Photoexcited Rylenediimide Radical Anions and Dianions for the Photoreduction of Carbon Dioxide Reduction CatalystsPublic
The development and use of organic anionic chromophores that absorb the entire visible spectrum & into the near-infrared region while providing highly reducing equivalents is pinnacle for artificial photosynthesis. This dissertation investigates the rational design of new donor-acceptor systems for artificial photosynthesis that couple naphthalene diimide (NDI)/perylene diimide (PDI) radical anions to rhenium(I)/manganese(I) tris carbonyl diimine catalysts and the parameters at play that govern photoinduced electron transfer. The synthesis of these new donor-acceptors that incorporate organic radical anions and their characterization via electrochemical and ultrafast spectroscopy grants new insights into the charge-separated species formed upon excitation and their capabilities for reducing thermodynamically difficult substrates. Most notably, photoreduction of carbon dioxide (CO2) catalysts and the fundamental photoinduced electron transfer events for solar fuel production. In this work, the first artificial photosynthetic system that incorporates NDI•− and PDI•− with an organometallic acceptor is explored. Femtosecond and nanosecond transient absorption spectroscopy were utilized to monitor the entire photoreduction process when NDI•− or PDI•− is attached to the bipyridine on Re(bpy)(CO)3X or Mn(bpy)(CO)3X. Femtosecond visible pump mid-infrared probe spectroscopy allowed for direct observation of Re(bpy•−)(CO)3X or Mn(bpy•−)(CO)3X upon electron transfer from the photoexcited organic radical chromophore. The extension of the distance between NDI•− and Re(bpy)(CO)3X by incorporating the intermediate acceptor diphenyl anthracene (DPA) proved fruitful in maintaining a high quantum yield of forward electron transfer while extending the lifetime of the charge separated species generated. In Mn(bpy)(CO)3X, simply by attaching the NDI•− chromophore at the 6-position of bipyridine with no intermediate acceptor lead to nanosecond charge separated species and the formation of Mn(0)(bpy)(CO)3.
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