Surface science and liquid phase investigations of oxanorbornadiene/oxaquadricyclane ester derivatives as molecular solar thermal energy storage systems on Pt(111).

This article investigates the surface chemistry and catalytic behavior of heteroatom-substituted norbornadiene/quadricyclane (NBD/QC) molecular pairs on a platinum Pt(111) surface, focusing on their potential as molecular solar thermal (MOST) energy storage systems. Two derivatives, 2,3-bis(methylester)-oxa-NBD/QC (O-NBD/QC) and the larger 2,3-bis(benzylester) derivatives (exO-NBD/QC), were studied using synchrotron radiation-based x-ray photoelectron spectroscopy (XPS) under ultra-high vacuum and photochemical infrared reflection absorption spectroscopy (PC-IRRAS) in the liquid phase. The study found that O-QC undergoes a catalytic cycloreversion to O-NBD between 310 and 340 K with high thermal stability up to 380 K, while exO-NBD/QC decomposes at much lower temperatures (~135 K) with significant molecular fragmentation. In liquid-phase experiments, Pt(111) catalyzed the back conversion of both QC derivatives to their NBD isomers with high selectivity (>98%) and moderate reaction rates, though differences in catalytic behavior observed in vacuum were less pronounced due to surface passivation by carbonaceous species. These findings provide insights into adsorption motifs, reaction pathways, and stability limits relevant for the design of MOST systems employing heteroatom-substituted NBD/QC molecules.