Benefitting from the flexibility in engineering their optical response, metamaterials have been used to achieve control over the propagation of light to an unprecedented level, leading to highly unconventional and versatile optical functionalities compared with their natural counterparts. Recently, the emerging field of metasurfaces, which consist of a monolayer of photonic artificial atoms, has offered attractive functionalities for shaping wave fronts of light by introducing an abrupt interfacial phase discontinuity. Here we realize three-dimensional holography by using metasurfaces made of subwavelength metallic nanorods with spatially varying orientations. The phase discontinuity takes place when the helicity of incident circularly polarized light is reversed. As the phase can be continuously controlled in each subwavelength unit cell by the rod orientation, metasurfaces represent a new route towards high-resolution on-axis three-dimensional holograms with a wide field of view. In addition, the undesired effect of multiple diffraction orders usually accompanying holography is eliminated.

A series of bipolar anthracene derivatives containing hole-transporting triphenylamine and electron-transporting benzimidazole moieties were synthesized and characterized. These compounds possess high thermal properties and quantum yield in toluene solution but their photoluminescence spectra are sensitive to the polarity of the solvent. Three types of devices were fabricated to investigate their electron-transporting and hole-transporting as well as light-emitting properties. The electroluminescence spectra for the three derivatives B1, B3 and B4 show that they emit blue light, while the B2-based devices produced white light at a low current density because of the electromer formation. Moreover, a single layer OLED device for B4 exhibited a current efficiency of 3.33 cd A⁻¹ with a pure blue color of CIE_(x,y) of (0.16, 0.16) at 20 mA cm⁻² and a maximum brightness of 8472 cd m⁻² at 8.7 V.