Halogenated π-conjugated polymeric emitters with thermally activated delayed fluorescence for highly efficient polymer light emitting diodes

Benefiting from the facile solution-processed fabrication, superior electrical and photophysical properties, pi-conjugated polymers with thermally activated delayed fluorescence (TADF) have drawn much more attention. But the credible designing principle for gaining high-performance TADF polymeric emitters is still demanded. Herein, we designed and synthesized the fluorinated and chlorinated pi-conjugated TADF polymers, and their non-halogenated analog, respectively. The halogenation can aggrandize the locally excited component of triplet states ((LE)-L-3), which is favorable to enhance spin-orbit coupling (SOC) and reverse intersystem crossing (RISC) processes. Therefore, two halogenated polymers gain high photoluminescence quantum yield (PLQY) of nearly 80%, meanwhile keep the small overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). In addition, the high molecular dipole moments in halogenated polymers induce the preferentially horizontal emitting dipole orientation and thus high optical out-coupling efficiency. Eventually, the halogenated emitters based polymer light-emitting diodes (PLEDs) can reach high external quantum efficiency (EQE) of over 20%, and extremely low efficiency roll-off with sustaining over 18% EQE at luminance of 1000 cd/m(2). This study opens a way to design high efficiency TADF materials by halogenation and thus guides the future research on the high-performance PLEDs.