Achieving Narrowband and Stable Pure Blue Organic Light-Emitting Diodes by Employing Molecular Vibration Limited Strategies in the Extended π-Conjugated Indolocarbazole Skeleton.

B- and N-heterocyclic fluorophores have reveal promising efficiency in blue organic light-emitting diodes (OLEDs) with small full-width-at-half-maximum (FWHM). However, their structural determinants for spectral broadening and operating stability are still needed to be investigated in further. Herein, a novel multi-N-heterocycles Diindolo[3,2,1jk:3',2',1'jk]dicarbazole[1,2-b:4,5-b] (DIDCz) is proposed to manipulate the emission color toward pure blue region by extending π-conjugation of the N-π-N bridge. By utilizing computed spectral technique, interrelationships between indolocarbazole (ICz)-cyclization sites and spectral broadening are defined. Molecular backbone modifications involving optimized 2,3,6,7-ICz cyclization and steric hindrance substituents are conducive to restricting swing of peripheral bonds and stretching resonances of the polycyclic aromatic hydrocarbon (PAH) frameworks, thereby contributing to the reduction of shoulder emission peaks. Consequently, the DIDCz-based chromophore exhibited narrowband blue emission with a FWHM of only 15 nm, achieving highly efficient (external quantum efficiencies of 8.87% in triplet-triplet fusion fluorescence and 22.3% in sensitized fluorescence) and long-term (95% of the initial luminance of 1000 cd m