Producing ultra-stabilized radicals via light irradiation has raised considerable concern but remains a tremendous challenge in functional materials.Herein,optically actuating ultra-stable radicals are discovered in a sterically encumbered and large π-conjugated tri(4-pyridyl)-1,3,5-triazine (TPT) ligands constructed photochromic compound Cu3(H-HEDP)2TPT2·2H2O (QDU-12;HEDP=hydroxyethylidene diphosphonate).The photogeneration of TPT radicals is the photoactive behavior of electron transfer from HEDP motifs to TPT units.The ultra-long-lived radicals are contributed from strong interchain π-π interactions between the large π-conjugated TPT components,with the radical lifetime maintained for about 18 months under ambient conditions.Moreover,the antiferromagnetic couplings between TPT radicals and Cu2+ ions plummeted the demagnetization to 35％ of its original state after light irradiation,showing the largest room temperature photodemagnetization in the current radicalbased photochromic materials.