Using azaacene as an acceptor unit to construct an ultraefficient red fluorophore with an EQE over 40%

Azaacenes, which have been known for a long time, are of scientific and practical importance in organic electronics. Azaacenes once shone as the luminophore in organic light-emitting diodes (OLEDs). However, due to the low exciton utilization efficiency and/or the aggregation induced quenching (ACQ) effect, N-heteroacene based OLEDs generally showed inferior device performance. In this work, azaacene has been revisited and applied as an acceptor for a red fluorophore (AZA-TPA), where the judicious connection pattern between donor and acceptor maximized the harvest of singlet and triplet excitons, resulting in a high photoluminescence efficiency of 94.6% in doped films (3 wt%). In addition, the linearly-fused polycyclic structure contributed to a high horizontal emitting dipole ratio (Θ‖ = 90%). As a result, an AZA-TPA-based OLED achieved an unprecedented external quantum efficiency of 41.30% at 610 nm. This work will pave a new path for the development of efficient N-heteroacene-based fluorophores.