Achieving high circularly polarized luminescence with push-pull helicenic systems: from rationalized design to top-emission CP-OLED applications

While the development of chiral molecules displaying circularly polarized luminescence (CPL) has received considerable attention, the corresponding CPL intensity, g(lum,) hardly exceeds 10(-2) at the molecular level owing to the difficulty in optimizing the key parameters governing such a luminescence process. To address this challenge, we report here the synthesis and chiroptical properties of a new family of pi -helical push-pull systems based on carbo[6]helicene, where the latter acts as either a chiral electron acceptor or a donor unit. This comprehensive experimental and theoretical investigation shows that the magnitude and relative orientation of the electric (mu (e)) and magnetic (mu (m)) dipole transition moments can be tuned efficiently with regard to the molecular chiroptical properties, which results in high g(lum) values, i.e. up to 3-4 x 10(-2). Our investigations revealed that the optimized mutual orientation of the electric and magnetic dipoles in the excited state is a crucial parameter to achieve intense helicene-mediated exciton coupling, which is a major contributor to the obtained strong CPL. Finally, top-emission CP-OLEDs were fabricated through vapor deposition, which afforded a promising g(El) of around 8 x 10(-3). These results bring about further molecular design guidelines to reach high CPL intensity and offer new insights into the development of innovative CP-OLED architectures.

Automated summary

The study reports the synthesis and chiroptical properties of a new family of pi-helical push-pull systems based on carbo[6]helicene, showing that the magnitude and relative orientation of the electric and magnetic dipole transition moments can efficiently tune the molecular chiroptical properties for enhanced CPL intensity. By optimizing the orientation of the electric and magnetic dipoles in the excited state, intense helicene-mediated exciton coupling was achieved, leading to strong CPL. The fabrication of top-emission CP-OLEDs through vapor deposition resulted in promising g(El) values, contributing to further molecular design guidelines and providing insights into innovative CP-OLED architectures.