Photocontrolled Molecular Recognition for Materials Applications

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The proposal describes the development of new molecules that interact with each other in a reversible manner to form "smart" materials that react to the application of external stimuli by changing their physical properties in useful ways. The long term goals of our research in this area are; 1) the creation of particular polymer (plastics, rubbers) materials properties through rational changes to the underlying molecular designs that compose them, 2) the use of particular stimuli to control the materials properties in defined ways - specifically in this proposal we intend to use light and heat to reversibly induce changes (e.g. switching from a solid to viscous liquid and back again) in the properties of the materials we make, 3) developing ways to achieve 1) and 2) both simply and inexpensively.These long term goals are addressed in this proposal through the planned development of hydrogen bond arrays that use the underlying skeleton of a class of known bis(heteroaryl)azo dyes in a unique way. We have found that these dyes form reversible complexes with new complementary molecules we have designed in a manner analogous to sequence-specific pairing of the nucleobases in the DNA double helix. Subjecting these systems to irradiation with UV light induces a change in the topology of the bis(heteroaryl)azo dyes and renders them less able (or unable) to interact with their complementary partners. This change in their arrangement causes the two molecules to dissociate and will ultimately alter the cohesion of any material that they are responsible, largely or in part, for holding together. We plan on using this phenomenon to create new polymer materials that exhibit properties such as: 1) Phototunable stiffness/elasticity/processability, 2) Photocontrollable self-healing ability. The proposed research is anticipated to add significantly to the catalogue of methods that may be used to control the properties of materials such as plastics and rubbers. The research outlined here will also aid in training chemists in a wide range of skills useful in both academic and industrial careers.