Highly Efficient Nondoped Near‐Ultraviolet Electroluminescence with an External Quantum Efficiency Greater Than 6.5% Based on a Carbazole–Triazole Hybrid Molecule with High and Balanced Charge Mobility

Low charge injection and unbalanced carrier transport are unfavorable factors for highly efficient near‐ultraviolet (NUV) electroluminescence (EL) emitters. The construction of weak donor‐ and acceptor‐containing fluorophores has been utilized as a common solution to these issues. Few fluorescent emitters simultaneously exhibiting NUV emission and high/balanced charge‐transport properties have been reported. Herein, a new 1D donor–π–acceptor molecule 9‐(4′‐(4,5‐diphenyl‐4H‐1,2,4‐triazol‐3‐yl)‐[1,1′‐biphenyl]‐4‐yl)‐9H‐carbazole named PCZTZ consisting of 9‐phenylcarbazole as a donor and 2,3,4‐triphenyl‐1,2,4‐triazole as an acceptor with a biphenyl π‐bridge is constructed. The backbone‐twisted PCZTZ exhibits not only strong solid‐state NUV fluorescence but also high and balanced hole and electron mobilities (both up to 10−4 cm2 V−1 s−1), benefiting from the 3D supramolecular H‐bonding network containing strong CH⋯N interactions. Remarkably, a fabricated nondoped light‐emitting diode (OLED) emits 408 nm bright NUV light with a maximal external quantum efficiency of 6.57% and Commission Internationale de L'Eclairage coordinates of (0.17, 0.07). Thus, this OLED is the most efficient NUV OLED reported thus far. These results provide a valuable strategy for the design of highly efficient NUV EL emitters by modulating the linking positions of carbazole and triazole on a biphenyl bridge.