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In this work triangular gold nanoplates (AuNTPs) are prepared by spontaneous conversion of spherical-like gold precursors induced by the shape-directing properties of the diacetylene N,N,N-trimethylpentacosa-10,12-diyn-1-ammonium bromide (PCD_ABr), employed as capping agent. In detail, thin AuNTPs with edge length below 200 nm are obtained by incubating premade isotropic gold nanoparticles protected with chitosan (Chit@AuNPs) in PCD_ABr solutions through a standard ligand-exchange reaction (LER) carried out in water at room temperature. Control of the AuNTPs size as well as the reaction shape-yield up to 65% is achieved by simply varying the reagents ratio in the incubation mixture. Because of the high anisotropy of the flat nanoparticles, the AuNTPs-containing hydrosols show intense, well-defined absorptions in the NIR spectral region, which make them excellent candidates as biosensors also for in vivo assays with biological tissues and fluids. When subjected to UV light, both triangular and nearly spherical PCD_ABr-coated gold nanoparticles exhibit fluorescent properties and Raman features typical of disordered, sp2-based carbon nanostructures. The photogeneration of graphite-like moieties within the diacetylene shell instead of expected polydiacetylene skeleton is most likely due to poor alignment of the monomer chains on the gold surfaces and seems to be favored on isotropic nanoparticles.

Spectroscopic and microscopic measurements show that 10,12-pentacosadiynoic acid is able to densely adsorb on the surface of silver nanoparticles by properly selecting the synthesis procedure. Its subsequent polymerization by UV irradiation under controlled photochemical conditions produces the blue form of poly(pentacosa-10,12-diynoic acid). The resulting nanohybrids are very stable in aqueous suspension and exhibit a bilayered, core–shell architecture. We propose a model of the polyPCDA self-assembled on silver nanoparticles and we evaluate the surface coverage density.

A perylene cholesteryl-benzoateethynylene co-polymer was synthesized by Sonogashira reaction and characterized by NMR, UV–Vis, static and dynamic fluorescence spectroscopy and cyclic voltammetry. The optical and electrochemical properties in solution are consistent with photoinduced energy transfer from the electron donor conjugated backbone to the electron acceptor perylene substituent. Photovoltaic properties are indeed found, even if the performance of the solar cells is quite low due to the formation of aggregates. The incorporation of (6,6)-phenyl C61–butyric acid methyl ester (PCBM), however, increases by an order of magnitude the efficiency of the prototype (from 10−4 to 10−3%) due to both better phase mixing and improved electrical continuity as supported by Atomic Force Microscopy (AFM) and Electrical Force Microscopy (EFM) studies.

The synthesis of a 2,5-bis(dodecanoxy)phenyleneethynylene-butadiyne series with 2, 4, 6 and 8 phenyl rings is reported. Sonogashira coupling reaction, rather than the Glaser/Eglinton/Hay reactions classically used for butadiyne formation was applied. The molecular structures of all compounds were confirmed by 1H, DEPT-135, APT 13C, MALDI-TOF, FTIR and FT-Raman analyses. The linear and nonlinear optical properties were studied in solution by UV/Vis, static and time-resolved fluorescence, and by two-photon absorption (2PA) spectroscopy. With the exception of the dimer, for which intersystem crossing is very favoured due to the low energy gap between the singlet and triplet states as theoretically predicted, the other oligomers present high fluorescence quantum yields (0.77–0.82) and large cross-sections (up to 5000 GM for the octamer) that could be applied in multiphoton microscopy or nonlinear optics.

The charge transport properties of organic semiconductors are one of the foremost limiting factors in technological applications of these materials, which are becoming important competitors with respect to the inorganic semiconductors. In fact, conjugated organic molecules are used at present as active materials in different types of devices. For this reason, the theoretical study of the electron and hole mobility, carried out in order to give hints for the design of new molecules or for the optimization of their supramolecular organization, is a task of great interest. Here, we present the results of a quantum chemical study, in the framework of the Marcus and density functional theories, on the effects of terminal groups (when they directly interact with the pi-conjugated system of the organic semiconductors) on the charge carriers mobility of organic semiconductors. In particular, using a representative oligomer of poly(para-phenylenevinylene) as a model system, we have found that strong effects on the predicted values of the intramolecular transfer integrals as well as on their dependence on the supramolecular organizations occur, when the vinyl moiety (as ending group) is taken into account.

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.

Surface Enhanced Raman Scattering (SERS) was employed for studying the polymerization of self-assembled carbazolyl-diacetylene monolayers chemisorbed on smooth gold substrates by depositing silver colloidal nanoparticles. After UV irradiation two polymer phases were observed by SERS measurements, with different structural order in the polymer chain.

The synthesis of a new DO3A -based macrocyclic ligand bearing a 8-hydroxyquinoline residue together with the preparation of its Eu 3+ and Er 3+ neutral complexes are described. In a previous report [F. Rizzo, A. Papagni, F. Meinardi, R. Tubino, M. Ottonelli, G.F. Musso, G. Dellepiane, Synth. Met. 147 (2004) 143], we have shown that lanthanide complexes display very high stability combined with a good luminescence in aqueous solution under UV radiation, which indicate an energy transfer process from the excited 8-hydroxyquinoline moiety to the metal. In this work, we correlate the ability to transfer the energy from the sensitizer to lanthanide ion with pH behaviour of the antenna. Furthermore, the variation of pH in Eu 3+ complex supports the hypothesis of presence of charge-transfer transitions. The good solubility and sensitized emission in different solvents (organic and water) are very important aspects for their technologic applications as luminescent probes or NIR-emitting devices.

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.

In this paper, we report on the optical properties of recently prepared symmetrical and asymmetrical polycarbazolyldiacetylenes (PCDA) carrying long alkyl or acyl substituents at the 3,6 positions of the carbazolyl groups. Ultra-thin polymeric films have been prepared on different substrates by spin coating of polymers or monomers solutions. Only the relevant results on the electronic absorption and fluorescence studies in solutions or as films are here reported. Evidence is given of the role played by the molecular and supramolecular ordered structures in the emission properties. The films organizations studied by Atomic Force Microscopy (AFM) technique reveal different surface morphologies for the different polymers.

The nonlinear optical properties of quasi-monomolecular layers of polyDCHD-HS spun on silver-coated plates were measured using surface plasmon spectroscopy at 1064 nm and with ps pulses. A surprisingly large value of χ(3) was obtained (|χ(3)| > 10−17 m2 V−2). This value was related to the presence of the silver film, whose nanostructured surface provides an electromagnetic mechanism for the enhancement of the nonlinearity through local field effects. This point was confirmed by SERS experiments performed on-resonance (515 nm) and off-resonance (647 nm) on the same samples. It is suggested that the experimental data can be accounted for by the existence of an interaction between the π-conjugated system of the polymer chain and the silver surface.

The collective electronic oscillator (CEO) approach recently proposed by Mukamel, which is based on an INDO/S Hamiltonian in the framework of the time-dependent Hartree–Fock approximation, is used to investigate the effect of the supramolecular architecture on the photogenerated excitations in different aggregates of a large-sized oligodiacetylene. The method gives the transition energies and the corresponding one-electron transition density matrices directly, which allows one to analyze, in terms of electron–hole motions in real space, the electronic redistribution upon photon absorption. Electronic excitations depend strongly on the arrangement of the oligomer molecules in the cluster, appreciable interchain effects being obtained even when the arrangement of the oligomer molecules corresponds to a minimum interchain interaction. Interchain interactions give rise to new transitions whose oscillator strengths depend on the nature of the aggregate (neutral or charged), and which can significantly modify the optical properties of the isolated molecular system.

The complex χ (3) of toluene solutions of polydiacetylene, polyDCHD-HS, was measured by using Z -scan at λ =1064 and 1500 nm and with picosecond pulses in order to estimate the potentials of this polymer for application to all-optical switching devices. The values of the real part of molecular hyperpolarizability γ were −2.3×10 −47 and −3×10 −47 m 5 /V 2 at 1064 and 1500 nm, respectively. The nonlinear absorption could be better modeled with a three-photon process at both the wavelengths instead of the expected two-photon mechanism.

Polydiacetylenes (PDAs) self-assembled onto silver nanoparticles (AgNPs) show superior performance relative to conventionally-structured PDAs because their unique optical properties are combined with the peculiar features of the nanosized noble metal cores. The present paper presents a study of the experimental factors influencing the photopolymerization of the carboxy-terminated 10,12-pentacosadiynoic acid (PCDA) monomer anchored to silver nanoparticles in an aqueous solution. Specific spectroscopic parameters have been identified that characterize the process both qualitatively and quantitatively, thus allowing the comparison of the polymerization yield carried out under different experimental conditions. On this basis, a well-defined synthetic protocol able to maximize the chromophoric potential of these novel optical transducers, as well as to give reproducible results, is proposed and tested on differently-stabilized and/or aged silver nanoparticles used as substrates for the PCDA chemisorption. The highly-conjugated blue polyPCDA has considerable potential in the optoelectronic, photovoltaic and sensing fields.

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...

We report the temperature dependence of the dielectric properties of poly[1,6-bis(3,6-didodecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-S) from 30 to 400 K. The data obtained from these measurements are confirmed, in selected temperature ranges, by FT-Raman spectroscopy, differential scanning calorimetry and X-ray diffraction. The transition from the blue to the red form in polyDCHD-S is detected in correspondence to the monomer melting point (about 340 K). Other transitions, above and below this feature, are reported and discussed.

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.

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 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 polarized, near-normal incidence, absolute reflectivity spectra of highly stretch-oriented unsubstituted poly(p-phenylene-vinylene). The data show a well-resolved vibronic progression in the lowest optical transition, a high dichroic ratio and weak signals due to conjugated segments with reduced effective conjugation length. On the high-energy side of the spectra, other transitions mainly related to excited states involving localized levels are detected. The low-temperature spectra confirm these assignments. The polarization properties of the reflectivity spectra are discussed in relation to correlated quantum–chemical calculations.

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 obtained chitosan-protected Au/Ag nanocages (NCs), i.e., hollow and porous metallic nanoparticles, by galvanic replacement reaction. Subsequently, we functionalized the NCs with a fluorescent derivative of 4-methoxy-1,8-naphtalimide (NAFTA6). The plasmonic properties of these structures, which exhibit an extinction maximum in the 700-800 nm range, allowed their use as SERS active substrates for excitation at 785 nm and an efficient identification of the vibrational bands of NAFTA6, in spite of the low ligand concentration (10(-5) M). Furthermore, NAFTA6 could also be identified from its fluorescence emission. The proposed functionalization with fluorescent compounds opens the way to the application of metal NCs using double-wavelength detection. Namely, Raman spectroscopy in the near infrared and fluorescence emission in the visible region, with considerable potential especially for in vivo medical applications, as the plasmonic band is centered in the visible light region where biological fluids and tissues are transparent.

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 fabricated stable gold nanostars (AuNSs) with tunable extinction properties from the visible spectral region up to 1800 nm, depending on the average values of core size and branch length. The results of their UV–Vis and transmission electron microscopy characterization are compared with computational data from finite elements method, which makes use of an approximated model of the branched structures. The theoretical computations put in evidence the existence of hot spots located on the tips of the nanostars even up to 1800 nm wavelength, which opens the way to the improvement of diagnostics in the IR region. Preliminary Fourier transform Raman experiments performed after functionalization with a fluorescent dye bearing end thiol groups seem to confirm the field enhancing capability of the nanostructures at 1064 nm.

Recently new molecular systems based on the pyrene moiety were developed for photovoltaic applications. Here we present the results of a quantum chemical study focused on the effects induced by some different substituents on the electronic properties of pyrene, to obtain general hints for the molecular design of new pyrene-based systems. In particular, a series of electron-donating (hydroxy, amino, acetylamino) and electron-withdrawing (cyano, carbamoyl, formyl, ethynyl, ethenyl) groups were considered. Furthermore, in addition to the single pyrene molecule, two pyrene units linked by ethenylene, ethynylene, 2,5-thienylene, and ethynylene-p-phenylene containing chains of different lengths were taken into account. For all of the model structures presented, the ground state geometries have been optimized using the density functional approach, while the vertical transition energies were calculated using the time-dependent density functional theory. We will show that the tuning of the lowest electronic excitation energy (i.e., the HOMO-LUMO energy gap) as well as the localization of the spatial distributions of the frontier molecular orbitals (i.e., the nature of the electron-hole pair, generated by photon absorption) can be obtained through the analysis of the pyrene frontier molecular orbitals. This approach allows to evaluate the most suitable position of the substituents on the pyrene moiety giving rise to enhanced electronic effects also in function of their electronic nature. In this way, pyrene-structures with tailored electronic properties could be modeled. Our screening shows that promising candidates for photovoltaic applications could be molecular structures formed by two pyrene units joined/linked by a short conjugated bridge containing double or triple bonds (henceforth pyrene-linked dimers). As far as the single pyrene units are considered, the most significant reduction of the transition energy of the lowest optical electronic excitation is obtained with disubstituted pyrenes with push-pull character.

The photopolymerization study of novel diacetylene-decorated platforms obtained by self-assembling of properlyfunctionalized monomers onto pre-existing silver nanoparticles is reported. For this purpose, differently-terminated diacetylenes of general formula X-(CH 2) m-C?C- C?C-(CH 2) 8-COOH have been synthesized and tested. Qualitative and quantitative evaluation of the blue polymer photogeneration, performed by means of spectroscopic techniques, is reported and discussed in order to select the best performing photoresponsive nanohybrids to be employed in sensoristics as well as in optoelectronic and biomedical applications.

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.

We present a simple seed-less synthesis procedure to fabricate stable gold nanostars (AuNSs) with tunable extinction properties from the visible up to 1800 nm, depending on the average values of core size and branch length. The experimental results are compared with data from Finite Elements Method computations by using an approximated model of the fabricated branched systems. The theoretical computations highlight the existence of hot spots located on the tips of the nanostars even up to 1800 nm wavelength, which opens the way to the improvement of IR diagnostics or chemical sensing.

The electronic and vibrational properties of polyPCDA have been examined by means of ab initio calculations on oligomers performed as a function of the number of monomeric units and of the torsional angle τ between them. The vertical excitation energies S 0 → S 1 and the double and triple CC stretching frequencies of blue, red and bluish-green forms of the polyPCDA have been correlated to conformational structures with different torsional angles.

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.

A simple tight-binding model extended to include the zig-zag structure of the chains and the interchain electronic coupling has been used to account for the dispersion of the real and imaginary part of the dielectric function of polyacetylene as derived from optical measurements. Intrachain and interchain contributions to the perpendicular absorption coefficient have been evaluated. It has been found that while interchain effects have a relatively small impact on the optical properties, they play a major role in determining the photogeneration rate of long-lived carriers in oriented trans-(CH) x .

Electrochemical doping of poly( p -phenylenesulfide) (pPPS) in concentrated sulfuring acid offers a promising way for studying electrical properties of this material because an accurate control of the doping level is possible. We have performed an extensive investigation of the electrochemical behaviour of pPPS in 96% H 2 SO 4 and, hence, measured in situ optical spectra, conductivity and ESR data of samples at different values of the injected charge; in this paper the results are presented and discussed in relation to data of pPPS and oligomers chemically doped.

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.

A cw photomodulation technique has been applied to study the photoexcitation of a form of soluble polyacetylene with controlled conjugation length. We have been able to change the average conjugation length from a few hundred units down to 20 units. A systematic blue-shift of the photoinduced absorption spectra is observed upon decreasing the electronic delocalization. The linear dependence of the observed shift of the charged soliton band on the average conjugation length is discussed in terms of two different limiting models to describe the electronic properties of polyenes, namely the single-particle Su-Schrieffer-Heeger Hamiltonian and the Hubbard Hamiltonian.

This paper deals with the electrochemical doping of poly(p-phenylene sulfide) in concentrated sulfuric acid. Cyclic voltammetry curves, as well as cyclic voltabsorptiometry curves and electronic spectra at different values of injected charge, are reported. The electronic spectra are discussed in relation to those of chemically-doped pPPS.

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.

The formation of polaron and/or bipolaron species upon chemical doping and photo- or electro-chemical generation is a scientific and technological problem which is still object of discussion. Here we use a simple electrostatic model to study the role of the interchain interaction in stabilizing or destabilizing the bipolaronic structure, which is usually neglected in theoretical studies. The results show that, as a consequence of the interchain interactions in the bulk system, a bipolaron generated on a single oligomer chain more than 12 units long will soon split into two polarons on adjacent chains, this process being maximized for specific interchain distances.

Novel data on the pump polarization anisotropy of the photoconductive response in oriented fibrous (CH)x have been obtained using both above gap (530 nm) and below gap (1060 nm) excitation. The measured anisotropy for below gap excitation is smaller and independent of the intensity. The implications of these data are discussed in the context of both the bimolecular recombination (BR) model and the direct interchain carrier generation.

Ab initio restricted Hartree-Fock STO-3G ∗ geometry optimizations have been carried out on diphenyl sulfide, its radical cation and its dication with the purpose of obtaining a first theoretical insight into the geometry changes occurring on doping poly( p -phenylene sulfide). The results indicate that, although modifications in geometry of diphenyl sulfide are somewhat difficult upon ionization, a clear tendency exists for a quinoid-type structure.

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.

The stability of lanthanide complexes and the efficiency of the energy transfer process, which makes these molecules interesting materials for technological applications, are correlated to the chemical environment surrounding the metal ion. In particular the efficiency depends on the relative position of the antenna (the ligand moiety that acts as photon absorption center) and the lanthanide ion (the emitting center), while the stability of the complex is correlated to the strength of the coordination between the rare earth and the ligands. For these reasons, knowledge of the structural properties of the complex is an interesting task to achieve. Since a large number of ligand structures hold the carboxylate group (COO - ), which is used as an anchor for binding the antennae to the lanthanide ion, in this work we will show how the vibrational shifts of this group, induced by the interactions between the carboxylate moiety and the metal center of the lanthanide complex, can be used for obtaining in a simple way information on the structure of the chemical environment surrounding the lanthanide ion. Lanthanide complexes have raised increasing interest for their potential applications in several research areas such as in the biomedical field, where use of these complexes as chemosensors for in vivo applications has been recently described, 1 and in the technological field, where the design of efficient lightemitting devices and their use in optical technology has been reported in several papers. 2,3 The physicochemical property of lanthanide complexes that is the basis for developing efficient light-conversion molecular devices is the luminescence intensity. This effect originates from the intramolecular energy transfer from one excited ligand to the f-electronic structure of the metal ion, and is critically dependent on the molecular geometry of the ligands aggregate as well as on the chemical nature of the single aggregate unit. In particular, the ligand should be able to promote the energy transfer of the optical excitation and, through suitable functional groups, to efficiently saturate the lanthanide coordination sphere and make a strong binding interaction with the rare earth ion. The saturation of the sphere should minimize the quenching of the complex luminescence that may occur due to the interactions with the solvent, while a strong binding should increase the complex stability. In turn, an increased complex stability implies an increased processability of the material, an important factor for its technological applications. One suitable functional group to this end is the carboxylate moiety that is present in several ligand structures. Moreover, due to the increasing interest in the molecular design of hetero- or homometallic multinuclear complexes (which are promising materials for practical applications due to their photophysical and magnetic properties 4 ) the control of the metal-ligand coordination type represents an important task to achieve. Ligands designed with different carboxylate clamps can be fully coordinated to the same metal ion or, due to the presence of competitive ligands and of steric hindrance, only one COO - group of the clamp at a time may be bonded to the metal center. In the latter case the rest of the carboxylate moieties remain free to coordinate to other metal ions of the same or of a different chemical nature.

Long neutral and doubly charged oligodiacetylenes (with a maximum of 30 repeat units) as well as some of their aggregates have been studied in a semiempirical framework. By analyzing the plots of the one-electron ground-state density matrices, we have shown that the 12-units long oligomer is the borderline between two different behaviors of the electronic structure of the isolated charged systems. For oligomers shorter than this limit the bipolaronic structure is the dominant one, while for larger oligomers the polaron-pair structure is preferred. The major conclusion of this work concerns the effects of the interchain interactions in bipolaron systems, which are usually neglected in theoretical works. It is predicted that as a consequence of the latter in the bulk system a bipolaron generated on a single polymer chain will soon split into two polarons on adjacent chains.

A series of neodymium complexes based on (alpha-oligothiophen-2-yl)(2-hydroxy-3-methoxyphenyl)methanone moiety was prepared and studied by FTIR, NMR, optical spectroscopies. As a function of the thiophene ring number in the ligand, a variation of both stoichiometry and optical properties of the complex are observed. The solid-state ligand structure indicates a close packing and a stressed situation in enolate residues, i.e. non-coplanarity between thiophene and phenyl moieties. An un-precedent stoichiometry of complexes was observed, namely two metal and five ligands, according to both the synthesis conditions and the encumbrance of ligand with respect to ionic radius of Nd3+. This fact is attributed to the contribution to the coordination of the methoxy group. Luminescence and lifetime determination are discussed in the light of the above factors. (C) 2007 Elsevier B.V. All rights reserved.

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.

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.