The overall efficiencies of the cell dramatically dropped when the donor group was replaced by a ... unit, as in the following dyes 11–13.The use of a ..... unit in 12 instead of a .... in 11 further reduced the cell efficiency, which was explained by aggregation of the dye. The further reduced efficiency in the case of 13 with ..... units was ascribed to possible cis–trans photoisomerization
of the C=C bonds.