in homogeneous solution that are switched between the diamagnetic and paramagnetic states at room temperature by light-drivencoordination-inducedspin-stateswitching (LD-CISSS). Switching of the coordination number (and concurrently of the spin state) was achieved by using Ni-porphyrin as a square-planar platform and azopyridines as photodissociable axial ligands. The square-planar Ni-porphyrin is