Constructing Pure Blue Multiple-Resonant Nanographene Emitters with an Enlarged π-Skeleton via a Sterically Stretched Hindered Diphenylfluorene Moiety

Nanographenes are promising candidates for high-performance organic light-emitting diodes (OLEDs) due to their rigid planar skeletons and versatile molecular engineering strategies. The incorporation of a prominent heteroatom into the π-skeleton of nanographene enables the emergence of multiple resonance effects for ideal narrowband emission. However, the development of high-performance pure blue emitters is hindered by strong face-to-face π–π stacking and inadequate bathochromic-shift emission in the violet and deep-blue spectral regions, necessitating novel molecular design principles. In this study, we introduced a nonfully conjugative and sterically stretched diphenylfluorene subunit into an indolo[3,2,1- jk ]carbazole-bearing NG skeleton to generate a moderate redshift toward pure blue emission (452–459 nm) and suppressed tight intermolecular packing, achieving high photoluminescence quantum yields >90% and narrowband emission with full widths at half-maximum (FWHM) of 17–19 nm. Consequently, the OLEDs employing these emitters achieved maximum external quantum efficiencies exceeding 22.6% and narrow electroluminescence emission with a FWHM of 33 nm, enabled by a sensitized fluorescence strategy.