Combined experimental-theoretical NMR study on 2,5-bis(5-aryl-3-hexylthiophen-2-yl)-thiazolo[5,4-d]thiazole derivatives for printable electronics.

Four 2,5-bis(5-aryl-3-hexylthiophen-2-yl)thiazolo[5,4-d]thiazole derivatives have been synthesized and thoroughly characterized. The extended aromatic core of the molecules was designed to enhance the charge transport characteristics, and solubilizing hexyl side chains were introduced on the thiophene subunits to enable possible integration of these semiconducting small molecules in printable electronics. Complete elucidation of the chemical structures by detailed one-dimensional/two-dimensional NMR spectroscopy is described, providing interesting input for chemical shift prediction software as well, because limited experimental data on these types of compounds are currently available. Furthermore, theoretical calculations have assisted experimental observations--giving support for the chemical shift assignment and providing a springboard for future screening and predictions--demonstrating the benefits of a coordinated theoretical-experimental approach.

Fingerprints for structural defects in poly(thienylene vinylene) (PTV): a joint theoretical-experimental NMR study on model molecules.

In the field of plastic electronics, low band gap conjugated polymers like poly(thienylene vinylene) (PTV) and its derivatives are a promising class of materials that can be obtained with high molecular weight via the so-called dithiocarbamate precursor route. We have performed a joint experimental-theoretical study of the full NMR chemical shift assignment in a series of thiophene-based model compounds, which aims at (i) benchmarking the quantum-chemical calculations against experiments, (ii) identifying the signature of possible structural defects that can appear during the polymerization of PTV's, namely head-to-head and tail-to-tail defects, and (iii) defining a criterion regarding regioregularity.

Study of the attachment of Na+ on glucose and on some of its methylated derivatives.

The mechanism of attachment of Na(+) on glucose, methyl-alpha-D-glucose, methyl-beta-D-glucose, 3-O-methylglucose, tetra-O-methylglucose, and also on galactose and methyl-beta-D-galactose, was studied. For this we measured the ion yields for the complex [sugar-Na(+)] formed by ionisation by matrix-assisted laser desorption/ionisation (MALDI) and ionspray. These data were compared with the relative volatilities and hydrophobicities of the sugars, measured by evaporative light scattering and reversed-phase liquid chromatography, respectively. Some formation enthalpies for the complexes [sugar-Na(+)], starting from the sugar and the cation, were obtained by ab initio calculations. No simple correlations could be observed between the ion yields and the parameters studied, so that the cationisation mechanism of the sugars remains unclear.

Attachment of alkali cations on beta-D-glucopyranose: matrix-assisted laser desorption/ionization time-of-flight studies and ab initio calculations.

In matrix-assisted laser desorption/ionization mass spectrometry, carbohydrates ionize by attachment of an alkali cation, and the ion yield varies with the nature of the cation. In an attempt to contribute to the understanding of the mechanisms involved, we have conducted matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) experiments on the simple glucose molecule with the alkali cations Li+, Na+ and K+, and have also performed ab initio calculations. The calculations show that, for the most stable carbohydrate-cation geometry, the carbohydrate ring is twisted and the cation is coordinated to four oxygen atoms. Calculations also show that in these complexes the positions of the three cations are very similar, and the smaller the cation, the closer it is to the oxygen atoms. Finally, the calculated formation enthalpies of the different complexes agree with the experimental results obtained for the order of stability of these complexes.