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
(kISC) and achieve high phosphorescence
quantum yields (ΦP). As a result, DBrCz and MeBrCz
achieved a profound increase of kISC ≈
108 s–1 and obtained excellent ΦP values up to 24.53 and 27.81% in solid powder, respectively.
Given the highly efficient ΦP and proper τp, 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.