Recently, smart 2D covalent organic frameworks (COFs), combining the advantages of both inherent structure features and functional building blocks, have been demonstrated to show reversible changes in conformation, color, and luminescence in response to external stimuli. This review provides a summary on the recent progress of 2D COFs that are responsive to external stimuli such as metal ions, gas molecules, pH values, temperature, electricity, light, etc. Moreover, the responsive mechanisms and design strategies, along with the applications of these stimulus‐responsive 2D COFs in chemical sensors and photoelectronic devices are also discussed. It is believed that this review would provide some guidelines for designing novel single‐/multistimulus‐responsive 2D COFs with controllable responsive behaviors for advanced photoelectronic applications.

An efficient strategy is reported to achieve rewritable and multi-level security printing based on the emission intensity and lifetime switching caused by manipulating the dynamic ionic coordination of Mn(II) complexes. Confidential information can be repeatedly printed on the fabricated security paper by controlling the dynamic ionic interaction of Mn(II) complexes. Moreover, multilevel security printing has been achieved through dynamically tuning the emission lifetimes of the Mn(II) complexes.

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Rewritable paper has recently become prevalent in both academic research and marketplace due to the potential environmental advantages, including forest conservation, pollution reduction, energy saving and resource sustainability. However, its real-life applications are limited by a lack of effective strategy to realize multicolour and water-jet printing on rewritable paper with long legible image-lasting times. Herein, we report an effective strategy to construct rewritable paper based on colour or luminescence switching induced by dynamic metal–ligand coordination. This type of rewritable paper can be conveniently utilized for multicolour water-jet printing by using aqueous solutions containing different metal salts as ink. In addition, the printed images on the water-jet rewritable paper can be retained for a long time (> 6 months), which shows great progress compared to previous work. We believe that this type of rewritable paper could be considered as a prototype for multicolour water-jet printing to meet the practical needs.

coupling effect induced by heavy-metal atoms. [5,6] For example, noble metal-based phosphors including iridium(III) complexes, [7][8][9][10][11][12][13][14][15][16] platinum(II) complexes, [17][18][19][20] and gold(III) complexes [21,22] have been widely used in phosphorescent OLEDs (PhOLEDs). However, these noble metals suffer from the low abundance and high cost. Hence, the relatively abundant, lowcost, and low-toxic phosphorescent metal complex have been drawing great interests for PhOLEDs.Recent explorations of phosphorescent manganese(II) complexes appear to be a new and attractive alternative toward highly efficient PhOLEDs. The manganese(II) complexes display strong photoluminescence in solid state originating from the metal-centered d-d ( 4 T 1 (G) → 6 A 1 ) radiative transition. [23][24][25] The well-known green light-emitting manganese(II) complexes are ionic compounds consisting of organic cations and inorganic tetrahalogenomanganate(II) anions. [26,27] Attributed to their excellent solid-state photophysical properties, this kind of organic-inorganic hybrid complexes have exhibited promising optoelectronic applications. For example, Chen and co-workers have realized the solution-processed PhOLEDs based on the ionic tetrabromide manganese(II) complex ((Ph 4 P) 2 (MnBr 4 )) as an emitting dopant, the external quantum efficiency (EQE) of this device can reach 9.6% for the doped OLEDs. [28] However, the ionic manganese(II) complexes often suffer from low stability and can be easily hydrolyzed Phosphorescent transition-metal complexes have played the vital role in the rapid development of organic light-emitting diodes (OLEDs) as the most promising candidates for next-generation flat-panel display and solid-state lighting techniques. In this work, novel and low-cost phosphorescent neutral tetrahedral manganese(II) complexes (DBFDPO-MnX 2 , X = Br, or Cl) based on dibenzofuran-based phosphine oxide derivative as ligand are designed and synthesized. The manganese(II) complexes exhibit intense green phosphorescence with high photoluminescence quantum yields (PLQYs) of as high as 81.4% (DBFDPO-MnBr 2 ). Using complex DBFDPO-MnBr 2 as dopant, a green OLED with current efficiency (CE max ) of 35.47 cd A −1 , power efficiency (PE max ) of 34.35 lm W −1 , and external quantum efficiency (EQE max ) of 10.49% is fabricated. Interestingly, red exciplex emission is also observed in electroluminescence, arising from the interaction between the host materials (bis(2-(2-hydroxyphenyl)-pyridine)beryllium (Bepp 2 ) or 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBi)) and the dopant (DBFDPO-MnBr 2 ).The exciplex-based red OLED in this study exhibits the maximum CE and PE reaching 18.64 cd A −1 and 17.92 lm W −1 , respectively, which are among the up-to-date highest values for exciplex-based red OLEDs. Beneficial from the exciplex, it has the great potential to broaden the electroluminescent spectra with manganese(II) complex. Phosphorescent OLEDsThe ORCID identification number(s) for the author(s) of this article can be fou...

Climate change and overgrazing are believed by policy makers to have been the drivers of grassland degradation in China over the past thirty years. However, recent work has suggested that policies that have led to privatization of use rights and household enclosures are more important drivers of degradation. An analysis of available evidence from scientifi c publications and national survey data relating to climate change, livestock numbers, and management policy was undertaken to evaluate the case for each of these possible drivers of degradation. The analysis suggests that, to date, policy measures imposed to avoid the 'tragedy of the commons' have been more important than either climate change or overgrazing as a driver of degradation. The resulting fragmentation of the pastoral landscape has caused localized grazing pressure and spatial and temporal mismatches between grassland production and livestock access to forage. Grazing rights negotiated and allocated at a multiplehousehold level would allow greater productivity, better rangeland condition, possible advantages of scale and pooling of herder resources, and better potential to adapt to future climate change.

bioimaging, [3] and anti-counterfeiting applications. [4] Pure organic OPRTP materials are more attractive compared to the transition metal or rare earth-based phosphorescent materials owing to their low production cost, easy synthesis, low toxicity, and good flexibility. [5] However, OPRTP is rare in pure organic molecules because of the forbidden transition from singlet to triplet excited states. The reported metal-free OPRTP materials are usually substituted with aromatic carbonyl groups [6] or heavy atoms [7] to facilitate the intersystem crossing (ISC) process, while crystallization, [8] host-guest interaction, [9] and polymer doping [10] are utilized to suppress the nonradiative decay and stabilize the triplet states.Solid-state phosphorescence is highly dependent on molecular stacking, such as aggregation-caused quenching. [11] Recently, OPRTP has been observed in H- [8a] or J-aggregates, [12] while the influence of T-shaped (edge-to-face) arrangement on phosphorescence has been rarely discussed. Published work mainly focused on the stabilization of triplet excited states by molecular packing, but packing-induced intermolecular charge transfer received less attention in OPRTP materials although it strongly affected ISC efficiency and the energy gap (ΔE ST ) between singlet and triplet excited states. [3c,13] Polycyclic π-conjugated compounds, such as indolo[3,2-b] carbazoles (ICZs) and their analogues, are important organic semiconductors, which have been widely used in organic optoelectronic fields, such as organic field-effect transistors and photovoltaic cells, owing to their excellent carrier transporting properties. [14] In this work, 6,12-diphenyl-5,6,11,12tetrahydroindolo[3,2-b]carbazole (Ben-H, Figure 1), one of the ICZ analogues, unexpectedly exhibited OPRTP after the cease of UV light irradiation. Unlike most reported OPRTP materials, there were no commonly used groups such as aromatic carbonyl groups or heavy atoms in Ben-H. Based on the energy level diagram and single-crystal structure of Ben-H, we hypothesized that charge transfer (CT) played a dominant role in persistent emission (Figure 2). In the isolated molecular state, intramolecular charge transfer (ICT) from the indole rings to the benzene rings gave rise to the ISC process with narrow ΔE ST energy gap, while in the dimers, T-shaped CH···π interactions induced Organic persistent room-temperature phosphorescence (OPRTP) materials show great prospects in optoelectronic and biomedical applications, such as display, anti-counterfeiting, sensing, and bioimaging. However, the reported OPRTP material systems are relatively rare, and it is a challenge to achieve the tunability of OPRTP. In this work, a series of polycyclic luminophores are developed based on an indole derivative (6,12-diphenyl-5,6,11,12tetrahydroindolo[3,2-b] carbazole, Ben-H) as the structural skeleton. These compounds unexpectedly exhibit dual OPRTP at 442 to 623 nm with lifetimes spanning from 2 to 759 ms. Experimental data and theoretical calculations suggest th...

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