Circular dichroism of polyethylenimine containing optically active thymine derivatives as grafted pendants

Optical properties of linear polyethylenimine containing optically active (+)- or (?)-2-(thymin-1-yl)propionyl group as grafted pendant were investigated by circular dichroism (CD) and compared with those of the related monomer and dimer model compounds. CD spectra of the polymer in neutral aqueous solution were different from those of related model compounds, which suggest that the polymer exists in some ordered conformation (at least locally) to allow exciton coupling of π–π^* (B_2u) transition in the base chromophores along the polymer chain. This ordered conformation tends to be randomized on heating. The effects of complementary base pairing on the CD spectra have also been studied by using a linear polyethylenimine containing (±)-2-(adenin-9-yl) propionyl grafts and its related monomer and dimer models.     

Investigation of the conformation of hyperbranched poly(arylene oxindole)s using hyper‐Rayleigh scattering

A hyperbranched poly(arylene oxindole), a poly(methacrylate), and a dendrimer, to which the same nonlinear optical chromophore was attached via a small, rigid spacer, were prepared. The difference in hyper‐Rayleigh scattering intensities was measured and compared. From this study, it was concluded that the chromophores, and hence the functional groups in the macromolecule before functionalization, are orientationally correlated in the dendrimer, whereas they are not in the linear and hyperbranched polymer. More in particular, the chromophores in the dendrimer are fixed in a centrosymmetric way because of the globular structure, whereas there is no orientational correlation between the chromophores in linear and hyperbranched polymer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3740–3747, 2009     

Nonlinear optical properties of novel H-shaped chromophores

Novel and effective H-shaped chromophores were doped into polymethyl methacrylate (PMMA) to form guest-host polymer thin films.The measurement results of Maker fringe method show that the polymer thin films containing the H-shaped chromophores as a guest exhibit high second harmonic coefficients (d33) compared with other two-dimensional chromophores.     

枝化二阶非线性发色团分子的合成及在聚合物体系中的电光性能

设计合成了一类以2-二氰基次甲基-3-氰基-4,5,5-三甲基-2,5-二氢呋喃(TCF)为受体、己氧基取代噻吩为π电子桥的新型有机非线性光学化合物, 并利用紫外光谱、红外光谱、核磁共振以及质谱对化合物分子结构进行了鉴定, 同时对此类化合物在有机聚合物体系中的电光性能进行了表征和研究. 结果发现, 该类发色团分子与聚合物相容性好, 电光活性高, 并且随着发色团分子在聚合物体系中浓度的升高, 聚合物体系的宏观电光活性也有所提高, 甚至当发色团的掺杂质量分数高达47.2%时, 体系的电光活性仍呈上升趋势, 显示了该发色团的静电相互作用得到了明显抑制. 此时测得聚合物体系的电光系数为30 pm/V(1310 nm).     

Chiral interactions in azobenzene dimers: a combined experimental and theoretical study

To investigate interchromophore interactions in azobenzene polymers, we have undertaken a thorough spectroscopic analysis of the azodye [(S)-3-pivaloyloxy-1-(4'-nitro-4-azobenzene)pyrrolidine] by modeling the repeating unit of poly[(S)-3-methacryloyloxy-1-(4'-nitro-4-azobenzene)pyrrolidine) and its dimeric derivative whose synthesis is presented here. The analysis of the electronic and Raman spectra of the azodye in several solvents is based on a previously proposed model for polar chromophores in solution. Electronic and CD spectra of the dimeric unit are collected and analyzed within the framework of a new model. On the basis of the information collected from the spectroscopic analysis of the solvated dye, this model accounts for interchromophore interactions in the dimer. The large CD signal measured for the dimer (amounting to about a third of the signal measured for the polymer) suggests the presence of important chiral interactions in the dimeric unit, and is modeled in terms of a right-handed relative orientation of the two chromophores.     

官能化度对环氧树脂类偶氮聚合物光致取向的影响

利用光诱导双折射和偏振红外光谱法研究了偶氮官能化度对环氧树脂类偶氮聚合物BP-AZ-CA的光致取向行为的影响,重点研究了偶氮官能化度对偶氮生色团和聚合物主链的光致取向速度及饱和取向程度的影响规律.结果表明,随着偶氮官能化度的增加,偶氮生色团和聚合物主链的光致取向速度均降低,但二者的饱和取向程度增加.体系中氢键相互作用的增强是导致BP-AZ-CA的光致取向行为随偶氮官能化度增加而变化的原因之一.     

The use of circular dichroism in the investigation of protein structure and function

Circular Dichroism (CD) relies on the differential absorption of left and right circularly polarised radiation by chromophores which either possess intrinsic chirality or are placed in chiral environments. Proteins possess a number of chromophores which can give rise to CD signals. In the far UV region (240-180 nm), which corresponds to peptide bond absorption, the CD spectrum can be analysed to give the content of regular secondary structural features such as alpha-helix and beta-sheet. The CD spectrum in the near UV region (320-260 nm) reflects the environments of the aromatic amino acid side chains and thus gives information about the tertiary structure of the protein. Other non-protein chromophores such as flavin and haem moieties can give rise to CD signals which depend on the precise environment of the chromophore concerned. Because of its relatively modest resource demands, CD has been used extensively to give useful information about protein structure, the extent and rate of structural changes and ligand binding. In the protein design field, CD is used to assess the structure and stability of the designed protein fragments. Studies of protein folding make extensive use of CD to examine the folding pathway; the technique has been especially important in characterising molten globule intermediates which may be involved in the folding process. CD is an extremely useful technique for assessing the structural integrity of membrane proteins during extraction and characterisation procedures. The interactions between chromophores can give rise to characteristic CD signals. This is well illustrated by the case of the light harvesting complex from photosynthetic bacteria, where the CD spectra can be analysed to indicate the extent of orbital overlap between the rings of bacteriochlorophyll molecules. It is therefore evident that CD is a versatile technique in structural biology, with an increasingly wide range of applications.     

Self-assembly of a hydrophobically modified naphthalene-labeled poly(acrylic acid) polyelectrolyte in water: organic solvent mixtures followed by steady-state and time-resolved fluorescence

The solution properties of two water-soluble polymers, poly(acrylic acid) (PAA), covalently labeled with the fluorescent hydrophobic dye naphthalene (Np), have been investigated in water:organic solvent mixtures. The naphthalene chromophores have been randomly attached, onto the polymer, with two different degrees of labeling. Fluorescence measurements (steady-state and time-resolved) have been used to follow the photophysical behavior of the polymers and consequently report on the self-association of the polymers in the mixed organic (methanol or dioxane):aqueous solutions. The emission spectra of the high-labeled Np PAA reveal the presence of monomer and excimer bands whereas with the low-labeled polymer only monomer emission is observed. The excitation spectra collected at the monomer and excimer emission bands show significant differences, depending on the water content of the mixture, which indicate the simultaneous presence of preformed and dynamic dimers as routes to excimer formation. The time-resolved data decay profiles of the high-labeled polymer in the mixtures were always triple exponential whereas in pure methanol and dioxane they follow biexponential laws. The data in the mixtures are consistent with two types of monomers and one excimer. Both monomers are able to give rise to excimer in the excited state, one type involving the movement of long distant Np chromophores and the other involving a local reorientation of adjacent Np chromophores. These correspond to different decay times: (1) a long which corresponds to the long distant approach of non-neighboring Np chromophores forming an excimer and (2) a short corresponding to the fast adjustment of two neighboring Np chromophores in order to have the adequate parallel geometry. An additional decay time corresponding to the excimer decay was found to be present at all wavelengths. All the decay times were dependent on the water content of the mixture. An estimation of the two excimer forming rate constants values is made for the mixed media considered in this work. On the whole, using both steady-state and time-resolved fluorescence parameters, and by comparing data for a polymer with a small number of hydrophobes with a more highly modified one, it is possible in great detail to demonstrate how association is controlled by solvent quality for the hydrophobes and by the distance between hydrophobes.     

STUDY ON PHOTODYNAMIC AND PHOTORESPONSIVE AZO POLYELECTROLYTES*

Several kinds of novel azobenzene-containing polyelectrolytes with special molecular design have been developedfrom acryloyl chloride or epoxy based precursor polymers. The acryloyl chloride based precursor polymer, poly(acryloylchloride), was prepared by free radical polymerization of acryloyl chloride. The azo polyelectrolytes were prepared by anesterification reaction between the precursor polymer and corresponding azo chromophores containing a reactive hydroxylgroup, followed by hydrolysis of the unreacted acyl chloride groups. The epoxy based precursor polymer was prepared by thereaction between 1,4-cyclohexanedimethanol diglycidyl ether and aniline, and postfunctionalized by azo coupling reaction toform azo polymers containing chromophores with ionizable groups. The polyelectrolytes were characterized by elementalanalysis, ~1H-NMR, IR and UV-Vis spectroscopy. The photodynamic and photoresponsive properties, as well as self-assemblyof these azo polyelectrolytes are reported in this paperp.     

Synthesis and characterization of polyurethane anionomers with bisazoaromatic chromophores and carboxylate groups

A new diol with a bisazoaromatic pendant was prepared to obtain photosensible polymers suitable for dyed aqueous systems. A polyurethane bearing bisazoaromatic chromophores, based on a poly(tetramethylene oxide) diol (average molecular weight = 2000), 2,4‐tolylene diisocyanate, and the aforementioned azo diol, was synthesized and characterized. Bichromophoric polyurethane anionomers, prepared by a two‐step substitution of urethane hydrogen atoms with sodium carboxylate groups, were studied. The influence of the concentration of carboxylate groups (30–158 mequiv of ionic groups/100 g of polymer) on some polymer properties and photoisomerism in polymer solutions and thin films was examined. In particular, the polymer structure and its morphology dictated the proximity of anchored bisazo chromophores and the capability of intermolecular forces between dyes producing hydrogen aggregates in solutions and thin films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5463–5470, 2004     

Preparation and Function of Poly(acrylic acid)s Modified by Supramolecular Complex Composed of Porphinatoiron and a Cyclodextrin Dimer That Bind Diatomic Molecules (O2 and CO) in Aqueous Solution

Poly(acrylic acid) (PAA) is modified by 5‐(4‐β‐alanylaminophenyl)‐10,15,20‐tris(4‐sulfonatophenyl) porphinatoiron(III) to yield iron porphyrin‐bearing PAAs (FeP(n)s) through a condensation reaction. FeP(n)s were further functionalized by Py3CD, which is a per‐O‐methylated β‐cyclodextrin (CD) dimer with a pyridine linker and includes the porphyrin pendants to form ferric hemoCD‐P(n)s. Ferrous hemoCD‐P(3), having three porphyrin chromophores in a polymer chain, is shown to bind molecular oxygen (P_1/2=7.9±1.4 Torr) in aqueous solution at pH 7.0 and 25 °C, affording oxy‐hemoCD‐P(3). Oxy‐hemoCD‐P(3) is biphasically autoxidized to ferric hemoCD‐P(3), with 27 % of the dioxygen adducts being rapidly oxidized. The rate of autoxidation of oxy‐hemoCD‐P(15), having 15 porphyrin chromophores in a polymer chain, was much faster than that of oxy‐hemoCD‐P(3), thus suggesting self‐catalyzed autoxidation of oxy‐hemoCD‐P(n)s. Oxy‐hemoCD‐P(n)s are markedly stabilized by catalase, thereby indicating that hydrogen peroxide generated from oxy‐hemoCD‐P(n) accelerates the autoxidation. Most of the hemoCD‐P(3) molecules injected into the femoral vein of a rat remained in the body, though about 16 % of the hemoCD‐P(3) molecules were excreted in the urine as a carbon monoxide adduct.     

Circular dichroism spectra of DNA hairpins studied by the green function method

The circular dichroism (CD) spectrum of a large biological molecule represented as an array of interacting chromophores is investigated. The configuration-averaged Green function formalism is developed to describe the CD and absorption spectra. The perturbation theory expansion is derived for absorption and CD spectra in the case of strong interaction of chromophores with their environment (solvent and/or internal dynamics) compared to their interaction with each other. We apply this formalism to study CD spectra of DNA hairpins.     

表面起伏光栅形成速率的影响规律 Ⅰ.偶氮生色团种类和官能度的影响

设计并合成了含有不同生色团以及不同官能度的环氧树脂基偶氮高分子 ,系统研究了偶氮生色团的种类和官能度对光栅形成速率的影响规律 .实验结果表明 ,偶氮苯对位是羧基的聚合物的光栅形成速率明显快于偶氮苯对位是硝基的聚合物 ,光栅形成速率随偶氮生色团官能度的增加而加快 .这两类聚合物都可以形成规整的可擦式表面起伏光栅     

Inhibition of energy transfer between conjugated polymer chains in host/guest nanocomposites generates white photo- and electroluminescence

The generation of white light requires the combination of two or more chromophores that emit simultaneously. The observed color of a mixture of light-emitting molecules, however, originates generally only from the lowest band-gap species because of efficient energy transfer between the chromophores which is difficult to avoid. Here we report on a nanocomposite material designed to yield pure and stable white photo- and electroluminescence. In this material, red, green, and blue emitting conjugated polymers are confined within the galleries of a layered semiconducting host matrix. The host hinders polymer pi-pi interactions which are responsible for the energy transfer between polymer chains, consequently, emission from the three chromophores is observed simultaneously resulting in white photoluminescence. The efficacy of the nanocomposites is demonstrated in simple single-layer white-emitting polymer diodes. The mechanism suggested here for white light generation, supported by extensive luminescence measurements, is in contrast to that previously reported in white-emitting polymer diodes where efficient energy transfer between polymer chains was essential for obtaining white light.     

低苯乙烯含量的丁二烯-苯乙烯共聚物的激基缔合物荧光研究

本文报导一种低苯乙烯含量(5％,Wt.)的丁二烯-苯乙烯共聚物,经~1H NMR证明其分子链上不存在相邻苯乙烯单元。荧光光谱结果表明,它在良溶剂(二氯乙烷)的稀溶液状态下只呈现单分子荧光。从良溶剂-θ溶剂(二氯乙烷-甲醇体系)及稀溶液-浓溶液-固体之荧光光谱的变化,证明形成了链内非近邻生色团之间和链间生色团之间的激基缔合物(Excimer)。从固体与θ溶剂的激基缔合物荧光的比较,还可区分链内非近邻和链间苯环形成激基缔合物对荧光强度的贡献。这一结果对阐明高分子链内非近邻和链间激基缔合作用提供了新的证据,并有助于了解高聚物本体中相互穿透、相互缠结的无规线团的形态。     

Single chromophore spectroscopy of MEH-PPV: homing-in on the elementary emissive species in conjugated polymers.

Low-temperature, single-molecule spectroscopy can provide unparalleled access to the primary emissive species of conjugated polymers. We demonstrate this with the example of one of the most commonly studied polymers, poly(2-methoxy-5-(2'-ethylhexoxy)-1,4-phenylenevinylene), MEH-PPV, which is shown to exhibit sharp fluorescence signatures over one hundred times narrower than the ensemble. These unprecedented narrow emission features can be assigned to single chromophores on the polymer chain, which are selectively addressed by the narrow band excitation. As with organic dye systems, the emission from single chromophores is not static with time, but shows a substantial spectral fluctuation. We find that, for single chromophores, this spectral fluctuation always follows a universal Gaussian statistical distribution. High-resolution spectroscopy provides unique insight into low-energy vibrational modes in the polymer emission, which are generally inaccessible with conventional spectroscopic methods such as site-selective fluorescence or Raman spectroscopy. Interchromophoric coupling can also occur owing to the flexible nature of the polymer backbone. This leads to substantial spectral broadening and a loss of resolution in the vibronic progression. We observe reversible switching within one single molecule between narrow and broad emission, which directly correlates with a discrete switching in emission intensity. We conclude that one and the same single molecule can support aggregated and nonaggregated emission, that is, emission from isolated and aggregated chromophores in one single molecule, rather than the tendency for aggregate emission being intrinsic to the molecule.     

Preparation of benzoylchitosans and their chiroptical properties in dilute solutions

Two benzoyl substituted chitosan derivatives, 3,6‐O‐dibenzoylchitosan (DBC) and 2‐N‐3,6‐O‐tribenzoylchitosan (TBC), were prepared, and their optical activities in organic solvent were investigated by circular dichroism (CD). For TBC, two splitting bands (a negative one at 288 nm and a positive one at 274 nm) corresponding to the ¹L_b transition of the benzoyl group were observed in chloroform and dichloromethane, while only a negative CD band was recorded in N, N‐dimethylformamide (DMF). These results indicated that the transition moments of benzoyl groups were orderly arranged along the helical polymer chain when TBC was dissolved in a solvent with low polarity, but the same ordered structure did not appear in a polar solvent of DMF. For DBC, only negative CD signals corresponding to the ¹L_b transition of the benzoyl group were observed, regardless of the solvent property, which indicated that the chromophores were not arranged in an ordered fashion with appropriate geometry to interact with one another to induce bi‐signate CD signals. Adding methanol or DMF to the solution of TBC/chloroform resulted in a progressive decrease of the intensity of the positive split band at 274 nm. The intensity of the positive band was weakened upon heating a solution of TBC/chloroform from 20 to 60 °C. The results suggested that the ordered arrangement of the chromophores in the TBC system was dependent on solvent and sensitive to temperature. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4107–4115, 2004     

Poly(4‐vinylpyridine) as the host ligand of metal‐containing chromophores for second‐order nonlinear optical active materials

Two formulas of grafted polymers with metal‐containing chromophores, potentially suitable for second‐order nonlinear optics applications, are described. Two chromophores were obtained from a tridentate ligand coordinated to Cu(II) or Pd(II) ions. The organometallic chromophore fragments were grafted to poly(4‐vinylpyridine) by the pyridinic nitrogen of the host polymer. Some qualities displayed by the new metallated polymers are remarkable: (1) a high value of the first hyperpolarizability coefficient of the chromophores, (2) a high content of the grafted chromophore in the polymers (up to 60 wt %), (3) a considerable increase in the glass‐transition temperatures (up to 240 °C), (4) good thermal stability in air (ca. 280 °C), and (5) good optical transparency of the films. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2987–2993, 2002     

Dye-containing S*c side-on/end-on copolymers

Mesomorphic copolysiloxanes, which combine 'normal' end-on linked chiral mesogenic units inducing S*_c phases and side-on fixed chromophores were prepared. The interplay of the different orientational tendencies of these moieties, which are perpendicular (end-on linked mesogenic groups) or parallel (side-on fixed chromophores) to the polymer chain, lead to a strong destabilization of the S*_c phase. However, copolymers with up to about 10 mol % of chromophores still show a smectic C* phase. FTIR measurements show that both moieties orient parallel to each other and perpendicular to the polymer chains. These copolymers are interesting to consider as coloured guest-host S*_c materials for coloured displays or as pyro-electric detectors.     

Photorefractive polymer composites based on nanosized nonlinear optical chromophores

Photorefractive (PR) polymer composites based on polymers with a high glass transition temperature in which the random distribution of a photosensitizer and a nonlinear optical chromophore as dopants is “frozen” were designed. In the case of the random distribution of chromophores, only the third-order electric susceptibility has a nonzero value. Therefore, nanosized structures having high third-order polarizability due to an extended conjugated-bond system (or cooperative electronic excitation) were used as nonlinear chromophores. Good PR characteristics are displayed by polymeric composites containing nanosized structures, such as cyanine dye J aggregates, supramolecular assemblies of ruthenium(II) complexes, and single-wall carbon nanotubes. The use of extended nanosized chromophores as simultaneous spectral sensitizers allowed polymer composites with PR sensitivity in the near IR region at 1064 and 1550 nm to be designed.