Fluorescence investigations of supramolecular systems

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Supramolecular structures consist of two or more molecules held together only by relatively weak intermolecular forces of attraction. One simple example is a host-guest inclusion complex, in which a "guest" molecule becomes included within the cavity of a larger, cage-like "host" molecule, like a ball in a bucket. Such structures can be surprisingly robust, despite the lack of true chemical bonds holding the components together, and have numerous applications. For example, if the host is soluble in water, this can make otherwise insoluble guests soluble. This can allow for improved drug delivery, for example. Such systems can also be useful as molecular sensors, which give some sort of a signal when a target molecule is present. One of the best ways to study such systems is using fluorescence spectroscopy. Fluorescence is the light that certain molecules emit when their electrons are excited (gain excess energy), for example after absorbing light (road signs), or by electricity (fluorescent lights). The fluorescence of the molecular components can undergo significant changes when they form supramolecular sturctures, providing a hihgly sensitive and accurate method for studying their formation, properties, and structures. This proposal involves various ways of using fluorescence to study and characterize supramolecular systems. Our group has done extensive work using fluorescent guests in non-fluorescent hosts. The hosts we have used include molecules which resemble molecular buckets and molecular pumpkins. In this proposal, one of the new areas of interest is the study of fluorescent hosts. This is important, as it allows for the study of any guest of interest, with no requirement for it to be fluroescent. We are proposing the use of such fluorescent hosts as building blocks, which can be joined together using appropriate double-headed guests to give extensive supramolecular structures, like molecular Tinkertoy. Since these structures will be flourescent, they could have a wide range of useful applications, including as fluorescent molecular sensors which turn on or off in the presence of particular substances.