title: Aqueous Ln(III) luminescence agents derived from a tasty precursor.
abstract: The synthesis, characterization, and photophysical properties are reported for several Ln(III) complexes of a tetradentate chelate, 5LIO-MAM, derived from the common flavor enhancer "maltol". Eu(III), Yb(III), and Nd(III) form stable ML2 complexes in aqueous solution that emit in the red or near-infrared (NIR) upon excitation at ca. 330 nm. The synthesis, aqueous stability, and photophysical properties are reported for a novel tetradentate ligand derived from maltol, a commonly used flavor enhancer. In aqueous solution, this chelate forms stable complexes with Ln(III) cations, and sensitized emission was observed from Eu(III), Yb(III), and Nd(III). A comparison with recently reported and structurally analogous ligands reveals a slightly higher basicity but lower complex stability with Eu(III) [pEu = 14.7(1)]. A very poor metal-centered quantum yield with Eu(III) was observed (Phi(tot) = 0.04%), which can be rationalized by the similar energy of the ligand triplet state and the Eu(III) (5)D0 emissive level. Instead, sensitized emission from the Yb(III) and Nd(III) cations was observed, which emit in the NIR.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: Christoph J
authors.initials: CJ
authors.lastname: Jocher
authors.forename: Evan G
authors.initials: EG
authors.lastname: Moore
authors.forename: Jason D
authors.initials: JD
authors.lastname: Pierce
authors.forename: Kenneth N
authors.initials: KN
authors.lastname: Raymond
mesh_terms: D005421:Flavoring Agents / Q000737:chemistry*; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D049408:Luminescent Agents / Q000138:chemical synthesis* / Q000737:chemistry; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D011753:Pyrones / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D005421:Flavoring Agents; D028581:Lanthanoid Series Elements; D049408:Luminescent Agents; D009942:Organometallic Compounds; D011753:Pyrones; D014867:Water; C008316:maltol