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High performance blue emitters with nice color purity are highly desired in the commercialization of organic light-emitting diodes (OLEDs). Herein, two blue-emissive hybridized local and charge-transfer (HLCT) phenanthroimidazole (PPI) derivatives were designed and synthesized. Comparing to the 9,9-dimethyl-9,10-dihydroacridine (DMAC) substituted DPCN , the 10H-spiro[acridine-9,9′-fluorene] (SAF) substituted SPCN demonstrates higher photoluminescence quantum yield (PLQY) and improved radiative transition rate (k r). With the same device structure, despite that SPCN and DPCN show similar electroluminescence (EL) spectra, the EL efficiency of SPCN is about 1.5 times that of DPCN. Especially the non-doped OLED based on SPCN , the maximum external quantum efficiency (EQE) is 7.1%, which is a competitive result among the conventional blue-emissive fluorescent emitters. More importantly, this work provides a general strategy to achieve high performance blue/deep-blue OLED by rational donor optimization. In this work, we report two blue-emissive hybridized local and charge-transfer (HLCT) materials (DPCN and SPCN) with different donor substitution. Comparing to the 9,9-dimethyl-9,10-dihydroacridine (DMAC) substituted DPCN , the 10H-spiro[acridine-9,9′-fluorene] (SAF) substituted SPCN displays an improved EL efficiency and blue purity, which provides an ideal molecular design strategy for efficient blue/deep-blue EL materials. [Display omitted] • Two blue-emissive HLCT materials with different donor substitution were designed and synthesized. • The relationship of structure-physical property as well as OLED performance are comprehensively explored. • Comparing to DPCN, the SAF substituted SPCN achieved a better OLED performance. [ABSTRACT FROM AUTHOR]

Two phenanthroimidazole-acridine derivatives (DPM and TDPM) were designed and synthesized for deep-blue organic light-emitting diode (OLED). Twisted combined rigid structures with hybridized local and charge-transfer (HLCT) state properties enable them to achieve excellent OLED performance. Non-doped OLEDs based on DPM and TDPM show decent deep-blue narrow-spectrum emission with Commission International de L'Éclairage (CIE) coordinates of (0.157, 0.053) and (0.158, 0.045), as well as maximum external quantum efficiency (EQE max) of 4.0% and 2.6%, respectively. More importantly, OLEDs based on TDPM exhibit a smaller efficiency roll-off (12%) than that of DPM (35%) at high brightness (820 cd m−2 for DPM and 893 cd m−2 for TDPM, respectively). Overall, our work provides a molecular design strategy of HLCT materials for efficient deep-blue OLED with high color purity using purely organic emitter. In this work, we report two phenanthroimidazole-acridine derivatives (DPM , TDPM). Twisted combined rigid structures with HLCT properties enable them show decent deep-blue narrow-spectrum emissions of 428 nm and 424 nm, as well as maximum external quantum efficiency (EQE max) of 4.0% and 2.6%, respectively. Our work provides a molecular design strategy of HLCT materials for efficient deep-blue OLED with nice color purity using purely organic emitter. [Display omitted] • Two phenanthroimidazole-acridine derivatives were synthesized for deep-blue OLED. • Non-doped OLEDs based on DPM and TDPM showed decent deep-blue emission with EQE max of 4.0% and 2.6%, respectively. • Extra C-H···π interactions and ordered π-π stacking make OLEDs based TDPM display a smaller efficiency roll-off than that of DPM. [ABSTRACT FROM AUTHOR]

In this work, two novel D-π-A compounds (PXZ-FR-DRZ and CZ-FR-DRZ) are designed and synthesized, aiming at the excited-state regulation from thermally-activated delayed fluorescence (TADF) to hybridized local and charge-transfer (HLCT) emission. This change of excited-state nature can be ascribed to the weakened electron-donating ability of carbazole relative to phenoxazine, together with the decreased twisting angle between carbazole and fluorine units. As a result of twisted charge-transfer (CT) excited state, the doped organic light-emitting diode (OLED) of PXZ-FR-DRZ demonstrates a blue-green TADF electroluminescence (EL) with a maximum external quantum efficiency (EQE max) of 11.5%, while its non-doped device shows a much lower EQE max. Due to HLCT state of CZ-FR-DRZ , both its doped and non-doped OLEDs achieve the deep-blue non-delayed EL with the satisfied external quantum efficiency (EQE), especially for the excellent efficiency roll-off. Overall, this excited-state transformation between TADF and HLCT allows us to harvest the better comprehensive performance of OLED emitters for the practical applications, which provides a feasible solution for the development of OLED industry. Two different donors (phenoxazine and carbazole) are designed to match the same acceptor of 2,4-diphenyl-1,3,5-triazine (DRZ) through a π-bridged linkage of 9,9-dimethyl-9H-fluorene (FR), resulting in two novel D-π-A molecules of PXZ-FR-DRZ and CZ-FR-DRZ , respectively. The PXZ-FR-DRZ realizes a blue-green thermally-activated delayed fluorescence (TADF) with high external quantum efficiency (EQE) in the doped organic light-emitting diodes (OLEDs) due to the twisted charge-transfer (CT) excited state, whereas the CZ-FR-DRZ achieves a deep-blue non-doped OLED with the better comprehensive performance as a result of the hybridized local and charge-transfer (HLCT) state. [Display omitted] • Two D-π-A materials CZ-FR-DRZ and PXZ-FR-DRZ are synthesized with HLCT and TADF properties respectively. • The TADF PXZ-FR-DRZ exhibits higher EQE than CZ-FR-DRZ. • As an HLCT material, CZ-FR-DRZ displays high performance in non-doped OLED. • The conversion between HLCT and TADF is investigated by changing different donors. [ABSTRACT FROM AUTHOR]

Efficient and robust organic light-emitting diodes (OLEDs) have always been of great interest for both academia and industry. In this work, two electroluminescence donor-π-acceptor structure materials 3,6-TC and 3,6-T2C were synthesized and investigated on their excited state properties and electroluminescence performances. The non-doped and doped OLED of the two materials both exhibited high maximum external quantum efficiency (EQE) of near 5% and exciton utilizing efficiency (EUE) of over 60%. More importantly, the introduction of an extra cyano group of 3,6-T2C facilitated a fine modulation of hybridized local and charge-transfer (HLCT) excited state with a crossed dipole of CT transition and an energy favorable high-lying reverse intersystem crossing (RISC), which contributed to a more stable photoluminescence (PL) and EUE than the 3,6-TC. This work provided a novel design strategy to realize high-performance OLED device by the fine modulation in HLCT state. The 1,2-diphenyl-1H-phenanthro [9,10- d ]imidazole (PPI) is integrated with symmetrical donor unit triphenylamine (TPA) regarded as the locally-excited (LE) backbone. The cyano group is used as acceptor to form hybridized local and charge-transfer (HLCT) excited state. As a result, the molecular configuration determines the direction of dipole moment endowing the extra cyano-substituted 3,6-T2C the property of more stable photoluminescence (PL) efficiency and exciton utilizing efficiency (EUE) of 67.5%. [Display omitted] • 1,2-diphenyl-1H-phenanthro[9,10-d]imidazole (PPI) and triphenylamine (TPA) are used as locally-excited (LE) backbone. • The cyano group is used to form hybridized local and charge-transfer (HLCT) excited state. • 3,6-T2C has the property of more stable photoluminescence (PL) efficiency and exciton utilizing efficiency (EUE). [ABSTRACT FROM AUTHOR]