TERS combines SPM with plasmon-enhanced Raman spectroscopy, and therefore provides chemical fingerprint and topographic information simultaneously. Because of the strong and highly confined field in a plasmonic nanocavity at the tip apex, the spatial resolution of TERS reaches a few nanometers , and even down to the Å scale (submolecular resolution) under ultrahigh vacuum and cryogenic conditions. TERS has been demonstrated to be a powerful analytical technique for the study of molecular switches, including azobenzene-based , and hydrazone-based switches. Recently, we reported a study of a hydrazone switch functionalized with a C6 alkyl thiolate linker (C6 HAT) anchored on various metal surfaces using TERS and UV-vis spectroscopy. We found that C6 HAT cannot isomerize on a Ag surface when irradiated at 415 nm (the activation wavelength for the Z-to-E isomerization); higher photon energies were required to cause photoisomerization in this case. Based on this finding and supported by density functional theory (DFT) calculations, we proposed a substratemediated photoisomerization mechanism to explain the behavior of C6 HAT on these metal surfaces. This mechanism predicts a significant influence of the length of the alkyl linker on the photoisomerization of hydrazone switches, but this length effect has not been explored experimentally.