First-generation dendritic polysilanes

Dendritic molecules have been constructed with only silicon-silicon linkages. Crystal structures have been obtained for three such molecules in which the core silicon is bonded to three silicons and each polysilyl wing branches once (one dendrimer generation). The three crystal structures differ in the number of spacer silicons between the core and the branch-point silicons and in the level of branching, which can be either 2-fold or 3-fold. Solution and mass spectral evidence was found for a fourth first-generation dendrimer. Despite having no all-anti pathway, these dendrimers show long-wavelength ultraviolet absorption. Because of the multiplicity of polysilane pathways, the ultraviolet absorption is intense, in one case 1 order of magnitude higher than for a comparable linear polysilane. The dendrimers are nonfluorescent at room temperature. The crystal structures provide quantitative data on numerous tetrasilane fragments, whose conformations fall into three families: gauche with dihedral angles in the range 30-64 degrees, orthogonal with dihedral angles in the range 80-106 degrees, and anti with dihedral angles in the range 131-177 degrees.