Extended pi-conjugated dendrimers based on truxene.

The largest pi-conjugated dendrimers containing up to nine 10,15-dihydro-5H-diindeno[1,2-alpha;1',2';-c]fluorene (truxene) moieties have been prepared with good yields by repetitive Friedel-Crafts acetylation and acid-promoted cyclotrimerization reactions. An alternative approach to the convergent synthesis of desired dendrimers has been developed, in which the core is generated "in-situ" by acid-promoted cyclotrimerizations of aryl methyl ketones. This proves valuable to afford large-size and precisely well-defined dendrimers in an accelerated dendrimer-growth strategy utilizing enlarged repeat units. The increasing amount of SiCl4 dramatically improves the yield of cyclotrimerization reactions. The introduction of hexahexyl groups onto C-5, C-10, C-15 positions of the truxene moiety greatly enhances the solubility of our compounds. Further investigation indicates that the torsion angle between the truxene segment and the benzene ring might play a key role in determining the photo properties of pi-conjugated dendrimers.