Local-Field-Induced Effective Magnetic Hysteresis of Molecular Magneto-Optical Effects in the Visible Region at Room Temperature: Phthalocyanine Thin Films on Ferromagnetic Inorganic Substrates

We report the first observation of molecular magneto-optical effects due to a π-conjugated system with local-field-induced magnetic hysteresis in the visible region at room temperature. Thin films were prepared on a ferromagnetic substrate (Ni and SrO·6Fe₂O₃) using ditrihexylsiloxy(tetra-<i>tert</i>-butylphthalocyanato)silicon (SiPc(OTHS)₂) since its surrounding substituents would prevent both aggregation and direct interaction with the ferromagnetic substrates. The magneto-optical effects of the diamagnetic SiPc(OTHS)₂ on the Ni and SrO·6Fe₂O₃ substrates show the magnetic field dependences that are similar to the corresponding substrates. In the case of the SrO·6Fe₂O₃ substrate, this is the first observation of magnetic hysteresis of the magneto-optical effects due to the π-conjugated system in the visible region at room temperature. The magnetic field dependences of the molecular magneto-optical effects can be explained by the interfacial magnetic field of the ferromagnetic inorganic substrates. Molecular magneto-optical effects coupled with ferromagnetic materials have several advantageous features such as a remanent magneto-optical effect at room temperature, facile preparation of thin films by the cast method, and a sharp signal with changeable wavelength and intensity.