Impact of Donor Substitution Pattern on the TADF Properties in the Carbazolyl-Substituted Triazine Derivatives

In this work, we report on the synthesis and photophysical investigation of a new star-shaped triazine-carbazole derivative 2,4,6-tris(3-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)-1,3,5-triazine. Comparative study of the photophysical properties of the newly synthesized emitter along with its para-substituted isomer 2,4,6-tris(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)-1,3,5-triazine was performed. While para-linkage caused higher oscillator strength of the lowest energy absorption band and high fluorescence quantum yield, the meta-linkage resulted in stronger charge transfer character as well as higher triplet energy. Delayed emission of meta-isomer was found to be 3 orders of magnitude more intense than that of para-isomer. Temperature dependent measurements of meta-isomer confirmed the thermally activated delayed fluorescence origin of its delayed fluorescence with the activation energy of 0.07 eV. Organic light emitting diode containing this emitter dispersed in bis[2-(diphenylphosphino)phenyl] et...