Dyes and their adsorption onto nanocrystalline TiO2 electrodes : Synthesis, characterisation and applications

Abstract: The syntheses of two type of dyes (phthalocyanine and ruthenium tris-bipyridyl) are presented here. Their characterisation involves the use of cyclic voltammetry, NMR- and UV-visible spectroscopy. Once adsorbed on nanocrystalline TiO2 electrodes, their electrochemical, spectroelectrochemical and photoelectrochemical properties were investigated.In the first part, the syntheses of aryl-substituted phthalocyanines are described. The key intermediate, an aryl-substituted phthalonitrile, was prepared by a Pd(0)-catalysed Stille-coupling. The physical properties of tetra-(2,5-dirnetoxyphenyl)phthalocyanine (1a), tetraphenylphthalocyanine (1b) are discussed, An interesting display behaviour was characterised by spectroelectrochemistry in the case of 1b. Considering the system, unexpectedly high efficiencies of the resulting solar cells are observed for both dyes.The second part deals with two types of ruthenium tris-bipyridyl complexes. Syntheses of three carboxylated heteroleptic ruthenium complexes [Ru(bpy)2(bpy-R)](PF6)2 (bpy-R, R= (COOLi)n, n= 1, 2, 4) were synthesised for a study of the influence of the number of carboxylic groups on solar cell efficiencies. A lateral electron transfer mechanism for the dyes adsorbed on TiO2, is observed. Homoleptic and heteroleptic ruthenium complexes possessing the polymerisable groups vinyl, methoxyphenyl or thiophene were prepared for an investigation of the substituent effect on the dye-monolayer in the solar cell, both by electrochemistry and absorption spectroscopy. The methoxyphenyl-substituted complexes showed good polymerisation behaviour both at negative and at positive potentials. They also showed good resistance towards water when adsorbed onto TiO2 electrodes.

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