Electron-Withdrawing meso -Substituents Turn On Magneto-Optical Activity in Porphyrins.

A series of square planar metalloporphyrins (M(TPP), TPP is 5,10,15,20-tetraphenylporphyrin and M(TPFPP), TPFPP is 5,10,15,20-tetrapentafluorophenylporphyrin; M is Zn 2+ , Ni 2+ , Pd 2+ , or Pt 2+ ) with distinct meso -substituents were prepared, and their magneto-optical activity (MOA) was characterized by magnetic circular dichroism (MCD) and magneto-optical rotary dispersion spectroscopy (MORD; also known as Faraday rotation spectroscopy). MOA is crucial in the development of next-generation magneto-optical devices and quantum computing. The data show that the presence of meso -pentafluorophenyl substituents results in significant increase in MOA in comparison to the homologous phenyl group. Differences in the MOA of these metalloporphyrins are rationalized using the Gouterman four-orbital model and pave the way for rational design of improved and tailorable magneto-optical materials.