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Purely organic emitters that can efficiently utilize triplet excitons are highly desired for organic light‐emitting diodes (OLEDs). Hot exciton channel has emerged as a competitive strategy for the efficient harvest of triplet exciton to improve the OLEDs performance and suppress efficiency roll‐off in devices. Here, two deep blue emitters, OPACN and SPACN are designed and synthesized, employing diphenylanthracene (PAnP) unit as central core, sp3 hybridized O and S atom as conjugation blocker, and electron‐withdrawing cyano group as intramolecular charge transfer (ICT) introducer. Especially, OPACN presents bluer emission with electroluminescence (EL) peak at 436 nm, CIE coordinates of (0.16, 0.10), and a maximum external quantum efficiency (EQE) of 8.7%, while SPACN shows an EL peak at 444 nm, CIE coordinates of (0.17, 0.12) and a maximum EQE of 9.0%. Furthermore, the single‐component white organic light‐emitting diode (WOLED) based on OPACN exhibits dual emission from monomer and excimer with EQE of 5.4%. And even the luminance increases to 1000–10 000 cd m−2, the EQE still remains as high as 5.2% and 4.4%, respectively, showing very low efficiency roll‐offs. These results demonstrate an alternative approach for designing high‐performance deep blue OLEDs and WOLEDs based on single component. [ABSTRACT FROM AUTHOR]

The pursuit for efficient deep blue material is an ever‐increasing issue in organic optoelectronics field. It is a long‐standing challenge to achieve high external quantum efficiency (EQE) exceed 10% at brightness of 1000 cd m−2 with a Commission International de L'Eclairage (CIEy) <0.08 in non‐doped organic light‐emitting diodes (OLEDs). Herein, this study reports a deep blue luminogen, PPITPh, by bonding phenanthro[9,10‐d]imidazole moiety with m‐terphenyl group via benzene bridge. The non‐doped OLED based on PPITPh exhibits an exceptionally high EQE of 11.83% with a CIE coordinate of (0.15, 0.07). The EQE still maintains 10.17% at the brightness of 1000 cd m−2, and even at a brightness as high as 10000 cd m−2, an EQE of 7.5% is still remained, representing the record‐high result among non‐doped deep‐blue OLEDs at 1000 cd m−2. The unprecedented device performance is attributed to the reversed intersystem crossing process through hot exciton mechanism. Besides, the maximum EQE of orange phosphorescent OLED with PPITPh as host is 32.02%, and remains 31.17% at the brightness of 1000 cd m−2. Such minimal efficiency roll‐off demonstrates that PPITPh is also an excellent phosphorescent host material. The result offers a new design strategy for the enrichment of high‐efficiency deep blue luminogen. [ABSTRACT FROM AUTHOR]

Multiple resonance thermally activated delayed fluorescence (MR‐TADF) emitters show great potentials for high color purity organic light‐emitting diodes (OLEDs). However, the simultaneous realization of high photoluminescence quantum yield (PLQY) and high reverse intersystem crossing rate (kRISC) is still a formidable challenge. Herein, a novel asymmetric MR‐TADF emitter (2Cz‐PTZ‐BN) is designed that fully inherits the high PLQY and large kRISC values of the properly selected parent molecules. The resonating extended π‐skeleton with peripheral protection can achieve a high PLQY of 96 % and a fast kRISC of above 1.0×105 s−1, and boost the performance of corresponding pure green devices with an outstanding external quantum efficiency (EQE) of up to 32.8 % without utilizing any sensitizing hosts. Remarkably, the device sufficiently maintains a high EQE exceeding 23 % at a high luminance of 1000 cd m−2, representing the highest value for reported green MR‐TADF materials at the same luminescence. [ABSTRACT FROM AUTHOR]

[Display omitted] • A HLCT emitter, PyPO, is constructed by selecting diphenyl ether as the weak electron donor and incorporating it with PyI unit. • The non-doped OLED exhibits an EL emission peak at 448 nm with an impressive EQE of 11.1%. • The PyPO-based red phosphorescent OLED acquires a maximum EQE of 31.3% and still remains 28.6% at 1000 cd m−2. The development of highly efficient deep-blue fluorescent materials applicable in non-doped organic light-emitting diodes (OLEDs) is still an appealing yet challenging task. Herein, we present a rational design of deep-blue material, PyPO, by linking pyreneimidazole (PyI) moiety with diphenyl ether unit through a benzene bridge. A weak charge transfer state between PyI and diphenyl ether in PyPO is observed from the photophysical investigation, and it is provided with the hybridized local and charge transfer (HLCT) feature as indicated by theoretical calculations. The neat thin film of PyPO shows high photoluminescence quantum yield (PLQY) of 70.7% and excellent horizontal dipole ratio of 84.0%, respectively. In particular, the non-doped OLED using PyPO as the active layer exhibits an electroluminescent (EL) emission peak at 448 nm with an impressive maximum external quantum efficiency (EQE) of 11.1% and negligible roll-off at 1000 cd m−2, which is one of the best results among PyI-based deep-blue luminogens. In addition, the red phosphorescent OLED applying PyPO as host achieves a maximum EQE of 31.3% and still remains 28.6% at 1000 cd m−2, demonstrating PyPO is also a suitable phosphorescent host material. The excellent device performance is ascribed to the high-lying reversed intersystem crossing (hRISC) via hot exciton mechanism. These findings may provide new insights for the development of highly efficient deep-blue emitters. [ABSTRACT FROM AUTHOR]

[Display omitted] • Modifications of BZ group in various ways afford three red emitters with high PLQY. • Their non-doped OLEDs all show better performance than doped OLEDs. • The non-doped device of TPyBZTPA exhibits a EQE max of 7.3% with a high EUE of 76%. Organic light-emitting diodes (OLEDs) have been widely used in flat-panel displays and solid-state lightings because of their unique advantages. The non-doped red OLEDs with satisfactory external quantum efficiency (EQE) still remains challenging. In this work, a series of red emissive materials are successfully designed and synthesized by adjusting the spatial structure and the property of excited state. PyBZTPA is constructed by the combination of electron-withdrawing benzothiadiazole (BZ), bipolar pyrene[4,5-d]imidazole (PyI) and electron-donating triphenylamine (TPA) groups, which exhibits a red emission peaking at 609 nm. On the basis of molecular structure of PyBZTPA, PyBZmTPA is obtained by introducing two methyl substituents on TPA unit, which leads to an increased charge transfer (CT) component in the molecule with a weaker exciton binding energy, facilitating the enhancement of upper-level reverse intersystem crossing (RISC). Further attaching TPA with big steric hinderance at the N1 position of PyI affords compound TPyBZTPA, which aims to increase the molecular distortion degree and reduce the non-radiative transition to improve the photoluminescence quantum yield (PLQY). The results show that both strategies can effectively improve the performance of non-doped devices. As compared with the maximum EQE of 5.3% for PyBZTPA-based non-doped OLED, the maximum EQEs of non-doped devices based on PyBZmTPA and TPyBZTPA go up to 6.8% and 7.3%, respectively. Especially, the maximum current efficiency (CE), power efficiency (PE) and brightness of TPyBZTPA device are corresponding to 12.6 cd A−1, 10.4 lm W−1 and 22682 cd m−2. To the best of our knowledge, the non-doped device performance of TPyBZTPA is fairly good among emitters containing BZ unit with CIE y ≈ 0.4. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two deep blue emitters are obtained with weak charge transfer characters. • The optimized device shows deep blue emission with CIE coordinates of (0.15, 0.06). • PyIAnTPh exhibits EQE max of 8.44% and high color purity with narrow FWHM of 52 nm. Organic light-emitting diodes (OLEDs) are expected to support the future applications in flat-panel displays and solid-state lightings owing to their advantages of flexibility, light weight, high resolution, energy conservation, etc. Achieving efficient deep blue electroluminescence with excellent color purity (narrow emission) remains a big challenge for OLEDs. Herein, two anthracene derivatives, PIAnTPh and PyIAnTPh, with a hybridized local and charge transfer (HLCT) excited state are obtained by attaching the large periphery groups of phenanthroimidazole/pyrenoimidazole and terphenyl unit to the 9,10-positions of anthracene. The sterically asymmetric strategy can efficiently suppress the unfavorable intermolecular interactions and realize deep blue emission. The introduction of neutral terphenyl unit avoids the potential reduction of fluorescence quantum yield from strong charge transfer (CT) characteristics. More importantly, the relatively weak CT state and the rigid molecular structure can significantly reduce the vibrational motion to obtain relatively narrow emission spectra. The doped devices based on PIAnTPh and PyIAnTPh show strong deep blue electroluminescence with CIE coordinates of (0.15, 0.06) and (0.15, 0.07), high color purity, and narrow full width at half maxima (FWHM) of merely 50 and 52 nm, respectively, meeting well with the EBU standard. The EQEs are as high as 8.09% and 8.44% for PIAnTPh and PyIAnTPh, which are among the state-of-the-art deep blue OLEDs. [ABSTRACT FROM AUTHOR]

[Display omitted] • PI unit is connected with biphenyl, diphenylmethane and diphenyl ether moieties to afford a series of blue luminogens of PPIDPh, PPIDPhC and PPIDPhO. • The non-doped OLED of PPIDPh exhibits an impressive EQE of 10.33%. • The PPIDPhC and PPIDPhO-based non-doped devices display even better color purity with high EQEmax of 8.56% and 7.90%, CIE coordinates of (0.17, 0.08) and (0.16, 0.08), respectively. Organic light-emitting diodes (OLEDs) promise many advantages for next-generation illumination and future display applications. Developing organic metal-free fluorescent emitter with wide bandgap and high efficiency is both significant and challenging in OLEDs. Here, phenanthroimidazole (PI) unit possessing ultraviolet emission is connected with biphenyl, diphenylmethane and diphenyl ether moieties to construct a series of blue luminogens of PPIDPh, PPIDPhC and PPIDPhO with hot exciton character. PPIDPh with biphenyl substituent at C2 position of PI group exhibits emission peak at 454 nm in non-doped film. The integration of diphenylmethane and diphenyl ether units with PI group in PPIDPhC and PPIDPhO further limits the π-conjugation owing to sp3 hybridized carbon atom and oxygen atom, which results in bluer emission peaking at 433 nm and 437 nm in the aggregated state, respectively. Particularly, the maximum external quantum efficiency (EQE max) of PPIDPh-based non-doped OLED reaches 10.33 % with CIE coordinates of (0.15, 0.10) and subtle efficiency roll-off of only 7.4 % at high brightness of 1000 cd m−2. The PPIDPhC and PPIDPhO-based non-doped devices display even better color purity with high EQE max of 8.56 % and 7.90 %, Commission Internationale de ĺEclairage (CIE) coordinates of (0.17, 0.08) and (0.16, 0.08), respectively, matching well with National Television Standards Committee (NTSC) requirement for saturated blue color. Such result is among the best outcomes of non-doped blue fluorescent OLEDs with the same emission color. This result will also shed light on the further development of efficient organic wide bandgap emitter and corresponding high-performance OLED. [ABSTRACT FROM AUTHOR]