Photochemistry of Bis(sulfonyl)diazomethanes

The photochemistry of a series of bis(sulfonyl)diazomethanes was investigated in solution and in low temperature matrices. These diazo compounds are of interest as photoacid generators in photoresists for deep UV lithography. Triplet carbenes could be trapped in solution, but attempts to isolate the carbenes in argon matrices at 10 K were unsuccessful, the corresponding sulfenes and other rearranged products being observed under these conditions instead. This is in line with DFT and ab initio calculations, which predict the singlet carbenes to be transition states on the pathway to oxathiirene oxides, which can be looked upon as intramolecularly stabilized carbenes. The triplet carbenes lie energetically above the singlet transition states and so are not expected to have a prolonged lifetime even in low-temperature matrices.