Fluorescent aggregates in naphthalene containing poly(urethane-urea)s

A series of segmented poly(urethane-urea)s containing naphthalene in the hard block and hexamethylene spacers in the soft block was prepared. The hard to soft segment ratio was varied systematically, to afford a series of polymers with various chromophore concentrations and a constant length of the chromophoric block, using a three-step synthetic procedure.The absorption, fluorescence and fluorescence-excitation spectra of solutions and films of the block copolymers provide strong evidence for aggregation. A red-shifted fluorescence spectrum peaking at gains in intensity as the naphthalene concentration is increased. The excitation spectrum of this new emission is well to the red of the normal naphthalene absorption spectrum, consistent with the UV spectrum. Formation of a fluorescent ground state dimer (or higher aggregate) is proposed to account for these observations.     

Energy migration and transfer between chromophores embedded in Gaussian space

We have used a Monte Carlo method to investigate energy migration and transfer between chromophores embedded in Gaussian space. In using this method we have obtained fluorescence quantum yields, fluorescence depolarization, and the respective decay profiles of donor fluorescence. It was shown that all photophysical observables are dependent upon the number of donor and acceptor chromophores and upon the Förster radii ratio. The latter feature is particularly interesting, and it indicates the existence of correlations between donor and acceptor chromophores. It was shown that the excitation of the donor chromophore at the origin leads to different values of observables, in comparison with an excitation of a randomly selected donor chromophore. The results presented show the importance of the averaging procedures needed to be developed while dealing with specific distribution functions, as, for example, in the case of energy migration and trapping in aromatic polymers and copolymers.     

l-Dityrosine: A time-resolved fluorescence investigation

We have investigated the time-resolved fluorescence properties ofll-dityrosine in aqueous solution. Typically, three exponential components were needed to fit the fluorescence pattern adequately, with pure decay terms for the low-intensity, high-energy state (_em = nm) but with a pronounced subnanosecond rise phase for the predominant red-edge fluorescence (_em > 380). Dual fluorescence behavior is indicative of an intramolecular precursorsuccessor pair, i.e., a consecutive intramolecular excited-state reaction. We suggest that this reaction is a torsional motion of the (deprotonated) monoanion along the biphenolic bond. Analysis of the fluorescence anisotropy decay of dityrosine yielded two rotational correlation times, the longer of which is associated with a negative preexponential term. The increase with time in the horizontally polarized component of the intensity decay is interpreted as the result of an electronic rearrangement in the excited state when the successor form of dityrosine is generated. Lifetime distributions of experimental data were probed by an unbiased exponential series method which uses a Tikhonov-type regularization function. The procedure revealed three well-separated groups of lifetimes, the short-lived ensemble forming a formally negative distribution. A photophysical model is introduced which interprets the biexponential decay of dityrosine in terms of overlapping emission signals from the precursor and the successor molecule.     

Photophysical Properties of Fluorescent Polymers Containing 1,10-Phenanthroline-3,8-ylene and Diethinylenebenzene Units and Their Model Compounds: A Comparison to 2,2′-Bipyridine Analogues

Investigation of the absorption and emission spectra (stationary and time-resolved) of phenanthroline-based polymers shows that the enforcement of a cisoid geometry in the bipyridine unit of the main chain via an ethenylene bridge does not significantly change the spectral and the deactivation behaviour. In close analogy to similar polymers, containing bipyridine units, the conjugation length in these polymers does not exceed ca. two chromophore units. At low temperatures, the model compounds show an additional, bathochromically shifted, intense luminescence with an increased lifetime which can be interpreted as an excimer (or aggregate) fluorescence. In addition, broad, superimposed emission bands arising from various aggregated species are observed. The relative intensity of these bands depends on the temperature processing occurring during cooling. Intersystem crossing is an insignificant deactivation channel.     

Structural and photophysical properties of anthracenyl and carbazolyl groups in silicone-based polymers

This paper describes a simple methodology to attach luminescent groups (anthracenyl and carbazolyl) to polysiloxanes (silicone), using hydrosilylation reactions between the Si–H groups from the silicone precursor to vinyl derivatives of the lumophores. The photophysical properties of these luminescent silicones were studied using both steady-state and dynamical photoluminescence spectroscopy. A strong correlation was obtained between the structural characteristics of the anthracenyl- and carbazolyl-based polysiloxanes, depending on the amount and the position of the Si–H bonds in the silicone precursors. For sparsely distributed Si–H groups, both the anthracenyl-labeled and carbazolyl-labeled polysiloxanes showed photophysical properties (fluorescence spectrum and fluorescence decays) similar to those of 1-alkyl anthracenyl and 1-alkyl carbazolyl derivatives, respectively. Nevertheless, for closely spaced Si–H groups, emission and decay are different. The presence of excimers was observed for anthracenyl but not for carbazolyl polysiloxanes. This latter observation is quite different from that observed for carbon-based polymers for which the carbazolyl excimer formation is a very common process probably due to the differences in the silicone structure.     

叶绿素聚集体的延迟发光

石油醚中的叶绿素聚集体在照光后数分钟内会发出微弱的光来。这延迟发光的衰减曲线包含两个相:持续十秒左右的快速相和持续数分钟的慢速相。在四氯化碳中的叶绿素聚集体的延迟发光的衰减曲线和石油醚中的不同。延迟发光的强度在电子供体或递体存在时减弱。当聚集体解聚后,延迟发光现象消失。     

Immobilization of pyrene via diethylenetriamine on quartz plate surface for recognition of dicarboxylic acids

A novel photo-luminescence film has been prepared by immobilizing pyrene on a quartz plate surface via diethylenetriamine. Imino structure was intentionally introduced into the long flexible spacer due to their hydrogen bond forming abilities with carboxylic acids. It has been found that the film shows combined monomer and excimer emission of pyrene both in wet and dry states. Steady-state and time-resolved fluorescence emission measurements demonstrated that the excimer emission mainly came from direct excitation of ground state dimers, and/or monomers in aggregated state. The structures of the excimers formed during the excitation are mixtures of “standard excimers” and “distorted excimers” of the fluorophore moieties. Fluorescence lifetime measurements showed that the decay of the film is complex, and a four exponential fit is necessary for getting a satisfied result. The photophysical behavior of the present film could be rationalized by employing the model proposed before. Sensing property studies showed that the emission of the film is sensitive to the presence of dicarboxylic acids, including ethanedioic acid, malonic acid, etc. In contrast, presence of monocarboxylic acids, such as formic acid and acetic acid, had little effect upon the fluorescence emission of the film. Compared with the films taking ethylenediamine or 1,3-diaminopropane as their spacer component, introduction of diethylenetriamine into the spacer improved the performance of the film greatly. In addition, the sensing process is reversible, and the film is stable within a number of months provided it is properly preserved. These characteristics showed that the film is worthwhile for further exploration.     

Steady-State and Time-Resolved Fluorescence Polarization Behavior of Acenaphthene

Steady-state and time-resolved fluorescence polarization studies have been carried out on acenaphthene (ACE) in low-temperature glass solutions and at room temperature. In the low-temperature glass the fluorescence polarization values vary considerably with both emission and excitation wavelength. There is a time dependence (on the nanosecond time scale) of the fluorescence anisotropy, r(t), at 77 K, which has a strong dependence upon the excitation and emission wavelengths. Under these conditions, the time-dependent decay of the anisotropy is not attributable to chromophoric motion. The observations are consistent with emission from two closely lying and interconverting excited states. Rate constants for the photophysical processes involved have been determined by fitting the data using a model proposed by Fleming et. al. The results are discussed with particular reference to the care required in using dynamic fluorescence polarization measurements to determine energy transfer rates in systems containing this chromophore.     

A series of copper(I) complexes with electron donor/acceptor embedded ligands: Synthesis, photophysical and electroluminescent properties

In this paper, we report the synthesis of four diimine ligands incorporated with an electron donor/acceptor, as well as their corresponding Cu(I) complexes with bis(2-(diphenylphosphanyl)phenyl) ether as an ancillary ligand, resulting in four phosphorescent Cu(I) complexes. Their crystal structures as well as photophysical and thermal properties are discussed in detail. Experimental data and theoretical calculations confirm that electron donor moieties and limited conjugation system may self-restrict geometry relaxation in excited states, leading to narrowed and blue-shifted emission bands. On the other hand, electron acceptor moieties and large coplanar conjugation system are ineffective in restricting geometry relaxation, leading to broadened and red-shifted emission bands. However, the introduction of electron donors compromises thermal stability of Cu(I) complexes. We also explore one of the Cu(I) complexes as a dopant for electroluminescence application, and a maximum luminance of 680 cd/m² peaking at 620 nm is achieved.     

混合界面对溶液制备的磷光OLED器件性能的影响

利用混蒸的方法、将空穴阻挡材料2,9-Dimethyl-4,7-diphenyl-1,10-phenanhroline及电子传输材料Tris(8-hydroxy-quinolinato)aluminium混合,在电子传输层及空穴阻挡层之间制备了薄层的混合界面.在相同驱动电压下,采用混合界面的器件比常规器件的电流密度和亮...     

吩噻嗪衍生物的分子内电荷转移激发态的特性

合成了一系列的N-10位取代的吩噻嗪给体受体化合物,这些受体包括苯、苯甲醚、吡啶、萘、苯乙酮和苯乙腈.研究了不同极性溶剂中这些化合物的分子内的光诱导电荷转移现象.稳态荧光的溶剂化效应和较大的Stokes位移清楚表明,仅仅后四种吩噻嗪衍生物的激发态存在着分子内的电荷转移,而苯和苯甲醚取代吩噻嗪因为受体部分氧化电势低,所以不具有这种特性.修正过的Lippert-Mataga公式被用来分析Stokes位移值,从而获得激发态偶极矩.较大的激发态偶极矩说明在激发态时这四种给体受体化合物体系内发生了完全的电子转移.氧化还原电势的数据表明基态时这四种衍生物给体受体部分的作用比较弱.分析荧光光谱获得的结果说明伴随着电荷转移这四种衍生物的激发态构型变化比较小,给体和受体间的扭转角在电荷转移后的激发态与在基态时相似.     

Relations between photophysical and lasing properties of rhodamines in solid polymeric matrices

2 laser) pulses. In these solid media the rhodamine chromophore shows a photophysical behaviour similar to that in a liquid solution, and its photostability clearly increases when the chromophore is bound to the polymeric chain. These new solid materials show laser efficiencies that depend on the HEMA/MMA ratio, in some cases with values close to 20%. Received: 15 May 1996/Revised version: 26 November 1996     

Synthesis of conjugated polymers for application in light-emitting diodes (PLEDs)

In the field of electroluminescent organic materials, conjugated polymers have attracted much attention over recent years owing to their versatile synthesis, their relative ease of processing and the possibility of establishing predictive structure–function relationships between chemical structures and optical properties. This review article highlights the advances made in the synthesis of conjugated polymers for use in light-emitting devices (LEDs) covering the last two years. Research efforts were largely directed towards the improvement of the synthesis of monomers and polymers involving classical polymer structures such as poly( p -phenylene vinylene)s (PPVs), poly( p -phenylene)s (PPPs), poly(2,7-fluorene)s (PFs), or poly(2,5-thienylene)s (PTs). Control of the color of emission by modulation of the effective conjugation length, improving balanced charge injection and transport properties by introduction of electron-donating or -withdrawing moieties directly into the polymer backbone or enhancement of the emission efficiency by attempts to influence film morphology are some examples of recent research directions. All these investigations contributed to a significantly better understanding of the chemical and physical processes spanning topics from the manufacturing process to the operation of LEDs and leading to the announcement of the first commercial products. In addition to the classical π -conjugated polymers a few examples of rather unusual structures have also emerged.     

The utility of resonant soft x-ray scattering and reflectivity for the nanoscale characterization of polymers

The utility of resonant soft x-ray scattering (RSoXS) and reflectivity (RSoXR) is extended and exemplified through the characterization of thin films of polymers relevant to organic solar cells and of dilute polymer solutions. RSoXS and RSoXR are methods that utilize anomalous scattering principles at soft x-ray energies. Soft X-rays cover the carbon, nitrogen and oxygen absorption edges, elements very relevant for polymers and colloids. The rapid changes of optical properties near these absorption edges provide selectivity to specific moieties and high contrast. RSoXR is shown to be a powerful tool for the characterization of bilayers of conducting polymers. The RSoXR results point to an interesting strategy that will allow the chemical interdiffusion and physical roughness at a buried polymer/polymer interface to be determined independently. The high scattering cross sections also allows the investigation of thin films of conjugated polymer blends in transmission at thicknesses for which hard X-rays or neutrons would yield relatively little scattering. By scattering at photon energies that provide strong scattering contrast, even very dilute polymeric solutions yield a useable signal.     

Oscillatory decay of magnetization induced by domain-wall stray fields

The demagnetization of a hard ferromagnetic layer via the fringing fields of domain walls created by reversing the moment of a neighboring soft ferromagnetic layer is explored experimentally. An unusual oscillatory decay of the magnetic moment of the hard layer is observed using structures in which the demagnetization occurs after a few hundred cycles. This surprising observation is confirmed on a microscopic scale by detailed imaging of the magnetization of the hard layer using high resolution photoemission electron microscopy and by micromagnetic simulations.     

Fluorescence Anisotropy of Branched Molecules Containing 1-Aminopyrene Chromophores

Fluorescence anisotropy measurements were performed on a set of multichromophoric compounds, which contain a different number of aminopyrenyl moieties linked to a triazine ring, in order to reveal the nature of both the electronic excited states and relaxation pathways of the compounds. Our experimental results complement quantum chemical calculations. We propose that the lowest excited state from which fluorescence proceeds is localized on a single individual aminopyrene moiety. In contrast, excitation to a higher excited state is likely followed by a migration of energy to another nearby aminopyrene chromophore before the internal conversion to the emitting state takes place. We suggest that this migration is responsible for the experimentally measured decrease of fluorescence anisotropy of the studied compounds.     

Synthesis,Aggregation Induced Emission and Mechanochromic Luminescence of New <Emphasis Type="Italic">β</Emphasis>-Diketone Derivatives Bearing Tetraphenylene Moieties

A series of β-diketone derivatives bearing tetraphenylene (TPE) moieties were synthesized and characterized. Their photophysical properties were investigated systematically via spectroscopic and theoretical methods. All compounds exhibit broad absorption bands between 300 and 450 nm, which are assigned to the ¹π-π* transition of the conjugated system mixed intramolecular charge-transfer (ICT) transitions. Meanwhile, the emission of these compounds in solution at room temperature (λ _em = 458 ~ 509 nm) can be attributed to the ¹π,π*/¹ICT state. Introduction of freely rotatable TPE to conventional β-diketone luminophors quenches their light emissions in the solutions, but endows these molecules with aggregation-induced emission (AIE) characteristics in the condensed phase due to the restriction of intramolecular rotation. The spectroscopic studies and theoretical calculations indicate that the photophysical properties of these β-diketone derivatives can be tuned by the appended substituents, which would be useful for rational design of AIE compounds with high solid state luminescence performance. Furthermore, these AIE-active compounds exhibited distinct piezofluorochromic properties and switched reversibly upon grinding-fuming. Their photophysical properties have been investigated with the aim to provide a basis for elucidating the structure-property correlations and developing new multi-stimuli responsive luminescent materials.     

Design of perylene-diimides-based small-molecules semiconductors for organic solar cells

A series of perylene-diimide-based small molecules have been designed to explore their optical, electronic and charge transport properties as organic solar cell materials. The frontier molecular orbitals analysis has turned out that the vertical electronic transitions of absorption are characterised as intramolecular charge transfer between perylene diimide moieties and substituent aromatic groups. Our results suggest that the optical and electronic properties and reorganisation energies are affected by the introduction of different aromatic groups to these molecules. The calculation results showed that the designed molecules own the large longest wavelength of absorption spectrum, the oscillator strength and absorption region values. On the basis of the investigated results, the designed molecules could be used as solar cell material with intense broad absorption spectra. Furthermore, they are expected to be the promising candidates for hole and/or electron transport materials.     

软凝聚态物质物理学

软物质是指其某种物理性质在小的外力作用下能产生很大变化的凝聚态物,典型的例子包括液晶、高分子体系、胶体、微乳液等。软物质的结构和性质主要不是由内能,而是由熵来决定,较通俗地介绍了软物质的概念,仔细分析了熵在软物质中所起的作用,同时详细介绍了聚合物体系、胶体及生物膜等几种典型的软物质,通过硫化橡胶和无管虹吸等十分有趣的例子。说明了聚合物对流变性质的影响;通过分析硬球胶体的相变及相分离等行为说明了熵力的概念;仔细分仔了电稳定胶体的相互作用,并介绍了DLVO理论以及近年来发现的对这一理论的偏离,特别是约束条件下同号带电胶球的长程吸引相互作用及其对此现象的一些解释;对生物膜也作了初步介绍。人们对软物质的研究和理解目前还处于一个非常原始的阶段,深入研究和理解软物质的各种性质必将促进人类对自然和人类自身的认识。     

External heavy atom effect on the emission of carbazole

External heavy atom induced quenching of luminescence emission of carbazole in n-hexane and methylcyclohexane in the presence of chloro- and bromoacetic acids at 300 K and 77 K is described. A straight line relation between fluorescence quenching rate constant and the acid dissociation constant of chloroacetic acids, which is related to electron affinity, is observed. Different photophysical parameters at 77 K of unperturbed and perturbed fluorescent carbazole in ternary solutions have been determined and suitable reaction mechanism for quenching has been proposed. Inference has been drawn about complex formation in the triplet state of carbazole from the biexponential nature of the phosphorescence decay curve.