To investigate this phenomenon, we analyzed the solid-state UV-vis diffuse reflectance spectra of each Cu CAM along with their individual linker molecules. The dpb linker molecule exhibited a broad absorption band in the 230-450 nm range (Fig. ), likely due to its π-π* transition. However, after incorporating the linker with the cluster node to form a 2D geometric structure, we observed a significant broadening of the absorption band accompanied by a blue shift in the maximum absorbance wavelength (dpb: 309 nm, Cu6-dpb: 275 nm, Cu10-dpb: 297 nm) (Fig. ). This blue shift becomes more pronounced as the cluster node size decreases. With the broadening of the absorption band, a distinct shoulder peak emerges in each case, likely corresponding to ligand-to-metal charge transfer. Notably, a slight red shift in this shoulder peak is observed for the larger cluster node compared to the smaller one (Cu6-dpb: 384 nm, Cu10-dpb: 414 nm). Similar absorption patterns are observed in Cu10-dpb, Cu10-dpe, and Cu10-dpt when varying the bidentate linker molecules while keeping the