Particle formation, intermolecular energy transfer and unexpected luminescence quenching of terbium complexes in polymer matrix

The very attractive luminescence activation of polymers by rare earth complexes to yield transparent hybrid materials can be severely hampered by inherently present impurities and other hard-to-predict chemical obstacles. Systematic investigations and corresponding information on quenching in rare earth – polymer hybrids have not come to our attention. Here, the luminescence quenching and and fluorescence lifetime depreciation of trioctylphosphinoxide co-coordinated terbium salicylate, Tb(sal)3(TOPO)2, by cinnamic acid has been measured in a silicone matrix as an example. Unexpectedly efficient energy transfer from the Tb3+ ions to quencher molecules has been observed and is interpreted in terms of invisible, micelle-like aggregates as derived from luminescence intensities and decay behaviors of the rare earth ions at room temperature. Other than in ‘classical’ (F)RETs, which exploit the emission of a donor and singlet absorption of an acceptor, we here have to assume quenching via a short range transfer to triplet states of the cinnamate impurity, which occurs despite fairly long distances of roughly 10 nm at low quencher concentrations. Reflecting existing energy transfer theories, the experimental results thus suggest the formation of emitter clusters within the silicone matrix.