Magnetic interaction of photoexcited terbium-porphyrin complexes with non-aromatic ligands having different symmetries

Identification of a Weak Interaction between the Spin-Only 4f-Electronic System of Trivalent Gd Ion and a Photoexcited Cyclic π Electronic System

An electronic interaction between the spin-only 4f-electronic system and the photoexcited π cyclic system has been identified in the anionic bis(phthalocyaninato)gadolinium(III) complex [Pc2Gd]- by using variable-temperature variable-magnetic-field magnetic circular dichroism (VTVH MCD). Two positive MCD A-term patterns, corresponding to the QH and QL absorption bands, were observed to increase in intensity as the temperature decreased, indicating a ferromagnetic-type interaction between spin angular momentum S of the 4f system and orbital angular momentum L of the photoexcited π system. A theoretical model incorporating the S-L interaction constant CSL was fitted to the VTVH MCD spectra, confirming the presence of a weak interaction, whose intensity was determined as CSL = 0.27 cm-1 for QL and CSL = 0.02 cm-1 for QH. Ab initio calculations using the RASSCF and RASSI methods revealed that the inclusion of the excited state calculations with the spin multiplicity (2S + 1) of 6 was crucial for assigning ΔSL and CSL values. This underscores the essential role of the 6PJ term in accurately modeling the S-L interaction in [Pc2Gd]-.

Construction of high-throughput magnetic circular dichroism measurement system and its application to research on magnetic and optical properties of phthalocyanine complexes

Magnetic circular dichroism (MCD) spectroscopy is a powerful method for evaluating the electronic structure and magnetic and optical properties of molecules. In particular, MCD measurements have been performed on phthalocyanines and porphyrins with various central metal ions, axial ligands, and substituents to elucidate their properties. It is essential to develop a robust high-throughput technique to perform these measurements comprehensively and efficiently. However, MCD spectroscopy requires very high optical quality for each component of the instrument, and even slight cell distortions can impair the baseline flatness. Consequently, when versatility and data quality are important, an optical system designed for a microplate reader is not suitable for the MCD spectrometer. Therefore, in this study, we develop a new magnetic flow-through cell and combine it with an existing CD spectrometer and autosampler to construct a high-throughput system. The effectiveness and performance of this new system are then evaluated. In addition, based on the MCD and absorption spectra of various phthalocyanine complexes, the effects of substituents and solvents on their magnetic and optical properties and the causes of these effects are discussed. The results demonstrate that this system is effective for the evaluation of the physicochemical properties of various phthalocyanine complexes.

Tuning of the antiferromagnetic-type interaction in photo-excited single-decker porphyrin-lanthanide complexes with different crown capping ligands

The magnetic interaction between the total angular momentum (J) of the 4f electrons in a lanthanide ion and the orbital angular momentum (L) of a porphyrin in the photo-excited states of 5,10,15,20-tetraphenylporphyrinato Dy(III) complexes capped with a crown ether with one of two different symmetries, 12-crown-4 or 1-aza-12-crown-4, was investigated by temperature- and magnetic dependent magnetic circular dichroism (VT-VH MCD). The analysis was conducted on the complexes with different non-aromatic ligands to investigate how different symmetries of the non-aromatic ligands have an impact on the electronic interaction causing an anti-parallel orientation of J and L. The magnitude of the J-L interaction was determined from simulation-based fitting to experimental ratios. While in both cases an antiferromagnetic-type interaction between J and L was identified, an asymmetric non-aromatic ligand resulted in an increased magnitude of the J-L interaction.