Executive Summary : | The research group is currently exploring the relationship between molecular structure and excited state with HLCT behavior in blue fluorophores. Pyrenoimidazole, a unique electronic structure, has been chosen as an attractive unit for constructing blue fluorophores with remarkable device performance. Traditional fluorescent materials can only utilize 25% singlet excitons, leading to poor electroluminescent performances. To achieve 100% internal quantum efficiency with full exciton utilization efficiency (EUE), hybrid local and charge-transfer state (HLCT) and thermally activated delayed fluorescence (TADF) are the two main methods. TADF materials have made significant progress with unambiguous design rules, emission colors covering deep-blue to deep-red regions, and excellent device performance. However, TADF materials and phosphorescent materials face complicated doping procedures, high concentration exciton annihilation, and scarcity of deep-blue materials with good color purity. HLCT emitters have the advantage of low efficiency roll-off in OLEDs due to the triplet-to-singlet conversion between the upper Tn and Sm states. The radiation efficiency remains high due to the overlap of molecular frontier orbitals of the electron donor and acceptor, while the balance between intramolecular charge-transfer (CT) state and locally excited (LE) state avoids the introduction of strong donor and acceptor, resulting in high color purity. Despite the record OLED efficiency of blue TADF materials, there is still room for improvement for blue fluorophores with HLCT character. This proposal aims to focus on developing new efficient blue HLCT materials and extending their applications in WOLEDs with high performance. |