SUBSTRATE-INDUCED PHOSPHORESCENCE FROM CYCLODEXTRIN-CENTER-DOT-LUMOPHORE HOST-GUEST COMPLEXES

Hydrogen bonding substrates (S) trigger bright phosphorescence upon th eir addition to aqueous solutions containing 1-bromonaphthalene (1-BrN p) and a glucosyl modified cyclodextrin (G beta-CC). Steady-state and time-resolved luminescence measurements establish that the phosphoresc ence arises from 1-BrNp as part of a 1-BrNp-G beta-CD S complex. In al l cases, the substrate comprises a bulky t-butyl or cyclohexyl group s paced from the functional group of an alcohol, amine, carboxylic acid, ester, or aldehyde. Association constants, molecular models, and subs trate binding studies are consistent with the substrate hydrogen bondi ng to the rim of the CD cup, with its aliphatic end flipped over the h ydrophobic interior of the CD. The phosphorescence enhancement induced by substrate is related to its effectiveness in shielding photoexcite d 1-BrNp from quenching by oxygen. The enhancements can be extremely l arge, approaching a 10(5) increase in intensity, depending on the fit of the substrate to the top of the CD. We have explored the topologica l features of the substrate that lead to the best shielding and hence greatest triggered luminescence response.