Ligand-Assisted Rational Design and Supramolecular Tectonics toward Highly Luminescent Eu3+-Containing Organic-Inorganic Hybrids

The ligands-assisted rational design of a Eu3+-containing organic-inorgnic hybrid (di-ureasil) displaying the highest emission quantum yield (0 60 +/- 0 06) reported so far is introduced. Two new lanthanide complexes were synthesized in which the meta (Eu3+ or Gd3+) first coordination sphere is formed by three beta-diketonate ligands (bifa is the 4,4,4-trifluoro-l-phenyl-1,3-butanedionate ion) and two methanol (MeOH) molecules The complexes also comprise the bpeta (1,2-bis(4-pyridyl)ethane) ligand. The Eu3+ complex crystal structure. determined by single crystal X-ray diffraction, confirms the hydrogen bonding ability, the high conformational flexibility and the versatile binding mode of the N, N'-bidentate bpeta in the architecture of the crystals. The bpeta spacers act as bridges, promoting the formation of supramolecular dimeric[Eu(btfa)(3)(MeOH)(2)](2)bpeta(2) species via the establishment of highly directional and strong hydrogen-bonds between the bpeta N atoms and the OH groups of the MeOH molecules. The synthesis of the Eu3+-doped di-ureasuls is an efficient three-step concerted process that results in the destruction of the bpeta-driven self-assembled dimeric units and the formation of a new complex in which the di-ureasil structure plays the role of ligand: (i) one or two labile MeOH molecules are released from the ion local environment and replaced by the oxygen atoms of the carbonyl groups of the urea cross-links, (II) an increase in the degree of order of the poly(oxyethylene) (POE) chains occurs concomitantly: (iii) the bpeta ligand remains in the neighborhood of the newly formed Eu3+ complex The synergy between the absorption ability of the btfa and bpeta cromophores and the hybrid's emitting centers creates additional and efficient bpeta-to-hybrid and bpeta-to-btfa transfer channels that optimize the metal sensitization process contributing for the large measured emission quantum yield.