Molecular tweezers with freely rotating linker and porphyrin moieties

Abstract

Molecular tweezers were synthesised by using a microwave accelerated alkene plus cyclobutane epoxide reaction between norbornyl appended porphyrin moieties and a diepoxide functionalised phenyl diimide spacer. The tweezers contain several rotational degrees of freedom; about the porphyrin with respect to the norbornyl linker, and between the two norbornyl backbone sections. The ability of Zn(super)II metallated tweezer 1 to complex 1,4-diazabicyclo[2.2.2]octane (DABCO) was studied by UV/Vis and ¹H NMR spectroscopy and multivariate global spectral analysis. The system was found to form a strong 1:1 intramolecular complex (1:DABCO) with an association constant of K₁₁ = 8.1 × 10⁷ M⁻¹, transforming to a 1:2 open complex [1:(DABCO)₂] with K₁₂ = 2.7 × 10⁹ M⁻² at high concentrations of DABCO.