Controllable Photoinduced [2+2] Cyclization Modulates Slow Magnetic Relaxation in Coumarin Based Cu(II) Coordination Compound

Cu(II) coordination compounds have ½ spin system; thus, they cannot exhibit single-molecule magnet behavior; however, under a static magnetic field, slow magnetic relaxation can occur. Such compounds are interesting because this type of magnetism is related to spin qubits. Nevertheless, examples of this type of Cu(II) compounds are still rare, and hence the search for novel synthetic approaches becomes a necessity. In this study we have presented the first example of photoreactive Cu(II) coordination compound exhibiting field induced slow magnetic relaxation. The introduction of an able to [2+2] photocyclization coumarin fragment resulted in the possibility to convert Cu(II) system, showing field induced slow magnetic relaxation at 16 K, to another one also exhibiting slow relaxation however shifted below 5 K. Light induced [2+2] cyclization occurs in the studied system practically quantitatively which opened the way to combine relaxation pathways in the one material via controllable partial photoconversion. This approach, to date unexplored, resulted in obtaining a half-photoconverted system exhibiting the characteristics close to the pre-conversion and post-conversion systems. Thus, controlled photoconversion has become a convenient way to modulate properties without having to synthesize compounds from their initially chemically modified building blocks.