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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.

We show that thin films grown by vacuum sublimation, or formed by melted powders, of semiconductor R-quinquethiophene (T5) exhibit a hierarchical self-affinity organization that spans scales from tens of nanometers to hundreds of micrometers. T5 organization was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), and optical microscopy. XRD showed that vacuum-evaporated T5 films were characterized by a preferred orientation of the h00 planes parallel to the glass substrate. Melting of the films followed by rapid quenching to room temperature led to the formation of micrometer-sized, single-crystal-like structures, characterized by uniaxially aligned stripes. XRD proved that the meltingquenching process enhanced molecular ordering and increased the size of domains with the molecule’s long axes tilted by about 65° with respect to the substrate plane and piled up side-by-side along parallel columns. AFM measurements on the melt-quenched structures showed that a hierarchical architecture was built by reiteration across multiple length scales of the same recurring motif. Because of the tendency of T5 to form highly crystalline vacuum-evaporated thin films, a field-effect hole mobility comparable to state-of-the-art FET mobility of R-sexithiophene films was reached, without any attempt to optimize deposition conditions.

Thiophene oligomers have been studied so far mainly for their semiconductor and charge-transport properties. However, these compounds are also highly fluorescent and soluble. Solubility and fluorescence frequencies and efficiencies can be tailored by means of appropriate functionalization of the aromatic backbone. Functionalization with the isothiocyanate group (-N=C=S) allows these molecules to form covalent bonds with NH2-containing biomolecules and give rise to optically and chemically very stable fluorescent bioconjugates. Examples of photostable conjugates formed with monoclonal antibodies are reported.

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 dithienothiophene 2 as internal core were synthesized and found to be characterized by high PL efficiencies in the solid-state (up to 48%) as well as in solution (up to 85%). The current-voltage and luminance-voltage plots of an electroluminescent diode fabricated with one of these new rigid-core oligothiophene-S,S-dioxides are reported.

In recent studies it was demonstrated that temperature-dependent optical spectroscopy is a valuable tool for revealing the differences in the geometries of flexible molecules like oligothiophenes (OTs) in the ground (S0) and first excited (S1) electronic states, by examining the symmetry relations between the absorption and emission spectra: while at low temperature the spectra show mirror symmetry, pointing to planar geometries in S0 and S1, the symmetry relation breaks down at ambient temperature due to thermal population of torsional modes. In the present joint spectroscopic and theoretical study, we demonstrate that this behavior is also observed for di- and tetramethyl-substituted OTs, suggesting an essentially planar equilibrium geometry not only in S1 but also in S0, despite the increasing sterical hindrance which is imposed by the substituents. This rather surprising result is rationalized by the softness of the carbon-sulfur bond, which is able to adapt to the geometrical constraints. © the Owner Societies.

The synthesis of multicolor fluorescent oligothiophene-N-succinimidyl esters (TSEs) is reported and their optical properties are discussed with the aid of ab initio calculations. The esters were coupled to proteins and to 3’-amino-modified oligonucleotides in mild conditions and with similar modalities. A comparative study of the bioconjugate of IgG1 anti-CD3 antibody labeled with a blue fluorescent TSE and with fluorescein isothiocyanate (FITC) is reported showing that the former achieves higher photoluminescence intensity and optical stability than the latter. Fluorescence resonance energy transfer experiments with TSE labeled oligonucleotides and examples of cellular imaging via TSE labeled proteins are reported.

Spin-glass theory is one of the leading paradigms of complex physics and describes condensed matter, neural networks and biological systems, ultracold atoms, random photonics, and many other research fields. According to this theory, identical systems under identical conditions may reach different states and provide different values for observable quantities. This effect is known as Replica Symmetry Breaking and is revealed by the shape of the probability distribution function of an order parameter named the Parisi overlap. However, a direct experimental evidence in any field of research is still missing. Here we investigate pulse-to-pulse fluctuations in random lasers, we introduce and measure the analogue of the Parisi overlap in independent experimental realizations of the same disordered sample, and we find that the distribution function yields evidence of a transition to a glassy light phase compatible with a replica symmetry breaking., 10 pages, 5 figures

The molecular-beam deposition of quaterthiophene (4T) oligomer on potassium acid phtalate (001) single crystals yields thin films exhibiting a peculiar supramolecular organization induced by the interaction with the substrate. The 4T thin films, which exhibit an extremely large optical anisotropy arising from the alignment of the 4T molecular axis along the b crystallographic axis of the substrate, allow one to carry out polarized transmission measurements over the whole \ensuremath{\pi}-${\mathrm{\ensuremath{\pi}}}^{\mathrm{*}}$ absorption band. The observation of a strong polarized band, together with very weak unpolarized absorption peaks originating from isolated molecules, is consistent with the formation of a tilted H aggregate in which the molecular transition moments form a 38\ifmmode^\circ\else\textdegree\fi{} angle with the substrate surface. The low luminescence quantum yield further supports the formation of this very ordered structure. Exciton migration and decay paths in the 4T films have been established by studying, with time-resolved photoluminescence spectroscopy, the emission originating from traps and imperfect aggregates.

We investigated the uptake and release of labeled antibodies from pH-sensitive hydrogel microparticles (i.e. microgels) by means of fluorescence analysis of labeled biological samples. The poly(methacrylic acid) (PMAA) hydrogel is a carbon-based network having carboxylic groups on the surface that dissociate according to their acid-base equilibrium. The ability of the PMAA microgel to encapsulate and release anti-CD4 and anti-CD8 monoclonal antibodies (MAbs), differing for the isotype and labeled with highly photostable fluorophore, was studied in solution by photoluminescence spectroscopy. The experimental results indicated that the uptake and release of the tested antibodies were controlled by pH. Furthermore, confocal microscopy analysis in the solid state revealed that the distribution of the labeled antibodies either on the surface or in the core of the microgel matrix was related to the specific properties of these MAbs. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

We report investigations of the photoluminescence (PL) and electroluminescence (EL) of a thiophene oligomer for which we have devised a variety of substitutions aimed at enhancing the solid-state efficiency. We find that the absolute PL quantum efficiency in the solid state is up 37% for both powders or spin-coated thin films of the compound. The material thus becomes competitive for applications in organic light-emitting diodes (LEDs). EL efficiencies up to 1.2 cd/A are demonstrated in LEDs prepared with indium–tin–oxide and Ca–Al electrodes.

We demonstrate wide tunability, from green to near infrared, of the electroluminescence emission of substituted oligothiophene compounds. The compounds are characterized by high chemical stability, electron affinities up to 3.1 eV and photoluminescence efficiencies up to 70%. These characteristics make these materials excellent candidates for application in light-emitting diodes. We obtain low turn-on voltage devices with electroluminescence efficiency up to 0.2%, more than one order of magnitude larger than the values reported for unsubstituted oligothiophene compounds.

Very low voltage organic light-emitting diodes using a fluorescent linear S,S-dioxide oligothiophene as emitting layer has been realized using a p-i-n structure. The device reaches a remarkable luminance of 10 000 cd/m(2) at only 9 V, which is two orders of magnitude higher than the simple bilayer structure already reported for this active material. Due to the doping of the transport layers, a maximum power efficiency of 2.1 lm/W was reached against 0.2 lm/W of the corresponding undoped device. As a consequence of this higher power efficiency, the reduced self-heating of the p-i-n device structure, compared to the undoped devices, determines the best operating condition to check the intrinsic stability of the emitting layer. Aging measurements reveal indeed a very high stability, with extrapolated device lifetimes at about 10(8) and 2200 h at starting luminances of 100 and 3200 cd/m(2), respectively.

Nanostructures displaying fluorescence and magnetic properties at the same time are potentially useful for achieving simultaneous bio-separation and bio-sensing (e.g., magnetic separation coupled with multiplexing optical detection of different tumour cell populations). Spherical nanobeads that display both fluorescent and magnetic features are reported; they are fabricated by grafting fluorescent oligothiophene molecules to an amphiphilic polymer that is then used to enwrap iron oxide nanoparticles, which acts as the magnetic domain. By tuning experimental conditions, control over the number of magnetic nanoparticles per bead and over the bead diameter (30–400 nm) was achieved. A cell separation efficiency of the level required for cell sorting applications is also reported.