Fabrication of Circularly Polarized MR‐TADF Emitters with Asymmetrical Peripheral‐Lock Enhancing Helical B/N‐Doped Nanographenes

Abstract

Circularly polarized thermally activated delayed fluorescence (CP-TADF) and multiple-resonance thermally activated delayed fluorescence (MR-TADF), which exhibit novel circularly polarized luminescence and excellent color fidelity, respectively, have gained immense popularity. In this study, integrated CP-TADF and MR-TADF (CPMR-TADF) are prepared by strategic design and synthesis of asymmetrical peripherally locked enantiomers, which are separated and denoted as (P,P″,P″)-/(M,M″,M″)-BN4 and (P,P″,P″)-/(M,M″,M″)-BN5 and exhibit TADF and circularly polarized light (CPL) properties. As the entire molecular frame participates in the frontier molecular orbitals, the resulting helical chirality of (+)/(-)-BN4- and (+)/(-)-BN5-based solution-processed organic light-emitting diodes (OLEDs) helps in achieving a narrow full width at half maximum (FWHM) of 49/49 and 48/48 nm and a high maximum external quantum efficiency (EQE) of 20.6%/19.0% and 22.0%/26.5%, respectively. Importantly, unambiguous circularly polarized electroluminescence signals with dissymmetry factors (g_EL ) of +3.7 × 10^-3 /-3.1 × 10^-3 (BN4) and +1.9 × 10^-3 /-1.6 × 10^-3 (BN5) are obtained. The results indicate successful exploitation of CPMR-TADF-emitter-based OLEDs to exhibit three characteristics: high efficiency, color purity, and circularly polarized light.