We introduce a new family of stable high-mobility organic π-type semiconductors based on the electron-rich 10,15-
dihydro-5H-diindolo[3,2-a:3',2'-c]carbazole (triindole) extended
π-conjugated system. This platform tends to form
columnar stacks of the aromatic cores maximizing π-orbital overlap between adjacent molecules, thus paving the way for
the one-dimensional migration of charge carriers along the columns. In addition these compounds have two different
types of positions that can be functionalized independently offering the possibility of tuning their electronic properties as
well as their morphology through chemical functionalization. The integration of the optimized triindole derivatives into
solution processed devices as active layer is explored in this work.
We report white electroluminescence from a single component-single layer solution processed organic light emitting
diodes (OLEDs). In this work, we have fabricated and characterized OLEDs based on a single polymer synthesized by
incorporating a small amount of the orange-light emitting chromophore 1,8-Naphtalimide derivative as side chain to
poly(fluorene-alt-phenylene) (PFP). The structure of the devices is ITO/PEDOT:PSS/Active layer/Al. The dopant unit
was convalenttly attached to the side chain of polyfluorene by alkyl spacers. We have fabricated devices with different
amounts of the orange chromophore (0, 0.0005, 0.005, 0.02 and 0.08 in weight) as well as a device based on a physical
blend in the same proportion of 0.08 for comparison purposes. Absorption and Photoluminescence (PL) studies in thin
films show no significant interaction can be observed between both moieties in the ground state, but after photoexcitation
an efficient energy transfer takes place from PFP to the orange chromophore. We have observed a more efficient energy
transfer in these compounds than for physical mixtures of the two chromophores due to a phase separation effect in the
blend confirmed by the optical measurements and ESEM analysis, obtaining energy transfer even in diluted solutions
from the intramolecular interaction in the copolymers. With this very simple device structure, white light with
Commission Internationale de l'Eclairage (CIE) coordenates (0.34;0.43) is obtained for the electroluminescence (EL)
emission and turn on voltage of 6 V for the device based on the copolymer with x = 0.02, together with a good match in the EL and PL spectra indicative that two emissions are produced by the same species, making this material very suitable
for large area solution processed devices in solid state illumination.
The search of new organic molecules with improved properties is of fundamental relevance for hybrid organic-inorganic
based devices (OLED, FET, PV, injection layers, flexible large area devices, lasers, etc.). Triindole based materials
present extended aromatic cores with disk-like geometry that allow tailoring their electronic properties through chemical
functionalization. In this work we present an optical and electronic study of new triindole based single crystals. Pistacking
gives rise to highly ordered columnar structures yielding to high mobilities, around 0.4 cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup>. External
oxidation is found to increase orders of magnitude the conductivity. Slight modifications of this platform modify
substantially the crystallization dynamics and therefore the quality of the thin films obtained by spin coating from
solutions with different solvents. The morphology, stability and properties of the optimized films are found to be
promising for device fabrication. A comparative study of the absorption and emission efficiency of solutions and thin
films of the different derivatives is presented. The first tests for OLED and OFET devices are under way.
New outstanding possibilities are emerging by the synthesis of organo-inorganic polymeric materials from a buildingblock
approach. Our approach has been to assemble extended solids from bent flexible arenedicarboxylate linkers that
offer totally new topologies with helical channels. A new family of Rare-earth Polymeric Framework (RPF-4) has been
obtained and its structure solved. The framework is formed by a Lanthanide (Ln) matrix, with the Ln atoms well
separated in two directions. The crystals are highly stable in air and the decomposition temperature is above 350°C.
Under UV excitation, the linker presents a bluish-white emission peaking around 450 nm. The emission corresponding to
the different crystals either present an emission similar to the linker, slightly modified depending on R, or an intense
emission due to Ln localized crystal field transitions. In the second case, an energy transfer from the linker to the Ln
ions, which relax radiatively with a very efficient emission, seems to occur. The observed emission properties and crystal
stability are of interest for applications as light emitting materials. The peculiarities of the structure may avoid the
concentration quenching of the luminescence since Ln ions form well separated chains along a-axis with interchain
distances around 12.5 Å.
We report a solution processed blue stilbenoid dendrimer based on a 1, 3, 5 - benzene core and endowed with a periphery
of electron donating and solubilizing alkoxy chains. Raman analysis it is revealed as a helpful tool to investigate changes
from the pristine material to the material in the OLED structure, explaining the differences between the dendrimer single
layer thin film photoluminescence (PL) and the electroluminescence (EL) dendrimer active layer emission in the device.
We report a blue EL emission (439 nm) and a very promising effective mobility value of 2.55 × 10<sup>-5</sup> cm<sup>2</sup>/(V•s)
suggesting good transport properties for non doped blue OLEDs that use air stable Al as the cathode.
We have investigated non-linear electrical characteristics in low bandwidth manganites R<sub>1-x</sub>Ca<sub>x</sub>MnO<sub>3</sub> with R=Pr, Nd, Ho, Er and x=0.3-0.5. In all these materials we observe strong nonlinear I-V characteristic that is manifested in negative differential resistance (NDR) and breakdown voltages V<sub>br</sub> as low as few volts. These effects are accompanied by intense Joule heating that seems to be inseparable from the effect itself. We present different types of measurements with the aim to resolve the origin of the phenomena. Melting of insulating state is observed regardless of its origin - antiferromagnetic, charge ordered or paramagnetic. This nonlinearity is found to have microscopic origin, indicating that it is some sort of percolation effect. Hysteretic effects also indicate that the heating is not the only cause of NDR. Theory of phase separation gives a plausible explanation for these nonlinearities, although it appears to be diffcult to prove. Pulsed and relaxation measurements show that the effect is time-dependent, similarly to nonlinearities induced by magnetic field.