Modulating charge transfer through cyclic D,L-alpha-peptide self-assembly.

We describe a concise, solid support-based synthetic method for the preparation of cyclic d,l-alpha-peptides bearing 1,4,5,8-naphthalenetetracarboxylic acid diimide (NDI) side chains. Studies of the structural and photoluminescence properties of these molecules in solution show that the hydrogen bond-directed self-assembly of the cyclic d,l-alpha-peptide backbone promotes intermolecular NDI excimer formation. The efficiency of NDI charge transfer in the resulting supramolecular assemblies is shown to depend on the length of the linker between the NDI and the peptide backbone, the distal NDI substituent, and the number of NDIs incorporated in a given structure. The design rationale and synthetic strategies described here should provide a basic blueprint for a series of self-assembling cyclic d,l-alpha-peptide nanotubes with interesting optical and electronic properties.