Force-induced cleavage of C-O bond in photochromic naphthopyrans

► The cleavage of C-O bond in photochromic naphthopyrans in solid state is described. ► Naphthopyrans occur ring-opening reaction in solid state under stress. ► Force-induced reaction of naphthopyrans produces the same products as photo-induced. ► The threshold stress to cleave C-O bond of naphthopyrans in solid state is determined.