The self-assembly mechanism and the associated molecular dynamics are studied for a series of poly-L-lysine-functionalized polyphenylene dendrimer melts as a function of the core size (generation), functionality, and polypeptide length using X-rays, solid-state NMR, calorimetry, and dielectric spectroscopy. A striking dependence of the polyphenylene self-assembly on the poly-L-lysine length is shown. In addition, the type (alpha-helix/beta-sheet) of peptide secondary structure is controlled by the packing restrictions imposed by the polyphenylene core. We show that constrained poly-L-lysines can adopt different secondary structures from their linear analogues. The dynamic investigation revealed significant mobility associated solely with the polypeptide through three processes: a glass transition, a slower process associated with the relaxation of alpha-helical segments, and a glassy mode whose origin could be resolved by site-specific solid-state NMR techniques. Solid-state NMR studies further indicated a mobility gradient in going from the rigid peptide backbone to the side chains.