Supramolecular organic photochemistry: incorporating function through molecular design

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Supramolecular organic photochemistry examines the interaction of light with supramolecular assemblies composed of organic molecules. Supramolecular assemblies that undergo light-induced processes are continually being developed to custom-tailor functions in areas such as drug delivery, catalysis, and optoelectronic molecular devices. The functionality achieved by supramolecular assemblies is a consequence of complementary intermolecular interactions that direct their formation and the photochemical properties of the molecular components. We are developing innovative, functional liposomes through the integration of photochromic compounds with elements of lipid complementarity and reversible photocontrols. These photochromic liposomes will undergo reversible changes in membrane permeability that will restore membrane integrity following the release of encapsulated compounds. We will achieve this objective by incorporating photochromes that span the entire lipid bilayer. Thus far, photochromic systems have lacked this aspect of organization, and the extent of their photoinduced release has been small, except when liposome stability is irreversibly compromised. By spanning the bilayer, isomerization will produce permeable channels through which entrapped molecules will diffuse, resulting from changes in photochrome structure. Charged tethers will anchor the disruptive, photochromic units in place until isomerization back to their more complementary form restores the local lipid order. This approach will be developed through the integration of lipid analogues with two photochromic moieties. These dimers will not only produce larger increases in membrane permeability than previous systems, but also restore membrane integrity. In addition, we will develop similar photochromes with improved two-photon absorption to enhance the spatial and temporal selectivity of these liposomes in practical applications such as photoregulated drug delivery where the delivered dosage will be precisely and reversibly controlled with light. This strategy will benefit public health through a reduction in hospitalization time, lead to patentable technologies, and generate an overall savings to Canada's health care system.