Intracavity folding of a perylene dye affords a high-affinity complex with cucurbit[8]uril.

A fluorescent perylene dye with two aromatic units was designed for binding to cucurbit[8] uril. The binding affinity of the complexes increased about 3 orders of magnitude compared to the dye without a secondary aromatic unit. The high affinity allows the complexes to act as fluorescent probes for detection of strong binding guests with nanomolar sensitivity.