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The reactions of coronene dehydrogenation and fusion upon heat treatment in the temperature range of 500–700 °C were studied using XRD, TEM, Raman, IR, and NEXAFS spectroscopy. The formation of a coronene dimer (dicoronylene) was observed at temperatures 530–550 °C; dicoronylene can easily be separated using sublimation with a temperature gradient. An insoluble and not sublimable black precipitate was found to form at higher temperatures. Analysis of the data shows that dimerization of coronene is followed at 550–600 °C by oligomerization into larger molecules. Above 600 °C amorphization of the material and formation of graphitic nanoparticles was observed. Coronene fusion by annealing is proposed as a road to synthesis of larger polycyclic aromatic hydrocarbons and nanographenes.

Estimations of ochratoxin A (OTA) and 4-deoxynivalenol (DON) exposure of the Belgian population through beer consumption were made using the results of the recent Belgian food survey and the compiled data set of OTA and DON levels in conventionally and organically produced beers in 2003–05. For the consumers of organic beers, the daily intake of OTA was 0.86 (in 2003), 1.76 (in 2004) and 0.72 (in 2005) ng kg−1body weight (bw), considering the mean beer consumption (0.638 litres) and the average level of OTA in 2003, 2004 and 2005, respectively. Using the 97.5th percentile of beer consumption (1.972 litres), the corresponding OTA daily intakes were 2.65, 5.44 and 2.24 ng kg−1 bw, which are close or above the tolerable daily intake (TDI) of 5 ng kg−1 bw. For the consumers of conventional beers, the OTA intakes were low: 0.23, 0.23 and 0.11 ng kg−1 bw day−1for the average beer consumption, in 2003, 2004 and 2005 against 0.72, 0.73 and 0.34 ng kg−1 bw day−1when the 97.5th percentile level was considered. As for the DON intake, the estimates were quite low for both conventional and organic beer consumers when the provisional maximum TDI (PMTDI) of 1 µg kg−1bw was considered. Average consumption of organic beer led to daily intakes of 0.05 and 0.04 µg DON kg−1 bw in 2003 and 2004, respectively, whilst for conventional beer, daily intakes were 0.07 and 0.05 µg DON kg−1 bw. At the 97.5th percentile level of beer consumption, daily intakes of 0.15 and 0.13 µg kg−1 bw were obtained for organic beers against 0.23 and 0.17 µg kg−1 bw for conventional ones. The results showed that beer could be an important contributor to OTA exposure in Belgium, even though a declining trend seems to be apparent during the last year of monitoring. Therefore, efforts should be devoted to maintain the OTA levels as low as reasonably achievable, especially for organic beer.

A database has been compiled with the levels of important contaminants (mycotoxins, heavy metals and pesticides) measured from 2002 to 2005 in winter wheat (Triticum aestivum) grown in Belgium according to the organic and conventional farming systems. Assuming no further change in contaminant levels during cereal processing and during the preparation of foodstuffs, conservative intakes are estimated for the consumers of cereal-based products such as flour, bread, breakfast cereals, dough and pastry. The results show that for the consumer of organic foodstuffs, estimated daily intakes are 0.56 µg deoxynivalenol (DON), 0.03 µg zearalenone (ZEA), 0.19 µg Cd, 0.28 µg Pb and 0.0006 µg Hg kg−1body weight, taking into account the average contaminant levels in unprocessed grains and the average cereal products consumptions in Belgium. For the consumers of conventional foodstuffs, the corresponding estimated daily intakes are 0.99 µg DON, 0.06 µg ZEA, 0.17 µg Cd, 0.12 µg Pb and 0.0007 µg Hg kg−1body weight. In addition, it appears that for the consumers of conventional products, intakes of some post-harvest insecticides have to be taken into account (0.11 µg chlorpyriphos-methyl, 0.2 µg dichlorvos and 0.24 µg pirimiphos-methyl kg−1bw). When expressed as a percentage of the tolerable/acceptable daily intake (TDI/ADI), it seems that the corresponding estimated (conservative) intakes are the highest for DON (56% for organic and 99% for conventional cereal products), ZEA (16% for organic and 32% for conventional cereal products), and Cd (19% for organic and 17% for conventional cereal products), all other estimated intakes of contaminants (including pesticides) being lower than 10% of the TDI/ADI.

The influence of the solvent on the morphology and performance of polymer solar cells is investigated in devices based on blends of the polyfluorene copolymer, poly(2,7‐(9,9‐dioctyl‐fluorene)‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)), and [6,6]‐phenyl‐C61‐butyric acid methyl ester. The blends are spin‐coated from chloroform or from chloroform mixed with small amounts of xylene, toluene, or chlorobenzene. The devices are characterized under monochromatic light and solar illumination AM1.5 (AM: air mass). An enhancement of the photocurrent density is observed in diodes made from chloroform mixed with chlorobenzene, and reduced photocurrent density is observed in diodes made from chloroform mixed with xylene or toluene, compared to diodes made from neat chloroform. The open‐circuit voltages are almost the same in all diodes. The surfaces of the active layers are imaged using atomic force microscopy. Height images indicate that a finer and more uniform distribution of domains corresponds to the diodes with enhanced photocurrent that are made from chloroform mixed with chlorobenzene, while a structure with larger domains is associated with the lower photocurrents in the diodes made from chloroform mixed with xylene or toluene. The influence of the morphology on the excited‐state dynamics and charge generation is investigated using time‐resolved spectroscopy. Fast formation of bound charge pairs followed by their conversion into free charge carriers is resolved, and excitation‐intensity‐dependent non‐geminate recombination of free charges is observed. A significant enhancement in free‐charge‐carrier generation is observed on introducing chlorobenzene into chloroform. Imaging photocurrent generation from the solar cells with a light‐pulse technique shows an inhomogeneous photocurrent distribution, which is related to the undulations in the thickness of the active layer. Thicker parts of the diodes yield higher photocurrent values.

Novel surface-functionalized metal oxo clusters were obtained using an in situ surface-modification method based on the sol−gel process. A reaction of 2-bromoisobutyric acid with Zr(OPr)4 or Ti(OⁱPr)4 resulted in the compounds Zr5O4(BrC(CH3)2COO)10(OⁿPr)2(ⁿPrOH)4 and Ti6O4(BrC(CH3)2COO)8(OⁱPr)8. The reaction of 2-bromopropionic acid with VO(OⁱPr)3 resulted in the cluster V3O3(BrC(CH3)COO)6(HOⁱPr). All obtained compounds have in common that the organic functionalities are exclusively located on the surface of the well-defined sub-nanometer metal oxo clusters. The prepared compounds were successfully used as macroinitiators in atom transfer radical polymerizations (ATRP) and produced inorganic−organic core−shell nanoparticles.

Abstract: Charge injection into an organic semiconductor can be improved by using a self-assembled monolayer of functionalized molecules grafted on the electrode. This new interface can be designed in order to reduce the Schottky barrier between the conductive electrode and the organic semiconductor. The polarizability of the molecules involved can also be chosen in order to increase the adhesion of the molecular semiconductor onto the electrode. We present Kelvin Probe experiments and saturated photovoltage measurements performed on a number of such derivatized electrodes. They permit a quantitative description of the potential shifts due to the self-assembled monolayers which are related to the electrical dipoles of the individual molecules constituting them. When conjugated sites contributing to the band states of the organic semiconductor are placed too close to the electrode in the negative part of the image-force potential, two new effects unfavorable to charge injection can appear. We demonstrate that it is convenient to separate the attachment group of the molecule from the conjugated core by a spacer of non-conjugated sites in order to reduce these undesirable effects.

The Fermi energy of spin-coated layers of pyridinium porphyrins on indium tin oxide (ITO) was determined by the Kelvin probe technique. The work function of zinc tetrakis(N-methyl-4-pyridinium)porphyrin (ZnTMPyP) was found to be 500 meV larger than the one of metal-free tetrakis(N-methyl-4-pyridinium)porphyrin (H2TMPyP), which indicates that the Fermi levels ascribed to these molecular layers do not lie in the middle of their energy gap but that the layers show a p-type and an n-type character, respectively. Furthermore, from the dependence of the work function on the layer thickness, we deduce that an electric field is present near the porphyrin/ITO interface. This field extends over 10−20 nm and is oriented such that the porphyrin layers are depleted from majority mobile carriers near the ITO interface. However, this field does not contribute significantly to the photovoltage, which indicates a high density of interface traps at the ITO interface. Surface photovoltage measurements under illumination of the porphyrin molecules indicate that an additional depletion region is present at the porphyrin/air interface. We therefore suggest for the porphyrin/ITO system a double junction model. This double junction was simulated numerically and values for the surface charge density and the interface charge density were extracted.