Vapor Phase Growth of Centimeter-Sized Band Gap Engineered Cesium Lead Halide Perovskite Single-Crystal Thin Films with Color-tunable Stimulated Emission

Single crystal metal halide perovskites thin films are considered to be a promising optical, optoelectronic materials with extraordinary performance due to their low defect densities. However, it is still difficult to achieve large-scale perovskite single-crystal thin films (SCTFs) with tunable bandgap by vapor-phase deposition method. Herein, the synthesis of CsPbCl_3(1–x)Br_3x SCTFs with centimeter size (1 cm × 1 cm) via vapor-phase deposition is reported. The Br composition of CsPbCl_3(1–x)Br_3x SCTFs can be gradually tuned from x = 0 to x = 1, leading the corresponding bandgap to change from 2.29 to 2.91 eV. Additionally, an low-threshold (≈23.9 µJ cm⁻²) amplified spontaneous emission is achieved based on CsPbCl_3(1–x)Br_3x SCTFs at room temperature, and the wavelength is tuned from 432 to 547 nm by varying the Cl/Br ratio. Importantly, the high-quality CsPbCl_3(1–x)Br_3x SCTFs are ideal optical gain medium with high gain up to 1369.8 ± 101.2 cm⁻¹. This study not only provides a versatile method to fabricate high quality CsPbCl_3(1–x)Br_3x SCTFs with different Cl/Br ratio, but also paves the way for further research of color-tunable perovskite lasing.     

Recent Progress of Bismuth Effect on All-Inorganic Lead-Free Metal Halide Derivatives: Crystals Structure,Luminescence Properties,and Applications

Bismuth (Bi³⁺)-included lead-free metal halide (LFMH) materials attract much attention in lighting, display, photodetectors, X-ray detectors, and photovoltaic fields, due to the tunable luminescence and optoelectronic performance in response to crystal and electronic structure, morphology, and particle sizes. This review summarizes Bi³⁺-included LFMH materials about their preparation approach, crystal and electronic structure properties, luminescence performance, and emerging applications. Notably, Bi³⁺ ions not only can act as framework cation to construct stable LFMH structure, but can also incorporate into LFMH materials as activators or sensitizers to generate remarkable luminescence tuning and band engineering. The Bi³⁺ effect on the luminescence and optoelectronic properties of LFMH materials, including, promotion of exciton localization, enhancement of light absorption in near-ultraviolet region, action as sensitizer ions to transfer energy to rare earth or transition metal ions and emission of highly-efficient light is systematically summarized. The proposed structure-luminescence relationship offers guidance for the optimization of current Bi³⁺-included LFMH materials and the exploitation of new LFMH derivatives.     

含茂钛低聚物的制备与光谱

文中报道两种新的含茂钛低钛物Cp_2Ti(Cl)-O-[-Ti(Cp)(O_2CCH_4CH-O)-O-]n-H(Ⅰ)与Cp_2Ti(Cl)-O-[-Ti(Cp)(O_2CCH_2CH)-O-]_u-H(Ⅰ)的制备并用元素分析和光谱(IR,1~H NMR,MS)对它们进行了鉴定。     

Ligand-promoted palladium-catalyzed β-methylene C–H arylation of primary aldehydes

The transient directing group (TDG) strategy allowed long awaited access to the direct β-C(sp³)–H functionalization of unmasked aliphatic aldehydes via palladium catalysis. However, the current techniques are restricted to terminal methyl functionalization, limiting their structural scopes and applicability. Herein, we report the development of a direct Pd-catalyzed methylene β-C–H arylation of linear unmasked aldehydes by using 3-amino-3-methylbutanoic acid as a TDG and 2-pyridone as an external ligand. Density functional theory calculations provided insights into the reaction mechanism and shed light on the roles of the external and transient directing ligands in the catalytic transformation.

Aliphatic aldehydes are among the most common structural units in organic and medicinal chemistry research. Direct C–H functionalization has enabled efficient and site-selective derivatization of aliphatic aldehydes.

Simple aliphatic functional groups enrich the skeletal backbones of many natural products, pharmaceuticals, and other industrial materials, influencing the utility and applications of these substances and dictating their reactivity and synthetic modification pathways. Aliphatic aldehydes are some of the most ubiquitous structural units in organic materials.¹ Their relevance in nature and industry alike, combined with their reactivity and synthetic versatility, attracted much attention from the synthetic organic and medicinal chemistry communities over the years (Fig. 1).² Efficient means to the functionalization of these molecules have always been highly sought after.Open in a separate windowFig. 1Select aliphatic aldehyde-containing medicines and biologically active molecules.Traditionally, scientists have utilized the high reactivity of the aldehyde moiety in derivatizing a variety of functional groups by the means of red-ox and nucleophilic addition reactions. The resourceful moiety was also notoriously used to install functional groups at the α-position via condensation and substitution pathways.³ Although β-functionalization is just as robust, it has generally been more restrictive as it often requires the use of α,β-unsaturated aldehydes.^4,5 Hence, transition metal catalysis emerged as a powerful tool to access β-functionalization in saturated aldehydes.⁶ Most original examples of metal-catalyzed β-C–H functionalization of aliphatic aldehydes required the masking of aldehydes into better metal coordinating units since free unmasked aldehydes could not form stable intermediates with metals like palladium on their own.⁷ Although the masking of the aldehyde moiety into an oxime, for example, enabled the formation of stable 5-membered palladacycles, affording β-functionalized products, this system requires the installation of the directing group prior to the functionalization, as well as the subsequent unmasking upon the reaction completion, compromising the step economy and atom efficiency of the overall process.⁸ Besides, some masking and unmasking protocols might not be compatible with select substrates, especially ones rich in functional groups. As a result, the development of a one-step direct approach to the β-C–H functionalization of free aliphatic aldehydes was a demanding target for synthetic chemists.α-Amino acids have been demonstrated as effective transient directing groups (TDGs) in the remote functionalization of o-alkyl benzaldehydes and aliphatic ketones by the Yu group in 2016.⁹ Shortly after, our group disclosed the first report on the direct β-C–H arylation of aliphatic aldehydes using 3-aminopropanoic acid or 3-amino-3-methylbutanoic acid as a TDG.¹⁰ The TDG was found to play a similar role to that of the oxime directing group by binding to the substrate via reversible imine formation, upon which, it assists in the assembly of a stable palladacycle, effectively functionalizing the β-position.¹¹ Since the binding of the TDG is reversible and temporary, it is automatically removed upon functionalization, yielding an efficient and step-economic transformation. This work was succeeded by many other reports that expanded the reaction and the TDG scopes.^12–14 However, this system suffers from a significant restriction that demanded resolution; only substitution of methyl C–H bonds of linear aldehydes was made possible via this approach (Scheme 1a–e). The steric limitations caused by incorporating additional groups at the β-carbon proved to compromise the formation of the palladacycle intermediate, rendering the subsequent functionalization a difficult task.¹²Open in a separate windowScheme 1Pd-catalyzed β-C–H bond functionalization of aliphatic aldehydes enabled by transient directing groups.Encouraged by the recent surge in use of 2-pyridone ligands to stabilize palladacycle intermediates,^15,16 we have successfully developed the first example of TDG-enabled Pd-catalyzed methylene β-C–H arylation in primary aldehydes via the assistance of 2-pyridones as external ligands (Scheme 1f). The incorporation of 2-pyridones proved to lower the activation energy of the C–H bond cleavage, promoting the formation of the intermediate palladacycles even in the presence of relatively bulky β-substituents.¹⁷ This key advancement significantly broadens the structural scopes and applications of this process and promises future asymmetric possibilities, perhaps via the use of a chiral TDG or external ligand or both. Notably, a closely related work from Yu''s group was published at almost the same time.¹⁸We commenced our investigation of the reaction parameters by employing n-pentanal (1a) as an unbiased linear aldehyde and 4-iodoanisole (2a) in the presence of catalytic Pd(OAc)₂ and stoichiometric AgTFA, alongside 3-amino-3-methylbutanoic acid (TDG1) and 3-(trifluoromethyl)-5-nitropyridin-2-ol (L1) at 100 °C (ii) sources proved Pd(OAc)₂ to be the optimal catalyst, while Pd(TFA)₂, PdCl₂ and PdBr₂ provided only moderate yields (entries 10–12). Notably, a significantly lower yield was observed in the absence of the 2-pyridone ligand, and no desired product was isolated altogether in the absence of the TDG (entries 13 and 14). The incorporation of 15 mol% Pd catalyst was deemed necessary after only 55% yield of 3a was obtained when 10 mol% loading of Pd(OAc)₂ was instead used (entry 15).Optimization of reaction conditions^a

Entry	Pd source	L (mol%)	TDG1 (mol%)	Solvent (v/v, mL)	Yield (%)
1	Pd(OAc)2	L1 (30)	TDG1 (40)	HFIP	30
2	Pd(OAc)2	L1 (30)	TDG1 (40)	AcOH	<5
3	Pd(OAc)2	L1 (30)	TDG1 (40)	HFIP/AcOH (1 : 1)	28
4	Pd(OAc)2	L1 (30)	TDG1 (40)	HFIP/AcOH (9 : 1)	47
5	Pd(OAc)2	L1 (30)	TDG1 (40)	HFIP/AcOH (1 : 9)	<5
6	Pd(OAc)2	L1 (30)	TDG1 (60)	HFIP/AcOH (9 : 1)	50
7	Pd(OAc)2	L1 (30)	TDG1 (80)	HFIP/AcOH (9 : 1)	25
8	Pd(OAc)2	L1 (60)	TDG1 (60)	HFIP/AcOH (9 : 1)	70(68)b
9	Pd(OAc)2	L1 (75)	TDG1 (60)	HFIP/AcOH (9 : 1)	51
10	Pd(TFA)2	L1 (60)	TDG1 (60)	HFIP/AcOH (9 : 1)	60
11	PdCl2	L1 (60)	TDG1 (60)	HFIP/AcOH (9 : 1)	52
12	PdBr2	L1 (60)	TDG1 (60)	HFIP/AcOH (9 : 1)	54
13	Pd(OAc)2	—	TDG1 (60)	HFIP/AcOH (9 : 1)	9
14	Pd(OAc)2	L1 (60)	—	HFIP/AcOH (9 : 1)	0
15c	Pd(OAc)2	L1 (60)	TDG1 (60)	HFIP/AcOH (9 : 1)	55

Open in a separate window^aReaction conditions: 1a (0.2 mmol), 2a (0.4 mmol), Pd source (15 mol%), AgTFA (0.3 mmol), L1, TDG1, solvent (2.0 mL), 100 °C, 12 h. Yields are based on 1a, determined by ¹H-NMR using dibromomethane as an internal standard.^bIsolated yield.^cPd(OAc)₂ (10 mol%).To advance our optimization of the reaction conditions, a variety of 2-pyridones and TDGs were tested (Scheme 2). Originally, pyridine-2(1H)-one (L2) was examined as the external ligand, but it only yielded the product (3a) in 7% NMR yield. Similarly, other mono- and di-substituted 2-pyridone ligands (L3–L10) also produced low yields, fixating L1 as the optimal external ligand. Next, various α- and β-amino acids (TDG1–10) were evaluated, yet TDG1 persisted as the optimal transient directing group. These amino acid screening results also suggest that a [5,6]-bicyclic palladium species is likely the key intermediate in this protocol since only β-amino acids were found to provide appreciable yields, whereas α-amino acids failed to yield more than trace amounts of the product. The supremacy of TDG1 when compared to other β-amino acids is presumably due to the Thorpe–Ingold effect that perhaps helps facilitate the C–H bond cleavage and stabilize the [5,6]-bicyclic intermediate further.Open in a separate windowScheme 2Optimization of 2-pyridone ligands and transient directing groups.With the optimized reaction conditions in hand, substrate scope study of primary aliphatic aldehydes was subsequently carried out (Scheme 3). A variety of linear primary aliphatic aldehydes bearing different chain lengths provided the corresponding products 3a–e in good yields. Notably, relatively sterically hindered methylene C–H bonds were also functionalized effectively (3f and 3g). Additionally, 4-phenylbutanal gave rise to the desired product 3h in a highly site-selective manner, suggesting that functionalization of the methylene β-C–H bond is predominantly favored over the more labile benzylic C–H bond. It is noteworthy that the amide group was also well-tolerated and the desired product 3j was isolated in 60% yield. As expected, with n-propanal as the substrate, β-mono- (3k1) and β,β-disubstituted products (3k2) were isolated in 22% and 21% yields respectively. However, in the absence of the key external 2-pyridone ligand, β-monosubstituted product (3k1) was obtained exclusively, albeit with a low yield, indicating preference for functionalizing the β-C(sp³)–H bond of the methyl group over the benzylic methylene group.Open in a separate windowScheme 3Scope of primary aliphatic aldehydes. Reaction conditions: 1 (0.2 mmol), 2a (0.4 mmol), Pd(OAc)₂ (15 mol%), AgTFA (0.3 mmol), L1 (60 mol%), TDG1 (60 mol%), HFIP (1.8 mL), HOAc (0.2 mL), 100 °C, 12 h. Isolated yields. ^aL1 (60 mol%) was absent and yields are given in parentheses.Next, substrate scope study on aryl iodides was surveyed (Scheme 4). Iodobenzenes bearing either an electron-donating or electron-withdrawing group at the para-, meta-, or ortho-position were all found compatible with our catalytic system (3l–3ah). Surprisingly, ortho-methyl- and fluoro-substituted aryl iodides afforded the products in only trace amounts. However, aryl iodide with ortho-methoxy group provided the desired product 3ac in a moderate yield. Notably, a distinctive electronic effect pattern was not observed in the process. It should be mentioned that arylated products bearing halogen, ester, and cyano groups could be readily converted to other molecules, which significantly improves the synthetic applicability of the process. Delightfully, aryl iodide-containing natural products like ketoprofen, fenchol and menthol were proven compatible, supplying the corresponding products in moderate yields. Unfortunately, (hetero)aryl iodides including 2-iodopyridine, 3-iodopyridine, 4-iodopyridine and 4-iodo-2-chloropyridine failed to produce the corresponding products. Although our protocol provides a novel and direct pathway to construct β-arylated primary aliphatic aldehydes, the yields of most examples are modest. The leading reasons for this compromise are the following: (1) aliphatic aldehydes are easily decomposed or oxidized to acids; (2) some of the prepared β-arylated aldehyde products may be further transformed into the corresponding α,β-unsaturated aldehydes.Open in a separate windowScheme 4Scope of aryl iodides. Reaction conditions: 1a (0.2 mmol), 2 (0.4 mmol), Pd(OAc)₂ (15 mol%), AgTFA (0.3 mmol), L1 (60 mol%), TDG1 (60 mol%), HFIP (1.8 mL), HOAc (0.2 mL), 100 °C, 12 h. Isolated yields.Density functional theory (DFT) calculations were performed to help investigate the reaction mechanism and to elucidate the role of the ligand in improving the reactivity (Fig. 2). The condensation of the aliphatic aldehyde 1a with the TDG to form imine-1a was found thermodynamically neutral (ΔG° = −0.1 kcal mol⁻¹). As a result, it was permissible to use imine-1a directly in the calculations. According to the calculations results, the precatalyst [Pd(OAc)₂]₃, a trimeric complex, initially experiences dissociation and ligand metathesis with imine-1a to generate the Pd(ii) intermediate IM1, which is thermodynamically favorable by 21.9 kcal mol⁻¹. Consequently, the deprotonated imine-1a couples to the bidentate ligand to form the stable six-membered chelate complex IM1. Therefore, IM1 is indeed the catalyst resting state and serves as the zero point to the energy profile. We have identified two competitive pathways for the Pd(ii)-catalyzed C–H activation starting from IM1, one of which incorporates L1 and another which does not. On the one hand, an acetate ligand substitutes one imine-1a chelator in IM1 to facilitate the subsequent C–H activation leading to IM2, which undergoes C(sp³)–H activation through concerted metalation-deprotonation (CMD) viaTS1 (ΔG^‡ = 37.4 kcal mol⁻¹). However, this kinetic barrier is thought to be too high to account for the catalytic activity at 100 °C. On the other hand, the chelate imine-1a could be replaced by two N-coordinated ligands (L1) leading to the Pd(ii) complex IM3. This process is endergonic by 6.4 kcal mol⁻¹. To allow the ensuing C–H activation, IM3 dissociates one ligand (L1) producing the active species IM4, which undergoes TS2 to cleave the β-C(sp³)–H bond and form the [5,6]-bicyclic Pd(ii) intermediate IM5. Although this step features an energy barrier of 31.2 kcal mol⁻¹, it is thought to be feasible under the experimental conditions (100 °C). Possessing similar coordination ability to that of pyridine, the ligand (L1) effectively stabilizes the Pd(ii) center in the C–H activation process, indicating that this step most likely involves a manageable kinetic barrier. This result explicates the origin of the ligand-enabled reactivity (TS2vs.TS1). Additionally, we considered the γ-C(sp³)–H activation pathway viaTS2′ which was found to have a barrier of 35.5 kcal mol⁻¹. The higher energy barrier of TS2′ compared to that of TS2 is attributed to its larger ring strain in the [6,6]-bicyclic Pd(ii) transition state, which reveals the motive for the site-selectivity. Reverting back to the supposed pathway, upon the formation of the bicyclic intermediate IM5, it undergoes ligand/substrate replacement to afford intermediate IM6, at which the Ar–I coordinates to the Pd(ii) center to enable oxidative addition viaTS3 (ΔG^‡ = 27.4 kcal mol⁻¹) leading to the five-coordinate Pd(iv) complex IM7. Undergoing direct C–C reductive elimination in IM7 would entail a barrier of 29.6 kcal mol⁻¹ (TS4). Alternatively, iodine abstraction by the silver(i) salt in IM7 is thermodynamically favorable and irreversible, yielding the Pd(iv) intermediate IM8 coordinated to a TFA ligand. Subsequently, C–C reductive coupling viaTS5 generates the Pd(ii) complex IM9 and concludes the arylation process. This step was found both kinetically facile (6.1 kcal mol⁻¹) and thermodynamically favorable (30.7 kcal mol⁻¹). Finally, IM9 reacts with imine-1avia metathesis to regenerate the palladium catalyst IM1 and release imine-3a in a highly exergonic step (21.0 kcal mol⁻¹). Ultimately, imine-3a undergoes hydrolysis to yield the aldehyde product 3a and to release the TDG.Open in a separate windowFig. 2Free energy profiles for the ligand-promoted Pd(ii)-catalyzed site-selective C–H activation and C–C bond formation, alongside the optimized structures of the C–H activation transition states TS1 and TS2 (selected bond distances are labelled in Å). Energies are relative to the complex IM1 and are mass-balanced.     

The Antibacterial Activity Mode of Action of Plantaricin YKX against Staphylococcus aureus

We aimed to evaluate the inhibitory effect and mechanism of plantaricin YKX on S. aureus. The mode of action of plantaricin YKX against the cells of S. aureus indicated that plantaricin YKX was able to cause the leakage of cellular content and damage the structure of the cell membranes. Additionally, plantaricin YKX was also able to inhibit the formation of S. aureus biofilms. As the concentration of plantaricin YKX reached 3/4 MIC, the percentage of biofilm formation inhibition was over 50%. Fluorescent dye labeling combined with fluorescence microscopy confirmed the results. Finally, the effect of plantaricin YKX on the AI-2/LuxS QS system was investigated. Molecular docking predicted that the binding energy of AI-2 and plantaricin YKX was −4.7 kcal/mol and the binding energy of bacteriocin and luxS protein was −183.701 kcal/mol. The expression of the luxS gene increased significantly after being cocultured with plantaricin YKX, suggesting that plantaricin YKX can affect the QS system of S. aureus.     

半导体锗纳米团簇和纳米层的生成与结构研究

我们在硅锗合金衬底上采用氧化等制膜方式生成零维和二维的纳米结构样品，用高精度椭偏仪(HPE)、卢瑟福背散射谱仪(RBS)和高分辨率扫描透射电子显微镜(HR-STEM)测量样品的纳米结构，并采用美国威思康新州立大学开发的Rump模拟软件对卢瑟福背散射谱(RBS)中的CHANNEL谱和RANDoM谱分别进行精细结构模拟，测量并计算出纳米氧化层与锗的纳米薄膜结构分布，并且反馈控制加工过程，优化硅锗半导体材料纳米结构样品的加工条件。我们测量出样品横断面锗纳米团簇和纳米层的PL发光谱。我们在硅锗合金的氧化层表面中首次发现纳米锗量子点组成的几个纳米厚的盖帽膜结构，我们首次提出的生成硅锗纳米结构的优化加工条件的氧化时间和氧化温度匹配公式的理论模型与实验结果拟合得很好。     

碳纳米管薄膜微光纤气体传感器的模场分析

基于包层薄膜折射率对微光纤中传输光能量分布的影响,进一步用模场分析仪观察碳纳米管薄膜微光纤在与二甲苯气体接触时,输出光的能量分布和倏逝场的变化。实验结果显示,未镀膜的微光纤暴露在一定浓度的二甲苯气体环境下时,表现出对光很弱的约束能力;而把碳纳米管薄膜微光纤置于与之相同浓度的气体环境时,微光纤的输出光强减小,高阶模的能量发生不稳定的变化,最后待气体挥发完全至浓度稳定后,薄膜微光纤输出光场高阶模能量减小,微光纤的能量分布趋向于高斯分布。     

非致冷焦平面热成象技术及其应用

９０年代以后，非致冷红外焦平面技术的实用化成为红外热成象技术中最引入注目的突破之一，基估军事和民用领域的广泛应用前景受到国内外的普遍重视。本文综述了非致冷红外焦平面技术的两大技术途径及其特点、发展趋势和应用情况，并了发展我国非致冷红外焦平面技术的途径。     

A 2D quadrangular pyramid photoelectric autocollimator with extended angle measurement range

A photoelectric autocollimator with high accuracy and extended measurement range based on the quadrangular pyramid is proposed, and the corresponding algorithms are also deduced. A new image processing algorithm has been proposed to improve the accuracy, and the corresponding errors are also estimated, the error does not exceed half a pixel when the distance between the marks more than two radii. The experimental results have verified that the measurement range of the proposed two-dimensional (2D) quadrangular pyramid photoelectric autocollimator can be increased times than that of the flat mirror photoelectric autocollimator from 10′ to 15′. The accuracy is better than 1″ when the deflection is less than 15′.