用“超分子板块构筑法”制备有机/无机组装体发光材料

一般说来,高分子材料可以由小分子单体通过化学键结合而成[1],也可以通过非化学键的所谓超分子组装而成[2～4].后者是近年来高分子合成中十分活跃的领域.我们尝试将上述两种方法相结合来设计合成高分子功能材料,利用超分子化学法在设计功能性基团方面的便利性[2,5]和经典化学法在成键方面的有效性,提出了用"超分子结构单元"构筑高分子的方法.     

Nanoscale connectivity in a TiO2/CdSe quantum dots/functionalized graphene oxide nanosheets/Au nanoparticles composite for enhanced photoelectrochemical solar cell performance

Electron transfer dynamics in a photoactive coating made of CdSe quantum dots (QDs) and Au nanoparticles (NPs) tethered to a framework of ionic liquid functionalized graphene oxide (FGO) nanosheets and mesoporous titania (TiO(2)) was studied. High resolution transmission electron microscopy analyses on TiO(2)/CdSe/FGO/Au not only revealed the linker mediated binding of CdSe QDs with TiO(2) but also, surprisingly, revealed a nanoscale connectivity between CdSe QDs, Au NPs and TiO(2) with FGO nanosheets, achieved by a simple solution processing method. Time resolved fluorescence decay experiments coupled with the systematic quenching of CdSe emission by Au NPs or FGO nanosheets or by a combination of the latter two provide concrete evidences favoring the most likely pathway of ultrafast decay of excited CdSe in the composite to be a relay mechanism. A balance between energetics and kinetics of the system is realized by alignment of conduction band edges, whereby, CdSe QDs inject photogenerated electrons into the conduction band of TiO(2), from where, electrons are promptly transferred to FGO nanosheets and then through Au NPs to the current collector. Conductive-atomic force microscopy also provided a direct correlation between the local nanostructure and the enhanced ability of composite to conduct electrons. Point contact I-V measurements and average photoconductivity results demonstrated the current distribution as well as the population of conducting domains to be uniform across the TiO(2)/CdSe/FGO/Au composite, thus validating the higher photocurrent generation. A six-fold enhancement in photocurrent and a 100 mV increment in photovoltage combined with an incident photon to current conversion efficiency of 27%, achieved in the composite, compared to the inferior performance of the TiO(2)/CdSe/Au composite imply that FGO nanosheets and Au NPs work in tandem to promote charge separation and furnish less impeded pathways for electron transfer and transport. Such a hierarchical rapid electron transfer model can be adapted to other nanostructures as well, as they can favorably impact photoelectrochemical performance.     

An effective oxidation route to blue emission CdSe quantum dots

Nearly monodisperse CdSe quantum dots with blue emission are obtained through an oxidation approach, in which CdSe particles can be etched into smaller ones. During the oxidation process, CdSe with yellow emission (546 nm) can be rapidly oxidized to blue emission (466 nm) due to its incompletely crystallized structure. Further oxidation results in the slow blue-shift of the photoluminescence peak to 433nm. The quantum fluorescence efficiency of CdSe with blue emission is about 10%, and surface-trap emission becomes evident when the PL peak of CdSe reaches the blue-violet region, since the surface atom ratio increases. This oxidation route offers a simple and mild way to get extremely small CdSe quantum dots.     

卟啉铜/CdSe纳米粒子复合膜的组装及其光学性能

采用静电自组装的方法,将带有相反电荷的水溶性卟啉--碘化三甲胺基苯基卟啉铜与CdSe纳米粒子交替沉积,制备了一种新型的有机-无机纳米复合薄膜。 紫外-可见吸收光谱表明,复合膜是逐层、均匀沉积的。 扫描电子显微镜照片显示复合膜中纳米粒子分布均匀,膜结构中缺陷少。 此外,还通过光谱手段系统地研究了该复合膜的发光性能、纳米粒子与卟啉之间的相互作用及膜的光稳定性。 研究结果发现,CdSe纳米粒子与CuTAPPI分子之间存在较强的相互作用,能产生由CuTAPPI到CdSe的光诱导电子转移。 而且,在该复合膜中CuTAPPI的光稳定性较高。     

Photoelectronic properties of horseradish peroxidase-functionalized CdSe/silica mesoporous composite and its sensing towards hydrogen peroxide

CdSe nanocrystals were prepared within a template of mesoporous silica (MS) spheres via chemical reaction, and then the as-synthesized CdSe/MS composites were dip coated on an optically transparent electrode. The photoelectric properties of CdSe/MS composite film were examined under ultraviolet (UV) illumination at the excitation wavelength of 365 nm. The CdSe/MS composite can facilitate charge rectification and minimize charge recombination as shown by its higher photocurrent. Most importantly, horseradish peroxidase (HRP)-functionalized CdSe/MS-modified electrode (HRP/CdSe/MS) had a stronger response toward hydrogen peroxide (H₂O₂) under UV illumination than in the dark. The result demonstrates the potential application of HRP/CdSe/MS composite film as a novel biosensor for monitoring H₂O₂ under UV illumination.     

Semiconductor nanoparticle/polystyrene latex composite materials

Cadmium sulfide and cadmium selenide/cadmium sulfide core/shell nanoparticles stabilized with poly(cysteine acrylamide) have been bound to polystyrene (PS) latexes by three methods. First, anionic 5 nm diameter CdS particles were electrostatically attached to 130 nm surfactant-free cationic PS latexes to form stable dispersions when the amount of CdS particles was less than 10% of the amount required to form a monolayer on the surface of the PS particles or when the amount of CdS particles exceeded the amount required to form a monolayer on the PS particles. Transmission electron microscopy (TEM) showed nanoparticles on the surface of the latex particles. Fluorescence spectra showed unchanged emission from the nanoparticles. Second, anionic, surfactant-free PS latexes were synthesized in the presence of CdS and CdSe/CdS nanoparticles. TEM showed monodisperse latex particles with trapped nanoparticles. Third, surfactant-stabilized latexes were synthesized by copolymerization of styrene with vinylbenzyl(trimethyl)ammonium chloride electrostatically bound to the CdSe/CdS nanoparticle surface. Brownian motion of the submicroscopic composite particles in water was detected by fluorescence microscopy.     

Preparation and stability of strongly luminescent CdSe/Cd(OH)<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> nanocomposite particles in aqueous solution

Cadmium hydroxide-deposited cadmium selenide nanoparticles were prepared by the addition of cadmium sulfate solution to cadmium selenide nanoparticles in a weak alkaline solution at room temperature. The photoluminescence measurements displayed that the luminescence intensity was greatly increased by the addition of cadmium ions due to the formation of cadmium hydroxide on the surfaces of the cadmium selenide nanoparticles. Then, CdSe/Cd(OH)₂/SiO₂ nanocomposite particles were synthesized using 3-mercatopropyl trimethoxysilane by Stöber method. After the formation of CdSe/Cd(OH)₂/SiO₂ nanocomposite particles, the emission ability was mostly stabilized. Additionally, the stabilization of the composite particles against dilution with the physiological saline was checked. The results showed that the photoluminescence stability was promoted after the deposition of silica on the surfaces of the CdSe/Cd(OH)₂ nanoparticles. Comparison of the stability of CdSe/SiO₂ nanoparticles with that of CdSe/Cd(OH)₂/SiO₂ ones showed that Cd(OH)₂ shell could enhance the photoluminescence effectively.     

Immobilization of quantum dots of cadmium selenide on the matrix of a graft liquid-crystalline polymer

A new luminescent composite based on quantum dots of CdSe immobilized on the polymer LC matrix prepared through the graft polymerization of the monomer of 4-(ω-acryloyloxyhexyloxy)benzoic acid on a fluorocarbon support after its preliminary irradiation with vacuum ultraviolet light is elaborated. The structure, composition, and optical characteristics of the prepared composite are studied via the methods of the FTIR spectroscopy, energy-dispersive and wave-dispersive analyses, and luminescence spectroscopy. The CdSe particles are shown to interact with the carboxyl groups of mesogenic fragments of the LC polymer, and this interaction leads to the integration of quantum dots into the ordered LC structure of the composite. As a result of immobilization, the luminescence peak of the quantum dots is shifted toward lower wavelengths owing to the interaction between the nanoparticles and the polymer LC matrix.     

In situ synthesis of polystyrene/nano-CdSe core/shell microspheres in aqueous solution at room temperature

Polystyrene/nano-CdSe (PS/CdSe) core/shell microspheres were synthesized via in situ soap-free emulsion polymerization using various functional monomers such as 2-(dimethylamino)ethyl methacrylate, 1-vinylimidazole, 2-vinylpridine, and 4-vinylpridine. They were co-polymerized with styrene monomer and provided the location for coordinating with Cd²⁺ ions on the PS particle surfaces. Then, we used an alkaline selenium solution as a selenium source. Reaction of the alkaline selenium solution with the previous emulsion produced nanocrystalline CdSe onto the surface of PS particles at room temperature under atmospheric pressure. The different kinds of functional monomers and the amount of both Cd²⁺ ion and functional monomer were playing important roles to obtain stable and uniform morphologies of CdSe particles. Morphological observations were carried out by both scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Through the SEM and TEM microphotographs, we could confirm the formation of PS/nano-CdSe composite particles. Ultraviolet–visible absorption measurement indicated the quantum dot effect in the resulted PS/nano-CdSe core/shell microspheres.     

Tuning the properties of CdSe nanoparticles in reverse micelles

A new and simple approach of synthesizing size-quantized CdSe colloids in reverse micellar suspension is described. The room temperature reaction between Cd²⁺ and selenosulfate is carried out within the water pool of di-octyl sulphosuccinate (Aerosol-OT) reverse micelles. The size dependent absorption and emission properties of these small CdSe particles (3—5 nm) are described. The Q-sized CdSe nanoparticles exhibit an emission yield of 0.13. Up to a factor of two enhancement in the emission efficiency can be achieved following the surface functionalization of CdSe colloids with triethyl amine.     

From Cd-rich to se-rich--the manipulation of CdSe nanocrystal surface stoichiometry

We report a protocol for manipulating the surface composition of CdSe nanocrystals. By combining the successive ion layer adhesion and reaction (SILAR) method developed by Li et al. J. Am. Chem. Soc. 2003, 125, 12567 with a phosphine-free selenium precursor, the surface stoichiometry of CdSe can be tunably altered from Cd- to Se-rich. By changing the overall surface stoichiometry, we demonstrate ligand binding to specific surface sites. Tertiary phosphines produce a dramatic enhancement in photoluminescence quantum yield of CdSe particles with Se-rich surfaces but have little effect on Cd-rich surfaces. Unpassivated selenium surface sites are also shown to be a cause of the photobrightening behavior of CdSe nanocrystals.     

Photochemical fine-tuning of luminescent color of cadmium selenide nanoparticles: fabricating a single-source multicolor luminophore

Size-selective photoetching was applied to silica-coated cadmium selenide (SiO2/CdSe) nanoparticles to precisely control their photoluminescence properties. The absorption spectra of CdSe was blue-shifted by irradiation of monochromatic light, and finally, the absorption onset agreed with the wavelength of irradiation light, indicating that CdSe particles were photoetched to smaller ones until the irradiated photons were not absorbed by the photoetched particles and that the SiO2 shell layer surrounding the CdSe core prevented coalescence between the photoetched particles. Although as-prepared SiO2/CdSe did not exhibit photoluminescence, the application of size-selective photoetching to SiO2/CdSe resulted in the development of the band gap emission, with the degree being enhanced with progress of the photoetching. The peak wavelength of photoluminescence decreased with a decrease in the wavelength used for the photoetching, so that the luminescence color could be tuned between red and blue. Partial photoetching of SiO2/CdSe nanoparticle films produced intense band gap emission of CdSe at the photoetched area, while the remainder of the SiO2/CdSe films did not exhibit detectable photoluminescence, resulting in the formation of a clear photoluminescence image under UV irradiation. This technique makes it possible to produce a multicolored photoluminescence image by irradiation with monochromatic lights having various wavelengths using a single source material.     

Analysis of the atomic structure of colloidal quantum dots of the CdSe family: X-ray spectral diagnostics and computer modelling

Colloidal quantum dots of the CdSe family have been studied by X-ray absorption near edge structure (XANES) spectroscopy and computer modelling. CdK edge XANES spectra in colloidal quantum dots based on varisized CdSe nanoparticles have been recorded. Atomic structure of CdSe particles and also CdSe particles doped by transition metal atoms Mn and Co has been modelled based on the density functional theory. The embedding of the doping atoms is shown to result in considerable changes in the local atomic structure of CdSe particles. XANES spectra have been calculated above the CdK edge in CdSe particles, above the MnK edge in CdSe:Mn particles, above the CoK edge in CdSe:Co particles. The sensitivity of XANES spectroscopy to small changes in structural parameters of the nanoparticles of CdSe family has been demonstrated that furnishes an opportunity to apply it for the verification of atomic structure parameters around positions of cadmium and doping atoms of transition metals in quantum dots based on CdSe.     

TiO_2纳米棒和CdSe纳米棒复合膜与聚3-甲基噻吩杂化太阳能电池研究

采用水热法制备了TiO2和CdSe两种纳米棒材料,将两种纳米材料制备成TiO2/CdSe复合纳米棒膜电极,并在复合膜上电化学聚合生成聚3-甲基噻吩poly(3-methylthiophene)(PMeT),研究了其光电化学性能.实验表明,当TiO2与CdSe的物质的量复合比为2:1,PMeT的聚合时间为40s,在电极电势为-0.2V下ITO/TiO2/CdSe/PMeT电极光电转换效率(IPCE)达到56%,对比ITO/TiO2/CdSe复合膜电极在长波方向的光电转换效率明显提高,光吸收截止波长发生了明显的红移.同时以ITO/TiO2/CdSe/PMeT组装了简易的杂化太阳电池,初步研究了光电池性能,光电池总效率为0.08%,Voc=0.4V,jsc=0.61mA/cm2,ff=0.33.     

Layer-by-layer assembled composite films of side-functionalized poly(3-hexylthiophene) and CdSe nanocrystals: electrochemical, spectroelectrochemical and photovoltaic properties

Regioregular poly(3-hexylthiophene) containing one diaminopyrimidine side group per ten repeat units (P3HT-co-P3(ODAP)HT) can form molecular composites with 1-(6-mercaptohexyl)thymine capped CdSe nanocrystals (CdSe(MHT)) via hydrogen bonds directed molecular recognition. Here we report complementary spectroscopic, electrochemical and spectroelectrochemical investigations of both the functionalized poly(thiophene) and its composite with the nanocrystals, the latter being fabricated using the layer-by-layer (LbL) deposition technique. UV-Vis-NIR and Raman spectroelectrochemical investigations unequivocally show that the onset of the first anodic peak in the cyclic voltammogram of the copolymer can be attributed to the oxidation of the pi-conjugated backbone in the polymer chains. For this reason, it is possible to determine the width and the position of its band gap (corresponding to the pi-pi* transition) by UV-Vis spectroscopy combined with cyclic voltammetry. These studies show that the polymer exhibits a slightly larger band gap with the HOMO level insignificantly lower in energy (by 0.03 eV) as compared to the case of regioregular poly(3-hexylthiophene) of comparable degree of polymerization. Hydrogen bond interactions of the polymer with CdSe(MHT) in the molecular composite result in a hypsochromic shift of the band corresponding to the pi-pi* transition from 504 nm to 488 nm. This can be taken as a spectroscopic manifestation of the conformational changes induced by shortening of the conjugation length. The observed spectral modifications are consistent with electrochemically determined lowering of the polymer HOMO level (from -4.91 eV in the pure polymer to -4.99 eV in the composite). Cyclic voltammetry studies supported by spectroelectrochemistry also show that the redox stability of CdSe(MHT) in the molecular composite with P3HT-co-P3(ODAP)HT is lower than that determined for stearate-capped nanocrystals. Their irreversible oxidation starts at E = +0.7 V vs. Ag/0.1 M Ag(+)i.e. at potentials by ca. 0.3 V lower than the oxidation of stearate stabilized CdSe nanocrystals of the same size. We show that-despite these modifications-the alignment of the HOMO and LUMO levels of the composite components remains appropriate for its use in hybrid solar cells, which is demonstrated by the photovoltaic effect observed for the LbL-processed composite sandwiched between two electrodes.     

Synthesis of core/shell nanoparticles of Au/CdSe via Au-Cd bialloy precursor

We present a novel method for the preparation of ultrasmall Au/CdSe core/shell particles. Au-Cd bialloy particles of 4.7 nm diameter were prepared as the precursor. The Cd component in the precursor reacted with the Se source at a temperature of 205 degrees C and was heated to 250 degrees C, leading to formation of a Au/CdSe core/shell structure. The sizes of Au/CdSe nanoparticles have a narrow distribution with an average size of 6.0 nm and Au core of 2.2 nm diameter. The X-ray diffraction pattern and the images of the high-resolution electron transmission microscopy show that the Au cores and the CdSe shells of Au/CdSe core/shell nanoparticles are both well crystallized, and the CdSe shells are in a cubic phase. The absorption spectrum of the Au/CdSe nanoparticles combines the absorption behaviors of the Au cores and the CdSe shells.     

聚3-氯噻吩修饰CdSe纳米棒复合膜电极光电化学性能研究

采用水热法制备了具有闪锌矿和纤维锌矿结构的CdSe纳米棒. 纳米棒直径约为100 nm, 长度约为300 nm. 当外加电极电势为-0.6 V 时, 经聚3-氯噻吩[Poly(3-chlorothiophene), P3CT]修饰的CdSe纳米棒具有最大光电流, 并且CdSe/P3CT复合膜电极最高光电转换效率(IPCE)为13.5%, 低于CdSe纳米棒膜电极17.7%的最高IPCE. CdSe/P3CT复合膜电极中存在p-n异质结, p-n异质结的存在使得CdSe/P3CT复合膜电极在长波区(>410 nm)的IPCE整体高于CdSe纳米棒薄膜电极的IPCE.     

Application of CdSe–PVK Nanocomposite as a Hole Transport Layer for OLEDs

An organic light‐emitting diode was fabricated using cadmium selenide (CdSe)/poly(N‐vinylcarbazole) nanocomposite as the hole transport layer (HTL). The CdSe nanoparticles (NPs) with a mean crystallite size of 6.2 nm were prepared by high‐energy ball milling. Based on the current–voltage curves, the threshold voltage (V _th) of the composite diode was found to be ~1.3 ± 0.1 V lower than that of the diode without CdSe, with a significant increase in the current density for the composite diode. Moreover, the electroluminescence (EL) properties (luminous flux, emittance, and intensity) of the diode were found to be enhanced by ~16% with respect to those of the diode without CdSe. The decrease of the threshold voltage and the increase of the current density and the EL were due to the CdSe NPs that operate as hole trap centers in the HTL.     

Hot‐Hole Extraction from Quantum Dot to Molecular Adsorbate

Ultrafast thermalized and hot‐hole‐transfer processes have been investigated in CdSe quantum dot (QD)/catechol composite systems in which hole transfer from photoexcited QDs to the catechols is thermodynamically favorable. A series of catechol derivatives were selected with different electron‐donating and ‐withdrawing groups, and the effect of these groups on hole transfer and charge recombination (CR) dynamics has been investigated. The hole‐transfer time was determined using the fluorescence upconversion technique and found to be 2–10 ps depending on the molecular structure of the catechol derivatives. The hot‐hole‐transfer process was followed after monitoring 2S luminescence of CdSe QDs. Interestingly, hot‐hole extraction was observed only in the CdSe/3‐methoxycatechol (3‐OCH₃) composite system owing to the higher electron‐donating property of the 3‐methoxy group. To confirm the extraction of the hot hole and to monitor the CR reaction in CdSe QD/catechol composite systems, ultrafast transient absorption studies have been carried out. Ultrafast transient‐absorption studies show that the bleach recovery kinetics of CdSe QD at the 2S excitonic position is much faster in the presence of 3‐OCH₃. This faster bleach recovery at the 2S position in CdSe/3‐OCH₃ suggests hot‐hole transfer from CdSe QD to 3‐OCH₃. CR dynamics in CdSe QD/catechol composite systems was followed by monitoring the excitonic bleach at the 1S position and was found to decrease with free energy of the CR reaction.     

Modification of TiO2 Microporous Electrode with Chemical Bath Deposited Quantum-Size CdSe Particles

The transparent titanium dioxide (TiO₂) electrodes have been modified with cadmium selenite (CdSe) particles by means of chemical deposition method. The sensitization of TiO₂ electrode with CdSe particles extends both the optical absorption spectrum and photocurrent action spectrum into the visible region. Furthermore, compared with CdSe bulk materials, a blue shift up to 0.24 eV in both absorption spectrum and photocurrent action spectrum of CdSe/TiO₂ electrode was observed and explained in terms of quantum-size effect.