Rapid limonene-induced mirror symmetry breaking in achiral polyfluorene containing pendant crown ether groups: Enhanced by ion complexation

A novel circular dichroism (CD)-silent π -conjugated polyfluorene bearing the bulky crown ether pendant ( PF8C4 ) as the potassium ion binding site was successfully prepared by polymerization of the corresponding monomers with palladium catalyst. The polymer containing polar groups was found to form the eximious helical assembly by aggregating in chiral limonene at a lower temperature. The aggregates obtained from R - and S -limonene exhibited mirror-image CD peaks in the UV–vis region of polymer backbone. Therefore, the chirality of enantiopure limonene was successfully transferred to the optically inactive PF8C4 , and the relative P - and M -helical supramolecules were successfully prepared. Moreover, after appending K + ion to the helical supramolecules, the complexation between the K + ion and the crown ether pendant helped to strengthen the optical activity , and thus more stable optically active supramolecular structures were achieved.