A blue thermally activated delayed fluorescence emitter developed by appending a fluorene moiety to a carbazole donor with meta -linkage for high-efficiency OLEDs

A new thermally activated delayed fluorescence (TADF) emitter, 3-(9,9′-spirobi[fluoren]-6-yl)-9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazole (SFCC), was developed for blue organic light-emitting diodes (OLEDs), and its thermal, photophysical and electrochemical properties were systematically investigated. Upon introducing a 9,9′-spiro-bifluorene group through its C3 position to the C3 position of carbazole, the resulting new backbone had a more delocalized highest occupied molecular orbital (HOMO) than carbazole itself which led to a higher photoluminescence quantum yield (PLQY) compared with that of the control material, 3-bromo-9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazole (TRTZ). The OLED based on SFCC as the blue TADF emitter has a maximum external quantum efficiency (EQE) of 10.59%, with Commission Internationale de L'Eclairage (CIE) coordinates of (0.17, 0.21), significantly surpassing the performance of the reference emitter TRTZ, indicating that the introduction of the 9,9′-spiro-bifluorene unit is a promising strategy for the modification of TADF materials.