Abstract Diazaxanthilidene dyes are photoconvertible small-molecule fluorophores with applications in live-cell imaging. Synthetic access has been limited by challenging dimerization reactions required to construct the sterically hindered tetrasubstituted olefin core. Herein, we report a TMS-diazomethane-mediated thione dimerization, and key intermediate, that enables rapid access to this framework at room temperature. The method provides new methyl-substituted diazaxanthilidene derivatives, including sterically hindered scaffolds that retain photoconvertible behavior and compatibility with live-cell imaging applications.