A Visual Demonstration of Supramolecular Chemistry: Observable Fluorescence Enhancement upon Guest-Host Inclusion

Supramolecular chemistry, or "chemistry beyond the molecule", is an increasingly important area of modern chemical research. It deals with highly organized structures involving two or more individual molecules held together by intermolecular forces. Supramolecular host-guest inclusion complexes refer to structures in which a smaller "guest" molecule is held within the internal cavity of a larger "host" molecule. Supramolecular systems have widespread practical applications to various areas of chemistry, including catalysis, molecular sensors and chemical separations. In this article, we describe a simple yet striking demonstration of supramolecular host-guest inclusion and fluorescence based on the extraordinarily large observed fluorescence enhancement of the probe ANS by a modified ß-cyclodextrin. The fluorescence enhancement is readily observable by the naked eye. This demonstration is appropriate for an advanced organic or physical chemistry class and requires only a simple hand-held UV lamp as the excitation source.