Molecular design strategy for through-space charge transfer blue polyimides with rigid non-conjugated backbone and the role of alicyclic imide linker

The exploration of blue polymeric emitters plays an important role in the application of solution-processed polymer light-emitting diodes (PLEDs) in full color display. But the development of highly efficient blue thermally activated delayed fluorescence (TADF) polymers is still extremely challenging. Here, a series of rigid non-conjugated polyimide (PI)-based blue thermally activated delayed fluorescence (TADF) polymers with through-space charge transfer effect were firstly reported based on our novel design strategy. Among them, TRZ-oC-ph (λem = 497 nm) with a typical face-to-face structure as TADF unit was introduced into a polyimide backbone using twisted alicyclic imide as Linker unit. The twisted Linker unit with different structures can effectively regulate the d-spacing between donor and acceptor in the TADF unit, thus obtaining a series of blue TADF polyimides with λem at 485 nm, and high thermal stability (Tg > 277 °C, Td > 477 °C). Remarkably, highly-efficient solution-processing blue polymer light emitting diodes (PLEDs) based on the above polyimides were successfully assembled, with a maximal external quantum efficiency of 23.2%. Such outstanding efficiency is amongst the state-of-the-art performance of non-conjugated PLEDs. It confirms the effectiveness of the structural design strategy, and provides useful and valuable guidance for the development of highly-efficient blue TADF polymer materials and PLEDs.