Manipulating excited states of non-doped deep blue emitter by adjusting the intramolecular torsion angle

The hybridized local and charge-transfer (HLCT) state of emitters concomitantly features high exciton utilization characteristics. However, it remains challenging to simultaneously regulate the excited states and intermolecular packing of blue emitters for non-doped organic light-emitting diodes (OLEDs) applications. Based on the previously developed star blue emitter TPA-1PN by us, herein, we designed and synthesized an isomeric star-shaped blue emitter, namely TPA-4PN, through adjusting the dihedral torsion angles between the triphenylamine and phenanthrene fragments. The torsion angle (37.72°) of TPA-4PN is smaller than that of TPA-1PN (61.69°), which endows TPA-4PN with stronger localized excited state characteristics and closer intermolecular packing, leading to higher luminous efficiency associated with a narrower emission spectrum. The corresponding external quantum efficiency of non-doped blue OLEDs based on TPA-4PN reached 7.76%, with CIE coordinates of (0.157, 0.071).