RUI: New Porphyrinoid Architectures with Extended Conjugation Pathways

With support from the Chemical Synthesis program of the NSF Division of Chemistry, Professor Timothy Lash of Illinois State University is exploring the synthesis, characterization, and reactivity of compounds that resemble naturally occurring porphyrins. Metalated porphyrins are widespread in nature, e.g. hemes, and play crucial roles in photosynthesis and oxygen transport. Porphyrins also have numerous applications in a number of diverse areas, including materials science, catalysis, and medicine. Porphyrins have 4 nitrogen atoms within a central cavity that allow the structure to bind metal ions. However, an important class of related compounds, called carbaporphyrins, have a carbon atom in place of one of these nitrogens. Carbaporphyrins have modified properties that often complement those of naturally occurring porphyrins. The supported work is leading to the development of efficient routes to novel carbaporphyrins and related porphyrin-like systems that have unique reactivity and unusual properties. The results are increasing our understanding of fundamental chemistry concepts such as aromaticity, a fundamental property of molecules that leads to enhanced stability. Furthermore, structures of this type act as ligands to form stable complexes with important catalytic metals such as palladium and rhodium. Professor Lash and his students are studying applications of these metalloporphyrins in the preparation of fine chemicals. In addition, related such complexes are being explored for use as photosensitizers in photodynamic therapy. These projects are not only providing an excellent environment for training undergraduates and Masters level graduate students for careers in science, technology, engineering, and mathematics (STEM) but are also exposing these students to the multidisciplinary nature of modern scientific research. In this research, new synthetic routes to porphyrin-like systems are being developed, including methodology that makes use of cyclopropane dialdehydes. Applications of the “3 + 1” variant of the MacDonald reaction will provide structures having extended conjugation with alternative properties. For instance, porphyrin-like structures with fused aromatic rings, including phenanthrene, pyrene and acenaphthylene, will extend the platform and are expected to substantially alter the properties of these systems. Other examples of unique porphyrins include carboporphyrins hydroxyporphyrinoids, and tripyrrolic porphyrins. All these molecules have unique conjugation pathways and, as a result, interesting properties. The strategy to synthesize these substrates should be applicable to virtually all fused aromatic ring systems. These investigations are quite fundamental, providing access to important new porphyrinoid systems, and thus have the potential for major impact on the field of porphyrin chemistry. 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.