Reticular Chemistry and In Situ "One-Pot" Strategy: A Dream Combination to Construct Metal-Organic Frameworks.

The establishment of reticular chemistry has significantly facilitated the development of porous materials, especially for metal-organic frameworks (MOFs). On the other hand, as an alternative approach, in situ "one-pot" strategy has been explored as a promising approach to constructing MOFs, in which the synthesis of organic linkers and the sequential construction of MOFs are integrated into one solvothermal condition. This strategy can efficiently avoid the limitations faced in the traditional construction method, such as time-consuming organic synthesis and multiple separation and purification. Herein, inspired by the reaction of aldehydes and o-phenylenediamine and deep structural analysis of UiO-68, a series of tetra-, hexa-, and octa-topic carboxylic acids are synthesized using 2',3'-diamino-[1,1':4',1'"-terphenyl]-4,4'"-dicarboxylic acid and di-, tri-, and tetra-topic aldehydes as precursor. Then nine multicarboxylate-based zirconium MOFs (Zr-MOFs) are successfully constructed via the combination of reticular chemistry and in situ "one-pot" strategy. The resultant Zr-MOFs can be regarded as the partial face decoration of UiO-68. More importantly, the emission properties of resultant Zr-MOFs can be well controlled using aldehydes with tunable electronic structures. This work provides a new path to rational design and construction of porous materials with specific structures guided by reticular chemistry and conducted using in situ "one-pot" strategy.

Modular Construction of Vinylene-Linked Covalent Organic Frameworks with Tunable Emission for Tumor Visualization.

Covalent organic frameworks (COFs) with ordered π structures are very promising in porous light-emitting materials. However, most of these COFs are either poor in luminescence or lack of water-stability. Herein, a series of isostructural D-A vinylene-linked COFs were constructed based a new D2h symmetric linker 1,4-bis(4,6-dimethyl-1,3,5-triazin-2-yl)benzene (TMTA) with high crystallinity, comparative high surface area and excellent chemical/thermal stability. Impressively, their adsorption and luminescence wavelength vary with respect to the density of π-systems in the electron-donating group, which constitute the foundation for molecular engineering the luminescent properties of vinylene-linked COFs. The DFT calculations further established the relationship between the luminescence properties and the donor electronic structure. Moreover, one of representative COF named FZU-203 showed inspiring applications in bioimaging, which may further provide strategic guidance for the use of vinylene-linked COFs as fluorescent nanoprobes in non-invasive medical diagnosis and visualization therapy of tumors.

Blue to Red Emission Tunable Bi3+ co-doped YPO4:Eu3+: Host Emission and Phase Change.

Bi3+(0, 1, 3, 5, 7, 10, 12 and 15 at.%) co-doped YPO4:Eu3+ have been hydrothermally synthesized. Bi3+ (x ≥ 1 at.%) co-doping in YPO4:Eu3+ renders mixed crystalline phase of tetragonal to hexagonal. Pure tetragonal phase of Bi3+ co-doped YPO4:Eu3+ could be achieved upon annealing at 900 °C. The luminescence intensity is improved significantly upon annealing at 900 °C. This is due to the reduction of quenching pathways such as water molecules, dangling bonds, etc. The probability of magnetic dipole and electric dipole transitions is observed to be altered. As-prepared samples show near blue emission, while 900 °C annealed samples exhibit red emission, which could be a potential candidate for display, sensing and biological labelling, etc.

Unconventional Luminescence Polymer with Color-Tunability based on Solvent-induced Electrostatic Potential Distribution of Fluorophore.

Tuning the full-color emission of polymers holds significant promise. However, preparing unconventional luminescence polymers with color-tunability in dilute solution and understanding the relationship between non-covalent interactions and luminescent behavior remains a great challenge. We report two emitters (P1 and P2) incorporating tetracoordinate boron. The P1 with non-conjugated D-π-A structure, exhibited red delayed fluorescence at 645 nm with quantum yield of 9.15% in aggregates. Notably, the emission wavelength of P1 can be tuned from 418 to 588 nm at different solvent. Similarly, the emission wavelength of P2 can also be adjusted by manipulating the interactions between the solvent and fluorophore. Experimental characterization and theoretical calculations indicate that the B←N bond and electronic interactions between solvent and fluorophore significantly regulate the equilibrium the electrostatic potential (ESP) and the intramolecular O···O interactions of P1, thereby modulating its emission wavelength. Additionally, these polymers showed excellent potential in fluoride ions detection. This work provides new insights into the complex effects of intermolecular interactions on luminescent properties.

Full-Color Emissive Zirconium-Organic Frameworks Constructed via in situ "One-Pot" Single-Site Modification for Tryptophan Detection and Energy Transfer.

Organic linker-based luminescent metal-organic frameworks (LMOFs) have received extensive studies due to the unlimited species of emissive organic linkers and tunable structure of MOFs. However, the multiple-step organic synthesis is always a great challenge for the development of LMOFs. As an alternative strategy, in situ "one-pot" strategy, in which the generation of emissive organic linkers and sequential construction of LMOFs happen in one reaction condition, can avoid time-consuming pre-synthesis of organic linkers. In the present work, we demonstrate the successful utilization of in situ "one-pot" strategy to construct a series of LMOFs via the single-site modification between the reaction of aldehydes and o-phenylenediamine-based tetratopic carboxylic acid. The resultant MOFs possess csq topology with emission covering blue to near-infrared. The nanosized LMOFs exhibit excellent sensitivity and selectivity for tryptophan detection. In addition, two component-based LMOFs can also be prepared via the in situ "one-pot" strategy and used to study energy transfer. This work not only reports the construction of LMOFs with full-color emissions, which can be utilized for various applications, but also indicates that in situ "one-pot" strategy indeed is a useful and powerful method to complement the traditional MOFs construction method for preparing porous materials with tunable functionalities and properties.

Molecular engineering and bioimaging applications of C2-alkenyl indole dyes with tunable emission wavelengths covering visible to NIR light.

As an important member of dyes, small-molecule fluorescent dyes show indispensable value in biomedical fields. Although various molecular dyes have been developed, full-color dyes covering blue to red region derived from a single chromophore are still in urgent demand. In this work, a series of dyes based on C2-alkenyl indole skeleton were synthesized, namely AI dyes, and their photophysical properties, cytotoxicity, and imaging capacity were verified to be satisfactory. Particularly, the maximal emission wavelengths of these dyes could cover a wide range from visible to NIR light with large Stokes shifts. Besides, the optical and structural discrepancies between the C2- and C3- alkenyl AI dyes were discussed in detail, and the theoretical calculations were conducted to provide insights on such structure-activity relationship. Finally, as a proof-of-concept, a fluorescent probe AI-Py-B capable of imaging endogenous ONOO- was presented, demonstrating the bioimaging potentials of these alkenyl indole dyes. This work is anticipated to open up new possibilities for developing dye engineering and bio-applications of natural indole framework.

Water contaminant: Use it but do not shield it to synthesize co-polymers with multiple emission colours.

Due to the high affinity with water molecules, amide compounds are easily contaminated by moisture; therefore, the water interference effect cannot be totally excluded from the amide-involved reactions. Thus, the perfect solution is to use the interference effect but not shield it in a real application. In this work, we introduced different contents of sodium acrylate (AAS) to scavenge water from the monomers of N-isopropylacrylamide (NIPAm) when copolymerized with TPA-Vinyl-4CN. Herein, water molecules play a role as nucleophilic reagents to attack highly active functional groups as -C=C-CN from TPA-Vinyl-4CN, leading to a blue emissive TPA-Vinyl-2CHO. From this study, we made a deep awareness of the interactions between three reaction partners of AAS and NIPAm as well as TPA-Vinyl-4CN. Our results clearly demonstrated the fact that water can be perfectly used and controlled by the water absorbent of AAS, developing a new approach to synthesizing multiple emission-coloured polymers by using only one luminogen of TPA-Vinyl-4CN.

Size- and Emission-Controlled Synthesis of Full-Color Luminescent Metal-Organic Frameworks for Tryptophan Detection.

The development of nanoscaled luminescent metal-organic frameworks (nano-LMOFs) with organic linker-based emission to explore their applications in sensing, bioimaging and photocatalysis is of great interest as material size and emission wavelength both have remarkable influence on their performances. However, there is lack of platforms that can systematically tune the emission and size of nano-LMOFs with customized linker design. Herein two series of fcu- and csq-type nano-LMOFs, with precise size control in a broad range and emission colors from blue to near-infrared, were prepared using 2,1,3-benzothiadiazole and its derivative based ditopic- and tetratopic carboxylic acids as the emission sources. The modification of tetratopic carboxylic acids using OH and NH2 as the substituent groups not only induces significant emission bathochromic shift of the resultant MOFs, but also endows interesting features for their potential applications. As one example, we show that the non-substituted and NH2 -substituted nano-LMOFs exhibit turn-off and turn-on responses for highly selective and sensitive detection of tryptophan over other nineteen natural amino acids. This work sheds light on the rational construction of nano-LMOFs with specific emission behaviours and sizes, which will undoubtedly facilitate their applications in related areas.

One-pot synthesis of double silane-functionalized carbon dots with tunable emission and excellent coating properties for WLEDs application.

Silane-functionalized carbon dots (SiCDs) can be exploited as effective color converting materials for the solid-state light-emitting devices. However, most of SiCDs reported thus far have shown photoluminescence emissions in the blue and green spectral range, which limit them to construct an efficient white light-emitting diodes (WLEDs) due to the lack of long-wavelength emission. Herein, a series of double silane-functionalized carbon dots (DSiCDs) were prepared via a one-step solvothermal method. The results show that the organic functional group of the silane has great influence on the optical properties of DSiCDs and the number of alkoxy group in the silane has great influence on coating properties of DSiCDs. In addition, the DSiCDs prepared by (3-aminopropyl)triethoxysilane and N-[3-(trimethoxysilyl)propyl]ethylenediamine with molar ratio of 7:3 show excellent optical properties with the maximum emission at 608 nm under 570 nm excitation. Furthermore, they can be completely cured within 1 h at room temperature to form fluorescent coating with high stability and strong adhesion to the substrate. Together with their excellent optical and coating properties, they can be directly coated on LED chips to prepare WLEDs, with a CIE coordinate of (0.33,0.31), color rendering index of 81.6, and color temperature of 5774 K.

Phase Engineering of Cesium Manganese Bromides Nanocrystals with Color-Tunable Emission.

For display applications, it is highly desirable to obtain tunable red/green/blue emission. However, lead-free perovskite nanocrystals (NCs) generally exhibit broadband emission with poor color purity. Herein, we developed a unique phase transition strategy to engineer the emission color of lead-free cesium manganese bromides NCs and we can achieve a tunable red/green/blue emission with high color purity in these NCs. Such phase transition can be triggered by isopropanol: from one dimensional (1D) CsMnBr3 NCs (red-color emission) to zero dimensional (0D) Cs3 MnBr5 NCs (green-color emission). Furthermore, in a humid environment both 1D CsMnBr3 NCs and 0D Cs3 MnBr5 NCs can be transformed into 0D Cs2 MnBr4 ⋅2 H2 O NCs (blue-color emission). Cs2 MnBr4 ⋅2 H2 O NCs could inversely transform into the mixture of CsMnBr3 and Cs3 MnBr5 phase during the thermal annealing dehydration step. Our work highlights the tunable optical properties in single component NCs via phase engineering and provides a new avenue for future endeavors in light-emitting devices.

Tuning and Directing Energy Transfer in the Whole Visible Spectrum through Linker Installation in Metal-Organic Frameworks.

While limited choice of emissive organic linkers with systematic emission tunability presents a great challenge to investigate energy transfer (ET) over the whole visible light range with designable directions, luminescent metal-organic frameworks (LMOFs) may serve as an ideal platform for such study due to their tunable structure and composition. Herein, five Zr6 cluster-based LMOFs, HIAM-400X (X=0, 1, 2, 3, 4) are prepared using 2,1,3-benzothiadiazole and its derivative-based tetratopic carboxylic acids as organic linkers. The accessible unsaturated metal sites confer HIAM-400X as a pristine scaffold for linker installation. Six full-color emissive 2,1,3-benzothiadiazole and its derivative-based dicarboxylic acids (L) were successfully installed into HIAM-400X matrix to form HIAM-400X-L, in which the ET can be facilely tuned by controlling its direction, either from the inserted linkers to pristine MOFs or from the pristine MOFs to inserted linkers, and over the whole range of visible light. The combination of the pristine MOFs and the second linkers via linker installation creates a powerful two-dimensional space in tuning the emission via ET in LMOFs.

Ligand-modulated aqueous synthesis of color-tunable copper nanoclusters for the photoluminescent assay of Hg(II).

Water-soluble Cu nanoclusters (NCs) with tunable emission were synthesized through an eco-friendly one-pot aqueous method. Blue-, green-, and red-emitting NCs with the emission peaks at 420 nm, 505 nm, and 630 nm were obtained by employing ethanediamine, cysteine, and glutathione as surface ligands, respectively. The ligand effects on the optical properties of Cu NCs were studied by the single variable method. It has been revealed by systematic characterizations that the dependence of emission color on the structures of ligands was mainly attributed to their different size-tuning effects. Glutathione has the strongest chelating ability and it can significantly reduce the monomer reactivity and thus decrease the supersaturation degree of the reaction, which is favorable for modulating Cu precursor to grow into larger NCs. In contrast, ethanediamine ligand resulted in smaller nanoclusters due to its weaker binding capability. Because of the strong emission and terrific fluorescent stability, Cu NCs capped with ethanediamine, possessing an emission peak at 420 nm when excited at a wavelength of 350 nm, were directly used for probing Hg(II) with satisfying selectivity, presenting a linear range of 0.1-5.0 mM and a detection limit of 33 µM. The sensor showed good performance in real sample analysis with recoveries ranging from 99% to 103%, and comparable accuracy with atomic fluorescence spectroscopy, manifesting the reliability of the current strategy for sensing Hg(II). Graphical abstract Water-soluble copper nanoclusters with blue, green, and red emissions were synthesized by employing ethanediamine, cysteine, and glutathione as surface ligands respectively, and the blue-emitting nanoclusters with strong emission and terrific stability were directly used for selectively sensing Hg2+.

Efficient and Tunable Electroluminescence from In Situ Synthesized Perovskite Quantum Dots.

Semiconductor quantum dots (QDs) are among the most promising next-generation optoelectronic materials. QDs are generally obtained through either epitaxial or colloidal growth and carry the promise for solution-processed high-performance optoelectronic devices such as light-emitting diodes (LEDs), solar cells, etc. Herein, a straightforward approach to synthesize perovskite QDs and demonstrate their applications in efficient LEDs is reported. The perovskite QDs with controllable crystal sizes and properties are in situ synthesized through one-step spin-coating from perovskite precursor solutions followed by thermal annealing. These perovskite QDs feature size-dependent quantum confinement effect (with readily tunable emissions) and radiative monomolecular recombination. Despite the substantial structural inhomogeneity, the in situ generated perovskite QDs films emit narrow-bandwidth emission and high color stability due to efficient energy transfer between nanostructures that sweeps away the unfavorable disorder effects. Based on these materials, efficient LEDs with external quantum efficiencies up to 11.0% are realized. This makes the technologically appealing in situ approach promising for further development of state-of-the-art LED systems and other optoelectronic devices.

Ultrasmall Pb:Ag2 S Quantum Dots with Uniform Particle Size and Bright Tunable Fluorescence in the NIR-II Window.

Ag2 S quantum dots (QDs) are well-known near-infrared fluorophores and have attracted great interest in biomedical labeling and imaging in the past years. However, their photoluminescence efficiency is hard to compete with Cd-, Pb-based QDs. The high Ag+ mobility in Ag2 S crystal, which causes plenty of cation deficiency and crystal defects, may be responsible mainly for the low photoluminescence quantum yield (PLQY) of Ag2 S QDs. Herein, a cation-doping strategy is presented via introducing a certain dosage of transition metal Pb2+ ions into Ag2 S nanocrystals to mitigate this intrinsic shortcoming. The Pb-doped Ag2 S QDs (designated as Pb:Ag2 S QDs) present a renovated crystal structure and significantly enhanced optical performance. Moreover, by simply adjusting the levels of Pb doping in the doped nanocrystals, Pb:Ag2 S QDs with bright emission (PLQY up to 30.2%) from 975 to 1242 nm can be prepared without altering the ultrasmall particle size (≈2.7-2.8 nm). Evidently, this cation-doping strategy facilitates both the renovation of crystal structure of Ag2 S QDs and modulation of their optical properties.

Controllable Synthesis of Organic Microcrystals with Tunable Emission Color and Morphology Based on Molecular Packing Mode.

Organic microcrystals are of essential importance for high fluorescence efficiency, ordered molecular packing mode, minimized defects, and smooth shapes, which are extensively applied in organic optoelectronics. The molecular packing mode significantly influences the optical/electrical properties of organic microcrystals, which makes the controllable preparation of organic microcrystals with desired molecular packing mode extremely important. In the study, yellow-emissive α phase organic microcrystals with rectangular morphology and green-emissive ß phase perylene microcrystals with rhombic morphology are separately prepared by simply controlling the solution concentration. The distinct molecular staking modes of the H/J-aggregate are found in these two types of perylene microcrystals, which contribute to the different emission color, morphology, and radiative decay rate. What is more interesting, the α-doped ß phase and the ß-doped α phase organic microcrystals can also be fabricated by modulating the evaporation rate from 100 to 10 µL min-1 . The findings can contribute to the future development of organic optoelectronics at the microscale.

Optical properties of Eu2+ /Eu3+ mixed valence phosphor Ca2 SiO2 F2 :Eu2+ /Eu3.

The Eu2+ /Eu3+ mixed valence phosphor Ca2 SiO2 F2 :Eu2+ /Eu3+ was prepared using a solid-state reaction synthesis method in a CO atmosphere, and the optical properties were investigated. The spectroscopic properties revealed that Ca2+ ions were occupied by both Eu2+ and Eu3+ ions in Ca2 SiO2 F2 , and both ions were able to generate their characteristic emissions. A broad 5d â†’ 4f Eu2+ band at ~470 nm and narrow 4f â†’ 4f Eu3+ peaks upon excitation with n-UV light were observed. The ratio between Eu2+ and Eu3+ emissions changed regularly, and the relative intensity of the red component from Eu3+ became systematically stronger with increasing overall Eu content. As a result, the emission color of these phosphors can be tunable from blue to pink under n-UV light excitation.

Tunable emission, energy transfer and charge compensation in SrMoO4:Sm(3+),Tb(3+),Na(+) phosphor.

A series of SrMoO4:Sm(3+),Tb(3+),Na(+) phosphors was synthesized using a high-temperature solid-state reaction method in air. On excitation at 290 nm, SrMoO4:Sm(3+),Tb(3+) phosphor emitted light that varied systematically from green to reddish-orange on changing the Sm(3+) and Tb(3+) ion concentrations. The emission intensities of SrMoO4:Sm(3+) and SrMoO4:Sm(3+),Tb(3+) phosphors were increased two to four times due to charge compensation when Na(+) was added as a charge compensator. The luminescence mechanism and energy transfer could be explained using energy-level diagrams of the MoO4(2-) group, Sm(3+) and Tb(3+) ions. SrMoO4:Sm(3+),Tb(3+),Na(+) could be used as reddish-orange phosphor in white light-emitting diodes (LEDs) based on an ~ 405 nm near-UV LED chip. This research is helpful in adjusting and improving the luminescence properties of other phosphors.

Linearly tunable emission colors obtained from a fluorescent-phosphorescent dual-emission compound by mechanical stimuli.

Organic mechanoluminochromic materials are mechano/piezo-responsive and promising for applications in sensors, displays, and data storage devices. However, their switching range of emission is seriously impeded by only one kind of emission (either a fluorescent or phosphorescent peak) in the spectrum of single organic compounds. This study presents a design strategy for pure organic compounds with excellent room-temperature fluorescent-phosphorescent dual-emission (rFPDE) properties, which combines the effective factors of dipenylsulfone group, crystalline state, and heavy atom effect. Following the principle of color mixing, myriad emission colors with a wide range from orange to purple and across white zone in a straight line in the chromaticity diagram of the Commission Internationale de l'Eclairage (CIE) can be obtained by simply mechanical grinding the compound. The unique properties could be concentrated on a pure organic compound through this design strategy, which provides a new efficient channel for the discovery of efficient mechano-responsive organic materials.

The use of a microreactor for rapid screening of the reaction conditions and investigation of the photoluminescence mechanism of carbon dots.

A microreactor is applied and reported, for the first time, in the field of research of carbon dots (CDs), including rapid screening of the reaction conditions and investigation of the photoluminescence (PL) mechanism. Various carbonaceous precursors and solvents were selected and hundreds of reaction conditions were screened (ca. 15 min on average per condition). Through analyzing the screened conditions, tunable PL emission maxima, from about 330 to 550 nm with respectable PL quantum yields, were achieved. Moreover, the relationship between different developmental stages of the CDs and the PL properties was explored by using the microreactor. The PL emission was observed to be independent of the composition, carbonization extent, and morphology/size of the CDs. This study unambiguously presents that a microreactor could serve as a promising tool for the research of CDs.

Ultranarrow Deep-Blue Luminescence of Perovskite Nanocrystals by A-Site Cation Control.

Metal-halide perovskite nanocrystals (NCs) are one of the most promising emitters for the application of display and nanolight sources. The full width at half-maximum (FWHM) of photoluminescence (PL) emission is essential for color purity, which however remains a difficulty to further reduce the FWHM of the perovskite NCs at room temperature. Here, we show the quasi-sphere perovskite NCs with narrow PL emission at a deep-blue wavelength of ∼430 nm; its PL FWHM reaches ∼11 nm at room temperature, owing to the monodispersion in size distribution as well as the symmetric quasi-sphere morphology of NCs releasing the fine structure splitting-induced inhomogeneous broadening. Through regulating A cations with respect to the ratio of FA (or MA)-to-Cs and Cs-to-Pb, the PL emission of the NCs could be tuned from ∼505 to ∼430 nm combined with varied morphologies from large cube to small quasi-sphere. Such spectroscopic and morphological discrepancies are supposed to be attributed to the different crystalline kinetics that is strongly dependent on the synthetic condition. To be specific, in the case of increasing FA (or MA)-to-Cs, the growth rate of CsPbBr3 and FAPbBr3 (or MAPbBr3) perovskites is determined by the reactivity of transient species, while in the case of decreasing the Cs-to-Pb ratio, the growth rate of perovskites is slowed down by the serious reduction of Cs+ in the precursor. This study provides an effective strategy to adjust the emission across from green to deep-blue color and promotes the perovskite NCs with a narrow FWHM, and tunable PL emission facilitates in application of optoelectronic devices.