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 ] ) is reported. Two π-π* excited states in the visible spectral region of the [DyPc ] complex, which are denoted here as Q and Q , 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 band) or antiparallel (for the Q band), depending on the excitation energy.