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Thin films of a series of symmetrical 2,5-bis(dodecanoxy)phenyleneethynylenes, bearing a butadiyne central group and 4, 6 and 8 phenyleneethynylene moieties, were prepared by spin coating. In general, narrower and red shifted peaks are observed in both absorption and emission spectra with respect to the solutions previously reported, however, the fluorescence quantum yield was quenched. All of these features are explained with the planarization of the conjugated chain, and intra/intermolecular interactions, as supported by spectroscopic aggregation studies and by atomic STM and microscopic AFM characterization. By cathodoluminescence spectroscopy, hot charged states are found that may also affect the fluorescence and electroluminescence properties. From the series, the latter were studied for the hexamer 6DAc for which an oLED with configuration ITO/PEDOT:PSS/6DAc/Al was constructed in ambient conditions, giving a threshold voltage of 11 V and quantum yield of 0.031 ph/e%, of the same order of other phenyleneethynylenes or phenylenebutadyines devices.

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.

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.

The collective electronic oscillator (CEO) method allows to analyze the electronic excitations in molecular systems. Using this technique the excitations are directly connected to the corresponding one-electron transition density matrices, obtained as eigenmodes of the time dependent Hartree–Fock (TDHF) Liouville operator, which represent motions of electron–hole (e–h) pairs. Two-dimensional plots of the density matrices establish the connection between the electronic spectra and the electronic rearrangement due to the photon absorption. In this paper, we use the CEO procedure to study the nature of the electronic excitations on three series of one-dimensional porphyrin systems, showing through the analysis of the CEO eigenmodes how they can be described in terms of Frenkel or Wannier–Mott excitons.

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.

A simple method is reported allowing the fast evaluation of the athermal limit that is implicitly present within the set of equations recently proposed by Jonah, Brostow and Hess, dealing with the anisotropic-isotropic equilibria of single monodisperse or nearly monodisperse semirigid liquid polymers, including polymer liquid crystals. We have found an athermal limit dependent on the degree of rigidity 0 of the given semirigid liquid polymer (θ being the fraction of its monomeric units belonging to rigid rodlike sequences within each semiflexible polymeric chain) and marked off by critical lengths η al of the rigid sequences, giving rise to non-finite asymptotic values of the anisotropic-isotropic temperatures.

The real spherical tensor theory of long-range intermolecular coefficients developed in previous papers is applied to derive explicit formulae for the first three dispersion coefficients for like centrosymmetric linear molecules. The expansion of angledependent coefficients in associated Legendre polynomials allows one to identify the isotropic and anisotropic components of the dispersion interaction in terms of London dispersion constants, the treatment of higher coefficients being simplified by the coupling of the elementary (1, 1′)-polarizations to resultant angular momenta LA and LB onto each molecule. The contributions from all coupling schemes are given explicitly for C6, C8, c10, and numerical results are presented for H2H2 using two-term reduced spectra values from the Kaiserlautern group.

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 determined the photophysical properties of [Eu(C12H8N2)2](NO3)3, (EuPhen), a complex which is very promising for photonic and optoelectronic applications, because of its easy synthetic procedure and high thermal stability (up to 300 °C) combined with large sensitization efficiency and good emission quantum yield. Available experimental absorption and emission data have been analyzed by using Judd-Ofelt analysis. Moreover, semi-empirical calculations have been used to determine the structure of the complex and to interpret the convoluted shape of the absorption spectrum. © 2009 Elsevier B.V. All rights reserved.

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.

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.

In this paper the quantum chemical semiempirical procedure recently proposed by us to predict ground- and excited-state geometries of lanthanide complexes, the pseudo coordination centre method (PCC), is preliminarily compared with the semiempirical sparkle model for the calculation of lanthanide complexes (SMLC). Contrary to the SMLC method, where the rare-earth ion is replaced by a reparameterized sparkle atom, in our approach we replace it with a metal ion which is already present in the chosen semiempirical parameterization. This implies that in the optimization of the geometry of the complexes a different weight is implicitly given to the complex region including the rare-earth ion and its neighbour atoms with respect to the region of the ligands aggregate. As a consequence our approach is expected to reproduce better than the SMLC one the geometry of the ligands aggregate embedded in the complex, while the contrary happens for the coordination distances.

Lanthanide ions emitting in the near-infrared (NIR) region possess an intrinsically small molar absorption coefficient in the ultraviolet (UV)–vis–NIR spectrum, which is unfavourable for pumping efficiency. On the contrary, using organic lanthanide complexes it is possible to populate the excited state levels of the emitting ion through an efficient intramolecular energy transfer from the optically excited ligands, which act as light-harvesting antennae. With the aim of studying and maximizing the transfer to lanthanide metals, we have synthesized oligothiophene and thiophenefluorene ligands bearing carboxylate clamps able to complex erbium and other lanthanide 3 + ions. The complexes of {4′-(hydroxycarbonyl)methyl-[2,2′;5′,2″]terthiophen-3′-yl}acetic acid and 9-(hydroxycarbonyl)-methyl-2,7-dithien-2-yl-[fluoren-9-yl-]acetic acid with Er 3+ and different ancillary ligands have been prepared and their optical properties were carefully studied. Moreover, relaxation dynamics measurements have been carried out on all complexes in order to determine emission lifetimes, which result to be of the order of magnitude 2 μs. Quantum chemical calculations have been performed to explain optical absorption data in terms of different coordination types. The complexes containing phenanthroline/pyridine are modelled by adding to the dianion of the ligand one univalent/divalent counterion. The absorption spectra computed in this way are in close agreement with experiment, and the univalent→divalent theoretical wavelength shift goes in the right direction. The addition of a counterion has an even bigger effect on the triplet states, and hence on their matching with the emitting states of the ion.

Absorption, photoluminescence, and photoinduced absorption (PIA) spectra of films of red phase polycarbazolyldiacetylenes (polyCzDAs) carrying selected acyl (polyDPCHD) or alkyl (polyDCHD-HS) groups are reported. The absorption spectrum of polyDCHD-HS, which is almost independent of the temperature down to 20 K, shows an excitonic absorption followed by an inhomogeneously broadened vibronic progression. Very different is instead the case of polyDPCHD whose thin films show a very sharp excitonic transition and a vibronic progression with a lower electron-phonon (el-ph) coupling with respect to that of polyDCHD-HS. These peculiar characteristics allow the detection of additional features in the spectra, which are assigned on the basis of quantum chemical calculations to string modes of the backbone. As far as thick films of polyDPCHD are concerned, broad electronic spectra are observed. Raman spectroscopy studies suggest that this broadening is due to the presence of two forms of the polymer. Unlike other polydiacetylenes (PDA's) including polyDCHD-HS films, polyDPCHD films are also strongly luminescent, thus suggesting a different ordering of the dipole forbidden and allowed states. For these materials, the photoinduced absorption spectra are dominated by triplet excitons. Effects of different forms in acyl substituted polymers are observed also in the PIA spectra. The rise and decay of the triplet signal for polyDCHD-HS are accounted for through a dynamical model, which includes saturation effects in the monomolecular decay regime. A more complex kinetics is instead observed for polyDPCHD. From the study of the kinetics of the PIA spectra both the triplet generation efficiency and the density of traps are evaluated.

In this paper, we present the results of a theoretical study of the electronic and optical excitations of isolated carbazolyl-substituted oligodiacetylenes using the collective electronic oscillator (CEO) method. Within this technique the excitations are directly connected to the corresponding one-electron transition density matrices, obtained as eigenmodes of the time dependent Hartree–Fock (TDHF) Liouville operator, which represent motions of electron/hole pairs. The two-dimensional plot of the transition density matrix (CEO mode) establishes the physical connection between the electronic spectra and the electronic rearrangement due to the photon absorption. Consequently this representation allows for an intuitive interpretation of the optical spectra in terms of the chemical structure, and gives a useful tool for the design of molecules showing the required physical properties.

In this work we report the synthesis and photophysical properties of a novel ligand and its lanthanide complexes based on macrocycle 1,4.7,10-tetraazacyclododecane-1,4,7-triacetic acid bearing 8-hydroxyquinoline as antenna. Visible and IR sensitized emission is obtained because of the efficient energy transfer from the antenna to the emitting ion. The interaction between ions and antenna is accounted for by suitable quantum chemical calculations. The good stability of the complexes and their solubility in organic solvents make them good candidates for the fabrication of plastic waveguides and optical amplifiers. (C) 2004 Elsevier B.V All rights reserved.

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.

Absorption and photoinduced absorption (PIA) spectra of thin films of polycarbazolyldiacetylenes carrying alkyl (polyDCHD-HS) or acyl (polyDPCHD) substitutions are reported. The absorption spectra are dominated by an excitonic absorption followed by a vibronic progression, and are quite insensitive to the temperature. The PIA spectra show the typical spectral feature of a triplet excitation whose rise and decay times are different. The PIA signal shows a strong sublinear pumping intensity dependence, which also affects the rise time.

We have performed a quantum chemical study on neutral and doubly charged oligodiacetylene clusters, using a recent time-dependent Hartree-Fock (TDHF) approach based on an INDO/S Hamiltonian. Our goal is to achieve information on the effect of the supramolecular architecture on the nature of the photoexcitations and on the non-linear optical properties of these systems, which are of relevant interest for their potential applications in photonics. Considering aggregates of three oligodiacetylene molecules with 15 repeat units, results for two geometrical configurations as models for maximal and minimal interchain interactions are reported.

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.

Pseudostate decomposition of static dipole polarizabilities for ground state H 2 + from a Givens-Householder diagonalization of the excitation operator ( H 0 − E 0 ) over an N -term basis of appropriate symmetry allows for a rapidly convergent evaluation of C 6 dispersion coefficients for H 2 + –H 2 + . 27-term pseudospectra of hypergeneralized James functions with a 30-term GGJ + unperturbed wavefunction with an optimized scale factor δ=0.918 at R =2α 0 give C 6 and γ 6 values that are accurate to no less than nine significant figures.

We perform quantum chemical calculations on the singly and doubly charged species of the lowest unsubstituted oligodiacetylenes, in order to achieve information on the charged states originated in the photoexcitation of polydiacetylenes. On the basis of the optimized AM1 geometries of the radical ions and dications we obtain their low-energy vertical transitions in an INDO-SCI framework to ensure a proper treatment of electron correlation effects. We get the simulated absorption spectra of the charged oligomers by a convolution of the transition energies, and compare the linearly extrapolated polymer values with the photoinduced absorption results.