Anchoring Bulky Moieties to Multi-Resonant Nanographenes for Solution-Processed OLEDs with High Efficiency and Narrowband Emission

Nanographenes (NGs) are highly promising emitters for efficient organic light-emitting diodes (OLEDs) due to their rigid planar structures and tunable molecular designs, enabling the construction of multiple-resonant (MR) fluorophores through heteroatom incorporation for narrowband emission. However, the poor solubility and strong π–π intermolecular stacking often hinder the development of solution-processable emitters with superior photophysical properties. In this study, we designed two MR-type indolo[3,2,1- jk ]carbazole (ICz)-based NGs featuring sterically hindered, nonfully conjugated peripheral substituents. These structural modifications effectively suppress tight intermolecular packing and enhance solubility, resulting in high photoluminescence quantum yields (PLQYs) of ≥95% and narrow emission spectra with full widths at half-maximum (FWHMs) of ≤30 nm. When employed in solution-processed OLEDs, these emitters achieved outstanding maximum external quantum efficiencies exceeding 22%, along with narrow electroluminescence (FWHMs ≤33 nm) and state-of-the-art low efficiency roll-offs even at high brightness.