Molecular-topology-guided multiple-resonance emitters with sub-10-nm bandwidths: ultranarrow high-efficiency solution-processable OLEDs.

Ultranarrow-band emitters are essential for high-color-purity organic light-emitting diodes, but their discovery remains largely empirical because spectral narrowing is difficult to predict. Progress has been limited by inefficient synthesis-and-testing cycles and the lack of simple design rules linking molecular structure to excited-state relaxation. Here, we establish a predictive design framework for ultranarrow multiple-resonance emitters by treating molecular topology as an explicit handle on structural relaxation. High-throughput screening of B,N-doped triangulene fusion modes identifies an alternating fusion pattern that minimizes reorganization energy and yields a ground-state descriptor for spectral narrowing without explicit excited-state calculations. Guided by this framework, we synthesize sky-blue emitters with photoluminescence bandwidths down to 9.1 nm and solution-processed devices with 10.9-nm electroluminescence bandwidths and 38.1% external quantum efficiency.