Synthesis and photoisomerization of fullerene- and oligo(phenylene ethynylene)-azobenzene derivatives

The presence of fullerenes and oligo(phenylene ethynylene)s (OPEs) in azobenzene derivatives have a large effect on the photoisomerization behavior of the molecules. Fullerenes reduce the photoisomerization yield for cis isomers, and the OPEs, when directly attached to the azobenzenes, have a similar yet smaller effect when compared with the fullerenes. While these effects have not been previously considered for fullerene--and OPE-azobenzene derivatives, they were clearly detected in our work using NMR and UV-vis spectroscopy methods. The intramolecular electronic energy transfer between the fullerene and azobenzene moiety was examined in two cases in which separation of the two functional groups was small, as in 1, or large, as in 2. Almost no photoisomerization was observed for 1, while significant photoisomerization was observed for 2, apparently due to the effective isolation and blocking of electronic communication between the two functional groups.