Synthesis of high aspect ratio quantum-size CdS nanorods and their surface-dependent photoluminescence

Colloidal CdS nanorods with diameters near 4 nm and narrow size distributions ( approximately +/-10%) were synthesized up to 300 nm long by a sequential reactant injection technique that utilizes phosophonic acids as capping ligands. The phosphonic acid strongly passivates the nonpolar CdS surfaces and sequential reactant injection provides controlled CdS formation kinetics to enable heterogeneous and facet-selective CdS deposition on the more reactive {002} surfaces. With this process, the nanorod length can be systematically increased by increasing reactant addition to extend nanorod growth. The phosphonic acid concentration, however, is quite important, as "low" concentrations allow radial deposition and branching to occur. These high aspect ratio (>100) CdS nanorods luminesce with relatively high efficiencies of 10.8% quantum yield at room temperature. The luminescence, however, mostly arises from trap-related recombination, and the emission is significantly red-shifted from the absorption edge. Various surface passivation treatments were explored to eliminate trap emission and increase the luminescence quantum yield. Thiol and amine passivation both significantly reduced trap emission and enhanced band-edge emission, but the total luminescence quantum yields dropped significantly, with a maximum measured value of 1.5% for the amine-passivated CdS nanorods.     

Probing Distance‐Dependent Plasmon‐Enhanced Near‐Infrared Fluorescence Using Polyelectrolyte Multilayers as Dielectric Spacers

Owing to their applications in biodetection and molecular bioimaging, near‐infrared (NIR) fluorescent dyes are being extensively investigated. Most of the existing NIR dyes exhibit poor quantum yield, which hinders their translation to preclinical and clinical settings. Plasmonic nanostructures are known to act as tiny antennae for efficiently focusing the electromagnetic field into nanoscale volumes. The fluorescence emission from NIR dyes can be enhanced by more than thousand times by precisely placing them in proximity to gold nanorods. We have employed polyelectrolyte multilayers fabricated using layer‐by‐layer assembly as dielectric spacers for precisely tuning the distance between gold nanorods and NIR dyes. The aspect ratio of the gold nanorods was tuned to match the longitudinal localized surface plasmon resonance wavelength with the absorption maximum of the NIR dye to maximize the plasmonically enhanced fluorescence. The design criteria derived from this study lays the groundwork for ultrabright fluorescence bullets for in vitro and in vivo molecular bioimaging.     

钙钛矿量子点在荧光分析检测中的应用

钙钛矿量子点(PQDs)是一种新兴的发光纳米晶体,相较于传统量子点材料,PQDs有着高荧光量子产率、强量子光发射、窄发射带宽、可调谐发射波长等更为优异的光学性能,故而在荧光分析检测领域内具有广阔的应用前景。本文简述了PQDs的结构、合成及其光学调控;综述了PQDs在重金属离子、有机物、气体及阴离子荧光分析检测中的研究进展,对其检测效果及机理展开讨论分析;此外,本文还总结了PQDs在实际应用中存在问题的应对策略及解决思路,展望了其发展前景,以期为PQDs在荧光分析检测领域的进一步应用提供参考。     

Study of the absorption and emission spectroscopy of "A-B" type photosensitive compounds including two-photon chromophore and benzophenone moiety

"A-B" type photosensitive compounds including two-photon chromophore and benzophenone moiety have been designed, synthesized and characterized. The UV-vis absorption and fluorescence emission of the compounds have been extensively studied in various solvents. The results show that the absorption of "A-B" type compounds displays obvious double absorption bands, one of which at short-wavelength is related to the benzophenone moiety, the other at long-wavelength is mainly contributed by chromophore. The emission of "A-B" type compounds at 500-700nm shows an "unexpected" blue-shift comparing with that of the sole chromophore. The photosensitive compounds with amino group display strong emission in apolar solvents and have a low fluorescence quantum yields in polar solvents. In contrast, the compounds without amino group exhibit strong fluorescence emission in polar solvents, and low fluorescence quantum yields in apolar solvents. The fluorescence quantum yields of "A-B" type compounds are higher than those of the sole chromophore. The discoveries suggest that charge redistribution induced by the introduction of benzophenone moiety plays a key role on the absorption and emission spectroscopy.     

Fluorescence emission control and switching of oxymethylcrowned spirobenzopyrans by metal ion

Oxymethylcrowned spirobenzopyran 1 and pyrenylspirobenzopyran 2 were synthesized, and fluorescence emission of their corresponding merocyanine form was examined in the presence of metal ions. For 2, fluorescence emission derived from the pyrene moiety was completely quenched by photoinduced electron transfer (PET) of the nitrogen atom when the merocyanine form was not produced, namely, without metal ions. However, when 2 was converted to the merocyanine form by the complexation of its crown ether with a metal ion, fluorescence resonance energy transfer (FRET) from the pyrene to the merocyanine moieties took place to produce fluorescence emission. This result demonstrates that the spirobenzopyran isomerization can function as a fluorescence emission switch. Fluorescence quantum yield measurement for 1 and 2 showed that fluorescence emission depends on the binding metal ion in which the fluorescence quantum yield generally increased with the increase of metal ion radius.     

Novel gallium(III) phthalocyanine derivatives – Synthesis,photophysics and photochemistry

The syntheses of gallium(III) chloride phthalocyanine {(Cl)GaPc}, octaphenoxyphthalocyaninato gallium(III) chloride {(Cl)GaOPPc} and octakis(4-tert-butylphenoxy)phthalocyaninato gallium(III) chloride {(Cl)GaOTBPPc}; as well as their photophysical and photochemical parameters are hereby presented. Fluorescence quantum yields do not vary much among the three metallophthalocyanines (MPcs); therefore it was concluded that the effect of the substituents is not significant amongst (Cl)GaPc, (Cl)GaOPPc and (Cl)GaOTBPPc. Solvents effects, however, had an effect on the results. Triplet quantum yields were found to be lower in DMSO than in DMF and toluene. The rate constants for fluorescence, intersystem crossing and internal conversion as well as fluorescence and triplet lifetimes are reported. We have also reported photodegradation and singlet oxygen quantum yields. There was no clear correlation between the later parameters. It was, however, established that the three MPcs were stable.     

Incorporation of graphene in quantum dot sensitized solar cells based on ZnO nanorods

We demonstrate a novel architecture of solar cell by incorporating graphene thin film in a quantum dot sensitized solar cell. Quantum dot sensitized nanorods with a graphene layer exhibited a 54.7% improvement comparing a quantum dot sensitized ZnO nanorods without graphene layer. A fill factor as high as ～62% was also obtained.     

Influence of medium viscosity on photophysical properties of kynurenic acid and kynurenine yellow

Dependences of the fluorescence and triplet state quantum yields of kynurenic acid (1) and kynurenine yellow (2) in water—glycerol mixtures on medium viscosity have been studied. The main channel of the singlet excited state decay of compound 1 is the intersystem crossing, which rate weakly depends on the viscosity; only a small (approximately 1.5-fold) increase in the fluorescence yield was found for this compound with the increase of the solution viscosity from 0.84 cP (aqueous solution) to 78 cP (86% glycerol). The deactivation of the S₁ state of compound 2 is caused mainly by the internal conversion, and a noticeable increase of the fluorescence yield (approximately 3-fold), as well as the change in the photolysis product yields, was observed with the increasing percentage of glycerol in the mixture. The triplet state quantum yields for compounds 1 and 2 remained unchanged with the variation of the glycerol content in the mixture.     

明胶溶液中笤帚状纳米CdS的合成及其光谱特性研究

以明胶为稳定剂, 制备出CdS纳米棒, 并实现其向笤帚状纳米CdS的形貌转化. 扫描电镜(SEM)图像表明, 生长时间为2 d, 样品为棒状结构, 直径为50～140 nm, 长度为150～710 nm; 生长15 d的CdS微晶为笤帚状, 结节点直径340～620 nm, 长度2.7～8.4 μm. 探讨了其形貌转化的原因. 结合红外吸收(IR)和荧光光谱的测试结果, 提出了可能的离子络合转化和定位生长机理. 合成的CdS微晶具有一定的荧光性质, 并在紫外和荧光光谱上均表现出明显的量子尺寸效应.     

Preparation and optical properties of worm-like gold nanorods

A type of worm-like nanorods was successfully synthesized through conventional gold nanorods reacting with Na2S2O3 or Na2S. The generated worm-like gold nanorods comprise shrunk nanorod cores and enwrapped shells. Therefore, a gold-gold sulfide core-shell structure is formed in the process, distinguishing from their original counterparts. The formation of the gold chalcogenide layers was confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy. Experimental results showed that the thickness of the gold chalcogenide layers is controllable. Since the increase of shell thickness and decrease of gold nanorod core take place simultaneously, it allows one to tune the plasmon resonance of nanorods. Proper adjustment of reaction time, temperature, additives and other experimental conditions will produce worm-like gold nanorods demonstrating desired longitudinal plasmon wavelength (LPW) with narrow size distributions, only limited by properties of starting original gold nanorods. The approach presented herein is capable of selectively changing LPW of the gold nanorods. Additionally, the formed worm-like nanorods possess higher sensitive property in localized surface plasmon resonance than the original nanorods. Their special properties were characterized by spectroscopic methods such as Vis-NIR, fluorescence and resonance light scattering. These features imply that the gold nanorods have potential applications in biomolecular recognition study and biosensor fabrications.     

Hybrid microgels photoresponsive in the near-infrared spectral range

We report for the first time a photothermally responsive composite material based on polymer microgel particles doped with gold nanorods. We used the dependence of the longitudinal surface plasmon of the gold nanorods on their aspect ratio to synthesize nanoparticles with strong absorption in the near-IR spectral range (in the "water window"). The nanoparticles were incorporated in the interior of temperature-responsive poly(N-isopropylacrylamide-acrylic acid) microgels. Upon irradiation at lambda = 810 nm, hybrid microgel particles doped with Au nanorods underwent a strong deswelling phase transition. These photothermally responsive microgels can be used to carry and release small molecules (e.g., small protein molecules and drugs).     

Synthesis and characterization of wurtzite ZnTe nanorods with controllable aspect ratios

ZnTe nanorods with controllable aspect ratios were synthesized using polytellurides a tellurium precursor. The use of polytellurides which allow nucleation and growth at relatively low temperature is the key to formation of wurtzite phase and controlled anisotropic growth along c-axis. The aspect ratio of the resulting ZnTe nanorods was controlled by tuning the temperature that in turn controls the kinetics of the nanocrystal growth. A diameter dependent quantum confinement effect in ZnTe nanorods was observed by UV-vis absorption spectroscopy. Transient absorption measurements show ultrafast charge injection dynamics from ZnTe nanorods, suggesting their strong potential for applications in photocatalysis.     

柠檬酸盐稳定的水溶性CdSe量子点的合成及表征

以柠檬酸三钠为稳定剂在水溶液中合成了水溶性CdSe量子点,用X射线粉末衍射、透射电镜、紫外-可见吸收光谱和荧光发射光谱对CdSe量子点的结构、形貌及其荧光性质进行了表征.结果表明合成的CdSe量子点为立方闪锌矿结构,呈球形,分散性良好,平均尺寸约为2.6nm,具有窄且对称的荧光发射光谱,半峰宽为45nm.     

Multiple BODIPY derivatives with 1,3,5-triazine as core: balance between fluorescence and numbers of BODIPY units

The multiple BODIPY derivatives could exhibit higher fluorescence than mono-BODIPY derivatives but also might produce the stronger aggregation-induced quenching effect. It is important to investigate the relationship between fluorescence and numbers of BODIPY units. In this work, series of multiple BODIPY derivatives 2–5 with 1,3,5-triazine as core were designed and synthesized in high yields. A subtle balance between the fluorescence enhancement of multiple BODIPY units and fluorescence quenching based on H-aggregation of multiple BODIPY units was observed for these multiple BODIPY derivatives. Compound 3 bearing two BODIPY units with triazine as core presented the strongest fluorescence emission and highest fluorescence quantum yield. Compound 3 was successfully applied in viscosity measurement, exhibiting the linear relationship between fluorescence intensity (or steady-state emission anisotropy) and viscosity.     

含吡啶环的芳香醚-噁二唑类化合物的合成及其光谱研究

为开发新的高强度的有机电致发光材料, 用含烷氧基的取代苯甲酸(2)与2,6-吡啶二甲酰肼(3)在POCl3作用下, “一锅煮”法合成6个结构对称的含吡啶环的芳香醚-噁二唑4a～4f. 通过MS, IR, 1H NMR, 元素分析等手段对其结构进行了表征. 化合物的荧光性能测定结果显示此类化合物具有良好的荧光性, 其荧光发射波长均在347～507 nm范围内, 最大荧光发射波长在384 nm附近处, 且荧光强度较强. 在芳环上引入5-Br基团(4e, 4f), 化合物的荧光发射波长发生红移, 荧光强度有所减弱. 以硫酸奎宁作参比, 测定6个目标产物的荧光量子产率, 5-Br基团的引入对荧光量子产率没有明显影响. 同时讨论了代表性产物4a在不同溶剂中最大荧光激发波长处的荧光量子产率, 发现溶剂极性对该类化合物的荧光量子产率基本没有影响.     

Convenient one-pot procedure for synthesizing 4,4′-dimethoxy-boradiaza-s-indacene dyes and their application to cell labeling

We succeeded in developing a convenient one-pot pathway for synthesizing 4,4′-dimethoxy-boradiaza-s-indacene dyes 4a-d. The structures feature two methoxy groups in place of the fluorine atoms in 4,4′-difluoro-4-boradiaza-s-indacene. These novel dyes emitted green fluorescence and possessed moderate to high fluorescence quantum yields (Φ=0.32-0.93). We demonstrated that these dyes have applicability to cell labeling.     

Syntheses and properties of new photochromic diarylethene derivatives having a pyrazole unit

New photochromic diarylethenes 1a, 2a and 3a bearing a pyrazole unit have been synthesized. Their properties, including photochromic reactivity, fluorescence and electrochemical properties were investigated. These compounds showed good photochromic properties, high cycloreversion quantum yield and relatively strong fluorescence. The cycloreversion quantum yields of 1a, 2a and 3a are 0.46, 0.53 and 0.57, respectively, which are larger than those of their cyclization quantum yields (0.43, 0.45 and 0.47, respectively). The oxidations of diarylethenes 1a, 2a and 3a were initiated at 0.73, 1.11 and 0.79 V, respectively. Moreover, the position of the methoxyl substituent had remarkable impacts on the above optical and electrochemical properties.     

Design and In-silico study of bioimaging fluorescence Graphene quantum dot-Bovine serum albumin complex synthesized by diimide-activated amidation

Graphene quantum dot possesses advantageous characteristics like tunable fluorescence, nanometer size, low cytotoxicity, high biocompatibility enabling them as an ideal material for fluorescence bio-imaging. It exhibits a unique characteristic of DNA cleavage activity enhancer, gene/drug carrier, and anticancer targeting applications. In this article, we discussed the preparation of graphene quantum dot through the bottom-up method. Carbodiimide-activated amidation reactions were used for the functionalization of graphene quantum dot with Bovine Serum Albumin. Fluorescence spectroscopy data showed that the graphene quantum dot has size-dependent fluorescence emission. TEM and AFM studies showed that the size of graphene quantum dot was around 20 nm with narrow size distribution. Carbodiimide-activated amidation conjugation was successful in binding the protein onto graphene quantum dot and these conjugates were characterized by DLS, FTIR, fluorescence spectroscopy, and agarose gel electrophoresis. We also studied the structural-based in-silico molecular dynamic simulation by AutoDock, PyRx, and Discovery Studio Visualizer. Based on the virtual screening analysis and higher negative energy incorporation, it is observed that graphene quantum dot conjugated with bovine serum albumin quickly and formed is highly stable complex, which makes them a potential candidate for future applications in the field of bio-imaging, bio-sensing, gene/drug delivery, and tumor theragnostic.     

Peculiarities of exited state intramolecular proton transfer in 2-amino-3-(2′-benzazolyl)-quinolines

It has been shown that a low fluorescence quantum yield of 2-amino-3-(2′-benzoxazolyl)-quinoline (ABO) and 2-amino-3-(2′-benzothiazolyl)-quinoline (ABT) is due to the relaxation process caused by excited state intramolecular proton transfer (ESIPT). Quantum-chemical calculations have revealed that ESIPT in these compounds is characterized by overcoming a potential barrier, with the lower basicity of the proton-accepting moiety in ABO resulting in a higher barrier than in ABT and, thereby, determining a substantial difference in their fluorescence quantum yields.     

Switchable assembly of ultra narrow CdS nanowires and nanorods

We report on a simple route for the production of uniform and ultra narrow wurtzite CdS nanowires and nanorods. The nanorods are medium friendly (can exist in organic and aqueous phase) thus making them flexibly suitable for various applications. The centimeter range switchable ordering of the nanowires/rods into 3D microstrings by application of low magnitude DC electric field simply via two graphite electrodes is demonstrated. More sophisticated electrodes can be used for the same system to achieve more complex and fine patterns that can find potential use in nanoelectronics. The aligned microstrings (also wires/rods) show strong polarization dependence along their long axes. The polarized emission with respect to the unique c-axis makes the system suitable for orientation sensitive devices.