Theoretical investigation on reverse intersystem crossing from upper triplet to lowest singlet: A “hot exciton” path for blue fluorescentOLEDs

Abstract

AbstractNowadays, blue fluorescent organic light‐emitting diodes (FOLEDs) have attracted considerable attention from both academia and industry. According to spin statistics, electrical excitation results in the formation of ∼25% singlet excitons and ∼75% triplet excitons (signifying ~75% energy loss), which triggered wide‐ranging efforts to harvest as many triplet excitons as possible. The materials that can convert triplet excitons into singlet excitons from the high‐lying excited triplet states (referred as “hot exciton” channel) to realize high efficiency were reported, which can also efficaciously avoid the accumulation of triplet excitons in T1state. In this study, by means of density functional theory (DFT) and time‐dependent DFT, we have theoretically investigated the electronic and photophysical properties of 16 newly designed molecules with donor‐bridge‐acceptor framework to search for the blue FOLED materials exploiting the “hot exciton” path. Important properties, such as singlet‐triplet energy gaps, absorption and emission parameters, and reverse intersystem crossing rates (kRISC), of five target molecules were studied. The calculated results demonstrate that thiophene‐diphenylamine (kRISCup to 1.03 × 108 seconds−1) may have promising potential as blue FOLED materials by virtue of the “hot exciton” effect.