Efficient narrowband deep-blue emission from carbazole-grafted diindolophenazine fluorophores

Nitrogen-containing polycyclic aromatic hydrocarbons (PAHs) have exhibited a great potential in deep-blue emission of organic light-emitting diodes (OLEDs), but efficient narrowband emission remains an enormous challenge with excellent color purity and high external quantum efficiency (EQEs) contemporaneously. Herein, two novel deep-blue-emitting diindolophenazine derivatives of OCzN and MCzN were obtained, in which a carbazole was respectively grafted in ortho- and meta-position of phenazine. It is found that the comparatively weak intramolecular charge transfer (ICT) state and rigid fused-ring structure of diindolophenazine can prominently reduce the molecular vibration relaxation, resulting in a comparatively narrow emission spectrum. And the attached carbazole at different grafted position plays an important role in color regulation. As a result, the OCzN- and MCzN-doped devices display deep-blue electroluminescence at 418 nm and 432 nm with CIE coordinates of (0.18, 0.08) and (0.16, 0.09), high color purity, as well as narrow full-width-at-half-maximums (FWHM) of 41 nm and 51 nm, respectively, which is commendably complied with CIEy about 0.08 of the National Television Standards Committee (NTSC) standard. More importantly, the eminent EQEs as high as 6.87% and 6.09% are obtained in the fluorophores-doped OLEDs using mCP as host, respectively. This is a first representation to realize high-efficiency and narrow-band deep-blue emission by PAH fluorophores with dual ortho-positioned N-atoms.