We have synthesized a novel 9,9′-spirobifluorene-cored donor-acceptor (D-A) bichromophore system in which the electron-donating (D) moieties are triphenylamine (TPA) and carbazole (CBZ) groups and the electron-withdrawing (A) moieties are 1,3,4-oxadiazole (OXD) groups. The electron-deficient OXD groups efficiently blocked the radical cations delocalization between the two terminal TPA groups, rendering the electropolymerization of the TPA groups feasible. The resulting polymer could be cross-linked further at higher oxidation potentials through electrodimerization occurring at the C3 and C6 positions of the CBZ group. The polymer film obtained exhibited reversible electrochemical oxidation, accompanied by strong color changes with high coloration efficiency and contrast ratio, which could be switched through potential modulation.

A new dye, SSD1, featuring two donor/acceptor chromophores aligned in a spiro configuration with two anchoring groups separated at a distance of 10.05 A (closely matching the distance between the adsorption sites of the anatase TiO(2) surface) undergoes efficient dye adherence on TiO(2) films. A dye-sensitized solar cell incorporating SSD1 exhibited a short-circuit current of 8.9 mA cm(-2), an open-circuit voltage of 0.63 V, a fill factor of 0.67, and a power conversion efficiency of 3.75%.

This Article describes the synthesis and physical properties of two bipolar starburst monomers: 1,3,5-tris{5-(7-(carbazol-9-yl)-(9,9′-spirobifluoren-2-yl)-1,3,4-oxadiazol-2-yl}benzene (OXD-CBZ) and 1,3,5tris[7-diphenyl-(9,9′-spirobifluorene)-1,3,4-oxadiazoyl]benzene (OXD-DPA) featuring an electron-deficient tris(1,3,4oxadiazole)phenylene ring as an interior core bridged by rigid spirobifluorene units to terminal electroactive carbazole (CBZ) and diphenylamino (DPA) groups. The electronic absorption spectra of OXD-CBZ and OXD-DPA depend only slightly on the solvent polarity, revealing that weak electronic coupling existed between the donor (CBZ and diphenylamino groups) and acceptor (1,3,4-oxadiazole) moieties in the ground state. In contrast, the emission spectra of these starburst bipolar molecules were strongly dependent on the solvent polarity, a phenomenon that we attribute to the polarized excited states generated through intramolecular charge transfer. The starburst monomer OXD-CBZ exhibited a redox gradient, where the peripheral CBZ moieties exhibited lower oxidation potentials than those of the fluorene units in the interior, allowing us to obtain a new electropolymerized macromolecule. The polymer films derived from OXD-CBZ exhibited good conductivity, reversible electrochemical processes, and stable color changes (from transparent to green to light blue) with high coloration efficiency upon electro-oxidation. The radical cations of OXD-CBZ were localized within the CBZ rings; the lack of substituents at the C3 and C6 positions of the CBZ unit led to the effective electrochemical cross-linking process. In contrast, electro-oxidation of OXD-DPA, which was end-capped with DPA groups, produced stable radical cations that did not undergo associated electrochemical reactions. The higher stability of the OXD-DPA radical cations through resonance stabilization with the fluorene ring impeded the progress of typical triphenylamine dimerization reactions.

The known O 2 ( 1