Highly Luminescent One-Dimensional Organic-Inorganic Hybrid Double-Perovskite-Inspired Materials for Single-Component Warm White-Light-Emitting Diodes.

Double perovskites (DPs) are one of the most promising candidates for developing white light-emitting diodes (WLEDs) owing to their intrinsic broadband emission from self-trapped excitons (STEs). Translation of three-dimensional (3D) DPs to one-dimensional (1D) analogues, which could break the octahedral tolerance factor limit, is so far remaining unexplored. Herein, by employing a fluorinated organic cation, we report a series of highly luminescent 1D DP-inspired materials, (DFPD)2 MI InBr6 (DFPD=4,4-difluoropiperidinium, MI =K+ and Rb+ ). Highly efficient warm-white photoluminescence quantum yield of 92 % is achieved by doping 0.3 % Sb3+ in (DFPD)2 KInBr6 . Furthermore, single-component warm-WLEDs fabricated with (DFPD)2 KInBr6 :Sb yield a luminance of 300 cd/m2 , which is one of the best-performing lead-free metal-halides WLEDs reported so far. Our study expands the scope of In-based metal-halides from 3D to 1D, which exhibit superior optical performances and broad application prospects.

Organic-Inorganic Hybrid Cuprous-Based Metal Halides for Warm White Light-Emitting Diodes.

Single-component emitters with stable and bright warm white-light emission are highly desirable for high-efficacy warm white light-emitting diodes (warm-WLEDs), however, materials with such luminescence properties are extremely rare. Low-dimensional lead (Pb) halide perovskites can achieve warm white photoluminescence (PL), yet they suffer from low stability and PL quantum yield (PLQY). While Pb-free air-stable perovskites such as Cs2 AgInCl6 emit desirable warm white light, sophisticated doping strategies are typically required to increase their PL intensity. Moreover, the use of rare metal-bearing compounds along with the typically required vacuum-based thin-film processing may greatly increase their production cost. Herein, organic-inorganic hybrid cuprous (Cu+ )-based metal halide MA2 CuCl3 (MA = CH3 NH3 + ) that meets the requirements of i) nontoxicity, ii) high PLQY, and iii) dopant-free is presented. Both single crystals and thin films of MA2 CuCl3 can be facilely prepared by a low-cost solution method, which demonstrate bright warm white-light emission with intrinsically high PLQYs of 90-97%. Prototype electroluminescence devices and down-conversion LEDs are fabricated with MA2 CuCl3 thin films and single crystals, respectively, which show bright luminescence with decent efficiencies and operational stability. These findings suggest that MA2 CuCl3 has a great potential for the single-component indoor lighting and display applications.

Filling Chlorine Vacancy with Bromine: A Two-Step Hot-Injection Approach Achieving Defect-Free Hybrid Halogen Perovskite Nanocrystals.

Mixed-halide (Cl and Br) perovskite nanocrystals (NCs) are of particular interest because they hold great potential for use in high-efficiency blue light-emitting diodes (LEDs). Generally, mixed-halide compounds are obtained by either a one-step synthesis with simultaneous addition of both halide precursors or a postsynthetic anion exchange using the opposite halogen. However, both strategies fail to prevent the formation of deep-level Cl vacancy defects, rendering the photoluminescence quantum yields (PLQYs) typically lower than 30%. Here, by optimizing both thermodynamic and kinetic processes, we devise a two-step hot-injection approach, which simultaneously realizes Cl vacancy filling and efficient anion exchange between Cl- and Br-. Both the identity of Br precursors and their injection temperature are revealed to be critical in transforming those highly defective CsPbCl3 NCs to defect-free CsPb(Cl/Br)3. The optimally synthesized NCs exhibit a saturated blue emission at ∼460 nm with a near-unity PLQY and a narrow emission bandwidth of 18 nm, which represents one of the most efficient blue emitters reported so far. The turn-on voltage of the ensuing LEDs is ∼4.0 V, which is lower than those of most other mixed-halide perovskites. In addition, LEDs exhibit a stable electroluminescence peak at 460 nm under a high bias voltage of 8.0 V. We anticipate that our findings will provide new insights into the materials design strategies for producing high-optoelectronic-quality Cl-containing perovskites.

Unraveling the Key Role of the Benzyl Group in the Synthesis of CL-20 Precursor HBIW.

As one of the most important energetic material molecules, hexanitrohexaazaisowurtzitane (CL-20) can only be synthesized using an amine with a benzyl group. Moreover, the reaction mechanism remains unexplored and the special role of the benzyl group has not been revealed. To address these issues, we perform an extensive theoretical study to investigate the synthesis mechanism of CL-20 precursor HBIW by employing density functional theory. Our calculated results demonstrate that the benzyl group can reduce the energy of the intermediate and the energy barrier of the rate-determining step due to the π-π stack interaction between two benzene rings of the benzyl group. For the first time, we revealed that the reactions can produce 16 intermediates with different chiralities during the formation of the first two side five-membered rings and only two of which can further form the bottom six-membered ring and finally obtain the product HBIW. The steric hindrance effect of the benzyl group leads to the formation of a higher-energy intermediate first, thereby providing an opportunity to correct the wrong chirality. All of these factors make the diimine with the benzyl group the most suitable reactant for the synthesis of CL-20.

Germanium Halides Serving as Ideal Precursors: Designing a More Effective and Less Toxic Route to High-Optoelectronic-Quality Metal Halide Perovskite Nanocrystals.

The three-precursors approach has proven to be advantageous for obtaining high-quality metal halide perovskite nanocrystals (PNCs). However, the current halide precursors of choice are mainly limited to those highly toxic organohalides, being unfavorable for large-scale and sustainable use. Moreover, most of the resulting PNCs still suffer from low quality in terms of photoluminescence quantum yield (PLQY). Herein we present all-inorganic germanium salts, GeX4 (X = Cl, Br, I), serving as robust and less hazardous alternatives that are capable of ensuring improved material properties for both Pb-based and Pb-free PNCs. Importantly, unlike most of the other inorganic halide sources, the GeX4 compound does not deliver the Ge element into the final compositions, whereas the PLQY and phase stability of the resulting nanocrystals are significantly improved. Theoretical calculations suggest that Ge halide precursors provide favorable conditions in both dielectric environment and thermodynamics, which jointly contribute to the formation of size-confined defect-suppressed nanoparticles.

Bright Triplet Self-Trapped Excitons to Dopant Energy Transfer in Halide Double-Perovskite Nanocrystals.

For inorganic semiconductor nanostructure, excitons in the triplet states are known as the "dark exciton" with poor emitting properties, because of the spin-forbidden transition. Herein, we report a design principle to boost triplet excitons photoluminescence (PL) in all-inorganic lead-free double-perovskite nanocrystals (NCs). Our experimental data reveal that singlet self-trapped excitons (STEs) experience fast intersystem crossing (80 ps) to triplet states. These triplet STEs give bright green color emission with unity PL quantum yield (PLQY). Furthermore, efficient energy transfer from triplet STEs to dopants (Mn2+) can be achieved, which leads to white-light emitting with 87% PLQY in both colloidal and solid thin film NCs. These findings illustrate a fundamental principle to design efficient white-light emitting inorganic phosphors, propelling the development of illumination-related applications.

New Protocol-Guided Exploitation of a Lysosomal Sulfatase Inhibitor to Suppress Cell Growth in Glioblastoma Multiforme.

Glioblastoma multiforme (GBM) is a highly invasive and aggressive malignant glioma. Current treatment modalities are unable to significantly prolong survival in patients diagnosed with glioblastoma, so more effective strategies of antitumor treatments are in urgent demand. Here, we found that lysosomal sulfatase expression was significantly correlated with poor prognosis of GBM. Hence, a new probe, MNG, was developed with a new protocol utilizing glucose groups to detect lysosomal sulfatase. It also exhibits potential for monitoring GBM cells, depending on the hyperactive lysosomal sulfatase expression of tumor cells. Meantime, we identified that sulbactam as the first reported lysosomal sulfatase inhibitor inhibits the tumor growth of GBM. Collectively, our work highlights that lysosomal sulfatase was detected using a new protocol and its potential as a therapeutic target in GBM and reveals a distinct mechanism that sulbactam inhibits cell proliferation related to lysosomal sulfatase, indicating that sulbactam could be a promising therapeutic agent against GBM.

Semi-Quantitatively Designing Two-Photon High-Performance Fluorescent Probes for Glutathione S-Transferases.

Glutathione S-transferases (GSTs), detoxification enzymes that catalyze the addition of glutathione (GSH) to diverse electrophilic molecules, are often overexpressed in various tumor cells. While fluorescent probes for GSTs have often adopted the 2,4-dinitrobenzenesulfonyl (DNs) group as the receptor unit, they usually suffer from considerable background reaction noise with GSH due to excessive electron deficiency. However, weakening this reactivity is generally accompanied by loss of sensitivity for GSTs, and therefore, finely turning down the reactivity while maintaining certain sensitivity is critical for developing a practical probe. Here, we report a rational semiquantitative strategy for designing such a practical two-photon probe by introducing a parameter adopted from the conceptual density functional theory (CDFT), the local electrophilicity ω k , to characterize this reactivity. As expected, kinetic studies established ω k as efficient to predict the reactivity with GSH, and probe NI3 showing the best performance was successfully applied to detecting GST activities in live cells and tissue sections with high sensitivity and signal-to-noise ratio. Photoinduced electron transfer of naphthalimide-based probes, captured by femtosecond transient absorption for the first time and unraveled by theoretical calculations, also contributes to the negligible background noise.

Salen-Based Conjugated Microporous Polymers for Efficient Oxygen Evolution Reaction.

Exploring high-performance electrocatalysts, especially non-noble metal electrocatalysts, for the oxygen evolution reaction (OER) is critical to energy storage and conversion. Herein, we report for the first time that conjugated microporous polymers (CMPs) incorporating salen can be used as OER electrocatalysts with outstanding performances. The best OER electrocatalyst (salen-CMP-Fe-3) exhibits a low Tafel slope of 63 mV dec-1 and an overpotential of 238 mV at 10 mA cm-2 . DFT and Grand Canonical Monte Carlo calculations confirmed that the significantly improved electrocatalytic properties can be attributed to the intrinsic catalytic activity of the salen moiety and the enrichment effect of the pore structures. This work demonstrates that salen-based conjugated polymers are a type of metal-coordinated porous polymer that show excellent catalyst performance.

Detection of atherosclerosis-related hypochlorous acid produced in foam cells with a localized endoplasmic reticulum probe.

We have synthesized a turn-on fluorescent probe, termed NB4OH, to detect cellular hypochlorite. NB4OH is mainly localized in the endoplasmic reticulum and detects ClO- in foam cells. The fluorescence change of the probe was explained by theoretical calculation as a PET process. The probe holds great promise for application in biomedical research, including atherosclerosis research.

A fluorophore's electron-deficiency does matter in designing high-performance near-infrared fluorescent probes.

The applications of most fluorescent probes available for Glutathione S-Transferases (GSTs), including NI3 which we developed recently based on 1,8-naphthalimide (NI), are limited by their short emission wavelengths due to insufficient penetration. To realize imaging at a deeper depth, near-infrared (NIR) fluorescent probes are required. Here we report for the first time the designing of NIR fluorescent probes for GSTs by employing the NIR fluorophore HCy which possesses a higher brightness, hydrophilicity and electron-deficiency relative to NI. Intriguingly, with the same receptor unit, the HCy-based probe is always more reactive towards glutathione than the NI-based one, regardless of the specific chemical structure of the receptor unit. This was proved to result from the higher electron-deficiency of HCy instead of its higher hydrophilicity based on a comprehensive analysis. Further, with caging of the autofluorescence being crucial and more difficult to achieve via photoinduced electron transfer (PET) for a NIR probe, the quenching mechanism of HCy-based probes was proved to be PET for the first time with femtosecond transient absorption and theoretical calculations. Thus, HCy2 and HCy9, which employ receptor units less reactive than the one adopted in NI3, turned out to be the most appropriate NIR probes with high-sensitivity and little nonenzymatic background noise. They were then successfully applied to detecting GST in cells, tissues and tumor xenografts in vivo. Additionally, unlike HCy2 with a broad isoenzyme selectivity, HCy9 is specific for GSTA1-1, which is attributed to its lower reactivity and the higher effectiveness of GSTA1-1 in stabilizing the active intermediate via H-bonds based on docking simulations.

Constructing Sensitive and Fast Lead-Free Single-Crystalline Perovskite Photodetectors.

We developed a high-performance photodetector based on (CH3NH3)3Sb2I9 (MA3Sb2I9) microsingle crystals (MSCs). The MA3Sb2I9 single crystals exhibit a low-trap state density of ∼1010 cm-3 and a long carrier diffusion length reaching 3.0 µm, suggesting its great potential for optoelectronic applications. However, the centimeter single crystal (CSC)-based photodetector exhibits low responsivity (10-6 A/W under 1 sun illumination) due to low charge-carrier collection efficiency. By constructing the MSC photodetector with efficient charge-carrier collection, the responsivity can be improved by three orders of magnitude (under 1 sun illumination) and reach 40 A/W with monochromatic light (460 nm). Furthermore, the MSC photodetectors exhibit fast response speed of <1 ms, resulting in a high gain of 108 and a gain-bandwidth product of 105 Hz. These numbers are comparable to the lead-perovskite single-crystal-based photodetectors.

Unveiling excited state energy transfer and charge transfer in a host/guest coordination cage.

Host-guest charge transfer (HGCT) plays a key role in applications from solar energy conversion to photocatalysis. Herein, a HGCT system, a pillared Pt(ii) metallacage with encapsulated coronene was synthesized and the ultrafast excited-state dynamics were investigated by combination of femtosecond transient absorption spectroscopy, nanosecond transient emission spectrocopy and quantum chemistry calculations. Two significant ultrafast dynamic processes were unveiled: (i) charge transfer from a singlet local excited (1LE) state associated with the coronene moiety to a 1HGCT state with τ = 9.5 ps; and (ii) triplet-triplet energy transfer from a high 3HGCT state to a 3LE state with τ = 139.5 ps. The resulting long-lived species, the lowest 3LE and 3HGCT states eventually decay to the ground state in microsecond time scales of 5.2 and 43.4 µs respectively. Moreover, a clear mechanism depicting the main excited-state decay pathways connecting the initial photoexcited transients with the resulting species was proposed.

Intraligand Charge Transfer Sensitization on Self-Assembled Europium Tetrahedral Cage Leads to Dual-Selective Luminescent Sensing toward Anion and Cation.

Luminescent supramolecular lanthanide edifices have many potential applications in biology, environments, and materials science. However, it is still a big challenge to improve the luminescent performance of multinuclear lanthanide assemblies in contrast to their mononuclear counterparts. Herein, we demonstrate that combination of intraligand charge transfer (ILCT) sensitization and coordination-driven self-assembly gives birth to bright EuIII tetrahedral cages with a record emission quantum yield of 23.1%. The ILCT sensitization mechanism has been unambiguously confirmed by both time-dependent density functional theory calculation and femtosecond transient absorption studies. Meanwhile, dual-responsive sensing toward both anions and cations has been demonstrated making use of the ILCT transition on the ligand. Without introduction of additional recognition units, high sensitivity and selectivity are revealed for the cage in both turn-off luminescent sensing toward I- and turn-on sensing toward Cu2+. This study offers important design principles for the future development of luminescent lanthanide molecular materials.

Orientation hydrogen-bonding effect on vibronic spectra of isoquinoline in water solvent: Franck-Condon simulation and interpretation.

The excited-state orientation hydrogen-bonding dynamics, and vibronic spectra of isoquinoline (IQ) and its cationic form IQc in water have been investigated at the time-dependent density functional theory quantum chemistry level plus Franck-Condon simulation and interpretation. The excited-state orientation hydrogen bond strengthening has been found in IQ:H2O complex due to the charge redistribution upon excitation; this is interpreted by simulated 1:1 mixed absorption spectra of free IQ and IQ:H2O complex having best agreement with experimental results. Conversely, the orientation hydrogen bond in IQc:H2O complex would be strongly weakening in the S1 state and this is interpreted by simulated absorption spectra of free IQc having best agreement with experimental results. By performing Franck-Condon simulation, it reveals that several important vibrational normal modes with frequencies about 1250 cm-1 involving the wagging motion of the hydrogen atoms are very sensitive to the formation of the orientation hydrogen bond for the IQ/IQc:H2O complex and this is confirmed by damped Franck-Condon simulation with free IQ/IQc in water. However, the emission spectra of the IQ and IQc in water have been found differently. Upon the excitation, the simulated fluorescence of IQ in water is dominated by the IQ:H2O complex; thus hydrogen bond between IQ and H2O is much easier to form in the S1 state. While the weakened hydrogen bond in IQc:H2O complex is probably cleaved upon the laser pulse because the simulated emission spectrum of the free IQc is in better agreement with the experimental results.

Correction: A versatile two-photon fluorescent probe for ratiometric imaging E. coliß-galactosidase in live cells and in vivo.

Correction for 'A versatile two-photon fluorescent probe for ratiometric imaging E. coliß-galactosidase in live cells and in vivo' by Xue-Xiang Zhang et al., Chem. Commun., 2016, 52, 8283-8286.

A versatile two-photon fluorescent probe for ratiometric imaging E. coliß-galactosidase in live cells and in vivo.

We have described the design, synthesis, spectroscopy and biological applications of NI-ßGal, a versatile fluorescent probe to detect E. coliß-galactosidase in live cells and mice sensitively and directly, which holds great promise for its application in biomedical research such as gene therapy for cancer in the future.

Effect of the Hydrogen Bond on Photochemical Synthesis of Silver Nanoparticles.

The effect of a hydrogen bond on the photochemical synthesis of silver nanoparticles has been investigated via experimental and theoretical methods. In a benzophenone system, the photochemical synthesis process includes two steps, which are that hydrogen abstraction reaction and the following reduction reaction. We found that for the first step, an intermolecular hydrogen bond enhances the proton transfer. The efficiency of hydrogen abstraction increases with the hydrogen bond strength. For the second step, the hydrogen-bonded ketyl radical complex shows higher reducibility than the ketyl radical. The inductively coupled plasma-optical emission spectroscopy (ICP-OES) measurement exhibits a 2.49 times higher yield of silver nanoparticles in the hydrogen bond ketyl radical complex system than that for the ketyl radical system. Theoretical calculations show that the hydrogen bond accelerates electron transfer from the ketyl radical to the silver ion by raising the SOMO energy of the ketyl radical; thus, the SOMO-LUMO interaction is more favorable.

Photophysical Properties of a Post-Self-Assembly Host/Guest Coordination Cage: Visible Light Driven Core-to-Cage Charge Transfer.

Supramolecular systems are capable of unique photophysical properties due to possible interactions between subcomponents, such as between an encapsulated molecule and its cage in a host/guest environment. Here, we report that the encapsulation of a chromophore by a metallacage dramatically enhances its photophysical properties. In the visible region, the encapsulated photosensitizer achieves a 6.5-fold enhancement to its absorptivity. The triplet lifetime of the encapsulated photosensitizer is three times longer than that of its free analogue. These enhancements are attributed to two key factors: (i) encapsulation-induced core-to-cage charge transfer (CCCT) generates new visible-light absorbing states, accounting for the enhanced absorption, and (ii) the microenvironment inside the metallacage inhibits nonradiative decay processes, resulting in prolonged triplet lifetime. The CCCT arises from the electrostatic interaction between the delocalized electrons of the guest coronene and the positive charge associated with the metallacage host. The work herein provides insight into the CCCT phenomenon.

Quantitative prediction of charge mobilities of π-stacked systems by first-principles simulation.

This protocol is intended to provide chemists and physicists with a tool for predicting the charge carrier mobilities of π-stacked systems such as organic semiconductors and the DNA double helix. An experimentally determined crystal structure is required as a starting point. The simulation involves the following operations: (i) searching the crystal structure; (ii) selecting molecular monomers and dimers from the crystal structure; (iii) using density function theory (DFT) calculations to determine electronic coupling for dimers; (iv) using DFT calculations to determine self-reorganization energy of monomers; and (v) using a numerical calculation to determine the charge carrier mobility. For a single crystal structure consisting of medium-sized molecules, this protocol can be completed in ∼4 h. We have selected two case studies (a rubrene crystal and a DNA segment) as examples of how this procedure can be used.