Thermally Activated Delayed Fluorescence Sensitizer with Through-Space Charge Transfer Manipulated by Atom Distribution for Solution-Processed Deep-Blue Multi-Resonance OLEDs

Organic light-emitting diodes (OLEDs) employing multi-resonance (MR) emitters have attracted much attention due to their high luminescent efficiency and color purity, however, the development of deep-blue multi-resonance OLEDs is hindered by the lack of suitable sensitizers. Here a novel design strategy is reported for thermally activated delayed fluorescence sensitizer with high reverse intersystem crossing (kRISC) and radiative transition (kR) rate by regulating atom distribution of a spatially-aligned carbazole donor/diphenylpyrimidine acceptor structure to manipulate through-space charge transfer (CT) process. It is found that diphenylpyrimidine acceptor with 1,3-position nitrogen atoms is un-conjugated to bridging phenyl moiety by the conjugation node of pyrimidine, while the acceptor with 1,5-position nitrogen atoms is conjugated to bridging phenyl through conjugation site, opening through-bond CT pathway via bridging phenyl besides through-space CT from spatial donor-acceptor interactions. As a result, the sensitizer with 1,5-position nitrogen atoms exhibits enhanced oscillator strength by 3.5 folds and accelerated kR of 3.57 x 107 s-1, while keeping high kRISC of 4.03 x 106 s-1 and high singlet (S1) state (2.88 eV). Solution-processed OLEDs using the sensitizer and deep-blue multi-resonance emitter exhibit efficient narrowband electroluminescence with CIE coordinates of (0.14, 0.13) and EQEmax of 15.6%, representing the state-of-the-art device performance for deep-blue multi-resonance OLEDs by solution process.