Bicolor Electroluminescent Pixels from Single Active Molecular Material

We report on the fabrication of the first bicolor micropixelated OLED from a single molecular material using a single-step bottom up procedure, The implementation of a deposition technique, based on a spatial-switch and con formational-sensitive STD surface-tension-driven lithography, has allowed us to exploit the spontaneous supramolecular properties and the conformational flexibility of a conjugated thiophene-based material, 6-bis-(50-hexyl-[2, 20]bithiophen-5-yl)-3, 5-dimethyl-dithieno[3, 2-b: 20, 30-d]-thiophene (DTT7Me). The existence of two regularly alternating emitting regions on a micrometer scale allows obtaining electroluminescent emission at two different wavelengths from a single material

Controlling non-radiative energy transfer in organic binary blends: a route towards colour tunability and white emission from single-active-layer light-emitting devices

We show how colour tunability (including white) can be achieved by controlling non-radiative intermolecular energy transfer from the donor to the acceptor in binary blends of oligomeric compounds. Blends of different concentrations of a novel functionalized thiophene-based oligomer and a low-molar-mass diamine derivative (N, N'-diphenyl-N, N'-bis(3-methylphenyl)-1, 1'-biphenyl-4.4'diamine) are used to tune both the photoluminescence and the electroluminescence (EL) from red to blue, including balanced white, according to the standards of the Commission Internationale de l'Eclairage. The single-active-layer light-emitting devices, realized by spin-coating, exhibit good EL performance. In particular, the white-emitting device shows an EL efficiency of 5 × 10−1 cd A−1 and a luminance of more than 180 cd m−2

Bright oligothiophene-based light emitting diodes

Abstract We demonstrate bright and efficient spin-coated yellow organic light emitting diodes (OLEDs) employing as active medium a novel thiophene-based compound, in which the conventional linear structure of the oligothiophenes has been replaced by a branched benzo[ b ]thiophene-based structure. Such a structure, combined with the oxygen functionalization of the core-thienyl sulphur atom and the cyclohexyl substitution of the lateral thienyl rings, allowed us to obtain a brightness up to 10,500 cd/m 2 and an external quantum efficiency up to 0.48%, which are the highest values so far obtained by substituted oligothiophene-based compounds

Oligomer-based organic distributed feedback lasers by room-temperature nanoimprint lithography

Room-temperature nanoimprint lithography in air is used in order to pattern a nonthermoplastic, low-molar-mass thiophene-based pentamer with excellent gain properties. No degradation of the luminescence efficiency of the active medium was observed after patterning. In this way, we fabricated single-mode emission distributed feedback lasers having a threshold excitation fluence of 140 μJ/cm2. The lasing line is peaked at 637 nm and exhibits a linewidth of less than 0.7 nm and a well-behaved input-output characteristic in the whole range of pump fluences. These results demonstrate room-temperature nanoimprint lithography as powerful and straightforward fabrication technique for oligomer-based nanostructured optoelectronic devices

White emission from organic light emitting diodes based on energy down-convertion mechanisms

Balanced white electroluminescence (EL) emission from binary organic blends was achieved via intermolecular down-convertion processes: the exciplex and the Foerster transfer mechanisms. This was obtained by combining a low electronic affinity (EA) molecule, a diamine derivative (TPD), with two high electronic affinity substituted oligothiophenes having high and low ionization potential (IP), respectively. Both the energy down-convertion mechanisms were exploited in two single active-layer organic light emitting devices, showing stable white emission, independent of the applied voltage

Solid‐state laser devices based on an optically‐confined oligothiophene‐S,S‐dioxide

We investigated the gain properties of spin coated films of a soluble substituted quinque-thiophene under ns pulsed optical excitation. The oligomer exhibits a clear line narrowing, due to amplified spontaneous emission assisted by waveguiding film slab, for excitation fluences larger than 0.8 mJ cm−2. The oligothiophene was employed as the active medium of different organic resonators. In particular, we report about directly printed organic distributed-feedback resonators, exploiting the one-dimensional periodic modulation of the organic surface. The devices exhibit single-mode emission between 630 and 640 nm, with a full width half maximum of about 1 nm and a pump threshold as low as 140 μJ/cm2 at room temperature. These results make the substituted oligothiophenes excellent candidates as active media of optically-confined nanostructures. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Rigid-Core Oligothiophene-S,S-dioxides with High Photoluminescence Efficiencies Both in Solution and in the Solid State

The photoluminescence (PL) frequencies and quantum efficiencies of dithieno[3,2-b;2',3'-d]thiophene-4,4-dioxide (1), its 3,5-dimethyl derivative (2), and the corresponding 4-oxide (3) are reported and discussed in relation to their single-crystal X-ray structures. The peculiar packing modalities of dioxides 1 and 2, based on dimeric units originated by short S···O contacts between molecules related by an inversion center, cause an unusually high bathocromic shift of PL frequencies from solution to solid state. This effect is accompanied by a marked decrease in solid-state PL efficiencies (12% and 16%) compared to those in solution (75% and 77%). In monoxide 3 the loss of local symmetry inherent to the change SO2 → SO deeply modifies the self-assembly and PL properties, and the PL efficiency in the solid state is close to that in solution. Ab initio calculations on the ground and excited states of compound 1 were performed and compared to those of a conformationally mobile counterpart. Oligomers containing..

Emission properties of printed organic semiconductor lasers

We investigated the emission properties of a distributed-feedback resonator based on an organic semiconductor patterned by a novel printing technology. We observed the peak splitting of the photonic bandstructure of the periodic grating and extracted the effective refractive index of the outcoupled guided modes. The laser works at the second diffraction order, exhibiting narrow single-mode emission at 637 nm, with a threshold as low as 37 microJ/cm2. The results suggest that direct printing is a promising fabrication technique for optically confined integrated optoelectronics

Full organic distributed feedback cavities based on a soluble electroluminescent oligothiophene

We have studied the emission spectra of spin-coated films of a novel soluble substituted quinque-thiophene under nanoseconds pulsed excitation. The photoluminescence spectra show a clear line narrowing, ascribed to amplified spontaneous emission assisted by waveguiding inside the film slab, for excitation energy fluence above 0.8\phantom{\rule{0.3em}{0ex}}\mathrm{mJ}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}. We employed our oligothiophene as active medium for a fully organic distributed feedback (DFB) resonator on a flexible transparent substrate of poly(dimethylsiloxane) (PDMS). The DFB has been fabricated by replica molding from a master grating realized by electron-beam lithography, and subsequent spin coating of the active material on the patterned side of PDMS. It shows a clear DFB emission at about $603\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ of linewidth $0.8\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$

Fabrication of Molecular Micro-NanoStructures by Surface-Tension-Driven Technique

We present the fabrication of a pixels structure by a well-defined pattern replication of a micrometer template driven by a surface free-energy lithographic technique, realized by molecular aggregation in dewetting conditions and by confining the liquid solution with geometric boundaries. The organization in the solid-state of the selected thiophene-based molecular materials allows to realize a bicoloured, green and red-emitting pixels structure, by exploiting the molecular structural arrangement, induced during a dewetting process, and the great conformational flexibility of DTT7Me