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

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..

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

Synthesis of Poly(acrylic acid) Nanogels and Application in Loading and Release of an Oligothiophene Fluorophore and Its Bovine Serum Albumin Conjugate

Nanometer-sized poly(acrylic acid) (PAA) hydrogels were synthesized by emulsion polymerization of methyl acrylate and subsequent acid hydrolysis, and their pH-dependent swelling behaviour was studied by dynamic light scattering. To determine the suitability of PAA nanogels as pH-sensitive carriers for biomedical applications, loading and release of an oligothiophene fluorophore and its albumin conjugate onto the PAA nanogels were investigated as a function of pH by absorption and photoluminescence measurements. it was observed that loading and release processes of both the oligothiophene and its conjugate could be controlled by changing pH of their solutions

Molecular Packing and Photoluminescence Efficiency in Odd-Membered Oligothiophene S,S-Dioxides

The single-crystal X-ray structures of three odd-membered thiophene oligomers bearing one central thienyl-S,S-dioxide moietytrimer, pentamer, and heptamerare reported. Absolute photoluminescence quantum yields in microcrystalline powders are given for all compounds. The solid-state photoluminescence efficiencies of the trimer (45%) and the pentamer (12%) were up to 1 order of magnitude higher than those generally measured in conventional oligothiophenes, while that of the heptamer amounted to only 2%. These results are accounted for in terms of molecular packing characteristics, which, owing to the competing effects of dipolar intermolecular interactions between the sulfonyl groups and intra- and intermolecular C−H···O hydrogen bondings and S···S interactions, change dramatically on changing the oligomer size. While the trimer is highly distorted and crystallizes in a chiral orthorhombic space group with the molecular long axes markedly tilted with respect to one another, the heptamer displays a coplanar ..

Smart surfaces for pH controlled cell staining

In this work, novel smart surfaces for in situ cell staining were realized by covalent attachment of pH-responsive microgels on platforms dedicated to microfluidics for lab-on-chip. The poly(methacrylic acid) microgels were firstly synthesized in solution and then covalently immobilized on a glass surface. As they preserve their pH-sensitive nature after the covalent immobilization, microgels were loaded with an oligothiophene-conjugated anti-human CD4 monoclonal antibody, and finally incubated with a Jurkat T-cell suspension. The physiological pH of the extracellular environment induced the pH-triggered release of the labeled anti-CD4 antibodies and the selective staining of the CD4-positive subpopulations within the Jurkat cell suspension. The realization of this type of smart surface for the encapsulation of specific monoclonal antibodies and their release in an on-demand way should have an enormous potential in developing fully integrated platforms for cell analysis

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

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