A Photoswitchable Molecular Lock

Significance

The authors report a precise, clean molecular lock that operates by light. They achieve the catenation in an elegant fashion by labilizing the inert Pt(II)-py bond by UV irradiation. The Pt(II)-clipped coordination ring 1a was obtained by heating (en)Pt(NO₃)₂ and the corresponding ligand at 90 °C in DMF for 1 h in 82% yield. The catenane formed quantitatively upon irradiation of 1a for 15 min in DMSO-d ₆-D₂O. Additionally, the mechanism of ligand substitution at the Pt(II) center was elucidated by a kinetic study of the catenation process. Furthermore, DFT calculations also supported the photolabilization of the platinum complex.

Comment

The reported catenation of the platinum complexes upon irradiation is unique since the process is reversible and very selective. Without irradiation, the formed catenane is locked and does not dissociate into separate rings even in a non-aqueous solvent. When dissolved in MeCN-MeOH (1:1), the catenane remained unchanged and dissociation was not observed despite the absence of an effective hydrophobic interaction between the two rings; however, smooth dissociation occurs if the catenane is irradiated in MeCN-MeOH (1:1). This selective photoswitchable molecular concept has potential applications in the construction of a variety of discrete Pt(II)-linked 3D architectures, which self-assemble under irradiation and freeze in the dark.