h was necessary to achieve the optimal yield. Furthermore, the on-off experiments confirmed that the presence of light was essential for product formation. To elucidate the role of light in our system, the ultraviolet/visible (UV/Vis) absorption spectra were obtained, revealing a clear red (bathochromic) shift between the organic base DBU and the N-tosylhydrazone anion, with the visible light absorption extending to 350-450 nm, indicative of the non-covalent complex formation. The radical quenching experiments confirmed the absence of radical processes in the system, indicating that the triplet carbene species did not play a significant role (Figure ). Subsequent carbene trapping experiments with styrene and alkynes demonstrated the formation of cyclopropane, and cyclopropene confirming the presence of singlet carbene species in our system (Figure ). Labelling experiments suggested that proton transfer was involved in this reaction (Figure ). To further elucidate the mechanism, DFT studies were conducted (please see Figure and Figure , supporting information). It showed that the non-covalent complex was formed between the excited N-tosylhydrazone anion and base, which furnished the diazo intermediate after light irradiation. The diazo intermediate further formed the singlet carbene species via photolysis, which subsequently underwent the stepwise or concerted transition states TS3 and TS3' to afford the final products. It should be noted that the stepwise barrier transition state TS3 is observed for the polyfluorinated alcohols, while the three-membered-ring transition state TS3' was located when tertiary alcohols were used. There is the other pathway via the formation of ylide species in previous metal-carbenoid O-H insertions. However, this process is not located, probably due to the low nucleophilicity or bulkiness of (polyfluorinated)alcohols. Based on the DFT calculation and our mechanistic studies, we supposed that concerted O-H insertion via singlet carbene was the favorable route to obtain challenging ethers (Figure ).