The intramolecular conformational response to the build-up of compressed intermolecular interactions in Blatter's radical (1,3-di­phenyl-1,4-di­hydro­benzo[e][1,2,4]triazin-4-yl) induces a second-order premonitory phase transition and then a first-order phase transition above 5.34 GPa.

The strongly ruffled, odd-alternant radical C₁₃Cl₉ stacks along crystallographic threefold axes, but the intrastack spacing is too large for the material to be a good conductor. The spacing is determined by interstack interactions, which are also responsible for the structural modulations.