Low-spin cobalt(ii) redox shuttle by isocyanide coordination

Coordination of the strong-field ligand 2,6-dimethylphenyl isocyanide (DMP-CN) to the Co(PY5Me2) framework, where PY5Me2 represents the pentadentate ligand 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine, has resulted in a new low-spin Co(II) complex with a relatively low reorganization energy and fast electron-transfer kinetics compared to the prototypical cobalt tris-bipyridine redox shuttle, [Co(bpy)3]3+/2+, where bpy represents 2,2′-bipyridine. Despite nearly 160 mV reduced regeneration driving force, the [Co(PY5Me2)(DMP-CN)]3+/2+ redox shuttle displayed an increased regeneration efficiency relative to [Co(bpy)3]3+/2+, however recombination losses hinder the performance as evidenced by a reduced recombination resistance. Future directions point to low-spin Co(II) redox shuttles with more negative redox potentials to be paired with a dye or dye mixture that absorbs into the near infrared region.