title: The structure of MLn(hfbc)4 and a key to high circularly polarized luminescence.
abstract: The heterobimetallic complex CsEu[(+)-hfbc](4) (hfbc = 3-heptafluorobutyryl camphorate), prepared by Kaizaki and co-workers, displays the highest ratio of polarization versus total luminescence (measured by the g(lum) factor), i.e., ~85% of the emitted photons at 595 nm are left-circularly polarized. We present a detailed structural analysis in solution, based on paramagnetic nuclear magnetic resonance (NMR), and discuss the possible dynamic processes, where its analogues are involved. We demonstrate that the first coordination sphere is very close to the achiral regular square antiprism (SAPR) with D(4d) symmetry, which rules out the intrinsic dissymmetry of the Eu environment for rationalizing the g(lum). In contrast, the dynamic coupling between the f-f transitions, responsible for the emission, to the ligand-centered π-π* transition at 310 nm displays almost ideal geometry to justify g(lum) and discloses a key to high circularly polarized emission.
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35, 56126 Pisa, Italy.
authors.forename: Sebastiano
authors.initials: S
authors.lastname: Di Pietro
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Di Bari