Friday, November 22, 2024
11/22/2024
Project Summary Photoredox reactions offer unique opportunities to develop synthetic routes for new drug discoveries that are otherwise unattainable via C-C bond formation through sp3 C-H and C-X (X = halogen) activations. However, current methodologies that employ metallic (such as ruthenium and iridium) complexes or explicit organic photosensitizer (PS) entail two critical challenges relevant to the implementation of atom-economic stereoselectivity (critical for biomedical activity) and easy separability and recyclability (required for large-scale syntheses). Heterogeneous photocatalysts with enzyme-like selectivity are required but remained elusive –mainly due to diffusion-related challenges where, unlike thermally activated transformations, the reactants, substrates, and chirality-inducing groups need to come close within a short (typically nano-to- microsecond) timescale. We propose to address the incumbent challenges with porous crystalline molecular frameworks as a photosensitizer to drive selective catalysis within their well-defined pore cavities. The diffusion-related challenge and relevant photophysical requirements are addressed within certain crystalline metal–organic frameworks (MOFs) where tens of photoactive linkers serve as light-harvesting antennas. The photoexcited energy transfer (also treated as molecular exciton migration), along the preferred direction of the molecular diffusion, can be tuned and primed. Efficient preferential exciton mobility can leverage the need for PS diffusion required to excite the substrates. Therefore, this AREA proposal will pioneer novel MOF compositions that: (i) control optoelectronic properties as a function of framework structure critically required for heterogeneous photoredox catalysis, (ii) elucidate the generality of the MOF photocatalytic reaction and products accessibility, and (iii) unveil the critical microenvironment needed for stereoselective transformations. Endowed with molecular-scale porosity and tunability, MOFs provide scalable, well-defined, modular heterogeneous platforms for fundamental photochemical developments. The methods, combining molecular assemblies to harvest light driving photochemical transformations within its confined, yet selective porous cavity, will provide transferrable and potentially transformative fundamental knowledge for developing recyclable and selective heterogeneous photocatalysts for the discovery of life-saving drugs.
HHS’ Tracking Accountability in Government Grants System (TAGGS) website provides access to detailed descriptions of grants, loans, aggregated direct payments and other types of financial assistance awarded by the HHS Operating Divisions (OPDIVs) and the Office of the Secretary Staff Divisions (STAFFDIVs).
