According to our previous experimental results of C6 HAT, isomerization of C6 HAT on Ag cannot be triggered by irradiation with 415 nm photons but only by irradiation at 280 nm. We therefore sought to verify, using UV-vis spectroscopy, whether Cn HAT SAMs on Ag can undergo Z-to-E isomerization with irradiation at 415 nm or 280 nm. The experimental results are shown in Figure . In contrast to the Cn HAT SAMs on Au, no significant shift of the maximum absorption wavelength in the absorption spectra of Cn HAT SAMs on Ag was observed, which demonstrates the absence of photoisomerization. Based on the substrate-mediated isomerization mechanism proposed, a light source with an energy of at least higher than 3.9 eV is needed to trigger the isomerization of HAT on Ag. We therefore irradiated the samples with a wavelength of 280 nm (E = 4.4 eV, Figure ). In the absorption spectra of C8, C10, and C11 HAT SAMs on Ag after irradiation at 280 nm, we found a significant blue shift in the absorption peak, which indicates that most of the molecules have isomerized to the E form. Interestingly, in the cases of C3 HAT, we did not observe such a peak shift, which could be tentatively attributed to the strong inhibition of the excited molecule by the Ag. Overall, these results support the proposed substrate-mediated isomerization mechanism.