The emergence of smart windows has been a pivotal innovation in the field of energy efficiency and carbon emission reduction, sparking considerable interest worldwide. This review consolidates the latest research developments in inorganic-based photochromic materials for smart windows applications, encompassing the design of device architectures, and their implementation in enhancing energy conservation, augmenting comfort levels, and optimizing indoor environmental control. Finally, this review culminates in an insightful analysis of the challenges and constraints in the existing research landscapes, which illuminates guidance for the directions and perspectives of future research.
Despite extensive research on piezoelectric polymers since the discovery of piezoelectric poly(vinylidene fluoride) (PVDF) in 1969, the fundamental physics of polymer piezoelectricity has remained elusive. Based on the classic principle of piezoelectricity, polymer piezoelectricity should originate from the polar crystalline phase. Surprisingly, the crystal contribution to the piezoelectric strain coefficient d31 is determined to be less than 10%, primarily owing to the difficulty in changing the molecular bond lengths and bond angles. Instead, >85% contribution is from Poisson’s ratio, which is closely related to the oriented amorphous fraction (OAF) in uniaxially stretched films of semicrystalline ferroelectric (FE) polymers. In this perspective, the semicrystalline structure–piezoelectric property relationship is revealed using PVDF-based FE polymers as a model system. In melt-processed FE polymers, the OAF is often present and links the crystalline lamellae to the isotropic amorphous fraction. Molecular dynamics simulations demonstrate that the electrostrictive conformation transformation of the OAF chains induces a polarization change upon the application of either a stress (the direct piezoelectric effect) or an electric field (the converse piezoelectric effect). Meanwhile, relaxor-like secondary crystals in OAF (SCOAF), which are favored to grow in the extended-chain crystal (ECC) structure, can further enhance the piezoelectricity. However, the ECC structure is difficult to achieve in PVDF homopolymers without high-pressure crystallization. We have discovered that high-power ultrasonication can effectively induce SCOAF in PVDF homopolymers to improve its piezoelectric performance. Finally, we envision that the electrostrictive OAF mechanism should also be applicable for other FE polymers such as odd-numbered nylons and piezoelectric biopolymers.
One of the long-sought-after goals in responsive material development is to generate and tune colors for advanced and emerging applications such as dynamic displays, light-emitting diodes, lasers, smart windows, chromic fabrics, high-security encryption, and visual sensors. Benefiting from the atomically thin nature as well as strong optical interaction, two-dimensional (2D) materials can serve as color-generating centers for both chemical pigment colors and physical interference colors in solution, gels, films, and matrix interface systems, to offer new promises for color science and applications. Concerning color tunability, 2D material systems have been demonstrated as one of the ideal responsive materials to achieve the desired goals, including the change of composition, layer thickness, strain, magic angle, and thermally/photically/chemically responsive, magnetically-responsive, electrically-responsive, mechanically-responsive. This makes it an attractive prospect for device applications such as optoelectronics, displays, and nanomedicine. However, to the best of our knowledge, no comprehensive review has been reported specifically on color-centered aspects of 2D materials. In this review, we highlight experimental approaches and related applications for tuning pigment colors, reflective structural colors, and transmissive interference colors, and we refine the challenges and propose opportunities in future studies for the further development of color science in the 2D material system. Eventually, it is anticipated that this review will serve as a resource and source of inspiration for scientists, as well as open up new avenues for the advancement of color science and related fields in responsive 2D material systems.
Over the past decade, 4D printing has revolutionized the field of advanced manufacturing by fabricating structures that dynamically respond to environmental stimuli. During this process, shape-memory polymers (SMPs) stand out, enabling transformations triggered by temperature, light, or other environmental factors, and show great potential for applications in biomedicine and beyond. Notably, biodegradable SMPs offer a compelling advantage in medical devices due to their ability to adapt within the body’s temperature range and to be absorbed by tissues, reducing the risks associated with permanent implants. While extrusion techniques have laid the groundwork for 4D printing in biomedicine, vat photopolymerization methods like stereolithography and digital light processing are now at the forefront, favored for their high printing resolution and flexibility in material design. However, the search for suitable biodegradable materials for these advanced techniques continues, with current research focusing on developing systems that meet both the mechanical demands and degradation profiles required for medical applications. This review aims to critically analyze the advancements in biodegradable 4D photopolymers, particularly biodegradable elastomers, and discuss the challenges that lie ahead for their clinical translation.
Room-temperature phosphorescence (RTP) materials have attracted significant attention due to their applications in various fields such as information storage and encryption, organic light-emitting diode (OLED), sensing, lighting and display, biological imaging, and photodynamic therapy. Traditionally, RTP materials can be efficiently developed using inorganic systems with noble metals or rare earth elements. Recently, many efforts have been devoted to the development of RTP materials based on small organic molecules. The strategies to construct RTP materials include hydrogen bonding, heavy atom effect, n–π* transitions, π–π stacking, donor–acceptor effect, and host–guest doping. Herein, we summarize the recent examples of RTP materials based on small organic molecules primarily focusing on their design strategies and properties. Moreover, their promising applications in information encryption, OLED, as well as bio-imaging and phototherapy are discussed. The challenges and perspectives are given to provide inspiration toward the future development of organic RTP materials.
In recent years, the advances in light-responsive soft materials with fascinating properties and functions have attracted tremendous attention, which are also enlightening when attempting to achieve the goals of complex deformations, motions, or attractive applications by precise regulation. Attractively, light is not only a clean and inexhaustible energy but also can be controlled remotely, quickly and accurately in a non-contact way. Moreover, light-responsive soft materials are capable of amplifying photo-triggered molecular changes at the microscopic scale into macroscopic deformations, that is, directly converting the input light energy into the output mechanical work, therefore enabling potential applications in the field of actuators and functional devices. To date, some wonderful reviews have reported the progress in photo-driven soft materials. However, the research progress in ultraviolet, visible (Vis) and near-infrared (NIR) light-driven soft materials containing azobenzene or other non-azobenzene moieties has not been reported yet. In this review, we summarize recent progress in light-responsive soft materials in terms of preparation methods, response wavelengths and potential applications. Firstly, the preparation methods of photoresponsive soft materials are introduced. Subsequently, photoinduced macroscopic deformations or motions are summarized, in which Vis and NIR light-responsive behaviors are especially highlighted. Finally, the potential applications of photoresponsive soft materials are classified. To guide the future work for researchers, the existing problems and future development prospects of light-responsive soft materials are proposed.
Ultrasound-induced circularly polarized luminescence (CPL) was achieved using planar chiral, binuclear clothespin-shaped trans-bis(salicylaldiminato)platinum(II) complexes. Solutions of the clothespin-shaped platinum(II) complexes anti-1a–c in cyclohexane immediately transformed into stable gels upon brief ultrasound irradiation. The ultrasound gels exhibited intense phosphorescent emissions at room temperature, whereas none of the solution exhibited significant emissions under UV light illumination. Interestingly, gels prepared from optically pure complexes exhibited CPL activity at room temperature with an anisotropy factor of |glum| = 1.5–2.6 × 10-3. The emissive gels were readily converted to the original non-emissive solution upon heating and cooling to room temperature and could be gelled again by ultrasound irradiation. In addition, chromogenic control from green to red emission can be achieved simply by introducing MeO groups at different positions on the aromatic rings.
The quest for mechanoluminescence (ML) in zinc sulfide (ZnS) spans more than a century, initially sparked by observations of natural minerals. There has been a resurgence in research into ML materials in recent decades, driven by advances in optoelectronic technologies and a deeper understanding of their luminescent properties under mechanical stress. ZnS, in particular, has garnered attention owing to its remarkable ability to sustain luminescence after more than 100,000 mechanical stimulations, positioning it as a standout candidate for optoelectronic applications. In contrast to conventional photoluminescent and electroluminescent light sources, ZnS composite elastomers have emerged as flexible, stretchable self-powered light sources with considerable practical implications. This review introduces the development history, ML mechanisms, prototype ML devices, ZnS-based ML material preparation methods, and their diverse applications spanning environmental mechanical-to-optical energy conversion, E-signatures, anti-counterfeiting, wearable information sensing devices, advanced battery-free displays, biomedical imaging, and optical fiber sensors for human–computer interactions, among others. By integrating insights from ML-optics, mechanics, and flexible optoelectronics, and by summarizing pertinent perspectives on current scientific challenges, application technology hurdles, and potential solutions for emerging scientific frontiers, this review aims to furnish fundamental guidance and conceptual frameworks for the design, advancement, and cutting-edge application of novel mechanoluminescent materials.