Self‐healing ability is an important survival feature in nature, with which living beings can spontaneously repair damage when wounded. Inspired by nature, people have designed and synthesized many ...self‐healing materials by encapsulating healing agents or incorporating reversible covalent bonds or noncovalent interactions into a polymer matrix. Among the noncovalent interactions, the coordination bond is demonstrated to be effective for constructing highly efficient self‐healing polymers. Moreover, with the presence of functional metal ions or ligands and dynamic metal–ligand bonds, self‐healing polymers can show various functions such as dielectrics, luminescence, magnetism, catalysis, stimuli‐responsiveness, and shape‐memory behavior. Herein, the recent developments and achievements made in the field of self‐healing polymers based on coordination bonds are presented. The advantages of coordination bonds in constructing self‐healing polymers are highlighted, the various metal–ligand bonds being utilized in self‐healing polymers are summarized, and examples of functional self‐healing polymers originating from metal–ligand interactions are given. Finally, a perspective is included addressing the promises and challenges for the future development of self‐healing polymers based on coordination bonds.
Coordination bonds have been demonstrated to be effective for constructing self‐healing polymers in recent years. The advantages of coordination bonds in constructing self‐healing polymers are discussed, and the various metal–ligand bonds being utilized in self‐healing polymers along with some examples of functional self‐healing polymers originating from metal–ligand interactions are summarized. A few concerns and future directions in this research field are proposed.
Research summary: Departing from the extant literature, which assumes that firms pursue strong environmental performance as a differentiation strategy, we analyze the general relationship between ...firms' competitive strategy and their response to heightened market competition. We find that, using a large sample of Chinese manufacturing firms between 2000 and 2005, intensified market competition has an overall negative impact on firms' environmental performance. The negative impact is exacerbated in firms adopting a cost-leadership strategy, but is attenuated in those adopting a differentiation strategy. The results emphasize the importance of including an examination of the particular competitive strategies chosen by firms in seeking to understand the impact of intensified market competition. Managerial summary: Advocates of corporate social responsibility (CSR) have long argued for the differentiation role of CSR. However, managers may be misguided if the assumed benefits of differentiation critically depend on certain presumptions. In the Chinese context and focusing on the environmental dimension of CSR, our study finds a negative relationship between market competition and corporate environmental performance. It suggests that firms, to a large extent, cannot escape competition via environmental differentiation. Managers should therefore be cautious about the value of strategic investment in CSR as a viable competitive device.
A composite material, {Fe(L)(TPPE)0.5⋅3 CH3OH}n, has been constructed by integrating the spin‐crossover (SCO) subunit ...FeII{diethyl(E,E)‐2,2′‐1,2‐phenyl‐bis(iminomethylidyne)bis(3‐oxobutanoate)‐(2‐)‐N,N′,O3,O3′} and the highly luminescent connector 1,1,2,2‐tetrakis(4‐(pyridin‐4‐yl)phenyl)‐ethene. Its structure contains four staggered 4×4 layers and intercalated methanol. The packing is dominated by considerable H‐bonds either between adjacent layers and between layers and guests. A crystal‐structure transformation was detected upon removal of the guest molecules. The SCO transition of the solvated crystals is centered at ca. 215 K with a non‐symmetrical hysteresis of 25 K wide, and the desolvated Fe(L)(TPPE)0.5n exhibits gradual SCO without hysteresis. Intriguingly, the intensity of the fluorescence at 460 nm for the latter is maximized at the SCO transition. The energy transfer between luminescent and SCO entities is achievable as confirmed by theoretical calculations.
A square‐grid layered FeII coordination polymer based on a luminophore connector TPPE was studied. This framework not only features a solvent‐dependent structure and spin crossover (SCO) behavior, but also exhibits a switch between spin transition and fluorescence for the guest‐free species. Theoretical calculation reveals an energy‐transfer mechanism.
Using an external stimulus to modulate the electronic structure of covalent organic frameworks (COFs) is very important because such a response will endow them with additional functions. A ...two‐dimensional (2D) COF, constructed from a photo‐responsive unit (1,2‐bis(5‐formyl‐2‐methylthien‐3‐yl)cyclopentene), can reversibly switch its electrical conductivity 200 times from low state (the open form) to high state (the closed form) upon irradiation with UV light and reversible with visible light. This reversible phenomenon can be monitored through a circuit containing a light‐emitting diode (LED). Photoinduced ring‐closing/opening reactions do not destroy the integrity of the frameworks, and both processes follow logarithmic carrier generation with time. Moreover, the correlation between COFs electronic properties and changes in photoinduced kinetics and absorption curves has been demonstrated.
Two‐dimensional COFs that are photostimulus‐responsive exhibit a change of electrical conductivity as a function of the photon energy. The modulation of electronic structures of COFs, associated with ring closing and opening, is visualized by the on/off of a light‐emitting diode (LED) owing to the corresponding variation in electrical conductivity.
Metal-organic frameworks (MOFs) that respond to external stimuli such as guest molecules, temperature, or redox conditions are highly desirable. Herein, we coupled redox-switchable properties with ...breathing behavior induced by guest molecules in a single framework. Guided by topology, two flexible isomeric MOFs, compounds 1 and 2, with a formula of In(Me
NH
)(TTFTB), were constructed via a combination of In(COO)
metal nodes and tetratopic tetrathiafulvalene-based linkers (TTFTB). The two compounds show different breathing behaviors upon the introduction of N
. Single-crystal X-ray diffraction, accompanied by molecular simulations, reveals that the breathing mechanism of 1 involves the bending of metal-ligand bonds and the sliding of interpenetrated frameworks, while 2 undergoes simple distortion of linkers. Reversible oxidation and reduction of TTF moieties changes the linker flexibility, which in turn switches the breathing behavior of 2. The redox-switchable breathing behavior can potentially be applied to the design of stimuli-responsive MOFs.
Organic long persistent luminescence (OLPL) materials with afterglow duration in the scale of minutes or even hours are still rare. Most OLPL systems are based on exciplexes, which require ...complicated multi‐component system in order to realize white afterglow but with slightly compromised duration and color stability. In this work, OLPLs lasting from 20 to 40 minutes are realized in a simple binary system based on two‐photon ionization mechanism, which can simultaneously harvest excitons from both singlet and triplet excited states, making it potentially one of the most promising candidates to achieve stable white OLPL. Through modulation and optimization of dopant molecules in dibenzob,dthiophen‐2‐yldiphenyl phosphine oxide host, the emission profiles of afterglow can be readily tuned from cyan (0.19, 0.22), cold white (0.31, 0.35), standard white (0.33, 0.33) to warm white (0.31, 0.46), with excellent color consistency.
Organic long persistent luminescence with afterglow lasting up to 20–40 minutes was achieved based on two‐photon ionization mechanism at room temperature in a simple binary system. Through modulation of molecular structures and potential ISC channels between excited states, the afterglow profiles can be rationally tuned from cyan (0.19, 0.22), cold white (0.31, 0.35), standard white (0.33, 0.33) to warm white (0.31, 0.46).
Abstract
Electrochromic (EC) materials with a dark-to-transmissive switch have great applications in optical communications, infrared wavelength detectors for spacecraft, and infrared camouflage ...coatings. However, such electroactive materials with high stability and cyclability are rare. Considering the advantages of the donor-acceptor approach (wide-range tuneable band position) and porous two-dimensional (2D) covalent organic framework (COF, well-ordered crystalline framework with stable structure and high surface area), in this work we constructed an extended delocalised π-electron layered dark purple EC-COF-1 by reacting the donor N,N,N′,N′-tetrakis(
p
-aminophenyl)-
p
-benzenediamine (TPBD) with the acceptor 2,1,3-benzothiadiazole-4,7-dicarboxaldehyde (BTDD). A sandwiched device made of EC-COF-1 exhibits the two-band bleaching (370 nm and 574 nm) in the visible region and becomes transparent under the applied potential with an induced absorption centring at 1400 nm. This discovery of a stable dark-to-transmissive switch in COF might open another door for their application in many EC devices for various purposes.
A series of stable radical 2D metal‐organic frameworks has been assembled. (m‐TTFTB)3 (m‐Tetrathiafulvalene‐tetrabenzoate) trimer building blocks are beneficial for the stability of the radicals due ...to delocalization of the unpaired electron. Hexanuclear rare‐earth‐cluster‐based 1D chains further enhance the stability of the frameworks. The radical state of the middle TTF in the trimer has been observed by the change of central C−C and C−S bond distances and the configuration of the TTF by single‐crystal X‐ray diffraction. The radical characteristics are also confirmed by electron paramagnetic resonance, UV/Vis–NIR absorption, and X‐ray photoelectron spectroscopy experiments. Stability tests showed that the radicals are stable even in solutions and under acid/base environments (pH 1–12). Owing to efficient light absorption due to intramolecular charge transfer, low thermal conductivity, and outstanding stability, the radical 2D Dy‐MOF shows excellent photothermal properties, an increase of 34.7 °C within 240 s under one‐sun illumination.
The incorporation of TTF radical trimers and RE6 cluster SBUs result in a stable 2D radical MOF that is stable under harsh conditions including aqueous acid/base solutions. Exhibiting the characteristics of light absorption and excellent stability, the radical Dy‐MOF shows excellent photothermal conversion with an increase in temperature of 34.7 °C upon irradiation by one unit of sunlight within 240 s.
A major challenge is the development of multifunctional metal–organic frameworks (MOFs), wherein magnetic and electronic functionality can be controlled simultaneously. Herein, we rationally ...construct two 3D MOFs by introducing the redox active ligand tetra(4‐pyridyl)tetrathiafulvalene (TTF(py)4) and spin‐crossover FeII centers. The materials exhibit redox activity, in addition to thermally and photo‐induced spin crossover (SCO). A crystal‐to‐crystal transformation induced by I2 doping has also been observed and the resulting intercalated structure determined. The conductivity could be significantly enhanced (up to 3 orders of magnitude) by modulating the electronic state of the framework via oxidative doping; SCO behavior was also modified and the photo‐magnetic behavior was switched off. This work provides a new strategy to tune the spin state and conductivity of framework materials through guest‐induced redox‐state switching.
A 3D FeII metal–organic framework (MOF) based on the tetrathiafulvalene tetrapyridyl ligand and its I2‐doped analogue were prepared. The TTF moieties provide redox activity, and I2 doping improves the conductive properties. Doping or light irradiation significantly alters the magnetic properties, indicating the material has electronically and photo‐switchable spin‐crossover properties.
There is often a trade-off between mechanical properties (modulus and toughness) and dynamic self-healing. Here we report the design and synthesis of a polymer containing thermodynamically stable ...whilst kinetically labile coordination complex to address this conundrum. The Zn-Hbimcp (Hbimcp = 2,6-bis((imino)methyl)-4-chlorophenol) coordination bond used in this work has a relatively large association constant (2.2 × 10
) but also undergoes fast and reversible intra- and inter-molecular ligand exchange processes. The as-prepared Zn(Hbimcp)
-PDMS polymer is highly stretchable (up to 2400% strain) with a high toughness of 29.3 MJ m
, and can autonomously self-heal at room temperature. Control experiments showed that the optimal combination of its bond strength and bond dynamics is responsible for the material's mechanical toughness and self-healing property. This molecular design concept points out a promising direction for the preparation of self-healing polymers with excellent mechanical properties. We further show this type of polymer can be potentially used as energy absorbing material.
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