Enhancing the Properties of Ruthenium Dyes by Dendronization

A family of dendrimers comprising [cis-di(thiocyanato)-({4,4'-dicarboxy}-2,2'-bipyridyl)-(4,4'-divinyl-2,2'-bipyridine)]ruthenium(II) cores, first-generation biphenyl-based dendrons and 2-ethyl-hexyloxy surface groups have been prepared. The dendrimers differ in the number of surface groups attached to the dendrons. The dendrimers were found to be more thermally stable than the corresponding simple complex, [cis-di(thiocyanato)-(bis{4,4'-dicarboxy}-2,2'-bipyridyl)]ruthenium (II) (N3), and to aggregate less in solution, The dendrimers were found to bind to titanium dioxide substrates via the two carboxyl groups oil the bipyridyl unit. Importantly, the dendrimers were found to be significantly less susceptible to desorption. N3 desorbed rapidly from the titanium dioxide substrates while the dendrimers were still mostly adsorbed even after a day under the same conditions. The dendrimers all formed efficient devices with the best having an efficiency of 6.3 +/- 0.1%, which compares favorably to N3 with an efficiency of 6.9 +/- 0.1% in the same device configuration.