A series of experiments were further conducted to verify the proposed mechanisms. To confirm the formation of the complex (Int-1) between 2 and Cu(II) in the solution phase, the ultraviolet-visible (UV-vis) absorption spectrum was recorded, as described in our previous study. As shown in Fig. , the absorption peaks observed at approximately 206, 270, and 324 nm could not be accounted for individual contributions from the spectra of substrate 2 and Cu(CF3COO)2, suggesting an association between these two species. To further investigate its structure, 1 H nuclear magnetic resonance (NMR) spectra were recorded (see Supplementary Information Fig. ) which indicate a molar ratio of 1:2 for Cu(II) and 2. This molar ratio is also evident from the splitting pattern of the peaks in the NMR spectra for Int-1. The overall changes in the NMR spectra and the increase in the number of peaks also indicate that the structure of Int-1 is composed of two molecules of 2 and a singular copper ion. Based on these results, the UV-vis absorption spectra of the two reaction systems were further explored. The peaks observed at approximately 205, 259, 273, and 350 nm could not be accounted for by adding the contributions from the individual spectra for substrate 2, Cu(CF3COO)2, and DMAP which suggests the presence of strong interaction between Int-1 and DMAP. However, the UV-vis absorption spectra indicate a weak interaction between Int-1 and LiOH, and an auxiliary role of the trifluoroacetate ion (see Supplementary Information Figs. S5-S6). X-ray photoelectron spectroscopy (XPS) demonstrate the presence of Cu(II) and Cu(I)