Hydrogen-bonding locked phenanthro[9,10-d]imidazole-anthracene emitter enables high-luminance blue OLEDs with low efficiency roll-off

Abstract

In this work, we report the rational design and synthesis of a novel deep-blue emitter, 2-(6-(10-(naphthalen-2-yl)anthracen-9-yl)pyridin-3-yl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (mPANNA), leveraging the synergistic integration of phenanthro[9,10-d]imidazole and anthracene as luminescent units, pyridine as a π-bridge, and naphthalene as a peripheral group. Theoretical calculations revealed that mPANNA exhibits a locally excited-dominated character in its frontier molecular orbitals, which is crucial for achieving high radiative transition efficiency. Single-crystal X-ray diffraction analysis demonstrated a non-planar molecular configuration, where intramolecular hydrogen bonds effectively restrict molecular rotation, enhancing structural rigidity despite the increased distortion from the naphthalene group. Photophysical characterization showed high photoluminescence quantum yields (PLQYs) of 73 % in tetrahydrofuran and 50 % in pure film, highlighting its potential for efficient emission. Electroluminescence performance studies revealed that non-doped device based on mPANNA achieved a remarkable luminance of 41,300 cd m⁻², while doped device exhibited a maximum external quantum efficiency of 4.70 % with low efficiency roll-off. Notably, the doped device displayed pure blue emission with an electroluminescence peak at 455 nm and CIE coordinates of (0.172, 0.183), strictly meeting the requirements for high-performance blue OLEDs. This work demonstrates a promising strategy for designing efficient pure blue emitters through molecular engineering and hydrogen-bonding stabilization, paving the way for advanced OLEDs applications.