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Different nanocomposite materials consisting of semiconducting CdSe nanocrystals (NCs) and a low band gap copolymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b:3.4-b’]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) were prepared, morphologically characterized, and tested in hybrid solar cells. In addition, a PCPDTBT-based rod-coil diblock copolymer was synthesized through a grafting-onto approach and a preliminary evaluation of the morphology of the hybrid nanocomposites with CdSe NCs was performed.

Structural colors are the object of a wide scientific interest, not only for the potential technical applications of their intriguing optical properties but also for the need of coloring agents to replace toxic and carcinogenic dyes. We present a simple methodology to obtain polymer opal surfaces of self-assembled core–shell nanoparticles with different degree of order for structural color applications. Polymer nanospheres prepared by surfactant-free emulsion radical copolymerization of an hydrophobic and an hydrophilic comonomer (styrene and methacrylic acid) spontaneously assemble into core–shell particles. Nanoparticles with identical composition and different diameters were prepared by modulating the degree of ionization of the weakly acidic comonomer. We report experimental results revealing how the synthesis parameters affect the properties of the core–shell particles and their influence on the optical properties of the final polymer opal surfaces, which depend on size, charge, and packing arrangement of the constituent nanoparticles.

A low band-gap copolymer PDTBTFValternating bis-thienyl-(bis-alkoxy)-benzothiadiazole blocks with difluorovinylene units and its non-fluorinated counterpart PDTBTVhave been synthesized and characterized as donor materials in bulk heterojunction (BHJ) solar cells with PCBM as the acceptor. The solar cells with the fluorinated polymer show better photovoltaic performances than those recorded with the non-fluorinated material. Comparative spectroscopic and computational studies, together with morphological, electrical and optical characterization of thin films, have been carried out to shed light on the reasons for the improvement of performances as induced by the double bond fluorination. Our study introduces the fluorinated double bond as a new conjugated unit in donor polymers for BHJ solar cells.

Nanosized zeolite L crystals containing about 550 strongly luminescent acceptor molecules have been modified by grafting a conjugated oligomer on their external surface. The 25 nm sized crystals have consequently been embedded in polymeric nanofibers obtained by electrospinning. The fluorescent molecule grafted on the external surface allows addressing the guests in the zeolite nanochannels through an efficient two-step energy transfer from the polymer nanofiber. The so obtained hybrid nanofibers exhibit intense emissions from the three fundamental colors using a single excitation wavelength. The molecule grafted on the external surface of the nanocrystal also induces a higher compatibility of the hybrid organic/inorganic nanomaterials in the conjugated polymer and therefore high concentrations of zeolites embedded in the nanofibers are obtained. Playing on this concentration, the emission of the nanofiber can be tuned and eventually be used for fabricating white-light emitting nanofibers. This hybrid nanomaterial opens new perspectives for low-cost nano organic light emitting diodes fabrication with considerable impact on the lighting and display technologies.

Tunable dichromic electroluminescence is obtained from a blend of Eu3+complex in polyfluorene by a single spin-coatable emitting layer device with external quantum efficiency as high as 1%, the highest reported in literature to our knowledge. The design of a complex whose ligand increases the site isolation of Eu3+ion allows reduction of the back-transfer quenching effects that prevented up to now the multicolor electroluminescence of Eu3+complex/polyfluorene blends. Energy transfer mechanisms involving singlet and triplet excitons are analyzed by focusing on the effects of site isolation and polarity of the new ligand that provide homogeneous dispersion of the complex in the conjugated polymer.

The crystallization of an organic semiconductor, viz., tetrahexil-sexithiophene (H4T6) molecules, confined into nanosized cavities of a self-organized polystyrene beads template, has been investigated by means of in situgrazing incidence X-ray diffraction measurements, during the solvent evaporation. Thanks to these real time experiments, the phase content and the crystalline domain orientation of H4T6 have been determined, from the onset of the first crystalline molecular assembly to the stable system. The correlation between the bead size dependent crystallization mechanism in this complex system and the enhanced transistor performance has been established. These results, which can be extended to a wide range of organic materials, are useful for developing an attractive sustainable process for fabrication of organic devices with enhanced performance.

Linear and third-order nonlinear optical (NLO) phenomena have been studied in three thiophene-containing polyimine classes. A complete characterization has been performed determining the real part of the refractive index n, its imaginary part k, and the third-order NLO value χ^(3). The NLO values derived for the polymers are related to both the electronic property and backbone conformational arrangement, affecting the overall conjugation. The highest third-order NLO coefficient has been measured on a very homogeneous spin-coated film of dialkyl substituted polyazine, showing a value of 5.2×10^−11esu at 1710nm, where the material is essentially transparent.

Different nanocomposite materials consisting of semiconducting CdSe nanocrystals (NCs) and a low band gap copolymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b:3.4-b’]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) were prepared, morphologically characterized, and tested in hybrid solar cells. In addition, a PCPDTBT-based rod-coil diblock copolymer was synthesized through a grafting-onto approach and a preliminary evaluation of the morphology of the hybrid nanocomposites with CdSe NCs was performed.

A new copolymer, constituted by the regular alternation of a fluorene derivative with a 1,1-dioxothiophene moiety, has been synthesised via Suzuki coupling. The molecular, thermal, structural, and photophysical characterisations have been performed. The material showed two dimensional order, enhanced by annealing; molecular modelling calculations afforded a consistent structural model accounting for the optical data. In comparison with both polyfluorenes and 1,1-dioxothiophene oligomers the unusual photoluminescence quantum yields observed in solution and in the solid state can be related to a significant contribution of internal conversion to the deactivation process in solution, and the formation of intra-chain hydrogen-bonds, due to a peculiar chain conformation, in the solid state. LED devices based on this new copolymer showed the highest efficiency compared with similar copolymers containing both fluorene and 1,1-dioxothiophene functionalities.

Fluorenic core oligomers, displaying interesting photoluminescence properties, have been synthesized by an organometallic route. The crystal and molecular structure of a fluorene derivative and three homologous oligomers have been studied. The spiro-derivative of dibromofluorene shows a very strong interaction between the H and Br atoms. The thienyl-terminated oligomer with a spiro-substituent adopts a particular herringbone arrangement with overlap of only the end-thienyl residues, conformationally disordered. The crystal of the all-phenyl derivative consists of the packing of discrete molecules cofacially arranged. The molecule with linear alkyl chains on the 9-position of the fluorene core and thienyl rings as end-groups exhibits polymorphism and its crystal structure, tetragonal, is very peculiar because of the loose packing allowing a good separation among adjacent thienyl rings.The absorption and emission properties of this series were investigated and the electroluminescence of single-layer devices was characterized. The photoluminescence properties of the molecules are strongly dependent on their structural organization, displaying a red-shift of the emission from the amorphous phase, to the crystalline structure, to the aggregated form.A comparison of the packing of these oligomers and oligothienylenes fully accounts for the optical properties of the reported molecules.

The electrochemical oxidation of 2,5-thienylene- (T) and 1,4-phenylene- (P) based arylene tetramers T4, TP2T and PT2P, in which the torsion angles between couples of adjacent rings are blocked by a chemical bridge, has been performed in acetonitrile. The products have been characterised by cyclic voltammetry, MALDI mass spectrometry, FT-IR, UV-vis and ESR spectroscopies, and in-situ conductivity and identified as radical cations, dimers or polymers depending on the T–P sequence in the monomer.

A series of new regioregular poly(arylene ethynylene)s were prepared by Pd-catalyzed condensation of 3-hexyl multisubstituted oligothiophene derivatives with either benzene or anthracene compounds. The NMR characterization of the starting materials and model compounds lead to a thorough investigation of the corresponding macromolecules. Both small and large molecules were characterized by optical methods. The former, particularly when containing anthracene moieties, display noticeable photoluminescence quantum yields. In the polymers, the photoluminescence quantum yield is lower than that of the starting materials when anthracene is present, while the polymers containing benzene show higher quantum yields.

We report a characterization of the graft copolymer of PA with polybutadiene by IR spectroscopy. The data obtained have been analyzed to clarify the band assignment, the structure of the polymer, its stability and the effect of different dopants. Also stretched films have been analysed with polarized light.

We report in this short paper a preliminary account on the optical characterization and photoexcitation of a class of novel conjugated polymers consisting of regularly alternating thiophene and benzene sequences, which might represent models for one-dimensional superlattices. Optical absorption and emission spectra suggest that the barriers produced by the phenylene moieties do not interrupt the conjugation but can produce localization effects. Resonant Raman spectra indicate that a selective response of the thiophene and phenylene moieties occurs by varying the excitation energy from visible to ultraviolet. Moreover these measurements confirm the presence of a confinement on the thiophene blocks, while the biphenyl moiety does not appear to feel the energy barrier and behaves as a poly(paraphenylene) oligomer of 5-6 ring length. CW photomodulation spectra show that the formation of long-lived bipolarons takes place only if the thienylenic moiety is long enough to accomodate the lattice distortion.

A molecular mechanics computational procedure, previously used for the refinement and the analysis of several crystalline polymers, was applied to investigate the crystal structures of the tetramer (T4) and hexamer (T6) of thiophene, as well as the crystal structure of polythiophene (PT). Simultaneous minimization of intra‐ and intermolecular energies of the T4 and T6 structures, obtained by Rietveld analysis of powder X‐ray diffraction profiles, leads to molecular conformations showing smaller deviations from the ring co‐planarity than the original models. For both oligomers the calculations confirm that the molecular centre of inversion is not a crystallographic centre of symmetry, as also revealed by X‐ray diffraction of the T6 single crystal. This surprising effect appears to arise from intermolecular interactions between the terminal residues, hence is not relevant with respect to the PT polymer structure. The small energy cost for constraining the molecules at the crystallographic centre of symmetry is in agreement with experimental findings that reveal the existence of polymorphs for both T4 and T6. The calculations on the T6 single crystal were used to upgrade the MM2‐like force field, which was then used to determine the minimum‐energy model of the monoclinic crystal structure of polythiophene.

The synthesis, crystal structure and detailed molecular mechanics calculations, including crystal packing interactions, of tetrahexylsubstituted sexithienylene are presented. Unexpectedly the molecule, which arranges in the P-1 space group, displays no herringbone arrangement, thienylenic rings are far from coplanarity and the alkylic side chains present different conformations. Molecular mechanics fully accounts for these findings. From crystal packing computations it is derived that different arrangements are unable to lower the packing energy, due to the closeness of two alkyl chains on the same side of the thienylenic backbone, which prevents interspersion of non-parallel molecules.

The synthesis, crystal structure and detailed molecular mechanics calculations, including crystal packing interactions, of tetrahexylsubstituted sexithienylene are presented. Unexpectedly the molecule, which arranges in the P-1 space group, displays no herringbone arrangement, thienylenic rings are far from coplanarity and the alkylic side chains present different conformations. Molecular mechanics fully accounts for these findings. From crystal packing computations it is derived that different arrangements are unable to lower the packing energy, due to the closeness of two alkyl chains on the same side of the thienylenic backbone, which prevents interspersion of non-parallel molecules.

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