Photochromism and Electrochemistry of a Dithienylcyclopentene Electroactive Polymer

A bifunctional substituted dithienylcyclopentene photochromic switch bearing electropolymerisable methoxystyryl units, which enable immobilization of the photochromic unit on conducting substrates, is reported. The spectroscopic, electrochemical, and photochemical properties of a monomer in solution are compared with those of the polymer formed through oxidative electropolymerization. The electroactive polymer films prepared on gold, platinum, glassy carbon, and indium titanium oxide (ITO) electrodes were characterized by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The thickness of the films formed is found to be limited to several monolayer equivalents. The photochromic properties and stability of the polymer films have been investigated by UV/vis spectroscopy, electrochemistry, and XPS. Although the films are electrochemically and photochemically stable, their mechanical stability with respect to adhesion to the electrode was found to be sensitive to both the solvent and the electrode material employed, with more apolar solvents, glassy carbon, and ITO electrodes providing good adhesion of the polymer film. The polymer film is formed consistently as a thin film and can be switched both optically and electrochemically between the open and closed state of the photochromic dithienylethene moiety.

Electrochemical and photoelectrochemical investigation of new carboxylatobipyridine(bis-bipyridine)ruthenium(II) complexes for dye-sensitized TiO2 electrodes

Methods for the prepn. and purifn. of new carboxylated 2,2'-bipyridine ligands, two of which contain the new anchoring functionality malonate, and a reliable method for the synthesis of the corresponding [Ru(bpy)2(L)](PF6)2 complexes are described. Their suitability for fundamental studies of the processes in wet solar cell applications has been investigated. All complexes show stable voltammograms in acetonitrile soln. and although the complexes were obtained as lithium carboxylate salts, they were sol. in non-polar org. solvents such as dichloromethane, which allowed for good reproducibility in the dye-coating step.The electrochem. and photoelectrochem. properties of dye-TiO2 systems are discussed. The photoelectrochem. properties in monochromatic and white light are related to the attaching group that is varied in the series of complexes: A formally non-conjugated malonate group as anchoring group generally gives similar results to that of a conjugated carboxylic group, the second carboxylate compensating the absence of conjugation. Also, the complexes with malonate as attaching group are more efficient than a complex with a non-conjugated carboxylic group, esp. in the red part of the action spectrum.The redox behavior of the adsorbed complexes is reversible at neg. potentials and quasi-reversible at pos. potentials. The latter feature is esp. interesting since it is possible to electrochem. oxidize the surface-attached ruthenium complexes even at potentials in the mid-bandgap region of the metal oxide film

Modification of electron transfer properties in photoelectrochemical solar cells by substituting Ru(terpy)(2)(2+) dyes with thiophene

A comparison of the properties of the 2-thienyl-substituted carboxyphenyl Ru-II(terpy)(2) dyes with their non-substituted analogues has enabled us to gain insight into the electronic properties that are prerequisite for efficient electron injection into the TiO2 conduction band in photoelectrochemical solar cells. Introducing the thienyl group has a profound effect upon the efficiency of photoinduced electron injection. This effect can be explained by a significant shift in the LUMO position from the terpy ligand anchored on the TiO2 surface towards the 2-thienyl substituted ligand, which is shown by means of electrochemistry and semi-empirical calculations. (C) 2003 Elsevier B.V. All rights reserved