Fluorene vs. Spirobifluorene: Effect of the π-system on TADF properties

There are many options to design a molecular structure that could result in thermally activated delayed fluorescence (TADF). One promising strategy is to use donor-π-acceptor motive where the electron-donating unit is linked to the electron-acceptor via an aryl moiety which reduces the HOMO-LUMO overlap. While this approach is widely used and well understood, the perfor-mance of the chromophores can be limited by different energy loss pathways, e.g. internal con-version or π-stacking. To circumvent these problems rigid structures with sterically demanding substituents are applied. In this work, we designed two TADF emitters based on phenothiazine and nitrile linked via spirobifluorene or 9,9-dimethylfluorene and compared the effect of the linker on the physical properties of the dyes.