Understanding the intimate coupling between photoexcitation, electron transfer, protonation, local electric fields, and solvation is an important challenge in photo-electrocatalysis. We parse this problem along several directions, with particular emphasis on coupling between photoexcitation and proton transfer, and measurement and modification of local electric fields at electrochemical interfaces. Photobasicity is the ability to transduce light energy to proton removal in molecular systems and has the potential for increasing the efficiency of processes that are rate-limited due to proton transfer. We will present experimental and computational studies on photobasicity in a family of 5-substituted quinolines, in which the basicity of the heterocyclic nitrogen increases by up to 10 units of pK<sub>a</sub> upon photo-excitation. We put one member of this family to test and demonstrate its ability to deprotonate a series of alcohols. We describe its potential as a new concept in dehydrogenation catalysis. Towards understanding the interplay between electric fields and catalysis at interfaces, we report advances based on studying vibrational Stark shift probes tethered at the surface and measured by Sum Frequency Generation Spectroscopy. We report several new developments using this approach. First, a new solvation model, as the interfacial analog of the bulk Onsager solvation theory, will be presented along with experimental support. Second, the extent of validity of the Guoy-Chapman-Stern (GCS) model and its variants as examined by Stark shift spectroscopy will be discussed. In particular, we highlight the deviation of the experimentally observed local fields from the GCS models when a Faradic current passes across the interface. Finally, we present results on the concept of Frustrated Lewis Acid-Base pairs (FLP) near the surface. FLPs are well-known in the bulk and have been used to activate non-polar molecules. We show creation of FLPs on surfaces and use vibrational spectroscopy to measure the extent of interfacial frustration. We argue that the concepts of interfacial field, solvation, protonation, and frustration will shed new light on understanding and controlling chemistry near electrocatalytic surfaces.

Proton dynamics, interfacial electric fields, and catalysis

256th National Meeting (2018)

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