Self-assembly dynamics of a cylindrical capsule monitored by fluorescence resonance energy transfer.

The constituent cavitands of a cylindrical capsule were labeled with donor and acceptor fluorophores, and fluorescence resonance energy transfer (FRET) was employed as a tool to study the dynamics of self-assembly. When donor and acceptor dyes are present in the same capsular assembly, they are brought within 25 A of each other, a distance suitable for efficient energy transfer to occur between them. This allowed for the study of interacting species at nanomolar concentrations providing information unattainable from NMR experiments. The kinetic stability of the capsule in the presence of various guest molecules was investigated which revealed a range of more than 4 orders of magnitude in the rates of cylindrical capsule exchange. While the thermodynamic stability of the capsule generally dictates the self-assembly dynamics, it was discovered that longer rigid guests can impart a significant kinetic barrier to monomer exchange.