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

Abstract

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. We have constructed a theoretical model that reproduces the temperature and field dependences, and quantitatively evaluated the J-L interaction.

Antiparallel Coupling between a 4f System and a Photoexcited Cyclic π System in a Dysprosium(III) Monoporphyrinato Complex

“…The peculiar behavior of the MCD spectrum of the [Dy­(TPP)­(cyclen)]­Cl complex in various temperatures or magnetic fields apparently indicates the presence of an electronic interaction between the 4f system in Dy III and the photoexcited cyclic π system. This interaction belongs to a new class of electronic interactions, which we refer to as the J – L interaction, and were observed in several lanthanide-based phthalocyaninato/porphyrinato complexes, such as Pc 2 Ln –/0 , [Tb­(TPP)­(cyclen)]­Cl, and [Tb­(Pc)­(cyclen)]­Cl. , …”

“…To give a numerical explanation for the temperature and magnetic-field dependence of the / ratio, we employed the theoretical model defined as follows: , The doubly degenerate ground state and the fourfold degenerate excited states | J Z ⟩ = |±⟩ and | J Z , L Z ⟩ = |±,±⟩ are considered. The components of J and L along the z -axis, corresponding to the molecular fourfold symmetry axis are set as J Z = ±11/2 and L Z = ±| L z |, respectively. Here, the J Z value used is the value obtained from our previous study, while L Z is a parameter.…”

“…Recently, our group studied the use of polarized light on the bis­(phthalocyaninato) lanthanide SMM complexes to seek other possibilities of controlling the quantum state . We found that in the π–π* excited states of the complexes, the J of the 4f electronic system interacts with an orbital angular momentum ( L ) generated in the cyclic π electronic system of the phthalocyaninato ligands by polarized light irradiation (henceforth called as J – L interaction).…”

Spectroscopic Investigation of Interaction between the 4f Electronic System and the Photoexcited Cyclic π System in Terbium(III) Monoporphyrinato Complex

“…Recently, MCD was used for investigating a new type of electronic interaction between the localized 4f electronic system and the photoexcited π electronic system delocalized in bisphthalocyaninato lanthanide­(III) complexes, Pc 2 Ln – . , In the lowest excited states corresponding to the so-called Q-bands, Pc 2 Tb – shows a ferromagnetic interaction by which the total angular momentum ( J ) of 4f and the orbital angular momentum ( L ) of the cyclic π system are coupled to stabilize a parallel orientation of J and L . In contrast to Pc 2 Tb – , Pc 2 Dy – with a 4f configuration shows two types of J – L interaction, ferromagnetic and antiferromagnetic coupling, in the excited states at 620 and 690 nm in the Q-band region, respectively . Because of the double-decker structure of Pc 2 Ln – , an interaction between the two π electronic systems results in a complicated excited state structure, which makes the essential understanding of this phenomenon difficult.…”

“…The complex has a large easy-axis magnetic anisotropy that is attributed to the Tb­(III) ion, 4f system, which is sandwiched by TPP and cyclen ligands in eight-coordinate square antiprismatic. In this investigation, we performed a varied-temperature and varied-magnetic-field (VTVH) MCD which is a manner similar to that performed on Pc 2 Ln – complexes. , Besides, we also present ab initio calculations with RASSCF method for gaining theoretical insight. We use simulation fitting to the experimental data of VTVH MCD measurement to estimate the J – L interaction and compare it to the theoretical result.…”