Pure-Green Circularly Polarized Multiple Resonance Thermally Activated Delayed Fluorescence Enantiomers with Discontinuous Fused Benzene Rings.

Abstract

Helicene-based circularly polarized luminescence (CPL) materials suffer from severely low color purity in circularly polarized organic light-emitting diodes (CP-OLEDs). Here, a novel molecular engineering strategy is introduced by replacing helicene containing continuous fused benzene rings with a multiple resonance (MR) framework comprising discontinuous fused benzene rings. This approach effectively suppresses high-frequency C─C bond stretching vibrations and enhances short-range charge transfer, enabling high color purity, CPL activity, and efficient thermally activated delayed fluorescence (TADF). The proof-of-concept green BN[7]helicene-based emitters (P/M)-DBN-mICz display bright and narrowband green emission peaking at 512 nm with a full-width at half-maximum (FWHM) of 25 nm. Notably, the enantiomers (P)- and (M)-DBN-mICz exhibit narrowband CPL spectra with FWHMs of 26 and 25 nm, the Commission Internationale de l'Éclairage (CIE) coordinates of (0.14, 0.72) and (0.15, 0.72), and photoluminescence dissymmetry factors of +2.3 × 10^-3 and -2.6 × 10^-3. (P)- and (M)-DBN-mICz-based CP-OLEDs deliver pure-green emission, characterized by a peak wavelength of 516 nm, a narrow FWHM of 27 nm, and CIE coordinates of (0.17, 0.72), representing the purest green CP-OLEDs reported to date. Furthermore, these devices exhibit high electroluminescence dissymmetry factors of +5.3 × 10^-3/-8.5 × 10^-3, and maximum external quantum efficiencies of 37.3% and 36.6%, respectively.