Light emitting materials result with lanthanide metals such as europium or terbium dibenzoylmethane complexes are combined with polymers.  Polymers lend processability and site isolation of metal in a protective polymer shell can hinder water access and non-radiative decay processes, and metal-metal self-quenching.  In Eu(dbm)₃ complexes, the aromatic ligand serves as an antenna, collecting light for energy transfer to the europium center, which ultimately emits.  It is also possible to excite into the metal center directly, however given low molar absorptivities, high-energy laser excitation is often required.  Lanthanide systems have bright, narrow bandwidth emission that is determined by the metal, and less so by the particular ligand set. However, distinctive signatures in europium emission spectra are useful for monitoring metal complex and materials architectural changes.  Lanthanide materials find application as molecular probes, imaging agents, and display technologies, among a vast many other uses.

Given the lability of lanthanide complexes, initially a macroligand chelation approach was adopted to access polymeric europium complexes.  That is, dbmPLA macroligands were generated first, followed by combination with EuCl₃. This method was successful.  Macroligands with low polydispersity indices (PDIs) and molecular weights up to ~10 kDa could be attained, and Eu(dbmPLA)_n (n = 3, 4) homopolymer and Eu(dbmPLA)₃(bpyPCL₂) block copolymer complexes were generated.  However polymerizations with dbmOH and the common tin octoate catalyst were very slow and molecular weight control was not maintained to high monomer conversion.  This limits the scope of the synthesis and materials that can be accessed.  For block copolymers in particular, higher molecular weights are often necessary for microphase separation to occur.  Ultimately, this prompted us to consider protecting groups for dbm during polymerization, namely iron and boron initiators, leading to materials with interesting and useful properties.  Link to other sections.

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Europium heteroarm stars, with a labile metal at the block junction, are of interest for fundamental studies exploring ways that triggered changes at the metal center, namely dissociation of a macroligand block, can be propagated through self-assembled, nanostructured materials.  Change at the europium center can be monitored spectroscopically for correlation with materials properties as a function of temperature or other perturbations.  These collaborative studies are ongoing with the research group of Prof. Edwin L. Thomas, in the Materials Science Department at MIT.

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“Site-Isolated Luminescent Europium Complexes with Polyester Macroligands:  Metal-Centered Heteroarm Stars and Nanoscale Assembles with Labile Block Junctions” Bender, J. L.; Corbin, P. S.; Fraser, C. L.; Metcalf, D. H.; Richardson, F. S.; Thomas, E. L.; Urbas, A. M.  J. Am. Chem. Soc.  2002, 124, 8526-7.

“Poly(epsilon-caprolactone) Macroligands with Beta-diketonate Binding Sites: Synthesis and Coordination Chemistry” Bender, J. L.; Shen, Q.-D.; Fraser, C. L. Tetrahedron 2004, 60, 7277-85.

“Thermal and Optical Properties of Europium Heteroarm Stars” Yoon, J.; Chen, J.; Lee, W.; Gorczynski, J.; Thomas, E. L.; Fraser, C. In preparation.