A series of compounds containing arylamine and 1,2-diphenyl-1Hbenz[d] Qimidazole moieties are developed as ambipolar, blue-emitting materials with tunable blue-emitting wavelengths, tunable ambipolar carriertransport properties and tunable triplet energy gaps. These compounds possess several novel properties: (1) they emit in the blue region with high quantum yields; (2) they have high morphological stability and thermal stability; (3) they are capable of ambipolar carrier transport; (4) they possess tunable triplet energy gaps, suitable as hosts for yellow-orange to green phosphors. The electron and hole mobilities of these compounds lie in the range of 0.68-144 X 10-6 and 0.34-147 X 10-6cm2 V-1 s-1 respectively. High-performance, single-layer, blue-emitting, fluorescent organic lightemitting diodes (OLEDs) are achieved with these ambipolar materials. Highperformance, single-layer, phosphorescent OLEDs with yellow-orange to green emission are also been demonstrated using these ambipolar materials, which have different triplet energy gaps as the host for yellow-orange-emitting to green-emitting iridium complexes. When these ambipolar, blue-emitting materials are lightly doped with a yellow-orange-emitting iridium complex, white organic light-emitting diodes (WOLEDs) can be achieved, as well by the use of the incomplete energy transfer between the host and the dopant.