emissions from both quantum cutting and upconversion were demonstrated by adjusting Er3+ and Yb3+ concentrations, and thermo-manage-applicable temperature sensing based on the luminescence intensity ratio of two super-low thermal quenching levels was discovered in an Er3+/Yb3+ co-doped tungstate system. The quantum cutting mechanism was clearly decrypted as a two-step energy transfer process from Er3+ to Yb3+. The two-step energy transfer efficiencies, the radiative and nonradiative transition rates of all interested 4 f levels of Er3+ in NaY(WO4)2 were confirmed in the framework of Föster-Dexter theory, Judd-Ofelt theory, and energy gap law, and based on these obtained efficiencies and rates the quantum cutting efficiency was furthermore determined to be as high as 173% in NaY(WO4)2: 5 mol% Er3+/50 mol% Yb3+ sample. Strong and nearly pure infrared upconversion emission of Yb3+ under 1550 nm excitation was achieved in Er3+/Yb3+ co-doped NaY(WO4)2 by adjusting Yb3+ doping concentrations. The Yb3+ induced infrared upconversion emission enhancement was attributed to the efficient energy transfer 4I11/2 (Er3+) + 2F7/2 (Yb3+) → 4I15/2 (Er3+) + 2F5/2 (Yb3+) and large nonradiative relaxation rate of 4I9/2. Analysis on the temperature sensing indicated that the NaY(WO4)2:Er3+/Yb3+ serves well the solar cells as thermos-managing material. Moreover, it was confirmed that the fluorescence thermal quenching of 2H11/2/4S3/2 was caused by the nonradiative relaxation of 4S3/2. All the obtained results suggest that NaY(WO4)2:Er3+/Yb3+ is an excellent material for silicon-based solar cells to improve photoelectric conversion efficiency and thermal management.

Electrospun glass nanofibers to strengthen polycarbonate plastic glass toward photoluminescent smart materials

Electrospun glass nanofibers (GNFs) were used to strengthen polycarbonate (PC) to create long-persistent photoluminescent and fluorescent smart materials such as afterglow concrete and smart window. Physical integration of lanthanide-activated aluminate (LA) nanoparticles (NPs) yielded transparent GNFs@PC smart sheets. Spectral investigations utilizing photoluminescence and CIE Lab parameters were performed to confirm that the translucent appearance of GNFs@PC changed to green when exposed to UV light. This fluorescence activity was quickly reversible for the GNFs@PC hybrids with low concentrations of LANPs, which indicate fluorescence emission. Higher phosphor concentrations in GNFs@PC led to longer-lasting afterglow photoluminescence and slower reversibility. The GNFs@PC hybrids showed an emission band detected at 518 nm upon excitation at 368 nm. The morphological characteristics of LANPs and GNFs were analyzed by transmission electron microscopy (TEM), which revealed sizes of 11-26 nm and 250-300 nm, respectively. GNFs were prepared using electrospinning technology and then used as a roughening agent into PC sheets. Morphological characteristics of GNFs and GNFs@PC smart sheets were examined using energy-dispersive X-ray spectroscopy (EDXA), X-ray fluorescence (XRF) and scanning electron microscopy (SEM). The GNFs@PC smart sheets were shown to have enhanced scratch resistance in comparison to LANPs-free PC control sample. Increases in LANPs concentration enhanced both hydrophobicity and UV protection.

Noncovalent Dualism in Perylene-Diimide-Based Keggin Anion Complexes: Theoretical and Experimental studies

We report the synthesis and comprehensive characterization of organic-inorganic hybrid salts formed by bis-cationic N,N'-bis(2-(trimethylammonium)ethylene)perylene-3,4,9,10-tetracarboxylic acid bisimide (PTCD2+) and Keggin-type [XW12O40]n- (X = Si, n = 4; X = P, n = 3) polyoxometalates. (PTCD)3[PW12O40]2·3DMSO·2H2O (2) and (PTCD)2[SiW12O40]·DMSO·2H2O (3) were structurally characterized by single crystal X-ray diffraction. The cations in both structures exhibited infinite chainlike arrangements through π-π interactions, contrasting with the previously reported cation-anion stacking observed in naphthalene diimide derivatives. A detailed theoretical study employing topological analysis of the electron density distribution within the quantum theory of atoms in molecules approach provided further insights into this structural dualism. Atomic force microscopy analyses revealed the formation of self-assembled supramolecular structures on graphite from molecular monolayers (3 nm of thick) to submicrometer aggregates for 2. Hyperspectral Raman spectroscopy imaging revealed that such heterostructures are likely formed by an enhanced π-π interactions. Both complexes demonstrated interesting electrochemical behavior, photoluminescence and X-ray-induced luminescence. Electron spin resonance analysis confirmed charge separation in both compounds, with enhanced efficiency observed in compound 2. Our findings of these perylene-based organic-inorganic hybrid salts offer the potential for their application in optoelectronic devices and functional materials.

Simultaneous magneto-dielectric transitions in a fluorescent Hofmann-type coordination polymer

The design of magnetic molecular materials exhibiting multiple functions has garnered significant interest owing to their potential applications in molecular switches, sensors, and data storage devices. In this study, we synthesized a two-dimensional (2D) FeII-based Hofmann-type coordination polymer, namely {Fe(DPPE)2[Ag(CN)2]2}·2EtOH (1), using a luminescent ligand 1,1-diphenyl-2,2-di(4-pyridylbiphenyl)ethylene (DPPE). Single-crystal structural analyses and magnetic measurements revealed a thermally induced spin crossover (SCO) with the transition temperature T1/2 = 231 K. Variable-temperature fluorescence emission spectra indicated the coexistence of spin crossover and fluorescence properties. Moreover, a pronounced dielectric change (Δε' = 1.2 at 0.5 kHz) was observed during the SCO process, confirming the simultaneous magnetic and dielectric switching arising from the rearrangement of 3d electrons and deformation of the FeII-centered coordination sphere. This work provides an approach to explore the interplay between magnetic, dielectric, and fluorescence properties, and holds significance for developing multifunctional molecular materials.

Multifunctional Crystalline Coordination Polymers Constructed from 4,4'-Bipyridine-N,N'-dioxide: Photochromism, White-Light Emission, and Photomagnetism

Multifunctional photochromic coordination polymers (CPs) have shown great potential in many areas, like molecular switches, anticounterfeiting, magnetics, and optoelectronics. Although multifunctional photochromic CPs can be obtained by introducing photoresponsive functional units or by exploiting the synergy effect of each component, relatively limited photochromic ligands hinder the development of various multifunctional photochromic CPs. In this work, we reported two multifunctional coordination polymers {[Zn(bpdo)(fum)(H2O)2]}n (1) and {[Mn(bpdo)(fum)(H2O)2]}n (2) based on an easily accessible but underestimated photoactive molecule 4,4'-bipyridine-N,N'-dioxide (bpdo). Compound 1 exhibits photochromism and white-light emission with an ultra-high color rendering index (CRI) of 92.1. Interestingly, compound 1 could emit intrinsic white light in the crystalline state upon UV irradiation both before and after photochromism. Meanwhile, compound 2 displays photochromic and photomagnetic properties, induced by the photogenerated radicals via a photoinduced electron transfer mechanism.

Dual Photo-/Electrochromic Pyromellitic Diimide-Based Coordination Polymer

By the combination of N,N'-bis(carboxymethyl)-pyromellitic diimide (H2CMPMD, 1) and zinc ions, a novel PMD-based coordination polymer (CP), [Zn(CMPMD)(DMF)1.5]·0.5DMF (2) (DMF = N,N'-dimethylformamide), has been prepared and characterized. 1 and 2 exhibit completely different photochromic properties, which are mainly reflected in the photoresponsive rate (5 s for 1 vs 1 s for 2) and coloration contrast (from colorless to light green for 1 vs green for 2). This phenomenon should be attributed to the introduction of zinc ions and the consequent formation of the distinct interfacial contacts of electron donors (EDs) and electron acceptors (EAs) (dn-π = 3.404 and 3.448 Å for 1 vs dn-π = 3.343, 3.359, 3.398, and 3.495 Å for 2), suggesting a subtle modulating effect of metal ions on interfacial contacts, photoinduced intermolecular electron transfer (PIET) and photochromic behaviors. Interestingly, the photochromic performance of 2 can be enhanced after the removal of coordinated DMF, which might be ascribed to the decrease of the distance of EDs/EAs caused by lattice shrinkage, which further improves the efficiency of PIET. Meanwhile, 2 displays rapid electrochromic behavior with an obvious reversible color change from colorless to green, which can be used in an electrochromic device. This work develops a new type of EA for the construction of stimuli-responsive functional materials with excellent dual photo-/electrochromic properties.

Multi-Stimuli-Responsive Chromic Behaviors of an All-in-One Viologen-Based Cd(II) Complex

A one-dimensional Cd(II) chain coordination polymer constructed by an electron-deficient viologen-anchored carboxylate ligand was successfully synthesized. Owing to the favorable stimuli-chromic properties of viologen, the title compound shows reversible photochromism, thermochromism, electrochromism, and naked-eye-detectable differentiable vapochromic response to different volatile amines. The chromic behaviors of it are ascribed to the formation of viologen radicals triggered by external stimuli. And the differentiated response to volatile amines is attributed to the size effect of the amines as well as the steric hindrance effect of forming α/β Cv-H···Namines interactions of the viologen unit to further affect the occurrence of electron transfer. Such an all-in-one crystalline material might have more practical applications in photoelectric, erasable inkless printing, light printing, and volatile amine detection fields.

The effect of conjugation degree of aromatic carboxylic acids on electronic and photo-responsive behaviors of naphthalenediimide-based coordination polymers

Three novel naphthalenediimide-based (NDI-based) coordination polymers (CPs), namely [Cd(3-PMNDI)(2,2'-BPDC)] (1), [Cd2(3-PMNDI)1.5(4,4'-BPDC)2(H2O)3]·DMF (2) and [Cd(3-PMNDI)(4,4'-SDC)] (3) (2,2'-H2BPDC = 2,2'-biphenyldicarboxylic acid, 4,4'-H2BPDC = 4,4'-biphenyldicarboxylic acid, 4,4'-H2SDC = 4,4'-stilbenedicarboxylic acid, 3-PMNDI = N,N'-bis(3-pyridylmethyl)-1,4,5,8-naphthalenediimide, and DMF = N,N'-dimethylformamide), have been designed and synthesized here from electron-deficient PMNDI (electron acceptors, EAs) and electron-rich aromatic carboxylic acids (electron donors, EDs) in the presence of cadmium ions. The introduction of aromatic carboxylic acids with different sizes and conjugation degrees leads to the generation of a two-dimensional (2D) layer in 1, a two-fold interpenetrated three-dimensional (3D) network in 2 and an eight-fold interpenetrated 3D framework in 3. Furthermore, the use of distinct electron-donating aromatic carboxylic acids and the consequent different numbers and strengths of lone pair-π and π-π interactions in the interfacial contacts of EDs/EAs give rise to distinct intermolecular charge transfer (ICT) and initial colors of the three CPs, and consequently cause different photoinduced intermolecular electron transfer (PIET) and distinguishing photo-responsive behaviors (weak photochromic performance for 1, excellent photochromic properties for 2 and non-photochromism for 3). This study indicates that an appropriate ICT is beneficial for PIET, but too weak or too strong ICT is not conducive to PIET, which provides an effective strategy for the construction of functional CPs with distinguishing photo-responsive properties through the subtle balance of ICT and PIET.

Controlling Isomerization of Photoswitches to Modulate 2D Logic-in-Memory Devices by Organic-Inorganic Interfacial Strategy

Logic-in-memory devices are a promising and powerful approach to realize data processing and storage driven by electrical bias. Here, an innovative strategy is reported to achieve the multistage photomodulation of 2D logic-in-memory devices, which is realized by controlling the photoisomerization of donor-acceptor Stenhouse adducts (DASAs) on the surface of graphene. Alkyl chains with various carbon spacer lengths (n = 1, 5, 11, and 17) are introduced onto DASAs to optimize the organic-inorganic interfaces: 1) Prolonging the carbon spacers weakens the intermolecular aggregation and promotes isomerization in the solid state. 2) Too long alkyl chains induce crystallization on the surface and hinder the photoisomerization. Density functional theory calculation indicates that the photoisomerization of DASAs on the graphene surface is thermodynamically promoted by increasing the carbon spacer lengths. The 2D logic-in-memory devices are fabricated by assembling DASAs onto the surface. Green light irradiation increases the drain-source current (I_ds ) of the devices, while heat triggers a reversed transfer. The multistage photomodulation is achieved by well-controlling the irradiation time and intensity. The strategy based on the dynamic control of 2D electronics by light integrates molecular programmability into the next generation of nanoelectronics.

Incorporating Photochromic Viologen Derivative to Unprecedentedly Boost UV Sensitivity in Photoelectrochromic Hydrogel

Developing ultraviolet (UV) radiation sensors featuring high sensitivity, ease of operation, and rapid readout is highly desired in diverse fields. However, the strategies to enhance sensitivity of UV detection remain limited particularly for photochromic materials, which show colorimetric response toward UV irradiation. Guided by our initial goal of facilitating easier handling, we formulated a viologen derivative ([H₂L]-SC) incorporating hydrogel-based UV sensor which not only inherits the photochromism of [H₂L]-SC but also engenders an unprecedented reversible photoelectrochromic response that is absent in either [H₂L]-SC or hydrogel alone. Judicious synergy between photochromic [H₂L]-SC and polyacrylamide (PAM) converts the colorimetric response of [H₂L]-SC into the electrical resistance change of [H₂L]-SC@PAM, which amplifies the UV sensitivity of [H₂L]-SC by 2 orders of magnitude. Explicitly, the limit of detection (LOD) for UV decreases from 296.3 mJ/cm² based on the UV-vis absorption spectra of [H₂L]-SC to 2.83 mJ/cm² derived from the resistance variation of [H₂L]-SC@PAM. Moreover, linear correlation between the resistance reduction rate of [H₂L]-SC@PAM and UV dose rate can be established, rendering it as a dual platform for quantifying both the accumulated UV dose and the instant dose rate. In addition, the proposed strategy based on constructing photoelectrochromic hybrids offers a new pathway to boost the UV sensitivity that could be universal for other photochromic materials.

Mussel-Inspired Two-Dimensional Halide Perovskite Facilitated Dopamine Polymerization and Self-Adhesive Photoelectric Coating

Polydopamine (PDA) is a good adhesion agent for lots of gels inspired by the mussel, whereas hybrid organic-inorganic perovskites (HOIPs) usually exhibit extraordinary optoelectronic performance. Herein, mussel-inspired chemistry has been integrated with two-dimensional HOIPs first, leading to the preparation of new crystal (HDA)₂PbBr₄ (1) (DA = dopamine). The organic cation dopamine can be introduced into PDA resulting in a thin film of (HPDA)₂PbBr₄ (PDA-1). The dissolved inorganic components of layered perovskite in DMF solution together with H₂O₂ addition can facilitate DA polymerization greatly. More importantly, PDA-1 can inherit an excellent semiconductor property of HOIPs and robust adhesion of the PDA hydrogel resulting in a self-adhesive photoelectric coating on various interfaces.

Preparation of Lighting in the Dark and Photochromic Electrospun Glass Nanofiber-Reinforced Epoxy Nanocomposites Immobilized with Alkaline Earth Aluminates

Alkaline earth aluminates (AEAs) as photoluminescent agents and silicon dioxide-based electrospun glass nanofibers with an average diameter of 150-450 nm as a roughening agent were prepared and applied to reinforce an epoxy resin toward the development of long-persistent photoluminescent and photochromic smart materials, such as smart windows and anticounterfeiting barcodes. With the physical immobilization of lanthanide-doped aluminate nanoparticles (NPs), a light-induced luminescent transparent glass@epoxy film was developed. The glass@epoxy samples were able to alter their color to green beneath ultraviolet rays and greenish-yellow in the dark, as explored by CIE Lab and luminescence spectral analyses. The morphology of the lanthanide-doped aluminate nanoparticles (43-98 nm) was examined by transmission electron microscopy (TEM). The morphologies and chemical composition of the luminescent glass@epoxy substrates were determined by different analytical techniques. The mechanical properties of the developed photoluminescent glass@epoxy substrates were inspected to show improved scratch resistance as compared to the AEA-free substrate. The photoluminescence spectra were measured to indicate the detection of two emission bands at 494 and 525 nm when excited at 365 nm. The photoluminescent glass@epoxy hybrids with lower AEA contents have showed fast reversibility of photochromism. On the other hand, the glass@epoxy substrates with higher phosphor contents underwent persistent luminescence. Results showed that the luminescent colorless glass@epoxy hybrids have enhanced superhydrophobicity and ultraviolet blocking.