Spin State Switching in Solution with an Azoimidazole-Functionalized Nickel(II)-Porphyrin

We herein report the synthesis and switching properties of an azo-1-methylimidazole-functionalized Ni2+ porphyrin. Upon irradiation and cis/trans isomerization of the azo unit, 1-methylimidazole is reversibly coordinated as an axial ligand to the Ni2+ porphyrin. Consequently, the Ni2+ is switched between a diamagnetic low-spin state (trans) and a paramagnetic high-spin state (cis) according to the light-driven coordination-in-duced spin state switching (LD-CISSS) principle. The spin state switching is operable in solution under ambient conditions. The paramagnetic cis-species is formed in exceptionally high amounts upon irradiation with UV light (365 nm), whereas an excess of the diamagnetic trans-species was obtained upon irradiation with blue light (430 nm).