Deep-Blue Electroluminescent Light-Emitting Diodes with Efficient Hot-Exciton Emission from Carbon Quantum Gear Rack

The quest for exemplary color purity, superior efficiency, and nontoxic deep-blue electroluminescence remains paramount for developing wide-color-gamut displays. However, achieving a Commission Internationale de l'Eclairage y value below 0.05, an exceptional external quantum efficiency (EQE), and a low-efficiency droop in deep-blue emitters presents a significant challenge. Here, the study reports a deep-blue emitting carbon quantum gear rack (DB-CQG) characterized by an emission wavelength of 406 nm and a high quantum yield of 80%. DB-CQG comprises nine benzene rings and four embedded nitrogen-centered tripods and exhibits a quasi-planar configuration that leads to hybridized local and charge-transfer (HLCT) excited-state characteristics. Both experimental investigations and theoretical calculations revealed the activation of the reverse intersystem crossing channel between the high-lying triplet state and lowest excited singlet state in DB-CQG via hot-exciton mechanism. DB-CQG exhibits characteristic HLCT behavior with deep-blue emission owing to the partial overlap of holes and electrons, which is facilitated by the formation of nitrogen-centered tripods in the quasi-planar configuration. The electroluminescent light-emitting diodes (LEDs) fabricated using DB-CQG exhibit a deep-blue color with chromaticity coordinates of (0.158, 0.048), a maximum luminance of 4560 cd m^-2, and an EQE of 10.45%, which is one of the highest reported efficiencies for solution-processable deep-blue LEDs.