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

Magnetic coupling resulted by an orbital angular momentum L of a photoexcited cyclic pi-conjugated system and total angular momentum J of a localized 4f electronic system in [Dy(TPP)(cyclen)]Cl (TPP = 5,10,15,20-tetraphenylporphyrinato; cyclen = 1,4,7,10-tetraazacyclododecane) has been identified using magnetic circular dichroism (MCD). The MCD A-term patterns of the compound show a negative increment in the intensity by decreasing temperature and nonproportionality to the magnetic field. This phenomenon is experimentally observed for the first time in porphyrin-based lanthanide complexes and indicates the presence of the J-L interaction, with the preferred orientation being antiparallel. A theoretical model in which J and L are assumed to couple antiferromagnetically yielded a quantitative agreement to the experimental data of variedtemperature and varied-magnetic-field MCD spectral measurements. The ab initio calculations were performed, revealing the relationship between two orbital angular momenta, i.e., L(pi) and L(f), which result from the delocalized pi system and the localized 4f system, respectively.

Automated summary

The magnetic coupling between the orbital angular momentum L of a photoexcited cyclic pi-conjugated system and the total angular momentum J of a localized 4f electronic system in [Dy(TPP)(cyclen)]Cl has been identified using magnetic circular dichroism (MCD). The experimental results show antiparallel J-L interaction, and theoretical models provided quantitative agreement with the data. The relationship between the two orbital angular momenta L(pi) and L(f) from the delocalized pi system and the localized 4f system, respectively, was revealed through ab initio calculations.