Direct Observation of the Photoreduction Products of Mn(NDI-bpy)(CO)3XCO 2 Reduction Catalysts Using Femtosecond Transient IR Spectroscopy

Martinez, JF ORCID: https://orcid.org/0000-0002-1294-5920, La Porte, NT ORCID: https://orcid.org/0000-0001-7467-4460, Young, RM ORCID: https://orcid.org/0000-0002-5108-0261, Sinopoli, A, Sohail, M ORCID: https://orcid.org/0000-0002-8221-818X and Wasielewski, MR ORCID: https://orcid.org/0000-0003-2920-5440 (2019) Direct Observation of the Photoreduction Products of Mn(NDI-bpy)(CO)3XCO 2 Reduction Catalysts Using Femtosecond Transient IR Spectroscopy. Journal of Physical Chemistry C, 123 (11). pp. 6416-6426. ISSN 1932-7447

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Abstract

The electrochemical reduction of the Mn(bpy)(CO)3X CO2 reduction catalyst is thought to proceed by the initial reduction of MnI to Mn0. We have covalently attached a naphthalenediimide radical anion (NDI•-) chromophore to the 4-, 5-, or 6-position of the bpy via a phenyl bridge to produce Mn(NDI•--bpy)(CO)3X, where X = Br, CH3CN, or DMF, and have used femtosecond and nanosecond transient IR spectroscopy to directly observe the intermediates produced by two electron-transfer reactions following selective photoexcitation of NDI•- to its lowest excited doublet state, 2∗NDI•-. In complexes where NDI•- is attached at the 4- or 5-position of bipyridine, only the reaction Mn(2∗NDI•--bpy)(CO)3X → Mn(NDI-bpy•-)(CO)3X is observed, whereas in the complex where NDI•- is attached to the 6-position of bipyridine, the reaction sequence Mn(2∗NDI•--bpy)(CO)3X → Mn(NDI-bpy•-)(CO)3X → Mn0(NDI-bpy)(CO)3 is observed. Moreover, in the complexes with an NDI•- bound to the 6-position of bipyridine, Mn0(NDI-bpy)(CO)3 exhibits a lifetime that is ∼105 times longer than those in complexes with an NDI•- bound at the four- or five-position of the bipyridine.