Orthogonal di-spiro skeleton engineering on suppressing π–π stacking and spectral broadening for high-performance narrowband electroluminescence

It is challenging to establish a universal design strategy to finely suppress exciton quenching and retain color purity for the development of multi-resonance thermally activated delayed fluorescence (MR-TADF) materials. Herein, a molecular design with the steric effect by incorporating an orthogonal di-spiro π-skeleton is proposed to create a weak π-π stacking structure and thus effectively eliminate the formation of detrimental excimers and aggregates. The resulting MR-TADF emitters feature high rigidity, low concentration dependence and high horizontal dipole ratio for efficient electroluminescence. Full-color narrowband organic light-emitting diodes exhibit wideband color tuning from blue to red emission (480-628 nm) and achieve external quantum efficiencies as high as 40.4%. This molecular design strategy offers a viable approach for developing efficient luminescent materials with high color purity.