Comparative Study on Two Kinds of Spiro Systems for Constructing Through-Space Charge-Transfer Emitters

Significant achievements have been demonstrated with thermally activated delayed fluorescence (TADF) emitters through a spatial charge transfer (TSCT). However, due to the difficulty in synthesis, introducing multiple donor/acceptor units into TSCT-TADF emitters remains a continuous challenge. This work proposed a TSCT-TADF material with the acceptor/donor/acceptor (A/D/A) structure based on a 10,12-dihydroindeno[2,1-b]fluorene (indenofluorene) framework, named DSTO. We also synthesized a molecule with an A/D structure for comparison, named STO. The introduction of multiple acceptors effectively modulates the excited-state properties, achieving a rapid reverse intersystem crossing process rate of 7.1 × 105 s–1. The OLED device with DSTO as the emitter shows a maximum external quantum efficiency (EQEmax) of around 20%. This study broadens the design of multiple donor/acceptor TSCT-TADF materials and deepens our further understanding of the structure–property relationship.