Photoresponsive Molecules and Materials - Controlling Chemistry and Biochemistry, Sensing and Imaging

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This proposal describes how molecular and nanomaterials that respond to light and subsequently perform important functions ‘on-command' will be developed. The projects use light to reversibly change molecular structure and consequently optical, electronic and mechanical properties of molecules or materials. Project examples include (1) controlling chemical and biochemical reactivity, (2) modifying the performance of polymeric materials, (3) detecting the presence of analytes or changes in the environment, (4) controlling optical imaging, and (5) providing novel means to release molecules from the surface of designer nanoparticles. Application areas that will be potentially impacted include catalysis and chemical processing, self-healing polymers, drug-delivery, bio-imaging, and detection and tracking.******Reversible control over structure-function relationships is the central theme and can be accomplished by using ‘molecular switches' – molecules that respond to different types of light by reversibly changing their structures in a predictable manner. The emphasis in molecular photoswitching has been on systems that can be used to control optoelectronic properties (absorption, emission, refractive index). A much less developed use for molecular photoswitches is how they can regulate chemical and biochemical reactivity, which is surprising considering the impact that this development would have on chemical synthesis, sensing and surveillance, polymers, and biochemistry.******This proposal describes how diarylethene and spiropyran architectures change their shape when stimulated with light. Because the shape of a molecule dictates how it reacts or interacts with others, the systems developed in the program will be examined for their ability to catalyze industrially relevant reactions, effect polymer mechanics, inhibit enzymes, act as delivery vehicles and detectors, and regulate on-off imaging.******The delivery of light is also an important aspect of the program and new methods to generate the light needed to trigger organic reactions will be utilized. Designer nanoparticles that can be surface decorated with organic photoresponsive molecules will be central to the success of this aspect. We will take advantage of metal nanoparticles that absorb low-energy light and convert it into heat, which can be used to drive chemical reactions. Because the heat is localized to the surface of the nanoparticles, highly selective reactions can be induced without damaging the environment. This is especially important in cellular systems because it overcomes the problem of using highly damaging UV light in sensitive environments in order to carry out important chemical reactions, by using ‘remote-control' methods.