Photosensitized luminescence of thermostable polynuclear Eu(III) complexes

Tetranuclear europium(III) complexes, [Eu-4(mu-O)(L-1)(10)] (L-1 = 2-hydroxy-4-octyloxybenzophenone,1) and [Eu-4(mu-O)(L-2)(10)] (L-2 = 2-hydroxy-4-dodecyloxybenzophenone,2) were synthesized by the reaction of lanthanide nitrates with L or L, in the presence of triethylamine in methanol. The photosensitized emission bands of the both Eu(III) complexes in THF-d(8) were observed around 579, 590, 615, 653, and 699 nm by the excitation of the ligands at 380 nm, whereas the emission from the mononuclear complex 3 containing ethanol molecules was almost quenched. The emission efficiencies were determined to be 3.1 +/- 0.1% for 1 and 3.9 +/- 0.1% for 2, respectively. The differential scanning calorimetry (DSC) measurements demonstrated that the decomposition points of 1 and 2 were 309 degreesC and 320 degreesC, respectively, indicating high thermostability of these complexes compared to the mononuclear Eu(III) complex 3 (250degreesC). New strategy for designing stable rare earth compounds giving strong emission would be emphasized by introducing polynuclear complexes. Polynuclear complexes should open a wide range of molecular design for photosensitized luminescence and thermal stability. (C) 2004 Elsevier B.V. All rights reserved.