Simultaneous Detection of Circularly Polarized Luminescence and Raman Optical Activity in an Organic Molecular Lemniscate

Circularly polarized luminescence (CPL) and Raman optical activity (ROA) were observed in a single spectroscopic experiment for a purely organic molecule, an event that had so far been limited to lanthanide‐based complexes. The present observation was achieved for [16]cycloparaphenylene lemniscate, a double macrocycle constrained by a rigid 9,9′‐bicarbazole subunit, which introduces a chirality source and allows the molecule to be resolved into two configurationally stable enantiomers. Distortion of oligophenylene loops in this lemniscular structure produces a large magnetic transition dipole moment while maintaining the π‐conjugation‐induced enhancement of the Raman signal, causing the appearance of the CPL/ROA couple. A two‐photon mechanism is proposed to explain the population of the lowest‐energy excited electronic state prior to the simultaneous emission‐scattering event. Raman optical activity (ROA) and circularly polarized luminescence (CPL) have been detected, in a single Raman experiment, for enantiomers of a lemniscular cycloparaphenylene‐based molecule stabilized by a bicarbazole unit. The balance between the rigidity of the chiral bicarbazole core and the torsional flexibility of the oligophenylene loops is able to stimulate magnetically allowed transitions detectable by conventional spectroscopic devices.