PURPOSE: To obtain a new heterocyclic compound containing nitrogen capable of irreversively generating red color by the irradiation of a light having a specific wave length, especially of an ultraviolet radiation, excellent in color stabilities and color generating responses and useful for an optical recording material for photon-mode writing, etc.

CONSTITUTION: This new heterocyclic compound containing nitrogen comprises 1,2,3,4,-5,8,9,10,11,12,14,14-dodecachloro-7-ketodibenzo[c, h]-6, 11-diazecine (A1) of the formula. The (A1) is obtained by reacting 4,5,6,7-tetrachlorophthalimide with phosphorus pentachloride in an organic solvent such as monochlorobenzene or chloroform at 70-220°C, especially 120-150°C, blending the obtained reaction product solution with water or aqueous ammonia well to precipitate byproducts, removing the byproducts by a filtration, separating an organic solvent layer and removing the solvent by a distillation under a reduced pressure.