Indolo[3,2,1-jk]carbazole-based narrowband multi-resonance polycyclic organic systems for high-performance OLEDs

Narrowband organic emitters with high efficiency and exceptional color purity are pivotal for next-generation ultra-high-definition OLEDs. Multi-resonance (MR) emitters based on boron/nitrogen-doped polycyclic aromatic hydrocarbons (B/N-PAHs) have set benchmarks with ultra-narrow emission (FWHM < 30 nm) and high EQE. However, their complex synthesis, limited structural diversity, and stability concerns restrict broader application. Emerging π-fused indolo[3,2,1-jk]carbazole (ICz)-based systems offer a compelling alternative by leveraging intrinsic carbon-nitrogen electronegativity differences to induce MR-features, eliminating the need for B-incorporation for narrow emission. Despite their promise, ICz-based MR-emitters face key limitations, including inefficient triplet exciton utilization, poor spin-orbit coupling, restricted emission beyond the blue region (>450 nm), aggregation-induced quenching, low EQE and suboptimal device stability. These challenges are closely tied to the molecular architecture of N-PAHs, such as π-conjugation, N-atom positioning and number, and core/peripheral modifications. Thus, understanding the molecular design and structure-function relationships is essential to develop efficient ICz-MR emitters. This review consolidates recent progress in ICz-based MR-emitters, emphasizing strategies to mitigate the above said challenges. By correlating molecular structure with photophysical behavior and device performance, it provides critical insights into overcoming current bottlenecks. The discussion concludes with forward-looking perspectives aimed at developing scalable, high-performance OLED technologies based on this emerging class of emitters.