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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 highly-efficient deep-blue materials DP and SP were synthesized, in which the more rigid SP performs even better photoluminescence quantum yield (PLQY) and horizontal dipole orientation (Θ //). As a result, the SP -based OLED achieves an extremely high external quantum efficiency (EQE) of over 11%, which is one of the best results among the non-doped, non-delayed deep-blue fluorescent OLEDs. [Display omitted] • Highly efficient HLCT deep-blue and near-ultraviolet emissions are realized. • Non-destructive C-H···π interactions decide a regular stacking for 89.5% Θ // of SP. • Non-doped, non-delayed deep-blue fluorescent OLED with EQE max of 11.3% is obtained. Efficient deep-blue emitters with nice color purity are fundamental in organic light-emitting diode (OLED) applications. Herein, we report two phenanthroimidazole (PPI) derivative deep-blue emitters (DP , SP) with hybrid local and charge-transfer (HLCT) properties of high photoluminescence quantum yield (PLQY) and nice color purity. More importantly, the horizontal dipole orientation (Θ //) of them are both superior to the isotropic emitters (66.7%), especially the Θ // of SP is 89.5%, which can greatly improve its OLED performance. As a result, non-doped OLED of SP exhibits deep-blue emission with Commission Internationale de lEclairage (CIE) coordinate of (0.158, 0.068) and maximum external quantum efficiency (EQE max) of 11.3%, which is nearly twice that of DP and is one of the best results among the non-delayed, non-doped deep-blue fluorescent OLEDs. Furthermore, SP -based doped OLED displays an excellent performance of near ultraviolet (NUV) emission at 406 nm with CIE coordinate of (0.157, 0.046) and EQE max of 7.5%, which is also a competitive result in the materials with comparable NUV OLED applications. [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]

Deep blue luminescent materials play a crucial role in the organic light-emitting diodes (OLEDs). In this work, a novel deep blue molecule based on hybridized local and charge-transfer (HLCT) excited state was reported with the emission wavelength of 423 nm. The OLED based on this material achieved high maximum external quantum efficiency (EQE) of 4% with good color purity. The results revealed that the locally-excited (LE)-dominated HLCT excited state had obvious advantages in short wavelength and narrow spectrum emission. What is more, the experimental and theoretical combination was used to describe the excited state characteristic and to understand photophysical property. [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]

The reverse intersystem crossing (RISC) process plays a decisive role in next-generation organic light-emitting diodes (OLEDs), which depends on the energy gap and spin-orbit coupling (SOC) between singlet state and triplet state. To investigate the excited state structure-property relationship and the SOC effect in electro-fluorescent donor-acceptor (D-A) materials, herein, we constructed four quinoxaline derivatives based donor-acceptor (D-A) materials and investigated their excited state properties with a theoretical combined experimental research. The four materials are of different hybridized local and charge-transfer (HLCT) characters. Among them, the most hybridized TPA-DPPZ achieved a higher quantum efficiency over 90% for the effective suppression of non-radiative transition, and it exhibited a higher exciton utilization of 42.8% in non-doped OLED due to a "hot-exciton" channel facilitated with sizeable SOC. Image 1 • Quinoxaline acceptors with boosted SOC are adopt for electroflurescence material. • Restricted non-emissive transition rates are realized in HLCT material TPA-DPPZ. • TPA-DPPZ achieved an exceeding exciton utilization of 43% in non-doped OLED. • "Hot-exciton" channel facilitated with large SOC helps high exciton utilization. [ABSTRACT FROM AUTHOR]