Selective Stabilization of the Spin States of a Magnetically Anisotropic Dysprosium Ion Induced by Photo‐Excitation of the Associated Cyclic π‐Conjugated System

The presence of a new electronic interaction, which couples a 4 f‐electronic system with a total angular momentum J and a photoexcited cyclic π‐conjugated system with an orbital angular momentum L , in the bis(phthalocyaninato)dysprosium single‐molecule magnet ([DyPc 2 ] − ) is reported. Two π–π* excited states in the visible spectral region of the [DyPc 2 ] − complex, which are denoted here as Q L and Q H , showed significantly different temperature and field dependences of the magnetic circular dichroism (MCD) A ‐term intensity. This phenomenon not only indicates the presence of a “ J – L ” interaction, but also that the interaction generates two different preferred orientations of the J – L pair, either parallel (for the Q H band) or antiparallel (for the Q L band), depending on the excitation energy. We have constructed a theoretical model that reproduces the temperature and field dependences, and quantitatively evaluated the J – L interaction.