Anatomy of the Photochemical Reaction: Excited-State Dynamics Reveals the C–H Acidity Mechanism of Methoxy Photo-oxidation on Titania
Fig. 1: Methoxy to formaldehyde excited-state reaction trajectory: evolution of lengths of the C–H bond being cleaved and the O–H bond being formed. [Copyright © 2015 American Chemical Society]
Light-driven chemical reactions on semiconductor surfaces have potential for addressing energy and pollution needs through efficient chemical synthesis; however, little is known about the time evolution of excited states that determine reaction pathways. Prof. Efthimios Kaxiras and colleagues from SEAS and the Department of Chemistry and Chemical Biology study the photo-oxidation of methoxy (CH3O) derived from methanol on the rutile TiO2(110) surface using ab initio simulations to create a molecular movie of the process. The movie sequence reveals a wealth of information on the reaction intermediates, time scales, and energetics. The reaction is broken in three stages, described by Lewis structures directly derived from the "hole" wave functions that lead to the concept of "photoinduced C–H acidity". The insights gained from this work, published in The Journal of Physical Chemistry Letters*, can be generalized to a set of simple rules that can predict the efficiency of photo-oxidation reactions in reactant-catalyst pairs.
*G. Kolesov, D. Vinichenko, G.A. Tritsaris, C.M. Friend, and E. Kaxiras, "Anatomy of the Photochemical Reaction: Excited-State Dynamics Reveals the C–H Acidity Mechanism of Methoxy Photo-oxidation on Titania," J. Phys. Chem. Lett.6 (April 14, 2015) DOI: 10.1021/acs.jpclett.5b00429