A variety of perylenetetracarboxy-3,4:9,10-diimide derivatives have been synthesized. Particular attention was paid to substituents in positions 1, 6, 7 or 12. The energy differences between the frontier orbitals have been determined using optical spectroscopy (UV and fluorescence). The energy of the lowest unoccupied orbitals (LUMOs) were obtained by cyclic voltammetry. From both studies, the energies of the highest occupied orbitals (HOMOs) were also been calculated. A Hammett-type relationship was observed for the reduction potentials (E red1 1/2 ) when correlated with the s À ortho parameter. The energies of the frontier orbitals define the domains of application of these compounds. They significantly depend on the substitution in positions 1, 6, 7, or 12.

By using the Suzuki–Miyaura reaction, a variety of 1,7‐ and 1,12‐disubstituted and 1,6,7,12‐tetraaryl‐substituted perylenetetracarbox‐3,4:9,10‐diimides have been synthesised starting from the corresponding halogen derivatives. Until now, the 1,12‐ and 1,6,7,12‐sustitutions were difficult to access and only single examples have been reported. Dehydrohalogenation was observed to be competitive with the Suzuki–Miyaura reaction. The extent of this side reaction depends on the substitution pattern of the perylene diimide core and on the nature of the boronic acid derivative. Photochemical pericyclisation also reduces the yield of the desired products. A mechanistic analysis has been performed on the special case of 1,12‐diphenylperylenediimides, in which benzene is eliminated as a consecutive process of such a reaction. The energies of the frontier orbitals were determined. By using cyclic voltammetry, the energy of the LUMO was measured, and the energy gap between the frontier orbitals was determined based on optical spectroscopy (UV and fluorescence). With these two parameters, the energies of the HOMO were determined. The 1,6,7,12‐tetraaryl‐ and 1,12‐diarylperylenediimides have been optically resolved by using HPLC with a chiral stationary phase. Determination of absolute configuration was carried out by recording circular dichroism (CD) spectra of the enantiomers.

A scanning surface potential measurement technique suited for thin-film devices operating under high voltages is reported. A commercial atomic force microscope has been customized to enable a feedback-controlled and secure surface potential measurement based on phase-shift detection under ambient conditions. Measurements of the local potential profile along the channel of bottom-gate organic thin-film transistors (TFTs) are shown to be useful to disentangle the contributions from the channel and contacts to the device performance. Intrinsic contact current-voltage characteristics have been measured on bottom-gate, top-contact (staggered) TFTs based on the small-molecule semiconductor dinaphtho[2,3-b:2 0 ,3-f]thieno[3,2-b]thiophene (DNTT) and on bottom-gate, bottomcontact (coplanar) TFTs based on the semiconducting polymer polytriarylamine (PTAA). Injection has been found to be linear in the staggered DNTT TFTs and nonlinear in the coplanar PTAA TFTs. In both types of TFT, the injection efficiency has been found to improve with increasing gate bias in the accumulation regime. Contact resistances as low as 130 X cm have been measured in the DNTT TFTs. A method that eliminates the influence of bias-stress-induced threshold-voltage shifts when measuring the local charge-carrier mobility in the channel is also introduced, and intrinsic channel mobilities of 1.5 cm 2 V À1 s À1 and 1.1 Â 10 À3 cm 2 V À1 s À1 have been determined for DNTT and PTAA. In both semiconductors, the mobility has been found to be constant with respect to the gate bias. Despite its simplicity, the Kelvin probe force microscopy method reported here provides robust and accurate surface potential measurements on thin-film devices under operation and thus paves the way towards more extensive studies of particular interest in emerging fields of solid-state electronics. V

Current-voltage and Kelvin probe force microscopy (KPFM) measurements were performed on single ZnO nanowires. Measurements are shown to be strongly correlated with the contact behavior, either Ohmic or diode-like. The ZnO nanowires were obtained by metallo-organic chemical vapor deposition (MOCVD) and contacted using electronic-beam lithography. Depending on the contact geometry, good quality Ohmic contacts (linear I-V behavior) or non-linear (diode-like) contacts were obtained. Current-voltage and KPFM measurements on both types of contacted ZnO nanowires were performed in order to investigate their behavior. A clear correlation could be established between the I-V curve, the electrical potential profile along the device and the nanowire geometry. Some arguments supporting this behavior are given based on technological issues and on depletion region extension. This work will help to better understand the electrical behavior of Ohmic contacts on single ZnO nanowires, for future applications in nanoscale field-effect transistors and nano-photodetectors.

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