FRET endows rare earth Eu(III) complex with stable ultra-dissymmetry and narrowband circularly polarized luminescence

Abstract

Narrowband circularly polarized luminescence (CPL) is a crucial parameter for high color purity display but rarely studied. However, it is rather challenging and significant to provide a route towards high-dissymmetry CPL with both persistent chiroptical stability and narrowband emission. Despite possessing a very narrowband emission and excitation from the unique f-f transition of electrons, the chiral rare earth complexes often racemize with the low inversion barrier, resulting in an undesirable decrease of CPL signal. Herein, we report a circularly polarized Förster resonance energy transfer (C-FRET) in a liquid crystal (LC) coassembly that contains axially chiral alkoxy binaphthyl (R/S-BN) as donor and narrowband emission-featured rare earth Eu(III) complex (EuOL) as acceptor. These highly ordered helical superstructures enable achiral EuOL to emit ultra-dissymmetric CPL, accompanying with a high dissymmetry factor up to 1.44 from LC microcavity resonance. The EuOL@R/S-BN exhibits extremely CPL narrowband with full width at half maximum of 10.8 nm. Compared with the direct excitation, the specific C-FRET strategy in LC coassembly can indirectly emit the highly dissymmetric and narrowband CPL, and completely overcome the CPL weakness from the essential chiral racemization of rare earth Eu(III) complexes. Such LC C-FRET strategy can guarantee the chiroptical stability, high dissymmetry and narrowband emission, which is anticipated to put forward a new route toward the further utilization of rare earth and advanced display technology.