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43347-AC3
Tailoring of Ligand Functionalization for Improved Lanthanide-Centered Emission in Eu(III) and Tb(III) Complexes

Ana De Bettencourt-Dias, University of Nevada (Reno)

The Ln(III) ions have interesting and wide-spread application in biological as well as materials areas due to the intense light emission properties. The f-f transitions of lanthanide ions Ln(III) are the origin of the bright and color-pure luminescence of these ions. As the f-f transitions are forbidden by selection rules, lanthanide ion complexes are utilized with ligands which efficiently harvest energy and transferring it to the metal ion.

We have acquired extensive experience in the study of the sensitization of Eu(III) and Tb(III) luminescence by small aromatic carboxylic acids as the sensitizers and ligands, which have been derivatized with thiophene for formation of polymeric films with potential application in emitting layers for light-emitting diodes.[1-4] We have also successfully utilized solid state luminescence techniques to probe the sensitization mechanism of coordination polymers containing two different lanthanide ions.[5]

Previously isolated nitrobenzoic acid complexes of Eu(III) and Tb(III) showed unexpected luminescence. The solid state structure of the complexes showed that sterically hindered ligands allow formation of homobimetallic complexes, while more hindered ligands lead to the formation of coordination polymers.[6,7] This solid state trend was confirmed when derivatizing the nitrobenzoates with thiophene, as only homobimetallic structures were obtained. These ligands also sensitize Ln(III) emission, with quantum yields of up to 10%.[8,9]

When initially choosing nitrobenzoic acid as a ligand for lanthanide ions the question of nitro group coordination to the hard cation had been raised. While in the case of the whole family of nitrobenzoates utilized by our group no coordination of the oxygen atoms of the nitro group was observed. Recently we have successfully designed and synthesized new ligands which do coordinate through the nitro moiety to Eu(III) and Tb(III) and are also efficient sensitizers of red and green emission.[10]

(1) de Bettencourt-Dias, A.; Viswanathan, S.; Ruddy, K. Cryst. Growth Des. 2005, 5, 1477-1484.

(2) de Bettencourt-Dias, A. Inorg. Chem. 2005, 44, 2734-2741.

(3) de Bettencourt-Dias, A. Curr. Org. Chem. 2007, in press.

(4) de Bettencourt-Dias, A. Dalton Trans. 2007, 2229-2241.

(5) de Lill, D. T.; de Bettencourt-Dias, A.; Cahill, C. L. Inorg. Chem. 2007, 46, 3960-3965.

(6) Viswanathan, S.; de Bettencourt-Dias, A. Inorg. Chem. Commun. 2006, 9, 444-448.

(7) de Bettencourt-Dias, A.; Viswanathan, S. Dalton Trans. 2006, 4093-4103.

(8) de Bettencourt-Dias, A.; Viswanathan, S. Chem. Commun. 2004, 1024-1025.

(9) Viswanathan, S.; de Bettencourt-Dias, A. Inorg. Chem. 2006, 45, 10138-10146.

(10) de Bettencourt-Dias, A.; Viswanathan, S.; Ayuk, A. in preparation 2007.

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