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Purely spin-vibronic coupling assisted triplet to singlet up-conversion for real deep blue organic light-emitting diodes with over 20% efficiency and y color coordinate of 0.05

Adv. Sci. (Advanced Science)

Finding narrow-band, ultrapure blue thermally activated delayed fluorescence (TADF) materials is extremely important for developing highly efficient organic light-emitting diodes (OLEDs). Here, we present spin?vibronic coupling (SVC)-assisted ultrapure blue emitters obtained by joining two carbazole-derived moieties at a para position of a phenyl unit and performing substitutions using several blocking groups. Despite a relatively large singlet?triplet gap (?EST) of >0.25 eV, efficient triplet-to-singlet crossover can be realized, with assistance from resonant SVC. To enhance the spin crossover, electronic energy levels are fine-tuned, thereby causing ?EST to be in resonance with a triplet?triplet gap (?ETT). A sizable population transfer between spin multiplicities (>103 s?1) is achieved, and this result agrees well with theoretical predictions. An OLED fabricated using a multiple-resonance-type SVC-TADF emitter with CIE color coordinates of (0.15, 0.05) exhibits ultrapure blue emissions, with a narrow full-width-at-half-maximum of 21 nm and a high external quantum efficiency of 23.1%.

Advanced Science 2021