A series of organic dyes derived from s-tetrazine have been synthesized, and their photophysical and electrochemical properties are systematically investigated. Testing these compounds as photoredox catalysts in a model oxidative C-S bond cleavage of thioethers has led us to identify new classes of active s-tetrazines. Moreover, some of them can be formed in situ from commercially available 3,6-dichlorotetrazine, making this photocatalyzed C-S bond functionalization simple and highly practical.