The sensitizing properties of cyanine dyes in dye-sensitized nanocrystalline TiO2 solar cells are shown to be controlled by the character of the carboxyl functions used to attach the molecules to the surface. These tether functions affect the degree of aggregation of the subject cyanine dyes attached to TiO2 as well as the short circuit photocurrents they produce in these solar cells. Use of two carbons, acetic acid linkages, on the dye results in performance in a sensitized solar cell comparable with a control ruthenium complex, in contrast to the greatly diminished performance of dyes with longer, methylbenzoic acid linkages.