Use of linear polymers to control the preparation of luminescent organic microcrystals

Microcrystals of an organic fluorescent dye, 4-octylamino-7-nitrobenz-2-oxa-1,3-diazole, were generated using the reprecipitation method, which is a solvent exchange process. In the presence of polymers, namely, poly(acrylic acid), molecular weight 5100 g mol(-1) and 15 000 g mol(-1), and poly(acrylic acid-co-maleic acid), average molecular weight about 50 000 g mol(-1), used as their sodium salts, the reprecipitation process was strongly accelerated. The reprecipitation kinetics was monitored by UV/vis absorption spectroscopy and revealed a three-step mechanism, each step being influenced by the polymer. The size and shape of the microcrystals were analyzed by fluorescence microscopy. The microcrystals obtained in the presence of polymers were smaller and more regular than those prepared in water alone and were not agglomerated. When the polymer was placed in the reprecipitation medium before introducing the dye solution, the microcrystals displayed a rectangular shape. When the polymer was introduced 20 min after the beginning of the reprecipitation process, intricately structured flowerlike microcrystals were observed. Microanalysis revealed that the microcrystals contained noticeable amounts of polymer. The measurement of the surface electric zeta potential suggested that a proportion of the polymer was present at the microcrystal surface. This work gives a thorough insight into a field where trials have until now been performed in an empirical way. It opens new perspectives to produce low-cost organic microcrystals, potentially useful in optics or pharmaceutical sciences.     

Morphology control of organic luminescent microcrystals and approach of their optical properties

Microcrystals of an organic fluorescent dye, 4-octylamino-7-nitrobenz-2-oxa-1,3-diazole, were prepared using a reprecipitation method, based on solvent-exchange. We show here that their shape and size can be nicely tuned by the presence of various macromolecules in the reprecipitation medium. To do so, poly(acrylic acid) and calf thymus DNA were used as additives. Homogeneous populations of microcrystals were thus obtained in a reproducible way. Their size and morphology varied with the additive used. The UV/vis absorption and luminescence properties of these microcrystals in suspension are briefly reported. To cite this article: M. Abyan et al., C. R. Chimie 8 (2005).     

Dendrimer-tuned formation of fluorescent organic microcrystals. Influence of dye hydrophobicity and dendrimer charge

The reprecipitation method is a simple and useful way to prepare microcrystals through a solvent exchange process. It was applied to three fluorescent dyes of the 4-amino-7-nitrobenz-2-oxa-1,3-diazole series. Compounds 1, 2, and 3 differ by the length of the alkyl chain, which comprises 8, 12, and 18 carbon atoms, respectively. The reprecipitation process was first studied in water, in the absence of additives. The kinetics was monitored by UV/vis absorption spectroscopy. The size and shape of the microparticles were analyzed by fluorescence microscopy and transmission electron microscopy. Dyes 1 and 2 lead to microcrystals, the whole process taking much more time for 2 than for 1. The long-chained dye 3 only gave stable aggregates. Therefore, it appears that the hydrophobicity of the organic dye markedly influenced the reprecipitation process. The latter was then studied in the presence of additives. Poly(amidoamine) dendrimers, terminated by 64 carboxylate or amino groups were placed in the reprecipitation medium. They had little effect upon the formation of aggregates for dye 3. In contrast, they drastically accelerated the reprecipitation of 1 and 2 and tuned the size and shape of the microcrystals. Platelets and spindles were thus obtained by varying the nature of the dendrimer, and their optical properties were briefly investigated.     

Dendrimer-tuned formation of luminescent organic microcrystals

Microcrystals of an organic fluorescent dye, 4-n-octylamino-7-nitrobenz-2-oxa-1,3-diazole (NBD-C8), were prepared by reprecipitation in water. The crystallization kinetics was monitored by UV/vis absorption spectroscopy, and a model was proposed. The size and shape of the microcrystals were analyzed by laser light scattering, fluorescence microscopy, and scanning electron microscopy. In the presence of PAMAM dendrimers of generation 2.5, 3.5, and 4.5, the crystallization process was drastically accelerated. The crystals obtained were smaller and more regular than those formed in pure water and were not agglomerated. There are probably two levels of interaction of NBD-C8 with the dendrimers, which act as both templates and colloid stabilizers.     

新型中空卤化银颗粒乳剂的制备和性能研究V.中空卤化银T颗粒乳剂的制备和性能研究

８０ 年代以来,许多新型的卤化银微晶已在新开发的各种高质量感光材料中得到应用．近十年来在国内外文献中又出现新型中空卤化银微晶制备方法的报道．本文着重研究一种表面有许多小孔及凹坑的中空卤化银Ｔ颗粒的制备方法和感光性能．由于其独特的孔洞结构,使位错、缺陷增加,填隙银离子浓度增加和电子陷阱增多,潜影形成效率提高,从而达到提高乳剂感光性能的目的．     

Femtosecond fluorescence dynamics imaging using a fluorescence up-conversion microscope

Femtosecond fluorescence dynamics imaging microscopy was performed. Femtosecond fluorescence dynamics images were constructed based on the "mean" fluorescence decay or rise time constants that were evaluated by the time-resolved intensity sampling using a fluorescence up-conversion microscope. This dynamics imaging microscopy was carried out for the organic microcrystals alpha-perylene and tetracene-doped anthracene microcrystal, and ultrafast dynamics in the organic microcrystals were clearly imaged in the two-dimensional manner. For the alpha-perylene microcrystal, the obtained dynamics images showed that the crystal edges exhibited relatively shorter free exciton and the Y-state lifetimes compared to the crystal center, reflecting the higher concentration of defects. For the tetracene-doped anthracene microcrystal, the image was constructed based on the time constant of excitation energy transfer from anthracene to tetracene. By experiments changing the doping ratio of tetracene in anthracene, it was concluded that the inhomogeneity observed in the dynamics image arises from the difference in the local concentration of tetracene in the mixed crystal.     

立方体溴化银颗粒光谱增感的电子转移超快动力学研究

本文利用皮秒时间分辨条纹相机技术检测了3种染料在立方颗粒溴化银上吸附后形成聚集体的荧光光谱,分析了3种染料在不同染料浓度下对染料聚集体到溴化银导带的超快电子转移过程的影响,进而分析其对增感效率的影响关系,并探讨了增感过程的微观机理.实验结果表明,荧光衰减的动力学曲线与一个双指数函数拟合得相当好,存在一快一慢两个衰减成分,快衰减成分占拟合较大比例,表明其源于与荧光衰减相竞争的从激发态染料聚集体到AgBr导带的电子转移.光致电子转移的速率及增感效率随着染料相对浓度的增加表现出一定的变化趋势,染料浓度增加,增感效率减小.     

新型中空卤化银颗粒乳剂的制备和性能研究Ⅵ.中空立方体卤化银颗粒乳剂的制备和感光性能研究

中空卤化银微晶制备方法已在国内外有关文献中报道[1～7],然而关于中空立方体颗粒乳剂的基本性能及实际应用方面的研究尚未见报道.     

Microcrystals of polydiacetylene derivatives and their linear and nonlinear optical properties

Organic microcrystals which are expected to have interesting and fascinating physical properties were fabricated by a reprecipitation method as aqueous dispersions. Many kinds of organic compounds have been microcrystallized by this convenient method. The size control has been extensively investigated for a polydiacetylene and succeeded in the range from several tens of nanometers to several micrometers by adjusting the temperature and concentration. Linear optical properties of these well-defined polydiacetylene microcrystals have been investigated and interesting size and temperature dependences of excitonic absorption are demonstrated. Nonlinear optical (NLO) properties of polydiacetylene microcrystals have also been evaluated by means of a Z-scan technique, and an extremely high nonlinear refractive index at the resonant wavelength was shown.     

CaWO4核/卤化银壳光敏微晶的制备及性能研究

用于感光材料的卤化银微晶合成技术近二十年来取得了很大进展,合成出了诸如T-颗粒、核壳乳剂和外延复合颗粒等,使感光材料的性能日趋优异。但由于感光化学反应(如化学增感、光谱增感、潜影形成及显影过程等)基本上都发生在微晶的表面,而微晶核内部的卤化银却未发生作用,而随定影过程被溶解成废液,这样便造成贵金属银的浪费。     

新型中空卤化银颗粒乳剂的制备和性能研究 Ⅲ.中空卤化银颗粒乳剂感光性能的研究

本文应用表面显影、Dember效应、化学成熟、光谱增感等方法,对照实心立方体溴化银乳剂研究了中空卤化银微晶的结构与光物理性质及感光性能的关系。实验结果表明:(1)中空卤化银的潜影在孔洞处优先形成;(2)中空卤化银微晶中位错、缺陷较多,其填隙银离子浓度较大,电子陷阱较多;(3)中空颗粒表面反应活性高,感光度高,光谱增感效果好;(4)中空颗粒乳剂其反差较大,最大密度较高;(5)上述结果均可归因于中空卤化银微晶所特有的孔洞结构。     

片状多层结构卤化银微晶的制备、结构和性能的研究Ⅰ

本文利用可控双注法制备了一系列片状多导层结构Ag(Br,I)微晶,用扫描透射电镜(STEM)与X射线能谱仪(EDS)对单个微晶进行了微区分析,结果表明碘离子在微晶中的分布正如所设计的那样呈层状分布。EDS分析结果表明,富碘层的碘离子向无碘层迁移,且富碘层的碘浓度愈高,迁移的趋势愈大。并用介电损耗Dember效应、表面显影和化学成熟等方法研究了片状多层结构微晶的结构与性能的关系。     

银－金红石复合纳米微晶的光谱性能

λ>330nm光照射含有金红石型TiO2微晶颗粒的AgNO3溶液,制备出了Ag-TiO2复合超微粒子,与纯的银溶胶相比,复合粒子上银的等离子体吸收峰宽化红移,位于400～600nm。这种复合超微粒子的溶胶,表现出表面增强拉曼散射(SERS)效应。吸附-共振增强可用来解释Ag-TiO2复合粒子的SERS效应。     

Solvent‐Induced Structural Transition of Self‐Assembled Dipeptide: From Organogels to Microcrystals

Organogels that are self‐assembled from simple peptide molecules are an interesting class of nano‐ and mesoscale soft matter with simplicity and functionality. Investigating the precise roles of the organic solvents and their effects on stabilization of the formed organogel is an important topic for the development of low‐molecular‐weight gelators. We report the structural transition of an organogel self‐assembled from a single dipeptide building block, diphenylalanine (L ‐Phe‐L ‐Phe, FF), in toluene into a flower‐like microcrystal merely by introducing ethanol as a co‐solvent; this provides deeper insights into the phase transition between mesostable gels and thermodynamically stable microcrystals. Multiple characterization techniques were used to reveal the transitions. The results indicate that there are different molecular‐packing modes formed in the gels and in the microcrystals. Further studies show that the co‐solvent, ethanol, which has a higher polarity than toluene, might be involved in the formation of hydrogen bonds during molecular self‐assembly of the dipeptide in mixed solvents, thus leading to the transition of organogels into microcrystals. The structural transformation modulated by the co‐solvent might have a potential implication in controllable molecular self‐assembly.     

Influence of Embedded Protons on the Structure of Ice Microcrystals. Computer Simulation

Ice microcrystals of 40 molecules with embedded proton and placed in the external electric field were simulated by the Monte Carlo method in connection with the problem of the destruction of the ozone layer in the stratosphere. The proton field does not disturb the cluster crystalline state, whereas the electric field of crystal defects on the ice surface can affect essentially the microcrystal melting and destroy the structural transition. The melting of microcrystals is mainly reduced to the distortion of orientational molecular order.     

板状复合型碘溴化银微晶的光物理性能与其碘含量的关系

本论文测定了碘含量对板状碘溴化银微晶的光吸收的影响,并利用Dember光电效应、低温荧光、高低照曝光等光物理方法研究所制备微晶的固体物理性质,发现微晶中碘含量的增加使光吸收增加。在低照曝光时,所有的乳剂均发生低照互易律失效,而在高照曝光时仅是碘含量为18 mol%的乳剂发生高照互易律失效。板状碘溴化银微晶乳剂的Dember效应和低温荧光的实验结果表明,微晶中的碘含量增加使Dember光生电压值下降,光电压表减时间变短,荧光强度下降,说明碘离子掺入量的增加使微晶中的缺陷数目增加,导致电子陷阱数和填隙银离子的浓度增加,造成光电子被捕获。     

卤化银乳剂微晶体的结构与性能研究——Ⅳ.八面体核壳复合结构乳剂的制备及其几何性质

应用自动控制pAg的双注仪制备了一个系列的溴碘化银核壳复合结构的乳剂。用STEM-EDS研究了碘的含量及其加入方式对于卤化银扎剂微晶体的几何性质(颗粒大小、形状)及其碘在微晶体中的分布的影响。结果表明:碘化钾加入的时间越早,加入的浓度越大,则碘离子越富集于微晶体的核心。微晶体中确实存在着富碘相与贫碘相的复合结构。随碘含量的增加,颗粒尺寸减小,颗粒的晶形由规整的八面体向圆角八面体过渡,而碘的分布也由体相核心向边缘表面不断扩散,从而使核壳型的富碘相和贫碘相复合结构的界面趋向模糊。     

Photochromism of spiropyran nanocrystals embedded in sol-gel matrices

Spectroscopic and kinetic properties of a new photochromic medium, consisting of nanocrystals of spyropyran molecules (1,3-dihydro-1,3,3,5',6',pentamethyl-spiro[2H-indole-2,2'-[2H]pyrano [3,2-b]pyridinium] iodide) embedded in an organo-silicate sol-gel film, are presented and compared to microcrystals obtained by slow evaporation of a solvent. High photoconversion efficiencies for both kinds of crystals have been observed. In microcrystals, the photomerocyanine form absorbs at 570 nm with a fading rate of 5 h, in nanocrystals the photomerocyanine form absorbs at 535 nm with a fading rate of 41 h. Therefore, the crystalline structure of nanocrystals is different from the microcrystal one.     

Copper hydroxide nano and microcrystal: facile synthesis, shape evolution and their catalytic properties

In this paper, the morphology of copper hydroxide nano/microcrystals is finely controlled by adjusting the concentration of surfactant and NH(4)Cl as well as the reaction temperature, to provide plates, belts, wires, rods and urchin-like spheres, among others. A tree-type multiple head surfactant, bis (amidoethyl-carbamoylethyl) octadecylamine (C18N3), was used to prepare the copper hydroxide nano/microcrystals and it acted as a face-selective additive in the reaction system. The morphology of the Cu(OH)(2) microcrystals could be transformed from elliptical plates into truncated square plates as the NH(4)Cl concentration was increased. The results showed that the Cu(OH)(2) crystals were better than the amorphous type of Cu(OH)(2) in catalyzing the oxidation of resorcinol with H(2)O(2). Additionally, an investigation of the formation process of the nano/microcrystals was performed, which we believe is valuable for a precise understanding of the formation and fabrication of other metal hydroxides and metal oxides.     

卤化银乳剂微晶体的结构与性能研究 ⅩⅡ.碘分布对电性质和照相性能的影响

本文应用双注法制备了一系列碘分布不同的八面体核壳乳剂。测定了乳剂微晶的光吸收、离子电导,微波光导和照相性能。