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Acceleration and Stabilization of Electron Transfer Products with Improved Quantum Yields upon Cation Binding to a Fused Bis-Zinc Porphyrin-Quinone Donor–Acceptor Conjugate

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journal contribution
posted on 28.08.2019, 21:44 by Michael B. Thomas, Yi Hu, Wenqian Shan, Karl M. Kadish, Hong Wang, Francis D’Souza
The role of metal ions in promoting electron transfer processes in biological coenzymes is of great significance not only to understand their mechanistic details but also due to their direct utilization in a number of chemical and biochemical processes. Here, we demonstrate an increased rate of forward electron transfer with improved reaction quantum yield and an enhanced lifetime of electron transfer products upon cation binding to the acceptor entity in a donor–acceptor conjugate. Selective binding of cations such as Mg2+ or Sc3+ to the electron acceptor, quinone, in a fused, bis-zinc porphyrin-quinone donor–acceptor conjugate leads to facile reduction of the quinone making the electron transfer process thermodynamically highly feasible. Furthermore, the binding of metal ions to the electron transfer product, quinone anion, decelerates the reverse electron transfer process due to ion-pairing interactions, resulting in improving both the lifetime and quantum yields of the electron transfer products. Systematic studies including spectral, electrochemical, computational, spectroelectrochemical, and transient absorption techniques, coupled with data analysis by Global Target Analysis are performed to demonstrate these novel findings that are relevant to further our understanding of electron transfer processes occurring in biological coenzymes and pertinent energy harvesting schemes.