Efficient Deep Blue Electroluminescence with an External Quantum Efficiency of 6.8% and CIE_y < 0.08 Based on a Phenanthroimidazole–Sulfone Hybrid Donor–Acceptor Molecule

Abstract

Tremendous efforts have been devoted to develop efficient deep blue organic light-emitting diodes (OLEDs) materials with CIE y < 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.

Anion-controlled dimer distance induced unique solid-state fluorescence of cyano substituted styrene pyridinium

“…Understanding the structure-property relationship is very important to guide the design of correct molecules for their providential applications1617181920212223. Artful molecular design through varying molecular backbone substituent groups and effective π-conjugation lengths or impacting the intra/intermolecular interactions to achieve high emission in the solid state is the most common method2425262728. In contrast the notorious aggregation-caused quenching (ACQ), branchy and twisted aggregation-induced emission (AIE) and aggregation-induced emission enhancement (AIEE) fluorogens are developed to tune the intermolecular stacking for efficient emissions in the solid state29303132.…”

A pyridine based meta-linking deep-blue emitter with high conjugation extent and electroluminescence efficiencies

“…26BTPIPy-based device achieved maximum CE and EQE (Fig. 25,36 For the 25BTPIPy-based device, EL emission peaked at 460 nm displays color coordinates of (0.15, 0.16) which was in accord with PL emission of 25BTPIPy. Deep-blue emission with CIE coordinates of (0.15, 0.09) was obtained from the 26BTPIPy-based device.…”

“…Thus a more rigid structure endows the meta-linking material with a higher T d . 25 and Z-BBPI 20 respectively). We did not observe obvious endothermic peak through the whole measuring process (two-cycle scanning between 50 and 420 °C) of 25BTPIPy, indicating no obvious phase change occurred.…”

Synthesis and Characteristics of Organic Red‐Emissive Materials Based on Phenanthro[9,10‐d]imidazole

“…The HOMO energy levels are estimated by cyclic voltammetry (CV) measurements. As shown in Figure , the oxidation potentials of PIDSB and PIDPh were determined to be 0.96 V and 0.95 V, corresponding to the HOMO levels of −5.56 eV and −5.55 eV, respectively, with regard to the energy level of ferrocene (4.8 eV below vacuum) . The oxidation potentials of PIDSB and PIDPh were similar to those of the donor group indicating that the HOMO levels were determined by the PIM.…”