Two novel naphtho[1,2-d]imidazole derivatives are developed as deep-blue, light-emitting materials for organic light-emitting diodes (OLEDs). The 1H-naphtho[1,2-d]imidazole based compounds exhibit a significantly superior performance than the 3H-naphtho[1,2-d]imidazole analogues in the single-layer devices. This is because they have a much higher capacity for direct electron-injection from the cathode compared to their isomeric counterparts resulting in a ground-breaking EQE (external quantum efficiency) of 4.37% and a low turn-on voltage of 2.7 V, and this is hitherto the best performance for a non-doped single-layer fluorescent OLED. Multi-layer devices consisting of both hole- and electron-transporting layers, result in identically excellent performances with EQE values of 4.12-6.08% and deep-blue light emission (Commission Internationale de l'Eclairage (CIE) y values of 0.077-0.115) is obtained for both isomers due to the improved carrier injection and confinement within the emissive layer. In addition, they showed a significantly better blue-color purity than analogous molecules based on benzimidazole or phenanthro[9,10-d]imidazole segments.