Abstract The photochemical and electrochemical behavior of thiophene-S-oxides as a class was studied for the first time. It was shown that in both cases deoxygenation of the S—O functionality takes place. The outcome of the photoirradiation is very dependent on the substituent pattern of the starting material. Thiophene-S-oxides show different reduction behaviors in presence and absence of proton donors. In the absence of proton donors the ...