Pure Polycyclic Aromatic Hydrocarbon Isomerides with Delayed Fluorescence and Anti‐Kasha Emission: High‐Efficiency Non‐Doped Fluorescence OLEDs

Pure polycyclic aromatic hydrocarbons (PAHs) consisting solely of carbon-hydrogen or carbon-carbon bonds offer great potential for constructing durable and cost-effective emitters in organic electroluminescence devices. However, achieving versatile fluorescence characteristics in pure PAHs remains a considerable challenge, particularly without the inclusion of heteroatoms. Herein, an efficient approach is presented that involves incorporating non-six-membered rings into classical pyrene isomerides, enabling simultaneous achievement of full-color emission, delayed fluorescence, and anti-Kasha emission. Theoretical calculations reveal that the intensity and distribution of aromaticity/anti-aromaticity in both ground and excited states play a crucial role in determining the excited levels and fluorescence yields. Transient fluorescence measurements confirm the existence of thermally activated delayed fluorescence in pure PAHs. By utilizing these PAHs as emitting layers, electroluminescent spectra covering the entire visible region along with a maximum external quantum efficiency of 9.1% can be achieved, leading to the most exceptional results among non-doped pure hydrocarbon-based devices.