An effective strategy for simply varying relative position of two carbazole groups in the thermally activated delayed fluorescence emitters to achieve deep-blue emission.

Abstract

The development of efficient deep-blue thermally activated delayed fluorescence (TADF) materials is especially important for organic light-emitting devices as displays and lighting sources. However, finding suitable deep-blue TADF emitters is still challenging. Based on an experimentally reported blue-light TADF emitter DCZ-TTR, two new molecules (DCZ1-TTR and DCZ2-TTR) have been designed to investigate the impact of the change of relative position in two carbazole groups on their TADF properties. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations coupled with the Marcus rate theory have been performed. It is found that the absorption and emission spectra simulated using the BMK functional can reproduce the available experimental data very well. The fluorescence emissions of DCZ1-TTR and DCZ2-TTR are predicted to show clear blue-shifting in cyclohexane with respect to their analogue DCZ-TTR. Especially, the emission wavelength of DCZ2-TTR is calculated to be 435nm, in the deep-blue light range. According to the Marcus rate theory, the rates of reverse intersystem crossing of DCZ1-TTR and DCZ2-TTR are estimated to be two orders of magnitude larger than that of DCZ-TTR, which is more favorable for the occurrence of delayed fluorescence. This strongly suggests that our newly designed two molecules DCZ1-TTR and DCZ2-TTR can be also expected to be potential blue-light or even deep-blue-light TADF emitters. This may be an effective strategy for realizing deep-blue emission by simply varying relative position of two carbazole groups in the TADF molecules. To our best knowledge, this is a novel finding, which may be useful in preparing highly efficient deep-blue TADF-OLED materials.