Oligopyrrole Macrocycles: Synthesis, Electronic Structure, Switching, and Communication

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Professor Jonathan L. Sessler and his team at The University of Texas at Austin supported by this award are exploring new analogues of the pigments that make blood red, vitamin B12 purple, and grass green. Also targeted for study are the principles of chemical communication that biology uses to transmit signals over short distances and long as exemplified, for instance, by neuroregulators and skunk sprays, respectively. By using small molecules to trigger downstream chemical events it could become possible to probe the complexity of biology within the chemical laboratory. With such long-term goals in mind, new molecules have been designed that are expected to advance our understanding of how molecular structure affects key properties, such as color, stability, and an ability to interact with other chemical entities. This is expected, in term, to lead to the development of new molecular systems that can be used to create information storage arrays or being used in the context of new medical modalities, such as photodynamic therapy, where light is used to treat diseases. This project involves work that spans the gamut of chemistry sub-areas. It is thus expected to enhance coworker training and provide a technically savvy workforce. It also should also provide an opportunity for young researchers to develop the skills needed to pursue academic or non-academic research-related careers.In terms of specifics, this project focuses on two classes of oligopyrrole macrocycles that have benefited from prior NSF support, namely expanded porphyrins and calixpyrroles. These molecules, alone and in concert, are being used to pursue the following specific aims, which involve respectively: 1) The preparation of new two- and three-dimensional expanded porphyrins. These systems allow explorations of the effects of oxidation, reduction, and donor-acceptor interactions on both ground and excited state (anti)aromaticity. They also allow determinations of which design features control localized vs. delocalized aromaticity and radical vs. closed shell conjugation pathways and thus advances in basic structure-function understanding as it relates to blood pigment analogues; 2) the synthesis of functionalized calixpyrrole systems that can access multiple discrete states, such as helices, capsules, and discrete monomers. In the context of this aim, off-equilibrium effects are being explored using chiral, non-racemic pyridine-functionalized calixpyrroles and their interactions with metalated expanded porphyrins; 3) further explorations of a previously reported benzotetrathiafulvalene calixpyrrole-TCNQ ensemble, particularly in the context of its ability to release ionic and molecular messengers and mediate various downstream chemical reactions. Combinations of monomeric and capsule-type calixpyrroles with expanded porphyrins, are being explored with a view to creating more complex information transfer systems. In this way, the effect of structure on cascade-like signal transduction in completely synthetic constructs can be assessed. Ultimately, this could lead to systems capable of highly dense information storage or able to perform rudimentary computing functions. This project is expected to be accomplished in four years.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.