Circularly Polarized Organic Long-Persistent Luminescence from Chiral Binaphthyl Guests

Abstract

Organic long-persistent luminescence (OLPL) materials with circularly polarized luminescence (CPL) characteristics remain a challenge in spite of their advanced luminescence and broadened applications. Herein, two pairs of axially chiral molecules were designed and doped as guest into the poly(ethylene glycol terephthalate) (PET), achieving the first examples of CPL-OLPL systems. The (R/S)-BINAC guests, featuring unlocked chiral binaphthyl backbones combined with phenyl-carbazole moieties, possessed not only higher intersystem crossing (ISC) efficiencies for triplet excitons' generation but also lower triplet states than PET to prevent triplet excitons' quenching. The OLPL systems containing (R/S)-BINAC thus exhibit a dissymmetry factor (g_lum) of 10^-3, higher phosphorescence efficiency (Φ_p) of 12.8%, and longer lifetime of 4000 s (>1 h). Additionally, the OLPL characteristics were also successfully extended into the near-infrared (NIR) region by codoping with an NIR dye via a Förster resonance energy transfer (FRET) strategy. This work provides a framework for developing CPL-OLPL systems through a careful design of chiral molecular guests, which can extend the characteristic and the application scope of both OLPL and CPL.