Triplet-Triplet Annihilation in 9,10-Diphenylanthracene Derivatives: The Role of Intersystem Crossing and Exciton Diffusion

Triplet triplet annihilation (TTA) is an attractive way to boost the efficiency of conventional fluorescent organic light-emitting diodes (OLEDs). TTA-active anthracene derivatives are Often considered as state-of-the-art emitters due to the proper energy level alignment. In this work, TTA properties of a series of highly fluorescent nonsymmetrical anthracene compounds bearing 9-(4-aryl-phenyl) moiety and 10-(4-hexylphenyl) fragments were assessed. Two different methods to enhance the TTA efficiency are demonstrated. First, the intensity of TTA-based delayed fluorescence directly depended on the intersystem crossing (ISC) rate. This ISC rate can be significantly enhanced in more conjugated compounds due to the resonant alignment of S-1 and T-2 energy levels. While enhanced ISC rate slightly quenches the intensity of prompt fluorescence, the rise of the triplet population boosts the intensity of resultant delayed fluorescence. Second; the triplet annihilation rate can be significantly enhanced by optimization of triplet excitors diffusion regime in the films of anthracene derivatives. We show that the proper layer preparation technology has a crucial influence on uniformity and energetic disorder of the film. This enhances the nondispersive triplet diffusion and ilia-eases the resulting delayed fluorescence intensity.