Localized Plasmon-Induced Bond Dissociation in a Two-Dimensional Metal-Organic Framework

Surface-supported two-dimensional metal-organic frameworks (2D-MOFs) are promising molecule-based platforms with tunable electronic, optical, magnetic, and quantum functionalities. However, directly correlating local photochemical responses with structural evolution remains challenging because conventional optical spectroscopies lack sufficient spatial resolution. Here, we combine low-temperature scanning tunneling microscopy (STM) and tip-enhanced Raman spectroscopy (TERS) to visualize plasmon-induced reactions of a cyano-terminated oligophenylene, [1,1':4',1'':4'',1'''-quaterphenyl]-4,4'''-dicarbonitrile (Ph4DN), on Ag(111), which forms a honeycomb 2D-MOF via cobalt (Co) atom coordination. The Ag-tip/Ag(111) plasmonic nanocavity locally induces degradation of the molecule-based 2D arrays. Without Co, the molecules undergo rapid cyano-group dissociation, hindering the TERS detection of the intact structure. In contrast, the Co-CN coordination-bond formation suppresses the molecular reactivity in the 2D-MOF, which allows nondestructive TERS observation of the 2D-MOF at a 2 nm spatial resolution. These results provide molecular-scale insights for designing photochemical frameworks and optically functional molecular materials.