Fluorescence quenching of a poly(para-phenylene ethynylenes) by C-60 fullerenes

Complex formation between fullerenes and poly(para-phenylene ethynylene) (PPE) is studied through fluorescence quenching of PPE by C-60. The influence of side chain chemistry, particularly with respect to electron donating capability, and molecular weight on the complex strength is examined in detail. Fluorescence quenching measurements indicate complex formation on the order of 10(3)-10(4) dm(3)/mol, six orders of magnitude larger than previously studied C-60-small organic molecule complexes and an order of magnitude larger than C-60-cyclic polymer systems. No significant difference in complex strength was observed among PPEs with different side chain chemistry, indicating that C-60 interaction occurs largely with the conjugated PPE backbone. At the lower PPE molecular weights investigated, the association constant for complex formation remains constant: however, an increase is observed at the highest molecular weight studied. We attribute this increase to the C-60 molecule quenching more than one PPE unit at once, resulting in enhanced quenching at higher molecular weights and larger association constant. Based on the strength of interaction and lack of side group contribution to the interaction, we conclude that pi-pi interactions between the C-60 cage and PPE backbone are responsible for the comparatively strong interactions observed. (C) 2012 Elsevier B.V. All rights reserved.