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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.

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.

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.

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.

We are studying how the electronic properties of an aggregate, built with conjugated oligomers carrying bulk substituents, are affected by intermolecular interactions. In this paper we apply the CEO (Collective Electronic Oscillator) method, on the basis of the semiempirical INDO/S Hamiltonian, to compute the electronic density matrix modifications following the photon absorption in a doubly charged cluster of two units of a fully carbazolyl-substituted oligodiacetylene tetramer, taken as a model system. The picture that had emerged from our previous calculations based on the less sophisticated CIS (Configuration Interaction including Singles) approach is seen to be confirmed. Despite the large separation between the backbones, a through-space charge transfer occurs between the two oligomers due to the fact that the excess charge, contrary to what is generally believed, is not localized on the conjugated backbone, but is spread out over the carbazolyl moieties of the charged molecule. Consideration of this kind of interaction improves the theoretical results obtained for the isolated charged oligomer chain, and aids in better explaining some features of the experimental photoinduced spectra of the corresponding polymer. (c) 2005 Elsevier B.V. All rights reserved.

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.

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.