Photoinduced Pyridine Cleavage-Closure in Viscous Polymer Solutions

We have found that photoinduced pyridine ring cleavage-closure occurs in polymeric viscous solution, because in certain polymer solutions, pyridine can serve as a photo-modulated crosslinker. We suggest this reaction as a way to control a polymer's optical properties. Irradiation of the system: poly(4-vinyl pyridine)/pyridine/water with 250-nm wavelength range leads to the appearance of a new absorption band centered at 360 nm, new red-shifted emission, and HOMO-LUMO band gap changes. The subsequent irradiation with 360 nm (the new absorption band maximum) leads to reversion almost to the initial stage. A main active product of the photoreaction is aldehyde enamine, which has two active groups: primary amine and aldehyde, which can associate with the polymer molecules to form a physical crosslinked supramolecular structure. We evaluated the activation energy of the pyridine ring cleavage and back reaction depending on the polymer/pyridine/water ratio and by changing the polymer structure. The activation energy of pyridine's ring cleavage in viscous polymeric solutions is in the range of 0.6–3.2 Kcal/mol. The activation energy of the back reaction is significantly lower and is in the range of 0.05–0.15Kcal/mole.     

Electron mobility in poly(3-hexylthiophene) enhanced by gamma-ray irradiation

Gamma-ray irradiation effects on the photoresponsive thin-film devices based on the regioregular poly(3-hexylthiophene) (RR-P3HT) conjugated polymer have been studied by means of atomic force microscopy, UV–vis absorption, photoluminescence (PL), and time-of-flight measurements. As a result, increased light absorption in the red region and PL quenching induced by the irradiation were observed. Besides, enhancement of the electron/hole mobilities, attributable to improved ordering or increased nanodomain size of the P3HT thin films, was revealed.     

Photoinduced chirality in a photochromic stilbene-molecule-doped polymeric liquid crystal film

Photoinduced chirality has been demonstrated in thin films of a main-chain polymeric liquid crystal (PLC) system doped with photochromic stilbene molecules by irradiation with circularly polarized light (CPL). CPL-induced chirality was observed in the intrinsically achiral films which were doped with low-molecular-weight stilbene molecules. It was found that the level of photoinduced chirality of the stilbene-molecule-doped system is comparable to that of the azobenzene-molecule-doped system. Moreover, reversible photo-rewriting property for the stilbene-doped system was also demonstrated by alternating irradiation with right- and left-CPL.     

新型蓝绿色磷光配合物二(1-苯基吡唑)铱(吡啶三唑)的发光性能

利用1-苯基吡唑、吡啶三唑与水合三氯化铱反应合成了一种新型铱配合物Ir(2N)₂(PZ),研究了配合物的吸收光谱、光致发光光谱以及光致发光效率。利用该材料作为磷光客体,掺杂到高分子主体材料中制作了电致发光器件,研究了其电致发光光谱。结果表明,该配合物在228,250,328nm处存在自旋允许的¹π-π^*跃迁;荧光光谱结果显示在470nm处有较强的磷光发射;电致发光光谱与光致发光光谱相比却发生较大程度的红移。     

High-PL efficiency of polyaniline using various dopants

Polyaniline (PANI) was doped with hydrochloric acid (HCl), succinic acid (C₄H₆O₄) and sulphuric acid (H₂SO₄) by chemical oxidation method. The samples were characterized by using various techniques such as XRD, photoluminescence IR and UV spectroscopy. FTIR study confirmed the presence of dopant molecules in the molecular structure. UV spectra revealed that absorption peaks at 350 nm and 600 nm are due to π–π* transition of polyaniline. The strong band at 600 nm showed extension of polymer chains in the prepared samples. XRD pattern confirmed the amorphous nature of polymer samples. The photoluminescence (PL) spectrum shows good emission at 490 nm. The intensity of photoluminescence depends upon the dopants nature.     

Excellent UV absorption in spin-coated thin films of oleic acid modified zinc oxide nanorods embedded in Polyvinyl alcohol

The aim of the study is to investigate the optical properties of spin-coated, highly transparent nanocomposite films of oleic acid modified ZnO (Zinc oxide) nanorods embedded in Polyvinyl alcohol (PVA) matrix. Pristine and oleic acid (OA) modified ZnO nanorods have been prepared by wet chemical synthesis and are characterized by X-ray diffraction, FESEM, TEM and FT–IR spectroscopy techniques. The optical properties of ZnO/PVA films are studied using UV–visible absorption and Photoluminescence (PL) spectroscopy. The results show that the optical absorption of the films in the UV region is quite high and more than 95% absorption is observed in films prepared from OA modified ZnO nanorods. The excellent UV absorption at around 300 nm offers prospects of applications of these films as efficient UV filters in this wavelength region. The PL spectrum of pristine ZnO nanorods shows almost white light emission whereas OA modified ZnO nanorods have a more intense peak centered in the blue region. The PL emission of OA modified ZnO/PVA film shows appreciable increase in intensity compared to the film obtained with pristine ZnO. The surface modification of ZnO by the polymer matrix removes defect states within ZnO and facilitates sharp near band edge PL emission at 364 nm.     

Sonochemical Synthesis of Optically Tuneable Conjugated Polymer Nanoparticles

The development of novel and simple methodologies for the obtaining of semiconductive polymer nanoparticles with fine‐tuned optical properties represents nowadays a challenging research area as it involves a simultaneous chemical modification and nanostructuration of the polymer. Here, starting from poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene], this objective is achieved with the one‐pot synthesis of oligomers with tunable conjugation length and their nanostructuration, employing a miniemulsion method. Ultrasound irradiation of heterogeneous mixtures leads to the formation of hypochlorous acid that disrupts the electronic conjugation through polymer chain cleavage. Moreover, control over the degree of the electronic conjugation of the oligomers, and therefore of the optical properties, is achieved simply by varying the polymer concentration of the initial solution. Finally, the presence of surfactants during the sonication allows for the formation of nanoparticles with progressive spectral shift of the main absorption (from λ_max = 476 to 306 nm) and emission bands (from λ_max = 597 to 481 nm). The integration of conducting polymer nanoparticles into polymeric matrices yields self‐standing and flexible fluorescent films.     

Model for UV induced formation of gold nanoparticles in solid polymeric matrices

UV irradiation of polymeric PMMA films containing HAuCl₄ followed by annealing at 60-80 °C forms gold nanoparticles directly within the bulk material. The kinetics of nanoparticle formation was traced by extinction spectra of nanocomposite film changes vs annealing time. We propose that UV irradiation causes HAuCl₄ dissociation and thus provides a polymeric matrix with atomic gold. The presence of an oversaturated solid solution of atomic gold in the polymeric matrix leads to Au nanoparticle formation during annealing. This process can be understood as a phase transition of the first order. In this paper we apply several common kinetic models of the phase transition for describing Au nanoparticle formation inside the solid polymer matrix. We compare predictions of these models with the experimental data and show that these models cannot describe the process. We propose that the stabilization effect of the matrix on the growing gold nanoparticles is important. The simplest model introducing some probability for the transition from growing nanoparticle to the non-growing, stabilized form is suggested. It is shown that this model satisfactorily describes the experimentally observed evolution of the extinction spectrum of Au nanoparticles forming in a polymer matrix.     

Structure and luminescent properties of LaNbO4 synthesized by sol-gel process

The luminescence properties of LaNbO₄ synthesized by the citric gel process were investigated. The crystallized orthorhombic and monoclinic biphasic structure forms at temperatures below 1100 °C and well-crystallized monoclinic LaNbO₄ is obtained by heat treatment at a temperature of 1200 °C for 3 h. All of LaNbO₄ phosphors derived from the citric gel method exhibit red-shifted excitation spectra as the calcining temperature increased from 700 to 1200 °C. The effect of the heat treatment conditions on the peak shape and the peak positions of the photoluminescence (PL) emission are undetectable, and the PL spectra excited at 260 nm have a blue emission band maximum at 408 nm, corresponding to the self-activated luminescence center of LaNbO₄. The sample heat treated at 1100 °C for 3 h showed the highest absorption and fluorescence intensities among the prepared samples.     

Effect of S- and Sn-doping to the optical properties of ZnO nanobelts

In this study, the optical properties of S- and Sn-doped ZnO nanobelts, grown by thermal evaporation, were investigated. The sulfur and tin contents in the nanobelts were about 12% and 8% (atomic), respectively. The average widths of the S- and Sn-doped ZnO nanobelts were 73 and 121 nm, respectively. Room temperature photoluminescence (PL) spectroscopy exhibits significantly different optical properties for the two types of nanobelts. The PL result of the S-doped ZnO nanobelts shows the broad visible emission with no detectable ultraviolet (UV) peak, while the PL result of the Sn-doped sample shows two emission bands, one related to UV emission with a strong peak at 376 nm that is blue-shifted by 4 nm in comparison to pure ZnO nanobelts, and another related to green emission with a weak peak. A weak peak in the UV region at 383 nm appeared after annealing the S-doped ZnO nanobelts at 600 °C. Additionally, the annealed S-doped nanobelts show a stronger peak in the visible emission region in comparison to that observed prior to annealing. The Sn-doped ZnO nanobelts are also affected by annealing, as the UV emission peak is blue-shifted to 372 nm after annealing.     

Combination of microstructuring and laser-light irradiation for the reversible wettability of photosensitised polymer surfaces

The wetting characteristics of surfaces of polymers doped with photochromic spiropyran molecules can be tuned when irradiated with laser beams of properly chosen photon energy. In particular, UV laser pulses at 308 nm are responsible for the enhancement of the hydrophilicity of the surfaces, since the embedded non-polar spiropyran molecules convert to their polar merocyanine isomers upon UV absorption. The process is reversed upon irradiation with green laser pulses at 532 nm. When the photochromic-polymeric surfaces are micropatterned using soft lithography or photo-polymerisation techniques, they can change their wettability towards a more hydrophobic or more hydrophilic behaviour depending on the dimensions of the patterned features and on the hydrophilicity-hydrophobicity of the flat surface. Furthermore, the light-induced wettability variations on these structured surfaces are greatly enhanced compared to the flat surfaces. This significant increase to the wettability changes is attributed to the combination of the photochromic interconversions upon laser irradiation together with the photoinduced reversible volume changes of the patterned features. PACS 61.82.Pv; 68.08.Bc; 81.16.Nd; 82.35.-x; 42.60.-v; 68.47.Mn     

Photoinduced color centers creation in superionic crystals RbAg 4 I 5

Abstract

A new phenomenon of a reversible photoinduced coloration caused by light irradiation is discovered and investigated in superionic RbAg ₄ I ₅ crystals. The reversible photoinduced absorption is found to be a result of irradiation by light with wavelengths in the region from 420 nm to 450 nm. The proposed mechanism of the discovered effect is associated with ambipolar diffusion of screened by mobile ions optically excited electronic carriers. The processes of color centers creation in superionic crystals RbAg ₄ I ₅ due to additive coloring in iodine vapours, ionic implantation and γ-ray irradiation are considered.     

采用紫外光照法在磷酸盐玻璃中合成CdS/Ag复合微粒

掺杂有Ⅱ-Ⅵ族半导体纳米颗粒(如CdS)或者过渡金属(如Ag)的玻璃由于其较大的非线性光学效应而引起人们的极大兴趣,而同时掺杂有半导体/金属的复合微粒则可以进一步增强玻璃的三阶非线性效应,因此成为目前的研究热点。我们利用玻璃沉淀技术及随后的热处理和紫外光还原技术制备了含高浓度(1%)Ag微粒的玻璃,并采用X射线衍射分析了其物相,用高分辨扫描电镜分析了其形貌,以及测试了其吸收和发光性能。从CdS/Ag复合微粒的扫描照片可以发现晶粒均匀分布在玻璃中,尺寸约为1μm。X射线衍射发现经过热处理和紫外光照的样品衍射峰中含有CdS和Ag,而只进行热处理的样品则只含有CdS,未处理的样品则显非晶态。CdS/Ag复合微粒的吸收峰呈现典型的表面等离子共振峰(420nm)以及CdS的峰(600nm),只含有CdS微粒的样品的吸收峰则在480nm附近,未处理的样品在320nm附近有一个吸收峰,这可能是由于样品在快速冷却过程中的微小晶化造成的。只含有CdS微粒的样品有三个明显的发光峰,然而CdS/Ag复合微粒的发过峰则消失。我们提出了共振能量转移机制来解释该现象。讨论了紫外光照还原Ag微粒的机制。可以认为通过紫外光照,CdS表面的电子被激发出来还原Ag+,从而形成银颗粒,伴随着空穴则被表面缺陷所捕获。     

新型蓝色磷光嘧啶铱(Ⅲ)配合物的合成及发光性质

设计并合成了以2-(2,4-二氟苯基)嘧啶(DFPPM)为主配体的两种新型二嗪铱配合物 (Ph:苯基)和,用核磁共振(NMR)和质谱等方法对其进行了表征,并用紫外-可见吸收光谱和光致发光光谱对其光学性质进行了研究。光致发光光谱结果显示:配合物 的发射峰波长为472 nm和489 nm;而配合物 的发射峰波长为447 nm和472 nm,1931CIE色度坐标为(0.14,0.15),是一种深蓝色磷光材料。以 为客体材料、PVK为主体材料制备了电致发光器件,研究了其电致发光光谱。结果表明,电致发光光谱与光致发光光谱相比有较大程度的红移。     

Novel properties of nanoscale organic–inorganic systems and photonic crystals — conducting polymers in nanoscale periodic structures,microcavities and photonic crystals

Conducting polymer/C₆₀and C₆₀doped conducting polymer/C₆₀heterojunctions have been fabricated and found to exhibit remarkably enhanced photoresponse due to the highly effective photoinduced charge transfer at the interface. In conducting polymer/C₆₀alkali metal nanoscale composite systems, multiphase superconductivity has been clarified and explained by taking the coupling of nanoscale grains by Josephson junctions into consideration. As examples of intramolecular organic-inorganic combined systems, unique electrical and optical characteristics have been revealed in oligosilanylene oligophenylene polymers. Electroluminescence has been demonstrated in organic-inorganic junction devices such as conducting polymer/porous Si and conducting polymer/diamond junctions. Conducting, polymer-based nanoscale multilayer systems have been studied utilizing molecular self-assembly method and novel photosensitive characteristics have been revealed. \indent Novel optical and electrical properties of conducting polymers infiltrated in a photonic crystal, synthetic opal made of SiO₂spheres of several hundred nm in diameter, and also a conducting polymer replica have been revealed. A clear diffraction pattern was observed in a photonic crystal infiltrated with conducting polymers, and transmission spectra are dependent on various ambient conditions. Their photoluminescence (PL) spectra, spectral narrowing of PL and lasing characteristics at relatively low optical excitation have also been clarified. Novel conducting characteristics of conducting polymers in a photonic crystal that was prepared by pyrolysis of a polymer replica of opal have also been observed.     

紫外激光和压力共同作用下C60-peapod的聚合相变研究

采用气相扩散方法将C₆₀分子填充到单壁碳纳米管(SWNTs)中，制备出高填充比率的豆荚形纳米材料C₆₀@SWNT，又称为peapod.用金刚石对顶砧(DAC)装置获得高压，在高压下同时利用紫外激光处理样品，通过激光和压力的共同作用研究了C₆₀分子在碳管内的聚合相变.在21.5GPa高压下，同时紫外激光(325nm)照射30min后，拉曼光谱表明C₆₀分子在碳管内发生了聚合，形成一维链状O相聚合结构，且该相变是不可逆的. 关键词： 60 peapod')" href="#">C₆₀ peapod 紫外激光 高压 拉曼光谱     

Influence of photoexcitation pathways on the initiation of ablation in poly (methyl methacrylate)

Experimental and theoretical studies of laser ablation of polymers, under various processing conditions, have identified many possible photoexcitation pathways and consequently many likely processes responsible for the onset of ablation. We investigate the role of these processes—namely the thermal, mechanical and chemical processes—occurring in a polymeric substrate during UV irradiation. Molecular dynamics simulations with an embedded Monte Carlo-based reaction scheme were used to study ablation of Poly (methyl methacrylate) at 157 nm. Laser-induced heating and chemical decomposition of the polymeric substrate are considered as ablation pathways. For the heating case, the mechanism of ejection is thermally driven limited by the critical number of bonds broken. This fragmentation process is well reproduced by the existing bulk photothermal ablation model. Alternatively, if the photon energy goes toward direct bond breaking, it initiates chemical reactions, polymer unzipping, and formation of gaseous products leading to near complete decomposition, loss of strength and cohesiveness of the top layers of the polymeric substrate. The ejection of small gaseous molecules weakens and hollows out the substrate, facilitating liftoff of larger fragments of material. These larger clusters are thermally ejected and the photochemical ablation process can be described by the two-step model proposed by Kalontarov.     

Deposition of quasi-crystal Al-doped ZnO thin films for photovoltaic device applications

Quasi-crystal aluminum-doped zinc oxide (AZO) films were prepared by in situ radio frequency (RF) magnetron sputtering (sputtering without annealing) on glass substrates. The influence of deposition parameters on the optoelectronic and structural properties of the in situ deposited quasi-crystal AZO films was investigated in order to compare resulting samples. X-ray diffraction (XRD) patterns show that the quasi-crystal AZO thin films have excellent crystallization improved with increase of the RF power and substrate temperature, with an extremely preferential c-axis orientation exhibit sharp and narrow XRD pattern similar to that of single-crystal. Field emission scanning electron microscopy (FESEM) images show that quasi-crystal AZO thin films have uniform grains and the grain size increase with the increase of RF power and substrate temperature. Craters of irregular size with the columnar structure are observed in the quasi-crystal AZO thin films at a lower substrate temperature while many spherical shaped grains appeared at a higher substrate temperature. The average optical transmittance of all the quasi-crystal AZO films was over 85% in the 400-800 nm wavelength range. The resistivity of 4.176 × 10⁻⁴ Ω cm with the grain size of 76.4891 nm was obtained in the quasi-crystal AZO thin film deposited at 300 °C, under sputtering power of 140 W.     

Electrochemic and Photophysics Properties of Pyridine-Based Electron Transmission Material

A pyridine-based polybenzobisoxazole (PBOPy) was synthesized via solution condensation polymerization. The polymer was characterized by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, thermogravimetric analysis, ultraviolet-visible (UV-Vis) absorption spectroscopy, photoluminescence (PL) spectroscopy, electrochemical cyclic voltammetry, and time-resolved PL decay dynamics. Results showed that the introduction of pyridine groups made the oxidation potential (1.82 eV) relatively larger than that of poly(p-phenylenebenzobisoxazole) (PBO) (1.65 eV), while the reduction potential (?1.18 eV) was smaller than that of PBO (?1.28 eV). It can be concluded, by comparing UV-Vis absorption spectroscopy and PL spectroscopy of PBOPy in film and in methanesulfonic acid (MSA), that PBOPy has a stronger protonation effect in the latter. The optical properties of PBOPy exhibited a PL emission band at 473 nm in thin films and a strong orange fluorescence (498 nm) after being protonated with MSA. The protonation effect resulted in a large Stokes shift, about 71 nm.     

Effect of irradiating ion fluence on optical properties of ZnO1−x:Nx thin films

Swift heavy ion (SHI) irradiation is an effective technique to modify the optical properties of the materials. In the present investigation, the effect of 100?MeV?Ag⁷⁺ SHI irradiation fluence on the optical properties of ZnO_1?x:N_x thin films was studied. The post irradiation spectroscopic characterizations such as UV–VIS reflectance spectroscopy, Raman spectroscopy and photoluminescence (PL) spectroscopy analysis were carried out. The studies imply that when the SHI passes through the solid, the higher electronic stopping power of ions can weaken oxygen bonds in ZnO, resulting in the formation of donor defects such as oxygen vacancies and zinc interstitials. The formation of donor defects has been acknowledged through the increase in bandgap with irradiating ion fluence. The blue shift observed from the Raman spectra for the 3?×?10¹³ ions/cm² fluence-irradiated films implies the existence of compressive stress in the films. The PL analysis acknowledges the formation of donor defects upon irradiation. Furthermore, it conveys that the presence of N atoms in ZnO lattice leads to the formation of a less number of defects as compared with undoped ZnO while irradiation.