Oxidation of an Internal-Edge-Substituted [5]Helicene-Derived Phosphine Synchronously Enhances Circularly Polarized Luminescence

Small chiral organic molecules with CD properties are in high demanded due to their potential use in promising electronic and biological applications. Herein, we reveal a system in which the oxidation of a phosphino group to the corresponding phosphine oxide on the inner rim of a helicene derivative induces a CPL response. Laterally pi-extended 7,8-dihydro[5]helicenes bearing phosphine and phosphine oxide groups on their inner helical rims (i. e., the C1 position) were synthesized, and their helical structures were unambiguously determined by X-ray crystallography. The photophysical (UV/visible and emission) and chiroptical properties of these compounds were investigated in various solvents. Despite their structural similarities, phosphine oxide showed a significantly better CPL response than phosphine, with a high dissymmetry factor for emission (vertical bar g(lum vertical bar)=(1.3-1.9)x10(-3)) that can be attributed to structural changes in the interior of the helicene helix.

Automated summary

This study reveals a system in which the oxidation of a phosphino group to the corresponding phosphine oxide induces CPL response in helicene derivatives. The helical structures of pi-extended helicenes with phosphine and phosphine oxide groups on their inner helical rims were determined by X-ray crystallography. The results show that phosphine oxide exhibits a significantly better CPL response compared to phosphine.