Highly Efficient Organic Room-Temperature Phosphorescent Luminophores through Tuning Triplet States and Spin-Orbit Coupling with Incorporation of a Secondary Group

Achieving efficient ultralong purely organic phosphorescent luminophores is still a big challenge due to the slow intersystem crossing (ISC) process. Herein, we present a facile molecular design strategy that incorporates a secondary group (Br atom or methoxy group) into o-BrCz that can significantly enhance the ISC rate constant (k_ISC) and achieve high phosphorescence quantum yields (φ_P). As a result, DBrCz and MeBrCz achieved a profound increase of k_ISC ≈ 10⁸ s^-1 and obtained excellent φ_P values up to 24.53 and 27.81% in solid powder, respectively. Given the highly efficient φ_P and proper τ_p, DBrCz and MeBrCz are applied to alternating current (AC) light-emitting diodes (LEDs), achieving a white LED with CIE coordinates (0.28, 0.29) and a CRI over 90. As a proof of concept, we demonstrate its compensation effect on the dark duration of AC-LED with a reduced percent flicker of 78%. This result extends a new potential application for RTP luminophores in the lighting field.