Synthesis, Spectroscopic and Nonlinear Optical Properties of Multiple [60]Fullerene-Oligo(p-phenylene ethynylene) Hybrids

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 C60 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 π‐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 (γ) and enhanced two‐photon absorption (TPA) cross‐sections (σ(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. Enhanced two‐photon absorption could be achieved by incorporation of multiple fullerenes. In the ground state, the hybrid compounds show insignificant electronic communication between the oligomer and fullerene moieties. The synthesis of the multiple fullerene‐terminated oligo(p‐phenylene ethynylene) hybrids (see picture) has been performed through an in situ ethynylation protocol with satisfactory yields.