Structural Effects on Guest Binding in Cucurbit[8]uril-Perylenemonoimide Host-Guest Complexes

A series of water-soluble fluorescent perylene dyes (perylene-monoimides PMI1, PMI2, and PMI3) with two aromatic binding units (a perylene-core and a phenyl group) as guest molecules for binding with cucurbit[8]uril (CB8) were synthesized. The guest structure was varied by modifying the phenyl group and the spacer between the two binding units. Differences in binding, self-assembly, and optical properties of the corresponding host-guest complexes were observed. At low micromolar concentrations, a highly emissive 1:1 CB8.PMI1 complex with high binding affinity (K-a = 1.5 x 10(7) M-1) was formed in water. Interestingly, at higher concentrations of the CB8.PMI1 complex (e.g., > 10(-4) M), non-emissive self-assembled nanowires were formed. In comparison, the binding affinity of CB8.PMI2 and CB8.PMI3 was determined to be only 5.0 x 10(5) M-1 and 1.7 x 10(4) M-1, respectively. The host-guest complexes with various binding affinities could serve as fluorescent displacement probes for the detection of a range of CB8-binding guest analytes.