Passivation of Organic-Inorganic Hybrid Perovskite with Poly(lactic Acid) to Achieve Stable Red-Light Flexible Films.

Low-dimensional organic-inorganic hybrid perovskites (OIHPs) have shown significant potential in the optoelectronic field due to their adjustable structure and properties. However, the poor air stability and flexibility of the OIHP crystals limit their further development. Herein, three OIHP crystals have been synthesized using cadmium chloride and the isomer of phenylenediamine as raw materials. Mn2+ doping turns on the red-light emission of Cd-based OIHPs at around 625 nm. Interestingly, the organic ligands with different steric hindrance can induce a transition of the OIHP structure from two dimensions (2D) to one dimension (1D), thereby regulating the quantum yield of red luminescence in the range of 38.4% to nearly 100%. It is found that the surface-exposed amino groups are easy to oxidize, resulting in the instability of these OIHP crystals. Therefore, poly(lactic acid) (PLA) is selected to passivate OIHPs through hydrogen bonding between C═O of PLA and -NH2 on the surface of OIHPs. As a result, the production of OIHP-based flexible films with highly efficient and stable red emission can be obtained after being encapsulated by PLA. They demonstrate enormous application potential in flexible X-ray imaging. This study not only realizes stable perovskite films but also provides an effective design idea for red flexible scintillators.

Anionic Hydrogen-Bonded Frameworks Showing Tautomerism and Colorful Luminescence for the Ultrasensitive Detection of Acetone.

Tautomers coexisting in an equilibrium system have significant potential for regulating luminescent properties because of their structural differences. However, separating and stabilizing tautomers at room temperature is a considerable challenge. In this study, it is found that hydrogen-bonded organic frameworks (HOFs) composed of Br- anions can effectively separate and stabilize two proton-transfer tautomers of triarylformamidinium bromide: namely, the nitrogen cation (BA-N) and carbon cation (BA-C). The BA-N crystal consisting of a dense anionic HOF and parallelly aligned organic cations exhibits green thermally activated delayed fluorescence and red room-temperature phosphorescence (RTP). The BA-C crystal contains acetone molecules that induce an antiparallel arrangement of the organic cations to form a loose HOF, producing blue prompt fluorescence and green RTP. Interestingly, switching of the HOFs between BA-N and BA-C can be achieved through the uptake and release of acetone, thereby dynamically adjusting multiple luminescent properties. Consequently, the HOF crystals can be used for the highly sensitive and specific sensing of acetone with a detection limit of 66.74 ppm. This study not only stabilizes tautomeric luminescent materials at room temperature, but also provides a new method for constructing smart HOFs with a sensitive response to a stimulus.

Multiexciton Generation from a 2D Organic-Inorganic Hybrid Perovskite with Nearly 200% Quantum Yield of Red Phosphorescence.

2D organic-inorganic hybrid perovskites (OIHPs) show obvious advantages in the field of optoelectronics due to their high luminescent stability and good solution processability. However, the thermal quenching and self-absorption of excitons caused by the strong interaction between the inorganic metal ions lead to a low luminescence efficiency of 2D perovskites. Herein, a 2D Cd-based OIHP phenylammonium cadmium chloride (PACC) with a weak red phosphorescence (ΦP  < 6%) at 620 nm and a blue afterglow is reported. Interestingly, the Mn-doped PACC exhibits very strong red emission with nearly 200% quantum yield and 15 ms lifetime, thus resulting in a red afterglow. The experimental data prove that the doping of Mn2+ not only induces the multiexciton generation (MEG) process of the perovskite, avoiding the energy loss of inorganic excitons, but also promotes the Dexter energy transfer from organic triplet excitons to inorganic excitons, thus realizing the superefficient red-light emission of Cd2+ . This work suggests that guest metal ions can induce host metal ions to realize MEG in 2D bulk OIHPs, which provides a new idea for the development of optoelectronic materials and devices with ultrahigh energy utilization.

Full-color Persistent Room-temperature Phosphorescence from Carbon Dot Composites Based on a Single Nonaromatic Carbon Source.

Herein, a series of carbon dot composites (CDC) with full-color and long-lived room-temperature phosphorescence (RTP) are prepared by a simple solid-phase one-step method from a single non-conjugated and non-aromatic carbon source. The RTP emission wavelength can be adjusted from 462 to 623 nm by changing the feeding ratio and reaction temperature. The luminescent lifetime and quantum yield of a green emissive CDC (AB-CDC-3) reach 1.1 s and 39%, respectively, because of the close interaction between carbon dots and inorganic matrix. Due to the existence of multiple luminescent centers, these CDC exhibit excitation wavelength-dependent RTP and a white emission when excited at a specific wavelength. A single-component afterglow luminescent diode based on AB-CDC-4 shows a high-quality white emission with CIE of (0.30, 0.33) and color-rendering index of 88. Based on the unique photophysical properties of the composites, they exhibit huge application potential in the field of multilevel anti-counterfeiting, fingerprint identification, and optoelectronic devices.

Nearly Unity Quantum Yield Persistent Room-Temperature Phosphorescence from Heavy Atom-Free Rigid Inorganic/Organic Hybrid Frameworks.

Synergism between covalent and non-covalent bonds is employed to fix an organic phosphor guest in a rigid inorganic framework, simulating the stiffening effect seen in the glassy state and realizing efficient and ultralong room-temperature phosphorescence (RTP). Twelve heavy-atom-free composites have been obtained through introducing arylboric or arylcarboxylic acid derivatives into the inorganic boric acid matrix by solid-phase synthesis. Owing to the stiffening effect of multiple bonds, all the composites show highly efficient and persistent RTP of guest molecules with a quantum yield ranging from 39.8 % to ca. 100 % and a lifetime up to 8.74 s, which results in a 55 s afterglow visible to the naked eye after exposure to a portable UV lamp. Interestingly, it is found that the substitution position and quantity of carboxyl in the guest have a great influence on the phosphorescent properties, and that the heavy-atom effect is invalid in such host-guest hybrid systems. The 100 g grade composite is easily prepared because of the solvent-free, green, and simple synthesis method. These results provide an important way for the development of RTP materials with ultrahigh quantum yield and ultralong lifetime, as well as their practical applications in the fields of anti-counterfeiting and information storage, among others.

Greatness in Simplicity: Efficient Red Room-Temperature Phosphorescence from Simple Halogenated Maleimides with a 2D Layered Structure.

Herein, two maleimide derivatives substituted by Br (DBM) and I (DIM) with a two-dimensional (2D) layered structure are found to have highly efficient red room-temperature phosphorescence (RTP) at 660 nm in solid state, which is independent of their morphology (crystal, powder, and film). The red RTP of DBM and DIM is closely related to the synergism of nπ-ct-π* transitions and the 2D halogen-bonded network. Interestingly, the red RTP can be excited by visible light of 500 nm, which should be ascribed to the forbidden absorption from the ground state to the triplet state activated in the layered halogen-bonded framework. Due to the rich intermolecular interactions in the rigid layered structure, the red RTP of DBM is very stable under water or external force stimulation. Notably, Hg(II) and Cd(II) ions in a pure aqueous solution result in an opposite change in the RTP intensity of the DBM film. The detection limit of Hg(II) ion is as low as 2.5 × 10-5 nM, lesser than all reported values. The above results not only provide a new idea for the design of simple and efficient red RTP materials but also make it possible to develop solid-state phosphorescent probes for toxic heavy metal ions in environmental sewage with high sensitivity and selectivity.

Light/Force-Sensitive 0D Lead-Free Perovskites: From Highly Efficient Blue Afterglow to White Phosphorescence with Near-Unity Quantum Efficiency.

Herein, new types of zero-dimensional (0D) perovskites (PA6InCl9 and PA4InCl7) with blue room-temperature phosphorescence (RTP) were obtained from InCl3 and aniline hydrochloride. These are highly sensitive to external light and force stimuli. The RTP quantum yield of PA6InCl9 can be enhanced from 25.2 % to 42.8 % upon illumination. Under mechanical force, PA4InCl7 exhibits a phase transform to PA6InCl9, thus boosting ultralong RTP with a lifetime up to 1.2 s. Furthermore, white and orange pure RTP with a quantum yield close to 100 % can be realized when Sb3+ was introduced into PA6InCl9. The white pure phosphorescence with a color-rendering index (CRI) close to 90 consists of blue RTP of PA6InCl9 and orange RTP of Sb3+ . Thus, this work not only overcomes long-standing problems of low quantum yield and short lifetime of blue RTP, but also obtains high-efficiency white RTP. It provides a feasible method to realize near-unity quantum efficiency and has great application potential in the fields of optical devices and smart materials.

A metal-free 2D layered organic ammonium halide framework realizing full-color persistent room-temperature phosphorescence.

Organic-inorganic hybrid metal halides have attracted intensive attention because of their unique electronic structure and solution processability. They have a rigid micro/nano-structure and heavy atom effect, which has obvious advantages in promoting organic room temperature phosphorescence (RTP). However, the toxicity of heavy metals has limited their further development. Herein, two metal-free 2D layered ammonium halides, homopiperonylammonium bromide and chloride (HLB and HLC), are described for the first time. Their layered structure consists of rigid inorganic ammonium halide laminates and neatly stacked organic layers. The rigid laminates and external heavy atom effect of halogen atoms make HLB and HLC produce green RTP. When phosphor guests with different triplet energies are doped into HLB, HLC, or phenylethylamine salt hosts, effective full-color and even white ultra-long RTP with phosphorescence quantum yield up to 18.7% and lifetime up to 1.7 s is realized through energy transfer between the host and guest. Due to the simple solution synthesis, 10 g-level doped layered organic ammonium halides with the same phosphorescence properties can be easily obtained. The information ink based on these doped halides and non-toxic ethanol solvent can form various patterns on filter paper. The fluorescence and phosphorescence of these patterns are sensitive to the excitation wavelength and acid-base vapor. Consequently, they can be applied to multiple complex anti-counterfeiting and fluorescence/phosphorescence dual-mode chemical sensors.

Multicolor Output from 2D Hybrid Perovskites with Wide Band Gap: Highly Efficient White Emission, Dual-Color Afterglow, and Switch between Fluorescence and Phosphorescence.

Herein, an organic fluorophore termed NLAC is introduced into 2D hybrid perovskites with wide band gap (>3.54 eV) to give a green emission with quantum yield up to 81%. The highly efficient luminescence is ascribed to avoiding the aggregation of NLAC and formation of an inorganic free exciton which is easy to thermally quench. On this basis, a new strategy to generate efficient white emission with afterglow has been proposed by codoping a short-wavelength fluorophore and long-wavelength phosphor into 2D organic-inorganic hybrid perovskites (OIHPs). As a result, a single-component white-light-emitting material PEPC-3N based on NLAC with CIE of (0.33, 0.36) and quantum yield up to 43% can be obtained. Interestingly, PEPC-3N shows a dual-color organic afterglow and excitation-wavelength-dependent emission, consequently forming a switch between green fluorescence and yellow afterglow. This unique performance indicates PEPC-3N has huge potential in afterglow WLEDs and information storage.

Highly Efficient Organic Afterglow from a 2D Layered Lead-Free Metal Halide in Both Crystals and Thin Films under an Air Atmosphere.

Organic afterglow materials (OAMs) with a lifetime longer than 0.1 s have recently received much attention for their fascinating properties meeting the critical requirements of applications in newly emerged technologies. However, the development of OAMs lags behind for their low luminescence efficiency. Usually, enhancing the phosphorescence efficiency of organic materials causes a short lifetime. Here, we report two kinds of OAMs, two-dimensional (2D) layered organic-inorganic hybrid zinc bromides (PEZB-NTA and PEZB-BPA), obtained in an environmentally friendly ethanol solvent by a low-temperature solution method. They display highly efficient and persistent luminescence in air in both crystals and thin films with phosphorescence quantum yields up to 42% in crystals and 27% in films. For OAMs, the two quantum yields are the highest values ever reported for crystals and films. Due to the excellent crystalline and film-forming ability, PEZB-NTA and PEZB-BPA in ethanol can be used as inks to construct patterns on various rigid and flexible substrates, including paper, iron, plastic, marble, tin foil, and cloth. Consequently, the novel OAMs show great application prospects in the fields of anti-counterfeiting and information storage because of their economic synthesis, solution processing, and easy operation.

Perylene Diimide-Based Electron-Transporting Material for Perovskite Solar Cells with Undoped Poly(3-hexylthiophene) as Hole-Transporting Material.

Perylene diimide-based small molecules are widely used as intermediates of liquid crystals, owing to their high planarity and electron mobility. In this study, tetrachloroperylene diimide (TCl-PDI) was used as a small-molecule replacement for TiO2 as electron-transporting material (ETM) for planar perovskite solar cells (PVSCs). Among hole-transporting materials (HTMs) for PVSCs, poly(3-hexylthiophene) (P3HT) gives the devices the highest stability and reproducibility. Therefore, PVSCs with the structure of indium tin oxide (ITO)/ETM/perovskite/P3HT/MoO3 /Ag were used to evaluate the performances of new ETMs. A reference device with compact TiO2 and P3HT gave a reasonable power conversion efficiency (PCE) of 12.78 %, whereas the PVSC with TCl-PDI as ETM gave an enhanced PCE of 14.73 %, which is among the highest reported values for PVSCs with undoped P3HT as the HTM. Moreover, TCl-PDI-based devices displayed higher stability than those based on compact TiO2 , owing to the superior perovskite quality.

High Color Rendering Index White-Light Emission from UV-Driven LEDs Based on Single Luminescent Materials: Two-Dimensional Perovskites (C6H5C2H4NH3)2PbBr xCl4- x.

Two-dimensional (2D) white-light-emitting hybrid perovskites (WHPs) are promising active materials for single-component white-light-emitting diodes (WLEDs) driven by UV. However, the reported WHPs exhibit low quantum yields (≤9%) and low color rendering index (CRI) values less than 85, which does not satisfy the demand of solid-state lighting applications. In this work, we report a series of mixed-halide 2D layered WHPs (C6H5C2H4NH3)2PbBr xCl4- x (0 < x < 4) obtained from the phenethylammonium cation. Unlike the reported WHPs including (C6H5C2H4NH3)2PbCl4, the mixed-halide perovskites display morphology-dependent white emission for the different extents of self-absorption. Additionally, the amount of Br has a huge influence on the photophysical properties of mixed-halide WHPs. With the increasing content of Br, the quantum yields of WHPs increase gradually from 0.2 to 16.9%, accompanied by tunable color temperatures ranging from 4000 K ("warm" white light) to 7000 K ("cold" white light). When applied to the WLEDs, the mixed-halide perovskite powders exhibit tunable white electroluminescent emission with very high CRI of 87-91.

Highly efficient room-temperature phosphorescence and afterglow luminescence from common organic fluorophores in 2D hybrid perovskites.

Regardless of rapid development of organic room-temperature phosphorescence (RTP) originating from phosphors in crystals, highly efficient and persistent RTP from common fluorophores is very rare. Herein, 1,8-naphthalimide (NI), a common organic fluorophore, is doped into organic cations of 2D layered organic/inorganic hybrid perovskites (OIHPs) to yield thin films and powders with yellow RTP of NI in air. The triplet excitons of NI are mainly derived from Wannier excitons of inorganic perovskite through energy transfer (ET) for films, and from singlet excitons of NI through intersystem crossing (ISC) for powder. Consequently, the quantum yield (Φ P), lifetime (τ) and color of RTP can be tuned by changing the fluorophore and halide in the perovskites, as well as their solid morphology. A white emission, comprising the blue one from the perovskite and yellow RTP (Φ P = 25.6%, τ = 6.3 ms) from NI, is obtained in Br-based OIHPs in powder. Cl-based OIHPs exhibit fluorescence/phosphorescence dual emission in thin films, and yellow afterglow phosphorescence in powders (Φ P = 56.1%, τ = 35 ms). The unique performance of the OIHPs with RTP can make them widely applicable in the field of information technology as security ink, and white and afterglow LEDs as single luminescent materials.

Large Changes in Fluorescent Color and Intensity of Symmetrically Substituted Arylmaleimides Caused by Subtle Structure Modifications.

Herein we report on four diarylmaleimides based on 3- or 2-substituted benzothiophene (M3S or M2S) and benzofuran (M3O or M2O), which show very different emission properties: aggregation-caused quenching (ACQ), aggregation-induced emission (AIE), and dual-state strong emission (DSE) in both solution and solid states. Their emission color in the solid state can be adjusted from green-yellow into red. M2O displays strong red solid-state emission at 630 nm with a quantum yield of 46.3 %. Single-crystal X-ray diffraction analysis confirms that their large distinction in solid-state emission originates from their different packing structures: hydrogen-bonded organic frameworks (HOFs) for M3S, a staggered structure for M3O, J-aggregation for M2S, and weak H-aggregation for M2O. HOF of M3S and weak H-aggregation of M2O make them produce inverse-type piezochromic fluorescence: blueshifted "turn-on" and redshifted "turn-off" emission, respectively. These results provide new insight in fluorescence manipulated by subtle structure modification.

Diarylmaleimide-based branched oligomers: strong full-color emission in both solution and solid films.

Maleimide and benzene are employed as a dendron and a core, respectively, to construct two series of non-conjugate branched oligomers (B3G1 and B1G2) based on diarylmaleimide fluorophores by an alkylation reaction. Surface aryl groups are changed to tune the emissive color of branched oligomers from blue (λem = 480 nm) to red (λem = 651 nm), realizing full-color emission. The investigation on the photophysical properties of the oligomers indicates that they display intense emission in both solution and solid films, due to the suppression of intramolecular rotation and intermolecular interaction. Molecular simulation and natural transition orbital analysis show that the electron transition takes place in the individual arylmaleimide for the non-conjugate linkage of fluorophores in branched oligomers. It can avoid the unpredictability of the luminescence properties caused by the interaction of fluorophores. In addition, the good solubility, thermostability and oxidative stability of the branched oligomers make them have huge potential in the solution-processable photonic application. These results demonstrate that such a design strategy of non-conjugate branched oligomers is a very efficient and constructive method to obtain high-performance light-emitting materials in both solution and solid films.

Dual-core star-shaped single white polymers: the effect of host structure on luminescence properties.

The non-emissive benzene ring and green-emissive arylmaleimide are employed as two independent cores to construct dual-core white star-shaped polymers (DC-PFMs). Due to the totally star-shaped structure, DC-PFMs display a higher quantum yield and electroluminescence efficiency for a more efficient energy transfer from the host to the guest than traditional single-core polymers (SC-PFMs).

Nondoped pure-blue OLEDs based on amorphous phenylenevinylene-functionalized twisted bimesitylenes.

The twisted bimesitylene scaffold hinders crystallization and imparts amorphous nature to the oligophenylenevinylenes (OPVs) generated by 2- and/or 4-fold functionalization. The resultant phenylenevinylenes 1-5 with unique molecular topology exhibit excellent thermal and solid-state luminescence properties. The amorphous nature permits their application as pure-blue emissive materials in OLEDs. Under nondoped conditions, the device performances observed surpass those for analogous and simple oligophenylenevinylenes known so far; for example, the device based on OPV 2 as an emitting material and structurally analogous Bim-DPAB as a hole-transporting material yields pure-blue electroluminescence with an external quantum efficiency of ca. 4.70% at 20 mA/cm(2), which is higher than those reported for nondoped pure-blue OPV emitters.

'Magic blue'--subtle reagent for EPR studies on H-abstraction from various substrates.

This paper is an EPR study on the generation of new 'magic blue' (MB) reagent containing bis{perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl}nitroxide 2 and perfluoro[1-nitroso-1-(2-fluorosulfonyl)ethoxy]ethane 3, both bearing chemically convertible terminal omega-fluorosulfonyl group -SO2F, and its H-abstraction reactions from arylalkanes, alcohols, aldehydes and polymers, leading to a large number of new fluorinated nitroxides (FN).

Macroreticular p-(omega-sulfonic-perfluoroalkylated) polystyrene ion-exchange resins: a new type of selective solid acid catalyst.

Macroreticular p-(omega-sulfonic-perfluoroalkylated) polystyrene (FPS) cation-exchange resins have been synthesized by sequential p-perfluoroalkylation of macroreticular polystyrene (PS) with omega-fluorosulfonylperfluorodiacyl peroxide 2, hydrolysis and acidification; the fluorinated mesoporous resins exhibited higher activity and selectivity than commercial Amberlyst 36 and Nafion NR50 in the cyclization of pseudoionone.