Synthesis, Spectroscopic and Nonlinear Optical Properties of Multiple [60]Fullerene–Oligo(<i>p</i>‐phenylene ethynylene) Hybrids

Abstract

A series of multiple [60]fullerene terminated oligo(p-phenylene ethynylene) (OPE) hybrid compounds has been synthesized through a newly developed in situ ethynylation method. Structural and magnetic shielding properties of the highly unsaturated carbon-rich C(60) and OPE scaffolds were characterized by 1D and 2D NMR spectroscopic analyses. Electronic interactions between the [60]fullerenes and the OPE backbones were investigated by UV/Vis spectroscopic and cyclic voltammetry (CV) experiments. Our studies clearly show that although the multiple [60]fullerene groups are connected via pi-conjugated OPE frameworks, they present diminutive electronic interactions in the ground state, and the electronic behavior of the [60]fullerene cages are only affected by the OPE backbones through modest inductive effects. Interestingly, sizable third-order nonlinear optical (NLO) responses (gamma) and enhanced two-photon absorption (TPA) cross-sections (sigma((2))) were determined for the multifullerene-OPE hybrid 31 relative to its OPE precursor from differential optical Kerr effect (DOKE) experiments. Such enhanced NLO performance is presumably due to the occurrence of periconjugation and/or charge transfer effects in the excited state. In addition, comparatively strong excited-state absorption was observed and characterized for OPE pentamer 12. Thus, the use of such fullerene-derivatized conjugated oligomers aids the quest for molecules with large third-order NLO and TPA properties.