Ligand-induced microsymmetry effects and magneto-optical correlations in EuIII complexes investigated by high-resolution luminescence spectroscopy

Understanding how subtle structural distortions influence the electronic structure and photophysical properties of lanthanide(III) (Ln^III) complexes is essential for the rational design of molecular photonic materials.¹ Due to the limited number of components in the ⁵D₀→⁷F_J (J = 0-4) emission manifold, Eu^III provides a direct spectroscopic fingerprint of its local coordination environment, where subtle variations in metal-ligand interactions or ligand electronics are reflected in emission splitting patterns, relative intensities, and excited-state dynamics.² Herein, two closely related Eu^III β-diketonate complexes, [Eu(dbm)₃(bipy)] (1) and [Eu(dbm)₃(5,5′-dm-bipy)] (2), differing only by methyl substitution on the ancillary bipyridine ligand, were investigated by high-resolution luminescence spectroscopy, temperature- and magnetic-field-dependent emission, excited-state lifetime measurements, and magnetic circularly polarized luminescence. The high-resolution techniques elucidate subtle structural perturbations which otherwise would not be easily distinguishable, providing deeper insights into opto-structural correlations for the development of Ln-based molecular systems.