Intramolecular Magnetic Interaction in a Photogenerated Dual Angular Momentum System in a Terbium-Phthalocyaninato 1:1 Complex

Intramolecular magnetic interaction between a localized open-shell 4f-electronic system and a photoexcited macrocyclic p-conjugate system in terbium-phthalocyaninnato (Tb-Pc) 1:1 complex was investigated using variable-temperature variable-field magnetic circular dichroism (VTVH MCD) spectroscopy. The 1:1 complex [Tb(Pc)(cyclen)]Cl (Pc2- = phthalocyaninato dianion, cyclen = 1,4,7,10-tetraazacyclododecane) with the capping ligand providing an exact fourfold symmetry showed a significant temperature dependence and a nonlinear field dependence in the MCD intensity of the Pc-centered highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) pi-pi* transition, while a diamagnetic congener [Y(Pc)(cyclen)]Cl showed a temperature-independent MCD with a linear-field dependence. This indicates that the (4f)(8) system of the Tb ion with a total angular momentum J and the photoexcited pi-system of the Pc macrocycle with an orbital angular momentum L are magnetically coupled. By numerical simulation using a model where ground doublet state |J(z)> = | +/- 6 > and excited quartet state |J(z), L-z > = |+/- 6, +/-|L-z|> are included, the J-L interaction magnitude Delta(JL) and the Pc-centered orbital angular momentum |L-z|h were determined to be 1.1 cm(-1) and 2.0., respectively. From ab initio restricted active space self-consistent field (RASSCF)-restricted active space state interaction (RASSI) calculations on the pi-pi* excited states of the Tb complex, the magnitude of the J-L interaction was estimated. The comparison between the calculations on the Y and Tb complexes revealed that the ferromagnetic-type coupling occurs between the orbital component in the J of Tb and the L on Pc, supporting the model that we employed for the analysis of the experimental data.

Automated summary

The study investigated the intramolecular magnetic interaction between a localized open-shell 4f-electronic system and a photoexcited macrocyclic p-conjugate system in a terbium-phthalocyaninnato 1:1 complex. Results showed that the Tb ion's 4f electron system is magnetically coupled with the photoexcited p-conjugate system of the phthalocyaninato macrocycle.