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Achieving the concurrent manifestation of thermally activated delayed fluorescence (TADF) and aggregation‐induced emission (AIE) within a single molecular system is highly sought after for organic light‐emitting diodes (OLEDs), yet remains rare. In this study, we present a novel TADF‐AIE dye, named PQMO‐PXZ, which has been designed, synthesized, and systematically characterized. Our comprehensive investigation, which includes structural analysis, theoretical calculations, and optical studies, evaluates the potential of PQMO‐PXZ for integration into OLEDs. Unlike existing azaryl‐ketone‐based emitters, PQMO‐PXZ exhibits red‐shifted emission and enhanced luminescence efficiency, due to its rigid structure and strong intramolecular charge transfer characteristics. Significantly, PQMO‐PXZ demonstrates pronounced AIE properties and TADF with a short delayed lifetime. When utilized as the emissive core, OLED devices based on PQMO‐PXZ achieve a respectable external quantum efficiency of up to 11.8 % with minimal efficiency roll‐off, underscoring PQMO‐PXZ's promise as a highly efficient candidate for OLED applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • An intramolecular-locked azaryl ketone acceptor IQLO is designed for TADF emitters. • The new compounds exhibit notable TADF properties, facilitating efficient triplet-to-singlet spin conversion. • IQLO-PXZ and IQLO-DMAC show long-wavelength emission with decent PLQYs of 42% and 47%, respectively. • High electroluminescence efficiency with EQE of up to11.7% is demonstrated. We have developed two novel thermally activated delayed fluorescence (TADF) emitters, IQLO-PXZ and IQLO-DMAC, featuring an intramolecularly locked indeno[1,2- b ]quinolin-11-one (IQLO) acceptor. Our comprehensive investigation, including structural analysis, theoretical calculations, and photophysical studies, aims to assess the viability of IQLO-PXZ and IQLO-DMAC as light emitters in electroluminescent devices. Unlike existing aryl ketone-based emitters, IQLO-PXZ and IQLO-DMAC exhibit red-shifted emission due to their structurally rigid and electron-deficient IQLO moiety. The stronger intramolecular charge transfer effect in IQLO-PXZ results in longer-wavelength emission compared to IQLO-DMAC. Both emitters demonstrate significant TADF properties, facilitating efficient triplet-to-singlet spin conversion. When utilized as the emissive core in electroluminescent devices, IQLO-PXZ and IQLO-DMAC achieved long-wavelength electroluminescence peaking at 612 nm and 578 nm, with commendable external quantum efficiencies of 10.3 % and 11.7 %, respectively. These findings underscore the potential of IQLO as an effective acceptor for constructing high-performance TADF electroluminescent materials. [ABSTRACT FROM AUTHOR]

Semiconductor junctions are among the most important material interfaces in modern technology. The solid polymer light‐emitting electrochemical cell (PLEC) possesses a semiconducting polymer homojunction that is reminiscent of a conventional p–n junction but also exhibits distinct features that are profoundly intriguing. The PLEC junction is formed under bias when the propagating p‐ and n‐doping fronts make contact. The PLEC junction can be immobilized by cooling after the initial junction formation. Further, the resulting frozen junction can be relaxed, or partially de‐doped into a p–i–n junction by controlled heating/cooling cycles. It is on such a frozen polymer p–i–n junction that the authors observed one of the most puzzling phenomena in organic electroluminescence (EL). The frozen p–i–n junction displays the brightest reverse bias (RB) EL ever imaged in a polymer junction and a large photovoltage. Moreover, the RB EL exhibits hypersensitivity to temperature, increasing in intensity by 22.6% K−1 when the de‐doped cell is cooled from 250 to 200 K. A model based on the tunnel injection of charge carriers with fast transit time across the intrinsic region explains the RB EL's hypersensitivity to temperature and super‐linear dependence on cell current. [ABSTRACT FROM AUTHOR]

Pure organic room‐temperature phosphorescence (RTP) materials are considered as potential candidates for replacing precious metal complexes to fabricate highly efficient organic light‐emitting devices (OLEDs). However, applications of the reported RTP materials in OLEDs are seriously impeded by their low photoluminescence quantum yields (PLQYs) in a thin film state. To overcome these obstacles, we established a new strategy to construct highly efficient OLEDs based on a pure organic RTP material sensitized fluorescence emitter by selecting benzimidazole‐triazine molecules (PIM‐TRZ), 2,6‐di(phenothiazinyl)naphthalene (β‐DPTZN), and 5,6,11,12‐tetraphenylnaphthacene (rubrene) as host, phosphor sensitizer, and fluorescent emitter, respectively. The perfect combination of host, phosphorescent sensitizer, and fluorescent emitter in the emitting layer ensure the outstanding performance of the devices with an external quantum efficiency (EQE) of 15.7 %. [ABSTRACT FROM AUTHOR]

Theoretical understanding of organic light-emitting diodes started from the quest to the nature of the primary excitation in organic molecular and polymeric materials. We found the electron correlation strength, bond-length alternation as well as the conjugation extent have strong influences on the orderings of the lowest lying excited states through the first application of density matrix renormalization group theory to quantum chemistry. The electro-injected free carriers (with spin 1/2) can form both singlet and triplet bound states. We found that the singlet exciton formation ratio can exceed the conventional 25% spin statistics limit. We proposed a vibration correlation function formalism to evaluate the excited-state decay rates, which is shown to not only give reasonable estimations for the quantum efficiency but also a quantitative account for the aggregation-induced emission (AIE). It is suggested to unravel the AIE mechanism through resonance Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Several examples of a new class of materials which exhibit thermally-activated delayed fluorescence (TADF) were designed and synthesised. Structure-activity relationships were explored in order to colour-tune the fluorescence (from yellow to blue) and to improve the luminescence quantum yield. Device architectures were optimised for four materials in this class. Notably, the yellow device (CIE1931xy coordinates 0.407, 0.557) displays a maximum external quantum efficiency (EQE) of 14.3%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Molecular design of anthracene-based deep-blue fluorescent emitter is presented. • External quantum efficiency improvement is achieved by TTA. • High efficiency with small roll-off in deep-blue nondoped OLED is realized. Three new anthracene-based emitters, 4-(10-(9,9′-spirobi[fluoren]-2-yl)anthracen-9-yl)benzonitrile (SBF - AnCN), 4-(10-(9,9-diphenyl-9 H -fluoren-2-yl)anthracen-9-yl)benzonitrile (DPF-AnCN) and 4-(10-(9,9-dimethyl-9 H -fluoren-2-yl)anthracen-9-yl)benzonitrile (DMF-AnCN) are developed for deep blue organic light-emitting diodes (OLEDs). Their photophysical properties, thermal properties, molecular configurations and device performances have been systematically investigated. As verified by crystallographic study, these anthracene derivatives possess highly twisted configuration, leading to deep-blue light emission by restraining π-conjugation extension. Furthermore, the difference in the molecular packing manner may influence the photoluminescence quantum yields (PLQYs) in solid state and the proportion of singlet exciton harvested by triplet–triplet annihilation (TTA) process. A nondoped device fabricated using DPF-AnCN as emitter exhibits a maximum external quantum efficiency (EQE) of 7.1% with insignificant efficiency roll-off (6.6%@1000 nit) and Commission Internationale de L'Eclairage (CIE) index of (0.149, 0.104), approaching the standard blue index of the National Television System Committee (NTSC) of (0.14, 0.08). It is demonstrated that TTA is responsible for the excellent electroluminescence (EL) performance. In comparison with doped OLEDs, transient EL decay measurements demonstrate that TTA process is more efficient in the nondoped device. This work would provide an efficient method for designing deep-blue nondoped EL materials. [ABSTRACT FROM AUTHOR]

Studies of delayed electroluminescence in highly efficient fluorescent organic light-emitting diodes (OLEDs) of many dissimilar architectures indicate that the triplet-triplet annihilation (TTA) significantly increases yield of excited singlet states--emitting molecules in this type of device thereby contributes substantially to their efficiency. Towards the end of the 2000s, the essential role of TTA in realizing highly efficient fluorescent devices was widely recognized. Analysis of a diverse set of fluorescent OLEDs shows that high efficiencies are often cor-related to TTA extents. It is therefore likely that it is the long-term empirical optimization of OLED efficiencies that has resulted in fortuitous emergence of TTA as a large and ubiquitous contributor to efficiency. TTA contributions as high as 20-30% are common in the state-of-the-art OLEDs, and even become dominant in special cases, where TTA is shown to substantially exceed the spin-statistical limit. The fundamental features of OLED efficiency enhancement via TTA--molecular structure-dependent contributions, current density-dependent intensities in practical devices and frequently observed antagonistic relationships between TTA extent and OLED lifetime--came to be understood over the course of the next few years. More recently, however, there was much less reported progress with respect to all-important quantitative details of the TTA mechanism. It should be emphasized that, to this day and despite the decades of work on improving blue phosphorescent OLEDs as well as the recent advent of thermally activated delayed fluorescence OLEDs, the majority of practical blue OLEDs still rely on TTA. Considering such practical importance of fluorescent blue OLEDs, the design of blue OLED-compatible materials capable of substantially exceeding the spin-statistical limit in TTA, elimination of the antagonistic relationship between TTA-related efficiency gains and lifetime losses, and designing devices with an extended range of current densities producing near-maximum TTA electroluminescence are the areas where future improvements would be most beneficial. [ABSTRACT FROM AUTHOR]