Orbital Symmetry Engineering in Fused Polycyclic Heteroaromatics toward Extremely Narrowband Green Emissions with an FWHM of 13 nm.

Multiresonance (MR) molecules generally face spectral broadening issues with red-shifted emissions. Thus, green emitters with full width at half maximums (FWHMs) of <20 nm are rarely reported, despite being highly desired. Herein, by properly fusing indolo[3,2,1-jk]carbazole (ICZ) and naphthalene moieties, we report on green MR emitters with FWHMs of merely 13 nm (0.064 eV) and 14 nm (0.069 eV) in dichloromethane, accompanied by high photoluminescence quantum yields of >95%, which represent not only the smallest FWHMs among all green MR emitters but also the first green emitters based on ICZ MR derivatives. Theoretical studies reveal that the orbital interactions between the antisymmetric sites of the segments play an important role in extending the conjugation length in the fusion architectures while simultaneously maintaining a small FWHM. The corresponding organic light-emitting diodes (OLEDs) exhibit green emission peaks at 508-509 nm and the first green electroluminescence FWHM of <20 nm ever reported. Benefiting from the preferential horizontal dipole orientation, a high maximum external quantum efficiency of up to 30.9% was obtained, which remained at 28.9% and 23.2% under luminances of 1,000 cd/m 2 and 10,000 cd/m 2 , respectively, outperforming most reported green devices based on narrowband emitters. This article is protected by copyright. All rights reserved.