Optically actuating ultra-stable radicals in a large π-conjugated ligand constructed photochromic complex

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 pi-conjugated tri(4-pyridyl)-1,3,5-triazine (TPT) ligands constructed photochromic compound Cu-3(H-HEDP)(2)TPT2-2H(2)O (QDU-12; HEDP=hydroxyethylidene diphosphonate). The photogeneration of TPT center dot radicals is the photoactive behavior of electron transfer from HEDP motifs to TPT units. The ultra-long-lived radicals are contributed from strong interchain pi-pi interactions between the large pi-conjugated TPT components, with the radical lifetime maintained for about 18 months under ambient conditions. Moreover, the antiferromagnetic couplings between TPT center dot 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 radical-based photochromic materials.