Di-cysteine S,S-tetrazine: A potential ultra-fast photochemical trigger to explore the early events of peptide/protein folding

► New photochemistry by symmetric sulfur substitution of s-tetrazines. ► Stepwise photocleavage of cysteine S,S-tetrazine tracked by femtosecond IR. ► Peptide structural changes can be initiated by S,S-tetrazine photochemistry.