Coordination environment driven luminescence in mononuclear and dinuclear dysprosium(iii) β-diketonate complexes

A series of Dy(iii) complexes with 4-bromobenzoylacetone (BBA) as a sensitizing β-diketonate ligand and pyrazine as an auxiliary N-donor ligand was synthesized to study the influence of coordination environment and nuclearity on optical properties. Three complexes - aqua (DyA), mononuclear pyrazine-coordinated (DyM) and pyrazine-bridged dinuclear (DyD) have been studied spectroscopically and photophysically. Electronic absorption and excitation analysis indicate that the ligand-centered π → π* transitions dominate the excitation process, highlighting the antenna role of the coordinating ligand framework in sensitizing the Dy(iii) center. The complexes emit the typical Dy(iii) emission peaks from the ⁴F_9/2 excited state upon excitation, producing blue and yellow emission peaks along with a peak at ∼669 nm. The variations in emission intensity, lifetime, quantum yield and branching ratios show that there is a strong dependence of optical properties on the coordinating environment. The chromaticity analysis indicates tunable emission towards the white region and the optical band gap estimation indicates that the complexes are in the semiconducting range, which indicates their potential application in the field of photonic and optoelectronic applications.