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Recently, two different groups have reported independently that the mobility of field-effect transistors made from regioregular poly(3-hexylthiophene) (P3HT) increases strongly with molecular weight. Two different models were presented: one proposing carrier trapping at grain boundaries and the second putting emphasis on the conformation and packing of the polymer chains in the thin layers for different molecular weights. Here, we present the results of detailed investigations of powders and thin films of deuterated P3HT fractions with different molecular weight. For powder samples, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were used to investigate the structure and crystallization behavior of the polymers. The GPC investigations show that all weight fractions possess a rather broad molecular weight distribution. DSC measurements reveal a strong decrease of the crystallization temperature and, most important, a significant decrease of the degree of crystallinity with decreasing molecular weight. To study the structure of thin layers in lateral and vertical directions, both transmission electron microscopy (TEM) and X-ray grazing incidence diffraction (GID) were utilized. These methods show that thin layers of the low molecular weight fraction consist of well-defined crystalline domains embedded in a disordered matrix. We propose that the transport properties of layers prepared from fractions of poly(3-hexylthiophene) with different molecular weight are largely determined by the crystallinity of the samples and not by the perfection of the packing of the chains in the individual crystallites.

We demonstrate up-conversion of noncoherent sunlight realized by ultralow excitation intensity. The bimolecular up-conversion process in our systems relies on the presence of a metastable triplet excited state, and thus has dramatically different photophysical characteristics relative to the other known methods for photon up-conversion (two-photon absorption, parametric processes, second harmonic generation, sequential multiphoton absorption, etc.).

gree of amorphous character. This would be expected as the deposition occurs at room temperature and the presence of any crystalline material is in itself remarkable. Different polymorphs have differing optical properties; hence this could provide a simple route to a generally inaccessible material with potentially interesting applications. Scanning electron microscopy (SEM) revealed the films (14 days deposition) were composed of nanosized HgS spheres, from 20 to 250 nm in diameter (Fig. 3). The nanodimensions of the particles could explain the stability of the b-polymorph film, as small particles can often exist in energetically unfavorable crystal phases.[20] Absorption spectroscopy on the same film showed an onset of absorption at ca. 1 eV with an excitonic feature at ca. 1.3 eV (Fig. 2b). Although this does not fit with any theoretical data, other studies have shown that band-edge measurement of HgS materials do not correlate with predicted bandgaps.[21]In conclusion, we have prepared a novel mercury(II) dithiocarbamate complex with an eight-membered ring structure. The molecule has been used as a room-temperature precursor to a metastable phase of mercury sulphide not normally accessible via low-temperature reaction pathways. ExperimentalIn a typical synthesis, [Hg(S 2 CNMe(EtPh)) 2 ] 2 was prepared by dissolving 1.95 g (6.1 10 ±3 M) mercury acetate in 150 mL ethanol, followed by filtration. To this was added dropwise a mixture of carbon disulfide (0.8 mL, 0.012 M) and N-methylphenethylamine (2 ml, 0.012 M) in 50 mL ethanol, producing an immediate white precipitate. After 4 h stirring, the precipitate was filtered, air dried, and redissolved in 50 mL dichloromethane. Storage at 4 C resulted in yellow needle-like crystals, the single-crystal X-ray structure (120 K) of which is shown in Figure 1. It is noteworthy that the precursor started to decompose in solution and a black material was observed (HgS). Once isolated, the yellow crystals were indefinitely stable at room temperature. To produce a b-HgS thin film, 0.05 g of [Hg(S 2 CNMe(EtPh)) 2 ] 2 was dissolved in 10 mL acetone producing a optically clear colorless solution, into which a glass substrate was placed vertically.

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The solid-state polymerization of functional derivatives of 2,4-hexadiin-l,6-diol caused by light or by heat was investigated. A qualitative survey demonstrates that the presence of groups capable of hydrogen-bonding are one of the most important factors for solid-state reactivity of conjugated triple-bonds. Compounds which do not form hydrogen-bonds were unreactive in most cases. Ure thanes were the most reactive class of derivatives, 2,4-hexadiin-l,6-diol-bis-phenylurethane giving the best results. The relation and the reactivity of several modifications of this compound are described. Heating of one modification of 2,4-hexadiin-l,6-diol-bis-phenylurethane at temperatures between 70 and 120 °C yielded in a topotactic reaction highly crystalline fibres of a coppercoloured polymer. Time-con version studies were made and the activation energy of the polymeriza tion determined to 19 kcal/mole. The mechanism of polymer-formation is discussed. It is highly probable that poly-1,4-bis-phenylcarbamoyloxymethyl-Jra/i.s-butatrien, a polymer with three cumu lated double-bonds per repeating-unit, is formed by a 1,4-addition reaction.

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Even though mixtures of polyelectrolytes and surfactants are used in a variety of technologies, little is known about the solidstate properties of complexes formed by the two components. Recently reported methods for preparing polyelectrolytesurfactant complexes and their solid-state structure will be described in the context of the self-assembly behavior of the source surfactant molecules. This facile process offers the opportunity of producing a variety of new materials with applications that may range from switchable, permselective biological membranes to fluorinated materials with non-wetting properties. In the form of a solid-state complex, remarkably diverse mechanical properties ranging from elastomers to crystalline solids can easily be achieved. This review discusses the growing quantity of research in this new field, and in particular, the fabrication of such complexes in the form of processable self-doped conducting polymers is described.