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Gold and silver nanoparticles of different size, decorated by a diacetylenic monomer having a COOH anchor group, were prepared in aqueous dispersions. Topochemical polymerization of the colloidal suspensions was obtained by UV irradiation and studied by means of spectroscopic techniques (UV–visible absorption, IR and Raman spectroscopies). A variety of polymer phases were found in the case of silver nanohybrids. The main contribution for this investigation was supplied by the Raman spectra, which provide detailed information on the polymer forms and on the preferred conformation of the alkylic side chains. Copyright © 2009 John Wiley & Sons, Ltd.

We report on the preparation and characterization of self-assembled monolayers (SAMs) of a novel diacetylene monomer, the 14-N-carbazolyltetradeca-10,12-diyndisulfide. The SAM/gold interface was investigated by means of spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS) and scanning tunnelling microscopy (STM). SE data indicate a layer thickness compatible with the formation of a monomolecular layer. The occurrence of molecular chemisorption is confirmed by XPS measurements which indicate the formation of a thiolate species. This result is confirmed by STM imaging which shows the formation of small pits, one gold layer deep, a typical feature of self-assembled organosulfur monolayers on gold.

We describe a method for the simultaneous determination of the five fibrinopeptide forms derived from the thrombin-promoted activation of human fibrinogen by capillary zone electrophoresis (CZE). The fibrinopeptide mixture was first desalted by a solid-phase extraction (SPE) step. The analysis was performed in reversed polarity in a highly cross-linked polyethylene glycol (PEG)-coated capillary with UV-light absorption detection at 200 nm. Several parameters including buffer concentration and pH, presence of an organic modifier, temperature, and applied voltage, have been tested. The best separations were obtained within 20 min, utilizing a 20 mM sodium phosphate buffer without organic modifier, in the narrow 6.1-6.2 pH range, at 25 degrees C, with an applied voltage of 20 kV. Quantitative analysis is made possible by the use of sheep fibrinopeptide A as an internal standard to correct for both extraction and injection errors.

The two-photon fluorescence excitation and optoacoustic spectra of red polyDCHD-HS in benzene solution at room temperature have been investigated in the 1600−750 nm exciting wavelength region (effe...

Waveguiding films of the highly soluble polycarbazolyldiacetylene polyDCHD-HS were prepared by spin coating and characterized at different wavelengths: 5 dB/cm propagation losses were observed at 1321 nm. Measurements of the third order nonlinearity at 1064 nm with the surface plasmon resonance (SPR) method gave the value χ(3)=4.4×10−17+i3.5×10−18 m2/V2.

The local dynamics of macromolecules is obtained to second-order in the mode-coupling expansion of the Smoluchowski diffusion theory. The NMR spin-lattice relaxation times of different 13C or 15N nuclei along the chains are calculated and compared to experimental data from the literature. The macromolecules are considered as fluctuating 3D structures undergoing rotational diffusion. The fluctuations can be evaluated with any technique for sampling the configurational space. In the presented test cases Molecular Dynamics simulations have been applied to a DNA fragment and to the NK-2 homeodomain. In the case of the double-stranded DNA fragment d(TpCpGpCpG)2, second and even first order theories are found to be in close agreement with experimental results. The major advantage of the diffusion technique is that only a good statistics is important as input while the solvent dynamic effects enter through hydrodynamic theory. Application based on Hybrid Monte Carlo schemes coupled with J-walking, are n...

Many biological supramolecular structures are formed by polymerization of macromolecular monomers. Light scattering techniques can provide structural information from such systems, if suitable procedures are used to collect the data and then to extract the relevant parameters. We present an experimental set-up in which a commercial multiangle laser light scattering photometer is linked to a stopped-flow mixer, allowing, in principle, the time-resolved extrapolation of the weight-average molecular weight M(w) and of the z-average square radius of gyration (z) of the polymers from Zimm-like plots. However, if elongated structures are formed as the polymerization proceeds, curved plots rapidly arise, from which M(w) and (z) cannot be recovered by linear fitting. To verify the correctness of a polynomial fitting procedure, polydisperse collections of rod-like or worm-like particles of different lengths, generated at various stages during bifunctional polycondensations of rod-like macromolecular monomers, were considered. Then, the angular dependence of their time-averaged scattered intensity was calculated in the Rayleigh-Gans-Debye approximation, with random and systematic noise also added to the data. For relatively narrow size distributions, a third-degree polynomial fitting gave satisfactory results across a broad range of conversion degrees, yielding M(w) and (z) values within 2% and no greater than 10-20%, respectively, of the calculated values. When more broad size distributions were analyzed, the procedure still performed well for semiflexible polymers, but started to seriously underestimate both M(w) and (z) when rigid rod-like particles were analyzed, even at relatively low conversion degrees. The data were also analyzed in the framework of the Casassa approximation, from which the mass per unit length of the polymers can be derived. These procedures were applied to a set of data taken on the early stages of the thrombin-catalyzed polymerization of fibrinogen, a rod-like macromolecule approximately 50 nm long. The polymers, grown in the absence of Ca(2+) by rate-limiting amounts of thrombin, appeared to be characterized by a much broader size distribution than the one expected for a classical Flory bifunctional polycondensation, and they seem to behave as relatively flexible worm-like double-stranded chains. Evidence for the formation of fibrinogen-fibrin monomer complexes is also inferred from the time dependence of the mass/length ratio. However, our data are also compatible with the presence of limited amounts of single-stranded structures in the very early stages, either as a secondary, less populated pathway, or as transient intermediates to the classical double-stranded fibrils.

We have investigated the effects of the chemical substitution of long alkyl chains in the carbazolyl group of a polycarbazolyldiacetylene on its electronic properties. The electronic absorption and Raman spectra of the unsubstituted unsoluble polycarbazolyldiacetylene polyDCHD and those of the alkyl-substituted soluble polymers (polyDCHD-S, polyDCHD-HS) in the blue form are very similar indicating that the backbone conjugation length is practically not affected by this substitution. Very different instead is the nature of the long-lived photoinduced excitations of these polymers. Charged carriers as well as triplet excitons are formed in the unsubstituted blue polymer while triplet excitons dominate the photoinduced spectrum when long alkyl chains are attached to the aromatic ring. Only triplet excitons are observed in the red form of the soluble polydiacetylenes. We have interpreted these findings as due to the different molecular and supramolecular structure of these polymers. The larger interchain separation achieved in the substituted polycarbazolyldiacetylenes favours the photogeneration of triplet excitons relative to charged species. This effect is even more pronounced for the red form of these polymers where the twisted conformation further decreases the interchain coupling. The femtosecond‐picosecond time evolution of the excited state dynamics of the red form of polyDCHD-S and -HS in a polyethylene matrix has also been measured by the pump-probe technique. Films of this type in which the polymer backbones of the different chains are isolated and in the twisted conformation are particularly suitable for this investigation. We believe in fact that these conditions can allow a meaningful comparison of the experimental data with the results of highly correlated quantum mechanical calculations carried out on oligomers. The transient differential transmission spectra display characteristic features depending upon the probe time delay. Photobleaching at 2.3 eV and photoinduced absorptions at 1.8 and 1.5 eV are present at short probe delay. The 1.5 eV feature, present also at large probe delays, is assigned to triplets which are formed by singlet fission as a pair with an overall zero spin. These pairs, when survived to their recombination and trapped in defect sites, can live up to milliseconds. On the basis of the quantum mechanical calculations on oligomers, we believe that the state responsible for the fission is the optically forbidden 2 1 Ag level below the first allowed 1 1 Bu state. q 2000 Elsevier Science B.V. All rights reserved.

The local dynamics of a double-stranded DNA d(TpCpGpCpG)(2) is obtained to second order in the mode-coupling expansion of the Smoluchowski diffusion theory. The time correlation functions of bond variables are derived and the (13)C-nmr spin-lattice relaxation times T(1) of different (13)C along the chains are calculated and compared to experimental data from the literature at three frequencies. The DNA is considered as a fluctuating three-dimensional structure undergoing rotational diffusion. The fluctuations are evaluated using molecular dynamics simulations, with the ensemble averages approximated by time averages along a trajectory of length 1 ns. Any technique for sampling the configurational space can be used as an alternative. For a fluctuating three-dimensional (3D) structure using the three first-order vector modes of lower rates, higher order basis sets of second-rank tensor are built to give the required mode coupling dynamics. Second- and even first-order theories are found to be in close agreement with the experimental results, especially at high frequency, where the differences in T(1) for (13)C in the base pairs, sugar, and backbone are well described. These atomistic calculations are of general application for studying, on a molecular basis, the local dynamics of fluctuating 3D structures such as double-helix DNA fragments, proteins, and protein-DNA complexes. Copyright 1999 John Wiley & Sons, Inc.

The synthesis of the monomer 1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne, its polymerization and the purification of the polymer, which is soluble in common organic solvents, are reported. Results from powder X-ray diffraction studies carried out on the red form of the polymer are discussed. The red polymer chains self-assemble into cylindrical shapes which produce hexagonal columnar mesophases with a transition from a more (Colho) to a less ordered (Colhd) structure around 85 C. The role played by the long alkyl chains in the formation of the supramolecular hexagonal mesophase is emphasized by comparing these results with those obtained from an analogous polymer with dodecyl substituents which exhibits only the Colhd structure over the whole range of temperature explored.

The carbazolyldiacetylenes show very different fluorescence behaviors depending on how the carbazolyl (Cz) moiety is connected to the diacetylenic backbone. In fact, when Cz is attached to the backbone through one or more CH2 spacer(s) fluorescence properties are observed which are closely related to those of the fluorescent Cz group. On the contrary, almost no fluorescence is observed when Cz is directly attached to the backbone. In this paper, these phenomena are studied quantum chemically and an explanation for the observed facts is provided. The relevant excited states are studied in detail, showing that in the lowest singlet excited state a considerable intramolecular charge transfer occurs from Cz to the backbone when they are directly bonded.

We report the results of steady-state photoinduced absorption experiments on PDA-4BCMU grown on silica substrate. We observe three photoinduced absorption bands at 0.82, 0.95, and 1.39 eV whose relaxation dynamics are identical for the two low-energy peaks but different for the 1.39-eV band. On the basis of the spectra, the pump intensity, modulation frequency, and signal phase dependences we conclude that the 0.82 and 0.95-eV absorption features are due to charged states while the 1.39-eV peak is originated by triplet excitons. The photogeneration of both charged and neutral states in PDA-4BCMU as previously observed in polycarbazolyldiacetylenes indicates that this is a general feature of polydiacetylenes. The relative weight of one excited species over the other one is influenced by the molecular and supramolecular organization of the polymer.

We report the photoinduced absorption spectra of an oriented form of poly[1,6- di(N-carbazolyl)-2,4-hexadiyne] (polyDCHD) grown by molecular epitaxy. The polarized absorption spectra of the polyDCHD point out the high quality of the sample and the very high degree of alignment of the polydiacetylene chains. The millisecond photoinduced absorption spectrum shows the same features already observed in polycrystalline samples assigned to triplet excitons in addition to bipolarons. The study of the dependence of the photoinduced absorptions on the polarization of the laser beam confirms this assignment. After correction for the same number of absorbed photons in both polarizations, the photoinduced signal assigned to bipolarons is stronger by pumping with the electric field of the radiation perpendicular to the chain axis direction. This fact is indicative of the interchain nature of the generation process of these photoexcited species. On the other hand, such an effect is not observed for the photoinduced triplet-triplet transition according to its intramolecular nature. \textcopyright{} 1996 The American Physical Society.

Some unsymmetrical diacetylenic monomers containing a carbazolyl group directly attached to the diacetylene skeleton as well as a flexible polar side group were synthesized. Thermal polymerization ...

We have studied the vibrational and electronic structure and the elementary excitations of poly [1,6-di(N-carbazolyl)-2,4-hexadiyne] (polyDCHD), poly[1-(N-carbazolyl)penta-1,3-diyn-5-ol] (polyCPDO), and poly[1-(N-carbazolyl)penta-1,3-diyn-5-acetoxy] (polyCPDA) by electronic absorption, Raman scattering, and photoinduced absorption in the infrared region. The long-lived photoexcitations are charged bipolarons with associated infrared-active vibrational (IRAV) modes. The results are also discussed in relation to the degree of chain order of the different polydiacetylenes as evidenced by the electronic spectra. Only poly(DCHD) shows an absorption spectrum dominated by a single exciton, suggesting a one-dimensional ordered structure. Consequently, for this polymer only, triplet excitons with a lifetime of the order of ms are photogenerated in addition to bipolarons. Among polydiacetylenes, only poly(CPDA) shows photoinduced IRAV modes not affected by Fano coupling between electronic and vibrational states.

Photoinduced absorption is observed for the polydicarbazolyldiacetylene in the microcrystalline state. The absorption spectrum shows well-defined excitonic features, very similar to those observed for the same polymer in the single-crystal form. Photoexcitation at 2.54 eV gives rise to a structured luminescence emission with the maximum around 1.7 eV. The photoinduced absorption spectrum shows three well-resolved peaks at 0.81, 0.96, and 1.26 eV, a shoulder at 1.04 eV, and a band with a maximum below 0.3 eV. By analyzing the dependence of the photoinduced signals on temperature, laser intensity, phase detection, and chopper frequency, we demonstrate that the long-lived photocarriers associated with the peaks at 0.81 eV and below 0.3 eV are charged bipolarons. The 0.96- and 1.04-eV bands are tentatively assigned to vibronic excitations of the bipolarons. Moreover, the 1.26-eV band has been assigned here to a triplet exciton transition. The existence of a correlation between the type of long-lived photogenerated defects and the polymer disorder is also discussed.

Human plasma fibronectin is a high molecular weight (530,000), multi-domain, modular glycoprotein, consisting of two nearly identical subunits disulfide-bridge close to their C-terminal ends. Three sites that can be differentially labeled with fluorescent probes are present on each fibronectin subunit, the transglutaminase-sensitive Gln3 residue and the two free sulfhydryl residues, Cys1201 and Cys2196. These sites are located, respectively, in the N-terminal heparin/fibrin-binding domain, between the central DNA and cell-binding domains, and just before the C-terminal fibrin-binding domain. To map the relative spatial arrangement of these domains, steady-state and lifetime fluorescence energy transfer techniques were employed. Our results show that the minimal intramolecular distances between labeled Gln3-Cys1201 and Gln3-Cys2196 pairs are 5·5(±0·6) nm and 5·7(±0·7) nm, respectively, as measured by steady-state methods. Lifetime methods gave somewhat higher distances of 8·1(±0·2) nm and 7·6(±0·2) nm, respectively, between these sites. The binding of heparin or subjection to high ionic strength had only a minor effect, while in the presence of 50% (w/v) glycerol, an increase of about 25% in the intramolecular distances between these sites was observed. A similar effect was induced by binding of fibronectin to the surface of Cytodex beads, an event which was previously shown instead to markedly increase the intersubunit distances between the Gln3-Gln3 and Cys1201-Cys1201 pairs. The solution structure of fibronectin was further investigated by elastic light-scattering and circular dichroism measurements. By elastic light-scattering, the radius of gyration of fibronectin was found to be 15·3(±0·8) nm in the presence of 30% (w/v) glycerol, in contrast to a value of 8·6(±0·3) nm under physiological conditions. Far and near ultraviolet circular dichroism spectra showed that only minor changes in the secondary structure of fibronectin take place on increasing the glycerol content of the solvent up to 34% (w/v). Our results complement previously available information on the solution structure of fibronectin and on its transition from the native compact conformation to a more expanded form on increasing ionic strength or glycerol content. In either situation, fibronectin seems to retain a basic structural core, in which the N-terminal, the central and the C-terminal regions of the two subunits strongly interacts with each other. A major role of hydrophobic forces, in stabilizing the fibronectin conformations under these conditions, is therefore postulated. The transition to the extended forms seen in many electron micrographs can instead be explained by disruption of the proposed structural core upon adsorption to surfaces.

Nonlinear tests performed by using surface plasmon spectroscopy (SPS) on ultrathin films (9–50 nm thick) of polyDCHD-HS are reported. PolyDCHD-HS is a new soluble polycarbazolyldiacetylene which seems to show a certain degree of supramolecular organisation even in spin coated films. The SPS tests, which were performed at 1064 nm with picosecond pulses, gave a large and negative value for the real χ (3) susceptibility: |Re{ χ (3) }|≥1.2×10 −17 m 2 /V 2 (significantly larger than what was found in the case of PTS). If further investigations at 1300 and 1500 nm confirm these results, polyDCHD-HS is promising for future applications.

The geometric and electronic structure of the doping-induced defects in Ph 2 S and Ph(-SPh) 2 (Ph = phenyl) as model compounds of poly( p -phenylene) sulfide are studied by comparing the theoretically computed properties of neutral, singly and doubly ionized species with experiment. A locally planar quinod-type geometry of the defect is suggested by ab initio geometry optimizations, while Valence Electron Hamiltonian calculations indicate that the generation of some bipolaron (in addition to polaron) concentration must be invoked to explain the structure of the electronic spectrum observed for the doped dimer.

Electronic spectra of poly-p-phenylene sulfide (PPS) and its oligomers doped in TaF 5 /CH 2 Cl 2 solutions are reported. Ab initio calculations for diphenyl sulfide and 1,4-bis(phenylthio)-benzene in the neutral and oxidated forms allow the understanding of the evolution of the electronic spectral pattern in the VIS-NIR region upon increasing the number of the Φ-S units.

Gold nanoparticles (AuNPs) coated with the diacetylene henicosa-10,12-diyn-1-yl (DS9) disulfide were successfully prepared by direct synthesis in toluene solutions. The average size of the nanohybrid metal core was finely adjusted by manipulation of the preparative conditions in the diameter range from 1.6 to 7.5 nm, as determined by TEM characterization. The topochemical polymerization of DS9 chemisorbed onto the gold nanoclusters of different size was carried out in colloidal suspensions by exposure to UV radiation and the process was monitored by UV-Vis and Raman spectroscopies. The results showed that in these assemblies the monomer undergoes an intra-particle polymerization and that the dominant polydiacetylene phase present is ruled by the core size. The deposition of the photoirradiated colloids onto different substrates was found to leave the polydiacetylene conjugation unaltered.

The interaction of the ethidium cation with calf thymus DNA is investigated in solutions of different ionic strength and temperature by observation of the enhancement of fluorescence of ethidium upon intercalation in the duplex structure. The quantum yield of the fluorescence of the intercalated dye is found to increase either upon lowering the Na+ concentration or upon increasing the temperature. The existence of a correlation between the geometry of the intercalation complex and the features of the secondary structure of DNA is suggested. Binding isotherms under corresponding environmental conditions are also quantitated by fluorescence enhancement and interpreted in terms of the neighbor exclusion model. Large contributions from change in hydration to the thermodynamics of binding are demonstrated by the temperature dependences of the equilibrium constants. The neighbor exclusion range is found to be practically independent of the salt concentration but its value increases from an average of 2.4 around room temperature to 4-5 at 80 degrees C, as inferred from the binding curves in 0.15 and 0.5 M [Na+] or from the DNA hypochromism vs temperature profiles of complexes at 10(-3) M [Na+]. All the data point to a possible sequence-conformation specificity in the intercalation of ethidium which in heterogeneous DNA is mediated by environmental changes.

Polarized Raman spectra at 77 K of all- trans -β-carotene stretch-oriented in polyethylene films are reported for the first time. The measurements were carried out either in the 90° and back-scattering geometries at excitation wavelengths in resonance with the lowest allowed 1 B u « 1 A g electronic transition, and indicate a rather good orientation of the polyenic chains along the stretching direction. By changing the excitation wavelength, a significant dispersion of the Raman shift relative to the CC stretching mode is observed. One interpretation of this effect, based on the existence of two (or more) species (rotational conformers, aggregates, etc.) whose resolved absorption structures are displaced by one half the CC vibrational frequency, is presented and discussed.

This paper reports on the fabrication of self-assembled monolayers containing disulfide-functionalized diacetylenes. To this purpose, two diacetylene derivatives were synthesized: the novel 14-(9H-9-carbazolyl)tetradeca-10,12-diyn-1-yl disulfide (CDS9) and the henicosa-10,12-diyn-1-yl disulfide (DS9). Both monomers were employed to prepare two-dimensional self-assembled monolayers (2D-SAMs) by chemisorption on gold-sputtered platforms and three-dimensional self-assembled monolayers (3D-SAMs) on gold nanoclusters by direct synthesis in organic solvent. The chemisorbed diacetylenes were then converted to the polymeric form by exposure to UV radiation, and their morphological and spectroscopic properties investigated by several techniques. From SERS data it was inferred that both monomers show the same behavior, in that the highly conjugated blue phase was observed in the 3D-SAMs, while only the less extended red conformation was found in the corresponding 2D-SAMs.

UV polymerization of self-assembled monolayers of a novel carbazolyl-diacetylene (CDS9) chemisorbed on silver films was demonstrated by surface plasmon resonance (SPR) and surface enhanced Raman scattering (SERS) experiments. SPR tests performed during UV exposure permitted one to observe the growth of the absorption coefficient, associated with the formation of the polymeric backbone. The Raman spectra of polymerized monolayers exhibited the bands associated with the C=C stretching modes of the conjugated backbone, typical of the blue and red polymeric phases usually present in polydiacetylenes, with a clear predominance of the red form. Moreover, the strong surface enhancement of the Raman band corresponding to the aromatic C=C stretching modes suggested that carbazolyl groups arrange nearly perpendicularly to the metal surface. In contrast, the absence of a SERS signal in the region of conjugated C[triple bond]C bond stretchings confirmed a polymerization scheme with conjugated triple bonds nearly parallel to the plane of the metal.

We grew self-assembled monolayers (SAMs) of a novel carbazolyldiacetylene, CDS9, on Ag-coated glass substrates and demonstrated the topochemical UV polymerization of CDS9 monolayers by recording the Raman spectra of the organic film before and after UV exposure. We observed coexistence of the blue and red polymeric phases, usually present in polydiacetylenes. The features of the organic/metal interfaces of our samples were properly varied, in order to achieve surface enhancement of the Raman (SERS) response of the ultra-thin molecular layers.

We report the optical properties and photoinduced absorption spectra of oriented poly [1,6-di( N -carbazolyl)-2,4-hexadiyne] (polyDCHD) grown by molecular epitaxy on a crystal of potassium acid phthalate. The absorption spectra in polarized light show the high degree of alignment of the polymeric chains obtained by this growth technique. The photoinduced absorption spectra show the typical structures (due to bipolarons and triplet excitons) already observed for the same polymer as a microcrystalline sample. The photoinduced signal is maximum when the pump beam is polarized perpendicularly to the chain axis direction. This is indicative of a direct interchain long-lived carrier generation, as already observed in other oriented conjugated polymers.

In this paper we report the results of a morphological and structural investigation on film properties of a soluble polydiacetylene, the poly[1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-HS). The red films of this polymer, prepared by standard spin-coating techniques, revealed absence of linear dichroism and birefringence in contrast with the ordered mesophases detected by powder X-ray studies. In order to interpret the optical behavior of this polymer, we performed AFM and SEM studies of polyDCHD-HS films spun on hydrophylic and hydrophobic glass substrates. We found the presence of surfaces organized in rod-like particles, more regularly oriented on the hydrophylic substrate. GIXRD studies, carried out on films sufficiently thick to allow the observation of the diffraction pattern, reveled the presence of a lamellar structure with a spacing of 3.22 nm. The low intensity of the diffraction peaks and the isotropic linear optical properties of the films show that the lamellar mesophases are not extended over large areas. These findings were compared with the data obtained from AFM and SEM studies on films of two other polydiacetylenes, the poly[1-(3,6-dihexadexyl-N-carbazolyl)-6-(N-carbazolyl)-2,4-hexadyine] (polya-DCHD) and the poly[1,6-bis(3,6-dipalmitoyl-N-carbazolyl)-2,4-hexadyine] (polyDPCHD), spun on hydrophylic glass substrate. The results confirmed the presence of nodular morphologies which seem to be a general characteristic of this class of materials. The particles organization appears instead related to the chemical nature of the substituents on the carbazolyl rings.

In this paper the results of studies carried out on thin films of new poly[bis(carbazol-9-ylmethyl)diacetylene]s (PCDAs) are reported. The preparation of the films has required clever synthesis to make processable the conjugated polymers without degrading their optoelectronic properties. To this end, the parent poly(diacetylene), (polyDCHD), has been modified by introducing long alkyl or acyl chains in the 3 and 6 positions of the carbazole rings. Electronic absorption spectra and linear and nonlinear optical characterization of three types of PCDAs are reported and compared.

The kinetics of release of fibrinopeptide A (FPA) and B (FPB) by thrombin were investigated on unfractionated fibrinogen samples as a function of CaCl(2) concentration. A 50 mM Tris, 104 mM NaCl, pH 7.4 (TBS) buffer, to which 1 mM EDTA-Na(2) (TBE) or 2.5 (TBC2.5), 14 (TBC14), and 30 mM CaCl(2) (TBC30) was alternatively added, was employed. The % FPA versus time curves were fitted with single stretched-exponential growth functions, where the stretch parameter beta likely reflects substrate polydispersity (beta = 1, monodisperse). For TBE, TBS, TBC14, and TBC30, we found beta approximately 1, with corresponding normalized rate constants (K(a)) of 3.8, 4.2, 2.7, and 1.9 x 10(-5) [(NIHu/L)s](-1). Surprisingly, in TBC2.5 we found beta = 0.69, with an "average" K(a) of 3.5 x 10(-5) [(NIHu/L)s](-1). This effect disappeared [beta = 0.97, K(a) = 2.7 x 10(-5) [(NIHu/L)s](-1)] with an increase in the ionic strength I to that of TBC30 with 186 mM NaCl (TBCaNa buffer). FPB releases were instead consistent with a nonstretched consecutive exponential growth function, except in TBC30 where some FPB appeared to be cleaved independently. Log-log plots of K(a) versus Ca(2+) concentration, Cl(-) concentration, or I showed a strong linear correlation with only the latter two except in TBCaNa, again suggesting specific effects of the physiological Ca(2+) concentration and I on FPA release. The corresponding K(b) plots showed instead that both total depletion and high Ca(2+) hampered FPB release. To further investigate the TBC2.5 beta = 0.69 effect, FG polydispersity was assessed by Western blot analyses. The thrombin-binding gamma'-chain isoform was approximately 4%, resulting in a bound:free thrombin ratio of approximately 25:75. With regard to the C-terminal ends of the Aalpha-chains, approximately 45% were either intact or lightly degraded, while the remaining approximately 55% were more degraded. Fitting the % FPA release data in TBC2.5 with a sum of two exponentials resulted in a faster component and a slower component (K(a1)/K(a2) approximately 6), with a ratio of approximately 48:52. While a role for the gamma'-chain isoform cannot be excluded, this good correlation with the C-terminal degradation of the Aalpha-chains suggests their calcium-dependent involvement in FPA release.

We report here on linear and non-linear optical characterisation of the polydiacetylene poly[1,6-bis(3,6-dipalmitoyl- N -carbazolyl)-2,4-hexadiyne] (polyDPCHD). Thin films (14 and 32 nm) of good optical quality have been obtained by deposition of the monomer from chloroform solutions on glass by standard spin-coating technique, followed by thermal polymerisation at 115 °C. Complex index of refraction of a thin film deposited on a 1 mm thick fused silica substrate has been determined in the spectral range from 270 to 1700 nm by ellipsometry. Third-order optical susceptibility ( χ (3) ) has been measured by Third Harmonic Generation (THG) technique on a thin polyDPCHD film deposited on a 160 μm thick BK7 substrate in the spectral range from 1000 to 1900 nm, using the Maker fringes method. The χ (3) dispersion shows the typical resonant behaviour due to multi-photon processes and is strictly related to the absorption spectra in the visible range. Values of χ (3) of the order of magnitude of 10 −11 esu have been obtained. A comparison between linear and non-linear optical properties of polyDPCHD and poly[1,6-bis(3,6-dihexaedcyl- N -carbazolyl)-2,4-hexadiyne] polyDCHD-HS will be presented.

We report on the absorption, photoluminescence and photoinduced absorption of polydiacetylenes (PDAs) having in the side groups the photoconductive carbazolyl rings substituted by acyl CO(CH 2 ) n CH 3 chains ( n =10, polyDLCHD; n =14, polyDPCHD). A novel feature in the absorption spectra is detected and assigned on the basis of theoretical calculation including the electron correlation. Different features are observed in the photoexcitations spectra of thin and thick samples and a preliminary interpretation is proposed.

The nonlinear optical response in uniaxially oriented films of poly[1.6‐di(N‐carbazolyl)‐2, 4‐hexadiyne], epitaxially grown on a potassium acid phthalate single crystal, has been measured by femtosecond pump and probe. A fast initial relaxation and the formation of long‐lived species at high excitation intensities have been observed. A high third‐order nonlinear optical susceptibility of 2×10−7 esu has been estimated at 627 nm. The effects of sample orientation on the relaxation dynamics have also been investigated.

Conjugated polymers are promising photonic materials due to the high values of non-linear optical coefficients when compared to inorganic compounds. A key point in view of applications is the figure of merit defined as the ratio between the non-linear optical and the absorption coefficients. We report on the NIR measurement of the third order optical susceptibility ( χ (3) ) by third harmonic generation in polydiacetylene (poly-[1,6-bis-(3,6-dihexadecyl- N -carbazolyl)-2,4-hexadiyne], polyDCHD-HS). Samples are prepared as thin films by spin-coating technique and the χ (3) is evaluated by Maker fringes method in the spectral range from 1200 to 2000 nm. The absorption coefficient has been derived from measurements in CS 2 solution. Spectra of χ (3) show typical resonant behaviour due to the multi-photon processes and are strictly related to the absorption spectra in the visible range. Values of χ (3) are in the range of 10 −11 esu. The absorption coefficient is as low as 0.25 cm −1 at 1.5 μm showing the good figure of merit of polyDCHD-HS.

Highly soluble alkyl-substituted derivatives of the polycarbazolyldiacetylene, with a particularly large value of the off-resonance third-order non-linearity have been obtained in our laboratories. In order to investigate the role played by the electron-donating character of the carbazolyl groups on the optical and electronic properties of the material, we have synthetized diacetylenic monomers carrying electron-withdrawing acyl-substituents on the carbazolyl rings. Acyl-substituents CH 3 (CH 2 ) n CO– with n =10,14,16 were introduced. The polymers derived by thermal polymerization of the microcrystalline monomers are sparingly soluble and only very dilute solutions are stable at room temperature. However, thin films of the polymers of excellent optical quality are obtained by solution casting of a monomer layer on various substrates, followed by thermal polymerization. These films have been characterized by spectroscopic techniques and by preliminary measurements of third-order susceptibility. Particular attention has been dedicated to the study of both their thermal and photochemical behavior.

The (15)N relaxation behavior and heteronuclear Overhauser effect data for the wild type and an H52R/T56W double mutant protein that encompasses the vnd/NK-2 homeodomain from Drosophila melanogaster were used to characterize and describe the protein backbone dynamics. This investigation, which includes a description of a model structure for the H52R/T56W double mutant vnd/NK-2 homeodomain, was carried out for the two proteins in both the free and DNA-bound states. The double residue replacement at positions 52 and 56 within the DNA recognition helix of vnd/NK-2 has been shown to lead to a significant secondary structural modification resulting in an increase in the length of the recognition helix for the unbound protein. These structural changes are accompanied by corresponding changes in the T(1) and T(1)(rho) relaxation times as well as in the heteronuclear Overhauser effect (XNOE) values that show that the structural stability of the protein is enhanced by the two residue replacements. The values of the rotational anisotropy, D(parallel)/D(perpendicular), derived from analysis of the (15)N T(1) and T(1)(rho) relaxation values are small (1.189 for the unbound homeodomain and 1.110 for the bound homeodomain; both analyzed as prolate ellipsoids of revolution). A comparison of the T(2) values of the wild type and double mutant homeodomain reveals the presence of a low-frequency exchange contribution for the wild type analogue. These relaxation studies show that the motional behavior of the protein primarily reflects the tertiary structure and stability of the homeodomain backbone as well as the respective changes induced upon site-directed residue replacement or DNA binding.

Spun films of polycarbazolyldiacetylene polyDCHD-HS were prepared from toluene solutions with a thickness ranging from 9 nm up to 3.6 μm. Thicker films were characterized as waveguides at 849 and 1321 nm; 5 dB/cm propagation losses were measured at 1321 nm. The off-resonance third-order nonlinearity of ultra-thin samples (9-14 nm) was measured at 1064 nm with picosecond pulses and using surface plasmon spectroscopy. The very large value λ (3) = 4.4 x 10 -17 m 2 /V 2 was detected for the real part of the third-order susceptibility.

We have performed theoretical calculations on the singly and doubly charged species of the lowest unsubstituted oligodiacetylenes, with the scope of achieving information on the charged photoexcitations of polydiacetylenes. On the basis of the AM1-optimized geometries of the radical ions and of the dications we have computed their low-energy vertical transitions, using the INDO-SCI method in order to take into account the electron correlation. Extrapolated polymer results are compared with the photoinduced absorption spectra.

We will focus in this paper on the orientation of thin films of conjugated systems induced either by epitaxy or by rubbing on a polymeric thin layer previously oriented by friction transfer onto glass. In friction transfer, oriented poly(tetrafluoroethylene) (PTFE) onto glass substrates are first prepared, and a layer of the conjugated system is then deposited by vacuum evaporation or by spin- coating. The rubbing technique also enables a mechanical orientation of the thin film of the conjugated system, itself deposited onto glass. We applied both techniques for the preparation of oriented thin films of polydiacetylenes and phenyl-ethynylene oligomers. For an asymmetrically substituted PDA (poly(9- (9-carbazolyl)-5,7-nonadiyne-1-ol ethylurethane) (pCNEU), a very high degree of orientation on aligned PTFE was demonstrated using several techniques, resulting in a high degree of orientation than previous films on potassium acid phthalate (KAP) crystals. For the first time a rather good orientation of soluble poly(1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-dexadiyne) (pDCHD-HS) films was obtained using a rubbing technique. Both epitaxy on PTFE and rubbing were also used for the orientation of phenyl-ethynylene derivative samples. For a sequenced rigid poly(p-phenylene ethynylene) ester (sPE5C8) fairly good orientations have been obtained.

The solution properties of a novel soluble polydiacetylene, poly[1,6-bis(3,6-dihexadecyl-9H-carbazol-9-yl)hexa-2,4-diyne] (polyDCHD-HS), have been investigated by using UV–Vis absorption, fluorescence, and FT-Raman spectroscopies. The polymer gives rise to stable, brilliant red solutions in aromatic solvents and in chloroform at room temperature with no evidence of the colour transition to yellow that usually takes place by increasing the temperature with other soluble polydiacetylenes. A particular role appears to be played by benzene–polyDCHD-HS interactions, because in this solvent a very narrow and intense excitonic peak is observed at room temperature in the electronic spectrum. Interestingly, these solutions show also a well-resolved fluorescence spectrum, with a very small Stokes shift and a rather high quantum yield (≅10−2). Furthermore, a very efficient transfer of the excitation energy from the carbazolyl substituents to the conjugated backbone is found to take place. On account of the observation that by increasing the temperature of the benzene solutions up to 75 °C the excitonic feature in both the absorption and the emission spectra undergoes fully reversible broadening and intensity reduction accompanied by the increase of the Stokes shift, without any dramatic colour change, it is likely that the rates of torsional motions in the polymer chains are thermally activated without modifying the average conjugation length of the polymer chains. FT-Raman measurements in benzene solutions in the same temperature range have confirmed this conclusion. The photophysical properties of polyDCHD-HS in benzene around 60 °C are quite similar to those observed in other aromatic solvents at room temperature. By heating up the red solutions in toluene or in chlorobenzene, no spectral shift is observed but only a limited increase of the absorption band broadening. All these findings strongly suggest that by the appropriate choice of the substituents it is possible to obtain stable solutions of the red form of polydiacetylenes.

Soluble polycarbazolyldiacetylene systems (PCDAs) having long alkyl chains on the carbazolyl substituents have been recently prepared. In these systems, PCDAs chains in the solid state are assembled in hexagonal columnar structures. Thin films of these PCDAs show a very high value for the third order susceptibility. In order to study the effect of the substituents in the electronic properties of PCDAs we have inserted -CO(CH 2 ) n CH 3 groups on the carbazolyl rings, thus decreasing the electron-donor effect of carbazole. Non-birefringent thin films of excellent optical quality are obtained whose optical and electronic properties are here reported.

Oriented thin films of good optical quality are necessary for applications of conjugated systems in non linear optical devices. In this paper, we focus on the preparation and spectroscopic characterization of thin films of two different polymers, a polydiacetylene, poly[9-(N-carbazolyl)-2,4-hexadyine-1-ol-1, ethylurethane] (pCNEU) and a polyphenylene–ethynylene, the (11-undecanol) benzoate containing polymer (pPEn). pCNEU gives the best orientation by epitaxial growth on polytetrafluoroethylene (PTFE) layers aligned on glass. On the contrary pPEn is best oriented on glass substrates by rubbing technique.

The solution properties of a novel soluble polydiacetylene, poly[1,6-bis(3,6-dihexadecyl- N -carbazolyl)-2,4-hexadiyne] (polyDCHD-HS), have been investigated by use of spectroscopic (UV–VIS absorption, fluorescence and FT-Raman) and light scattering techniques in benzene and toluene. The unique spectroscopic and molecular properties of these solutions are reported and discussed in relation to the particular interactions of the polymer substituents with aromatic solvents. The introduction of the long alkyl-substituents on the carbazolyl side groups not only improves the processability relative to the parent unsubstituted polymer but also suppresses the chromic effects observed in other soluble polydiacetylenes. The side groups are also responsible for the peculiar supramolecular organization observed in the powder phase of the red form.

We have prepared a novel polycarbazolyldiacetylene (polyDCHD-HS) soluble in several organic solvents. The electronic absorption spectra in different solvents show the presence of the red form of the polymer with the excitonic absorption peak around 540 nm. Thin films with thickness in the range 0.02–2.5 μm were prepared by the spin cast technique to characterize the linear optical properties and test the possibility of obtaining guided propagation of light. Films from chloroform solution, though with considerable surface roughness, allowed the measure of the TE and TM refractive indices at both 849 and 1321 wavelengths. Higher quality films, obtained from toluene, allowed to observe a substantial improvement in the waveguiding properties. The results here reported seem quite promising in view of future photonics applications.

We report results of steady-state photoinduced absorption experiments on PDA-4BCMU grown and oriented on silica substrate. A high degree of axial order, checked by linear and nonlinear optical dichroism and correlated with X-ray measurements was found. Polycrystalline films were obtained with a preferential orientation of crystallites. Unlike the solution cast films exhibiting the so called `red form' only, the deposited films are blue thus showing a better (pi) -electron conjugation than in the former case due to a better planarity of polymer chains. The films were used to perform steady-state photoinduced absorption experiments. Three photoinduced absorption bands at 0.82, 0.95, and 1.39 eV were observed. The 0.82 and 0.95 eV absorption features are assigned to charged states while the 1.39 eV peak is originated by triplet excitons. The photogeneration in PDA- 4BCMU of both charged and neutral states is discussed and compared with the results obtained in polydiacetylenes having carbazolyl groups as substituents. The relative weight of one excited species over the other one is dictated by the molecular and supramolecular organization of the polymer.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The peculiar electronic properties of polydiacetylenes are largely determined by the nature of their electronic excited states. This paper reports the results of a detailed quantum chemical study of the excited states of their shortest oligomers.

We report results of steady-state photoinduced absorption experiments on PDA-4BCMU grown on silica substrate. We observe three photoinduced absorption bands at 0.82, 0.95 and 1.39 eV whose relaxation dynamics indicate that the first two are due to charged states while the third is originated by triplet excitons. The photogeneration of both charged and neutral states in PDA-4BCMU previously observed in polycarbazolyldiacetylenes, indicates that this is a general feature of polydiacetylenes. The relative weight of one excited species over the other one is influenced by the molecular and supramolecular organization of the polymer

Results from femtosecond/picosecond transient absorption spectra measurements in the near-infrared/visible spectral region of the red form of a soluble polycarbazolyldiacetylene in a polyethylene matrix are reported. Intrachain singlet and triplet excitons are identified by the different dynamics of the photoinduced bands. The results are consistent with the ultrafast generation (