Triplet energy harvesting by lanthanides in conjugated polymers

Abstract

We report the design, synthesis, and spectroscopic characterization of polyphenylene-type polymers that can be used to sensitize europium complexes. Although benzophenone is widely studied and characterized, polybenzophenones have not been widely used in photophysical studies. The properties of poly(4'-methyl-2,4-benzophenone) (MB), poly(4'-methyl-2,5-benzophenone) (PB) and poly[2,2'-bipyridine-5,5'-diyl(2,5-didecoxy-1,4-phenylene)] (PBP) are described in this paper. All three polymers have backbones that are similar to polyphenylene. PBP has a bipyridine unit that alternates with a phenyl ring. Benzophenone rings are polymerized with para or meta linkages in PB and MB, respectively. All three polymers have similar emission maxima at 430 nm, but PBP has a higher quantum efficiency of emission. The polymers studied in this paper proved to be of lower energy than what is needed to sensitize many europium complexes. In almost all of the lanthanide complexes the ligands played a major role in the emission properties. This was elaborated in studies done previously. Europium chelates of the two different ligands: di(2-thienoyl)methane (DTM) and di(2-naphthoyl)methane (DNM) proved to be of comparable energies with the polymers studied. Results showed that energy transfer did occur between the polymers and the europium chelates, but the energy transfer was not 100% because residual emission from the polymers was detected.