Hybrid Local and Charge‐Transfer Material with Ultralong Room Temperature Phosphorescence for Efficient Organic Afterglow Light‐Emitting Diodes

Abstract Organic ultralong room temperature phosphorescence (OURTP) materials capable of combining various emission behaviors for diversified optoelectronic properties and applications have recently gained a vigorous development, but it remains a forbidden challenge in designing OURTP molecules with hybrid local and charge‐transfer (HLCT) feature, possibly due to the elevated difficulties in simultaneously meeting the stringent requirements of both HLCT and OURTP emitters. Here, through introducing multiple heteroatoms into one‐dimensional fused ring of coumarin with moderate charge transfer perturbation in donor‐π‐acceptor architecture, we demonstrate a HLCT‐featured OURTP molecule showing both promoted fluorescence with a quantum yield of 77 % in solution and long‐lived OURTP with a lifetime of 251 ms in conventional host material used in electroluminescent device. Thus, efficient OURTP organic light‐emitting diodes (OLEDs) were fabricated, exhibiting bright electroluminescence with an exciton utilization efficiency of 85 % and yellow OURTP lasting over 2 s for afterglow. Impressively, the HLCT OURTP‐OLEDs can be further optimized to reach an unprecedented total external quantum efficiency (EQE) of ~12 % and OURTP EQE up to 3.11 %, representing the highest performance among the reported OURTP‐OLEDs. These impressive results highlight the significance to fuse HLCT and OURTP together in enriching OURTP materials and improving the afterglow OLED performances.