The reaction of the cyanide anion [M(CO)(5)CN](-) (M = Cr or Mo) with metallocenes of Groups 4 and 6 produced polynuclear complexes of the type [CpCp 'M(CO){-NC-M ' (CO)(5)}]BF4 (M = M0, W; M ' = Mo, Cr, Cp '= Cp, Ind), Cp2TiCl{-NC-Mo(CO)(5)} and Cp2Ti{-NC-Mo(CO)(5)}(2). These complexes were characterised by H-1-, C-13- and Mo-95-NMR, IR and UV-vis spectroscopies, elemental analysis and examined by cyclic voltammetry. These methods show that the [M(CO)(5)CN]- ligands shift the electron density towards the metallocene centres. The complex [Cp2W(CO){-NC-Mo(CO)(5)}](+) is additionally examined by single crystal X-ray structure determination. The Density Functional Theory (DFT) calculations with the ADF program were performed on selected compounds to understand the nature of the redox processes taking place. Compared with a nitrile, the coordination of a [M(CO)-,CN]- fragment to the metallocene moiety does not significantly change the geometrical features. but leads to the stabilisation of the HOMO of the latter. with all the oxidation processes occurring in the pentacarbonyl moiety of the binuclear species. Time-dependent DFT calculations were used to identify the band appearing in the visible spectrum of Cp2TiCl{-NC-Mo(CO)(5)} as a Mo to Ti charge transfer. (C) 2001 Elsevier Science BN. All rights reserved.

Seven flavylium salt dyes were employed for the first time as sensitizers for dye-sensitized solar cells (DSSCs). The theoretical and experimental wavelengths of the maximum absorbances, the HOMO and LUMO energy levels, the coefficients, the oscillator strengths and the dipole moments are calculated for these synthetic dyes. The introduction of a donor group in the flavylium molecular structure was investigated. Photophysical and photoelectrochemical measurements showed that some of these synthetic analogues of anthocyanins are very promising for DSSC applications. The best performance was obtained by a DSSC based on the novel compound 7-(N,N-diethylamino)-3',4'-dihydroxyflavylium which produced a 2.15% solar energy-to-electricity conversion efficiency, under AM 1.5 irradiation (100 mW cm(-2)) with a short-circuit current density (J(sc)) of 12.0 mA cm(-2), a fill factor of 0.5 and an open-circuit voltage (V-oc) of 0.355 V; its incident photocurrent efficiency of 51% at the peak of the visible absorption band of the dye is remarkable. Our results demonstrated that the substitution of a hydroxylic group with a diethylamine unit in position 7 of ring A of the flavylium backbone expanded the pi-conjugation in the dye and thus resulted in a higher absorption in the visible region and is advantageous for effective electron injection from the dye into the conduction band of TiO2.