•A series of highly efficient deep blue emitters are designed and synthesized.•They present narrow FWHM, high quantum yields and high thermal stabilities.•The doped green device with CIE of (0.31, 0.62) and a ηc of 33 cd A−1 is obtained.•The doped white device with CIE of (0.31, 0.31) and a ηc of 5.5 cd A−1 is obtained.A series of highly efficient deep blue emitters comprising of carbazole and phenanthro[9,10-d]imidazole moieties are designed and synthesized. These compounds present deep blue emission, narrow FWHM, high quantum yields, high thermal and morphological stabilities. Among them, the design strategy of 2:1 ratio of phenanthro[9,10-d]imidazole and carbazole unit affords M2 with more balanced carrier injection and transporting properties. OLEDs using M2 as emitting layer is observed to deliver a truly deep blue CIE of y < 0.06 with a highest external quantum efficiency of 3.02%. By taking the full advantage of these deep blue emitters, they are further served as excellent hosts for fluorescent and phosphorescent dyes. High-performance green phosphorescent device based on M2/Ir(ppy)3 is attained with a maximum current efficiency of 33.35 cd A−1, a power efficiency of 22.99 lm W−1 and a maximum external quantum efficiency of 9.47%. When doped with an orange fluorescent material, upon careful tuning the doping proportion, the two-emitting-component white OLED is successfully fabricated with a maximum current efficiency of 5.53 cd A−1 and CIE coordinates of (0.313, 0.305). Both the non-doped and doped devices exhibited high operational stability with negligible efficiency roll-off over the broad current density range.

Tremendous efforts have been devoted to develop efficient deep blue organic light-emitting diodes (OLEDs) materials with CIEy < 0.10 (Commission International de L’Eclairage (CIE)) and match the National Television System Committee (NTSC) standard blue CIE (x, y) coordinates of (0.14, 0.08) for display applications. However, deep blue fluorescent materials with an external quantum efficiency (EQE) over 5% are still rare. Herein, we report a phenanthroimidazole–sulfone hybrid donor–acceptor (D–A) molecule with efficient deep blue emission. D–A structure molecular design has been proven to be an effective strategy to obtain high electroluminescence (EL) efficiency. In general, charge transfer (CT) exciton formed between donor and acceptor is a weak coulomb bonded hole–electron pair and is favorable for the spin flip that can turn triplet excitons into singlet ones. However, the photoluminescence quantum yield (PLQY) of CT exciton is usually very low. On the other hand, a locally excited (LE) state normally possesses high PLQY owing to the almost overlapped orbital distributions. Hence, a highly mixed or hybrid local and charge transfer (HLCT) excited state would be ideal to simultaneously achieve both a large fraction of singlet formation and a high PLQY and eventually achieve high EL efficiency. On the basis of such concept, phenanthroimidazole is chosen as a weak donor and sulfone as a moderate acceptor to construct a D–A type molecule named as PMSO. The PMSO exhibits HLCT excited state properties. The doped device shows deep blue electroluminescence with an emission peak of 445 nm and CIE (0.152, 0.077). The maximum external quantum efficiency (EQE) is 6.8% with small efficiency roll-off. The device performance is among the best results of deep blue OLEDs reported so far.