Azulenylium and guaiazulenylium cations as novel accepting moieties in extended sesquifulvalene type D-pi-A NLO chromophores

The novel series of monometallic monocations Fc-[n]-Az(+) and Fc-[n]-Guaz() (where Az(+) and Guaz(+) denote azulenylium and guaiazulenylium cations r espectively and n=0-3), and a bimetallic dicationic complex Fc-[0]-Guaz(RuC p)(2+) have been prepared. Single crystal structures of Fc-[0]-Guaz(+) and Fc-[0]-Guaz(RuCp)(2+) have been determined. Analysis of the bond lengths an d angles coupled with the electrochemistry data provides evidence for stron g ground state charge transfer in the series which diminishes upon pi -brid ge extension. The electronic absorption spectra reveal that alkylation of t he cationic terminus (1) diminishes the electron-accepting ability, (2) res ults in a larger dipole moment change upon excitation and (3) causes a smal ler sequential lowering of the CT transitions with pi -bridge extension. Th e NLO properties which were characterised by hyper-Rayleigh scattering tech niques indicate the potential of the azulenylium based donor-acceptor chrom ophores, but also that the extended complexes exhibit two-photon absorption fluorescence.