The Influence of Substituents in Anthracene Derivatives on the Performance of Triplet-Triplet Annihilation Upconversion

Triplet-triplet annihilation (TTA) upconversion is a spectral conversion technique with large anti-stoke shift under the incoherent low-power photoexcitation. And the excitation and emission wavelengths are adjustable. Therefore, TTA upconversion has an important application value in improving solar energy utilisation. Tremendous advances have been made on the sensitizers, but the research on the emitters is relatively backward. In this paper, 2-substituted anthracene derivatives (DTACl and DTACN) were used as the emitter doped with Ru (II) polypyridine complex [Ru(bpy)(2) Phen](2+) (as the sensitizer) to set up the TTA upconversion models. The effects of anthracene 2-substituents on the luminescence efficiency, triplet-triplet energy transfer (TTET) TTA have systematically studied through the emission and upconversion spectra of the sensitizer the emitter. It is found that DTACl has higher fluorescence quantum yield, larger triplet quenching constant and higher TTA efficiency than DTACN. These results make the upconversion efficiency of [Ru(bpy)(2) Phen](2+)/DTACl higher than that of [Ru(bpy)(2) Phen](2+) /DTACN. Additionally, from the aspect of orbital energy level, the relationship between the triplet energy difference of the sensitizer and the emitter and the TTET efficiency, as well as the relationship between the singlet/triplet energy difference of the emitter and the TTA efficiency, were studied based on the emission spectra and the density functional theory calculation. The research results show that reducing the ability of the 2-substituted group to withdraw electrons can effectively improve the triplet energy level, which is conducive to the TTET efficiency due to the decrease of the triplet energy difference between the emitter and the sensitizer. At the same time, it is good for the TTA efficiency due to the increase of the emitter's singlet/triplet energy difference. The triplet energy level has an important influence on the TTA upconversion efficiency. This work provides a simple and feasible method for designing new and efficient triplet emitters.