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 (diPDI) 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 diPDI, NH-diPDI to 2NH-diPDI by the nitrogen heteroannulation at the bay region. The CPL brightness (BCPL) of 2NH-diPDI reaches a recorded value of up to 573.4 M−1 cm−1, among the highest values of chiral small molecules reported so far. Very recently, by taking advantage of the introduction of four chlorine atoms at the bay region of the double π-helix, we could obtain cyclooctatetraene-embedded PDI oligomers(tetramer, hexamer...) through a one-pot Ullmann-Coupling reaction. Such PDI oligomers exhibit particularly complicated chiral structures, for instance, the PDI-tetramer possesses two pairs of enantiomers (P,P,P,P & M,M,M,M; meso,P & meso,M) that reveal the CD and CPL responses with distinct intensities. By exploiting the theoretical calculation, we intensely investigate the corresponding consequence of the chiral inversion in oligomers with multiple chiral centers on the overall chiral optical response. This work has provided a comprehensive insight into a new class of chiral materials with high CPL activities, which is conducive to interpreting the relationship between the molecular chirality and the chiral optical properties, and further laying molecular fundamentals for chiral optoelectronics.

Boosting circularly polarized luminescence performance by linear-extended double π helices and heteroannulation

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