Substrate Induced Phosphorescence from Cyclodextrin·Lumophore Host-Guest Complexes

Document Type

Article

Publication Date

2-29-1996

Keywords

Cyclodextrin, Hydrogen bonding, Molecular recognition, Optical sensing, Oxygen quenching, Phosphorescence

Abstract

Hydrogen bonding substrates (S) trigger bright phosphorescence upon their addition to aqueous solutions containing 1-bromonaphthalene (1-BrNp) and a glucosyl modified cyclodextrin (Gβ-CD). Steady-state and time-resolved luminescence measurements establish that the phosphorescence arises from 1-BrNp as part of a 1-BrNp·Gβ-CD·S complex. In all cases, the substrate comprises a bulky t-butyl or cyclohexyl group spaced from the functional group of an alcohol, amine, carboxylic acid, ester, or aldehyde. Association constants, molecular models, and substrate binding studies are consistent with the substrate hydrogen bonding to the rim of the CD cup, with its aliphatic end flipped over the hydrophobic interior of the CD. The phosphorescence enhancement induced by substrate is related to its effectiveness in shielding photoexcited 1-BrNp from quenching by oxygen. The enhancements can be extremely large, approaching a 105 increase in intensity, depending on the fit of the substrate to the top of the CD. We have explored the topological features of the substrate that lead to the best shielding and hence greatest triggered luminescence response.

Journal Title

Inorganica Chimica Acta

Volume

243

Issue

1-2

First Page

239

Last Page

248

DOI

10.1016/0020-1693(96)04914-6

First Department

Chemistry and Biochemistry

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