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In this paper, we report on the synthesis of 0-carotenes of variable chain length with between 5 and 23 double bonds (1-7). These oligoenes were prepared by McMurry and Wittig reactions. The tetradecapreno-P-carotene ? would seem to be the longest 0-carotene yet reported. Furthermore, we investigated the electronic properties using cyclic voltammetry and photoelectron spectroscopy (UPS) to generate openshell and closed-shell ions of carotenoids in solution and in the solid state, respectively. With increasing chain length ( 2 11 double bonds), even the generation of tetracations and tetraanions could be observed by cyclic voltammetry. Extending the number of conjugated bonds causes the potentials to converge to limiting values. All electron-transfer processes occur in one-electron steps, which are close to each other in pairs. The potential difference between the first oxidation potential and the first reduction potential is a linear function of the reciprocal chain length. Despite the different techniques used (CV and UPS) and the different condensed phases, there is an excellent correspondence between the energies of the radical cation states generated by the two methods. This shows that the radical cation formation is principally determined by the chain length. The structures of the ion states were investigated using semiempirical methods at the NDDO level. Charge delocalization and bond relaxation are not identical and do not utilize the same number or the same kind of atoms. It can be shown that from the length of 20 double bonds onwards, the effective conjugation length for doubly-charged cations converges slowly to a limiting value.

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Time-dependent extended X-ray absorption fine structure (QEXAFS) measurements using the total external reflection geometry were used for the in situ investigation of the potentiostatic silver oxide formation in 1 M NaOH. It is demonstrated that this EXAFS tool yielding near range order structural information is well suited for time-resolved studies of electrode surfaces under potential control. As examples, the initial growth stages of thin silver(I) oxide layers are presented as well as changes of the near range order of thick Ag 2 O films induced by potentiostatic transients. A comparison of the experimental results with those of model calculations permits the determination of the reaction kinetics of electrochemical phase formation.

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