Boosting Circularly Polarized Luminescence Performance by a Double π-Helix and Heteroannulation.

Abstract

Design challenges in the development of circularly polarized luminescence (CPL) materials are focused on balancing the luminescence dissymmetry factor (glum) and photoluminescence quantum yield (ΦPL) by regulating the electric (μ) and magnetic (m) transition dipole moment vectors. Aiming at designing efficient CPL emitters and clarifying the chiroptical variation mechanism, herein, we present a double π-helix based on a cyclooctatetraene-embedded perylene diimide dimer that combines chirality with molecular entanglement and very high barriers for racemization. Through finely regulating the magnitudes of μ and m, the maximal dissymmetry factors |gabs| and |glum| can be boosted to 0.035 and 0.030, respectively, as revealed by circular dichroism (CD) and CPL spectra. The results indicate a 3-fold improvement of g values and a modulated ΦPL from 1a, 4, to 5 by nitrogen heteroannulation at the bay region. The CPL brightness (BCPL) of 5 reaches a recorded value of up to 573.4 M-1 cm-1, among the highest values of chiral small molecules reported so far. This work has provided a comprehensive insight into a new class of chiral materials with high CPL activities, further laying molecular fundamentals for chiral optoelectronics.