(557f) Hydrogen Adsorption- and Hydrogenation-Triggered Orientational Transitions of Liquid Crystals Adsorbed on Palladium Surfaces

Liquid crystals (LCs) are fluid phases within which molecules exhibit preferred orientations in the bulk. The orientations of LCs can also be manipulated by molecular interactions occurring at interfaces. Therefore, LCs are capable of providing insight into molecular events at solid-liquid interfaces by amplifying changes in surface interactions into the macroscopic-scale such that they can be transduced optically.^1-6 Recently, we have shown that computational chemistry-guided experiments using Cl₂ gas can change the orientation of LCs on metal surfaces due to adsorption and surface reactions.⁶

In this presentation, we will show that the optical response of LCs adsorbed on Pd surfaces can be used to extract information on the kinetics of surface reactions by utilizing the combined knowledge of computational chemistry and catalytic reaction kinetics experiments. We show a system with two consecutive optical transitions at different time-scales due to changes in surface chemistry. Specifically, we present strong evidence that the first optical transition is due to the dissociative adsorption of hydrogen on Pd, whereas the second optical transition is due to the Pd-surface catalyzed hydrogenation of the LC. Our insights from this study demonstrate a fundamental convergence between principles governing functional interfaces with those governing heterogeneous catalysis.

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