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This work reports the first observation of circularly polarized electroluminescence (CPEL) in thin films of self‐organized oligothiophenes. Four new 1,4‐phenylene and 9H‐carbazole‐based oligothiophenes were ad hoc designed to ensure efficient spontaneous formation of chiral supramolecular order. They were easily synthesized and their chiroptical properties in thin films were measured. Circularly polarized luminescence (CPL) spectra revealed glum in the order of 10−2 on a wide wavelengths range, originating from their self‐organized chiral supramolecular organization. These molecules have reasonable properties as organic semiconductors and for this reason they can constitute the active layer of circularly‐polarized organic light‐emitting diodes (CP‐OLEDs). Thus, we could investigate directly their electroluminescence (EL) and CPEL, without resorting to blends, but rather in a simple multilayer device with basic architecture. This is the first example of a CP‐OLED with active layer made only of a small organic compound. [ABSTRACT FROM AUTHOR]

We report on electroabsorption (EA) and built-in voltage (VBI) measurements of polymer light-emitting diodes with the general structure ITO/PEDOT:PSS/emitting polymer/LiF/Ca/Al where ITO is indium tin oxide, PEDOT:PSS is poly(3,4-ethylene dioxythiophene) doped with poly(styrene sulfonate), and the emitting polymer is either poly(9,9-dioctylfluorene), poly(9, 9-dioctyl-fluorene-alt-bis-N,N′-(4-butyl-phenyl)-bis-N, N′-phenyl-1, 4-phenylenediamine), or poly(9,9-dioctylfluorene-alt-N-(4-butylphenyl)-diphenylamine). We find that the EA nulling voltage, i.e., the dc bias at which the EA signal vanishes, depends on the frequency of the ac voltage and on the incident photon wavelength. Such dependence poses a problem for accurate measurement of the built-in voltage (VBI), which is the voltage generated between the electrodes upon equilibration of the Fermi levels through the heterostructure. We find that the EA signal is mixed with a smaller intensity signal which can be ascribed to excited state absorption (ESA). We propose a method for separating the excited state absorption signal and producing accurate VBI measurements. We also demonstrate that in our devices the ESA contribution to the electromodulated (ΔT/T) signal is negligible with respect to the accuracy with which VBI can be determined from the nulling voltage of ΔT/T and can thus be safely ignored. [ABSTRACT FROM AUTHOR]

Presents information on a study on the absolute photoluminescence (PL) and electroluminescence quantum efficiencies for thin films and polymer light-emitting diodes. Limitation on the use of thiophene based conjugated polymers and oligomers as active, luminescent layers of polymer light-emitting diodes (PLED); Methodology used in conducting the study; Results.

Two new soluble block copolymers are reported in which chromophores and hexa(ethylene oxide) units alternate along the polymer backbone. In polymer 1 the chromophore was the distyrylbenzene unit. The polymer was synthesised via the Wittig reaction and the ionisation potential of 5.4±0.2 eV was measured by cyclic voltammetry and photoelectron spectroscopy. Polymer 1 showed a high solid-state photoluminescence efficiency (34%) and was used to make efficient (0.5 cd/A) light emitting diodes (LEDs). Polymer 1 was also used in light emitting cells; these showed luminescence in reverse bias and a reduced turn-on voltage compared to the LEDs. Polymer 2, in which the chromophore was dodecafluoro-distryrylbenzene, was prepared via the Horner–Wittig reaction and showed an ionisation potential of 6.25±0.15 eV and a solid-state photoluminescence efficiency of 17%. It was used as electron-conducting layer in a LED but failed to give significant electroluminescence. The optical energy gap for both polymers was 3.0 eV. [Copyright &y& Elsevier]

We have synthesised and characterised a new low-gap conjugated polymer, with a broad absorption profile. In blends with a C70derivative we demonstrate power conversion efficiencies of 0.76%. We show electroluminescence from the polymer peaking at 956 nm, and quantum efficiency of 0.02% in a blend. [ABSTRACT FROM AUTHOR]

Poly(9,9′-dioctyl fluorene) (F8) and poly(4,4′-diphenylene diphenylvinylene) (PDPV) are conjugated polymers with optical transitions that are nonresonant thanks to the particular structural features of PDPV that yield a very large Stokes’ shift (∼1.14 eV) between absorption and emission spectra. We present steady-state and time-resolved photoluminescence (PL) experiments showing that F8:PDPV blends are “optically disconnected” systems for which the emission spectra and PL quantum yields are the linear combination of the contributions of the individual constituents with weights given by the respective absorption coefficients and concentration in the films. Single-layer light-emitting diodes incorporating F8:PDPV blends show white electroluminescence resulting from the simultaneous exploitation of the spectral features of both blend constituents (Commission Internationale de l’Eclairage, CIE, coordinates: x=0.27 and y=0.36, in the case of 8:2 F8:PDPV molar ratio). [ABSTRACT FROM AUTHOR]

Abstract: We report a scanning force microscopy study on the growth from solution of poly(ethylene-oxide) (PEO) architectures on solid surfaces. A systematic investigation performed varying the concentration of the solutions spin-coated on either mica or indium-tin-oxide revealed that different ordered assemblies, including fibers and layers, can be produced. While in ultrathin films the assembly at surfaces is governed by the interplay of intramolecular as well as intermolecular and interfacial interactions, in films with a nominal thickness of several nanometers the latter contribution appears to be minimal. Achieving a careful insight on the growth of PEO films on different substrates is important to better understand and control of PEO phases in light-emitting electrochemical cells which make use of blends of PEO and conjugated electroluminescent polymers. [Copyright &y& Elsevier]

Abstract: Optical and electrical properties of conjugated polymers are often strongly affected by aging, not only during operation but also during storage, because of the variety of chemical degradation pathways available. Here we report the properties of a phenylated poly(arylene vinylene), after a decade of storage in powder form, in air, at room temperature, and in the dark. We find that the values for both the photoluminescence efficiency (60% or higher) and the electroluminescence are comparable with those reported for a similar but (then) freshly prepared batch of material, measured over 13years ago. The optical properties of this material relevant for display applications are thus essentially stable over more than a decade for storage in the dark. [Copyright &y& Elsevier]