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Although sensitizing traditional fluorescent dyes with thermally activated delayed fluorescence (TADF) exciplexes has been extensively studied, the device performance of solution‐processed organic light‐emitting diodes (OLEDs) still lags far behind in this regard. Herein, the novel exciplex with high up‐conversion efficiency composed of a triazatruxene‐based donor and a triazine‐based acceptor is employed as a TADF sensitizer to fluorescent dye in solution‐processed hyperfluorescent OLEDs. Benefiting from the small activation energy for triplet up‐conversion and less non‐radiative recombination of triplet excitons, the new TADF exciplex can up‐convert efficiently non‐radiative triplet excitons through reverse intersystem crossing. Besides, expeditious up‐conversion processes also shorten the residence time of triplet excitons, giving rise to significant suppression of detrimental Dexter energy transfer from the exciplex sensitizer to the dopant. By maximizing the triplet up‐conversion efficiency of exciplex sensitizers, the optimized OLEDs achieve a maximum external quantum efficiency (EQEmax) of 16.0%, which is the first report for the solution‐processed exciplex‐sensitized hyperfluorescent OLEDs with EQEmax exceeding 15%. These results validate that the up‐conversion efficiency of triplet excitons in the exciplexes strongly affects the performance of exciplex‐sensitized fluorescent devices, and the triazatruxene‐based molecules are promising donor candidates for constructing the exciplexes with high up‐conversion efficiency. [ABSTRACT FROM AUTHOR]

The hyperfluorescence has drawn great attention in achieving efficient narrowband emitting devices based on multiple resonance thermally activated delayed fluorescence (MR‐TADF) emitters. However, achieving efficient solution‐processed pure blue hyperfluorescence devices is still a challenge, due to the unbalanced charge transport and serious exciton quenching caused by that the holes are easily trapped on the high‐lying HOMO (the highest occupied molecular orbital) level of traditional diphenylamine‐decorated emitters. Here, we developed two narrowband blue organoboron emitters with low‐lying HOMO levels by decorating the MR‐TADF core with weakly electron‐donating carbazoles, which could suppress the hole trapping effect by reducing the hole traps between host and MR‐TADF emitter from deep (0.40 eV) to shallow (0.14/0.20 eV) ones for facilitating hole transport and exciton formation, as well as avoiding exciton quenching. And the large dihedral angle between the carbazole and MR‐TADF core makes the carbazole act as a steric hindrance to inhibit molecular aggregation. Accordingly, the optimized solution‐processed pure blue hyperfluorescence devices simultaneously realize record external quantum efficiency of 29.2 %, narrowband emission with a full‐width at half‐maximum of 16.6 nm, and pure blue color with CIE coordinates of (0.139, 0.189), which is the best result for the solution‐processed organic light‐emitting diodes based on MR‐TADF emitters. [ABSTRACT FROM AUTHOR]

A simple N,S-chelated four-coordinated difluoroboron-based emitter is reported with three polymorphs, which emit high contrast green (G), yellow (Y) and red (R) light. Interestingly, the G and R-Crystals show different thermally activated delayed fluorescence (TADF) at 530 nm and 630 nm with a remarkable emission spectral shift of up to 100 nm, while the Y-Crystal exhibits room temperature phosphorescence (RTP) at around 570 nm with a high solid-state quantum yield of 77%. Single crystal analysis and theoretical calculations reveal that different molecular conformations and packing modes lead to distinct triplet exciton conversion channels. [ABSTRACT FROM AUTHOR]

Two boron‐, sulfur‐ and nitrogen‐doped polycyclic aromatic hydrocarbon multiple resonance thermally activated delayed fluorescence emitters with high photoluminescent quantum efficiency (88 %) and rapid reverse intersystem crossing (kRISC= 1.0×105 s−1) are designed and synthesized, enabling efficient narrow‐band blue electroluminescence at 473 nm with full width at half maximum of 29 nm and maximum external quantum efficiency of 22.0 %, which provides an avenue to expand the structure library for multiple resonance emitters and an approach to regulate their emission properties. [ABSTRACT FROM AUTHOR]

A series of host materials (1FTAT-2Ph, 2FTAT-1Ph, 3FTAT) containing a hole-transport triphenyl-substituted triazatruxene conjugated skeleton and different numbers of diphenyl methylene-bridging groups were developed for solution-processed yellow thermally activated delayed fluorescence (TADF) organic light emitting diodes (OLEDs). These host materials possessed relatively high triplet energy (≈2.8 eV), which ensured effective energy transfer from host to TADF emitter. Meanwhile, the peripheral diphenyl methylene bridging groups effectively separated the TADF emitters to suppress intermolecular aggregation and exciton quenching. They also showed high thermal stability and good solubility in organic solvents. Benefited from the elevated highest occupied molecular orbital level matched well with the Fermi level of ITO/PEDOT:PSS anode and significantly suppressed excited state non-radiative transition of TADF emitter, solution-processed OLED using 2FTAT-1Ph as host exhibited a low turn on voltage of 2.8 V and high external quantum efficiency of 20.9% with a remarkable high power efficiency of 72.7 lm W−1, which was far superior to those of the control device with 4,4′-N,N′-Dicarbazole-biphenyl (CBP) as host. This work demonstrated the great potential of diphenyl methylene bridged triazatruxene derivatives as host materials to achieve high-performance solution-processed TADF OLED. [Display omitted] • A series of bridged triazatruxene-based host materials (1FTAT-2Ph, 2FTAT-1Ph, 3FTAT) were developed for the solution-processed TADF OLEDs. • These bridged triazatruxene hosts possess high T 1 energy (2.8 eV), proper HOMO levels (−5.2∼−5.3 eV) and good thermal stability and solubility. • Solution-processed 2FTAT-1Ph-based TADF-OLED exhibited a turn on voltage of 2.8 V, an EQE of 20.9% and a PE of 72.7 lm W−1. [ABSTRACT FROM AUTHOR]

Boron, sulfur-doped polycyclic aromatic hydrocarbon emitters with multiple-resonance-dominated lowest excited states are developed by tuning energy level alignment between 5,9-dithia-13b-boranaphtho[3,2,1- de ]anthracene skeleton and peripheral arylamine moieties, which reveal narrowband deep-blue electroluminescence with full-width at half maximum of 29 nm, Commission Internationale de l'Éclairage color coordinates of (0.13, 0.09) and maximum external quantum efficiency of 21.8%. [Display omitted] • Novel B,S-doped polycyclic aromatic multiple resonance emitters are developed. • Sulfur atoms enhance spin-orbital coupling and reverse intersystem crossing. • The lowest excited state characteristics are regulated by arylamine substituents. • The emitters exhibit narrowband deep-blue electroluminecence with EQE of 21.8%. Different from boron, nitrogen-based multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters, boron (B), sulfur (S)-doped polycyclic aromatic hydrocarbons (PAHs) containing 5,9-dithia-13b-boranaphtho[3,2,1- de ]anthracene (BSS) skeleton and arylamine moieties in para -positions of boron atoms are developed as a novel kind of MR-TADF emitters for narrowband deep-blue electroluminescence. The molecular design not only utilizes heavy-atom effect of sulfur atoms in BSS skeleton to enhance spin-orbital coupling and promote reverse intersystem crossing, but also uses arylamines as peripheral substituents to modify excited state characteristics. By decreasing electron-donating ability and downshifting HOMO level of arylamines, the lowest excited state for resultant emitter is converted from intersegmental charge transfer state to multiple resonance state localized on BSS skeleton, leading to blue-shifted and narrowed emissions. The B,S-doped PAH emitter bearing carbazole moiety exhibits deep-blue electroluminecence with full-width at half maximum of 29 nm, Commission Internationale de l'Éclairage color coordinates of (0.13, 0.09), and the maximum external quantum efficiency of 21.8 %, representing a new approach toward efficient narrowband deep-blue emission beyond boron, nitrogen-based MR-TADF emitters. [ABSTRACT FROM AUTHOR]