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Isomeric emitters with the same donor and acceptor but different connection sites that have a non-negligible influence on molecular properties including radiative/non-radiative decays, reverse intersystem crossing, photophysical and electrical performances.

Benefitting from the concurrent intramolecular TBCT and TSCT of ortho-linked TADF materials, high kF and kRISC are achieved simultaneously and the devices using o-DCz-TRZ and BN-DMAc as emitters achieved high EQEs of 20.3% and 24.2%.

Developing highly efficient red/near-infrared thermally activated delayed fluorescence (TADF) materials is of great importance for organic light-emitting diodes (OLEDs). Here, we reported an asymmetric TADF emitter (TCPQ), which exhibits a high reverse intersystem crossing rate as well as a low non-radiative rate due to molecular symmetry breaking through multiple donor substitution. The coexistence of multiple donors endows TCPQ with not only near-infrared emission but also excellent device performances. As for the TCPQ-based OLEDs, the 10 and 20 wt % doped devices exhibit outstanding external quantum efficiencies (EQEs) of 21.9 and 19.2% with red emission peaks at 612 and 642 nm, respectively. Meanwhile, the non-doped device achieves an EQE of 5.4% with an emission peak at 718 nm, showing near-infrared emission. These device efficiencies are among the best performances of red/near-infrared TADF-OLEDs, demonstrating that the asymmetry design is a potential strategy for constructing long wavelength TADF materials with high efficiency.

Room-temperature phosphorescence (RTP) materials based on phosphor-doped polymers have been studied for more than sixty years. In these polymer-based RTP materials, the intrinsic structures and properties of polymeric matrixes are critical to their triplet emission. However, RTP materials with non-homogeneous matrixes are rarely studied, and far too little attention has been paid to the possible interferences of structures and components of polymeric matrixes on the final photophysical properties. In this work, we reported RTP materials with phase-separated matrixes consisting of two incompatible polymers, i.e., polystyrene (PS) and polyisoprene (PI). By doping difluoroboron β-diketonate derivatives into the blends or block copolymers of PS and PI, bright and long-lived green RTP emissions can be obtained under ambient conditions, while no afterglow can be observed in pure PS or PI homopolymers. The mechanism of triplet emission in heterogeneous matrixes was investigated. The findings of this work provide a new approach to the low-cost fabrication of RTP materials with comprehensive performances through high-throughput processing methods.

By attaching a few kinds of two aryl-side groups into pyrene core at 5,9-positions, five pyrene-based color-tunable blue emitters have been developed for highly efficient nondoped and doped blue OLEDs.

Nonconventional luminescent polymers (NCLPs) have attracted considerable attention due to their unique luminescence behavior. Although various routes can be employed to synthesize such vinyl-based NCLP, the dependence of their photophysical properties on the polymerization method used and thus potential small variations of the overall macromolecular architecture is rarely reported. In this study, we have investigated in detail the luminescence behavior of polyacrylonitriles (PANs) synthesized with two different polymerization methods, namely by free-radical polymerization (FRP), and reversible addition-fragmentation chain transfer (RAFT). Dependent on the polymerization route and initiator used, the PANs show distinct PL and excitation wavelengths, and their emission covers a wavelength range from 400 to 630 nm, respectively. Moreover, the synthesized PANs easily can be homogeneously blended both in solution and solid states, and the resulting emission is a superposition of the emission of the blend components. This study provides a facile approach to tune the photophysical properties of PANs and related vinyl-based NCLPs and provides new fundamental insight to further booster application development of NCLPs.

Fast spin-flipping is the key to exploit the triplet excitons in thermally activated delayed fluorescence based organic light-emitting diodes toward high efficiency, low efficiency roll-off and long operating lifetime. In common donor-acceptor type thermally activated delayed fluorescence molecules, the distribution of dihedral angles in the film state would have significant influence on the photo-physical properties, which are usually neglected by researches. Herein, we find that the excited state lifetimes of thermally activated delayed fluorescence emitters are subjected to conformation distributions in the host-guest system. Acridine-type flexible donors have a broad conformation distribution or bimodal distribution, in which some conformers feature large singlet-triplet energy gap, leading to long excited state lifetime. Utilization of rigid donors with steric hindrance can restrict the conformation distributions in the film to achieve degenerate singlet and triplet states, which is beneficial to efficient reverse intersystem crossing. Based on this principle, three prototype thermally activated delayed fluorescence emitters with confined conformation distributions are developed, achieving high reverse intersystem crossing rate constants greater than 106 s−1, which enable highly efficient solution-processed organic light-emitting diodes with suppressed efficiency roll-off.

An unprecedented Pd/Rh cooperatively catalyzed arylalkynylation of alkynylsilanes was developed to merge an alkynylidene moiety with benzosilacycle. These silaarenes possess a particular aggregation-induced emission behavior. Mechanistic investigations demonstrate that the relay trimetallic transmetalation plays a pivotal role in governing this transformation.

Although tremendous progress has recently been made in quasi-2D perovskite light-emitting diodes (PeLEDs), the performance of red PeLEDs emitting at ≈650-660 nm, which have wide prospects for application in photodynamic therapy, is still limited by an inefficient energy transfer process between the quasi-2D perovskite layers. Herein, a symmetric molecule of 3,3'-(9H-fluorene-9,9-diyl)dipropanamide (FDPA) is designed and developed with two functional acylamino groups and incorporated into the quasi-2D perovskites as the additive for achieving high-performance red PeLEDs. It is demonstrated that the agent can simultaneously diminish the van der Waals gaps between individual perovskite layers and passivate uncoordinated Pb

A series of ultrapure-blue thermally activated delayed fluorescence (TADF) emitters featuring through-space charge transfer (TSCT) have been constructed by close stacking between the donor and acceptor moieties in rigid heteroaromatic compounds. The obviously accelerated radiative transition of singlet excitons, the diminished vibrionic relaxation of ground and excited states, and the consequent reduced Stokes shift and the narrow emission are evident. The corresponding organic light-emitting diodes (OLEDs) based on AC-BO realize the best performance among all deep-blue TSCT-TADF emitters, with an external quantum efficiency (EQE

Constructing organic near-infrared (NIR) luminescent materials to confront the formidable barrier of "energy gap law" remains challenging. Herein, two NIR thermally activated delayed fluorescence (TADF) molecules named T-β-IQD and TIQD were developed by connecting N,N-diphenylnaphthalen-2-amine and triphenylamine with a novel electron withdrawing unit 6-(4-(tert-butyl)phenyl)-6H-indolo[2,3-b]quinoxaline-2,3-dicarbonitrile. It is confirmed NIR-TADF emitters concurrent with aggregation-induced emission effect, J-aggregate with intra- and intermolecular CN⋅⋅⋅H-C and C-H⋅⋅⋅π interactions, and large center-to-center distance in solid states can boost the emissive efficiencies both in thin films and non-doped organic light-emitting diodes (OLEDs). Consequently, the T-β-IQD-based non-doped NIR-OLED achieved the maximum external quantum efficiency (EQE

Highly efficient organic thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) emitters for organic light-emitting diodes (OLEDs) generally consist of a twisted donor-acceptor skeleton with aromatic amine donors. Herein, through introducing sulfur atoms into isomeric pentaphene and pentacene frameworks, we demonstrate a set of polycyclic luminophores exhibiting efficient TADF and RTP characters. The incorporation of sulfur atoms confirms a folded molecular plane, while intensifies singlet-triplet spin-orbit coupling. Further, the isomeric effect has a significant effect on the electronic structure of excited state, giving rise to the investigated compounds tunable luminescence mechanisms of TADF and RTP. With efficient triplet harvesting ability, maximum external quantum efficiencies up to 25.1 % and 8.7 % are achieved for the corresponding TADF and RTP OLEDs, verifying the great potential of sulfur-bridged frameworks for highly efficient devices.

Summary The inferior light extraction efficiency (LEE), which is generally less than 20%, based on optical modeling, and the difficulty in achieving white emission are the two main challenges in the metal-halide-perovskite light-emitting diode (PeLED) field. Herein, we report a simple and efficient approach to construct high-performance white PeLEDs with much-enhanced LEE by coupling a blue PeLED with a layer of red perovskite nanocrystal (PeNC) down-converter through a rationally designed multilayer semitransparent electrode (LiF/Al/Ag/LiF). The red PeNC layer allows the extraction of the trapped waveguide mode and surface plasmon polariton mode in a blue PeLED and converts them to red emission, resulting in over 50% LEE improvement. Simultaneously, the complementary emission spectrum of blue photons and down-converting red photons contributes to a white PeLED with a high external quantum efficiency and luminance of more than 12% and approximately 2,000 cd m−2, respectively, which represent state-of-the-art results in this field.

Luminescence behaviors in organic emitters are influenced greatly by the molecular conformation. However, the current research on room-temperature phosphorescence (RTP) mainly focuses on fixed molecular conformation, such as that in single crystals and rigid hosts. Herein, by linking the phenothiazine moiety with nitrogen heterocycles, we constructed four phenothiazine derivates having planar structure in the ground state. In the excited state, a large conformation relaxation occurs to give a dynamically tunable fluorescence and phosphorescence by the extent of the intramolecular charge transfer (ICT). In systems with a reduced ICT character, multiple emissions consisting of fluorescence and phosphorescence were observed and a white light emission was obtained in the amorphous film state. When increasing the ICT, strong spin mixing between the singlet and triplet occurs in the twisted intramolecular charge transfer (TICT) state, which is favorable for a short triplet lifetime. The emission of the thermally activated delayed fluorescence (TADF) or short RTP depends on the allowance or forbidden of fluorescence in the twisted excited state conformation. This work demonstrates the adjustment of the singlet and triplet emission behaviors through controlling the extent of TICT and provides an insight into the relationship between the molecular conformation and triplet exciton dynamics for future applications.

Luminescence from organic clusters has gained increasing interest recently because of their distinct emission characteristics compared with the monomer, such as color tunable emission with different wavelength excitations. Herein, we reported three lactams with different ring-members of heterocyclics: indolin-2-one (OID), 3,4-dihydroquinolin-2(1H)-one (OID-6) and 1,3,4,5-tetrahydro-2H-benzo[b]azepin-2-one (OID-7) with dual persistent room-temperature phosphorescence (p-RTP) in the crystalline state owing to the formation of clusters. Due to the dual p-RTP with different but comparable phosphorescence lifetimes of multiple triplet states, it is of interest that OID-6 and OID-7 exhibit time-dependent afterglow color emissions from blue to green to yellow, and this is the first report on organic crystalline clusters with time-dependent color-tunable dual persistent room-temperature phosphorescence. The longest phosphorescence lifetime and the highest photoluminescence quantum yield among these three compounds were observed for OID-7 with the most twisted molecular configuration, owing to the simultaneously suppressed triplet quenching and intramolecular vibrational relaxation by the small orbital overlap due to its weak π–π stacking and strong intermolecular hydrogen bonding interactions in the crystalline state.

A series of pure organic halogenated hexaphenylmelamine (HPM) derivatives featuring remarkably weakened ultralong room-temperature phosphorescence (RTP) were meticulously investigated. As the p-substituted atoms of these HPM derivatives sequentially changed from H to F, Cl and Br, both the RTP lifetimes and efficiencies dramatically decreased from 608 ms with 13.4% (HPM-H) to 337 ms with 5.3% (HPM-F), 99 ms with 1.3% (HPM-Cl), and 2.8 ms with undetectable efficiency (HPM-Br), respectively. Most notably, the severely weakened efficiencies are fundamentally different from the trends of the effect of halogenation on phosphorescence properties previously reported. Coupled with experimental results and theoretical simulations, the subtle change of molecular packing induced by halogenation should be responsible for the distinctive RTP properties. This finding not only provides a unique halogen-involved RTP phenomenon, but also offers a very special perspective to understand the effect of halogenation on phosphorescence.

Purely organic materials usually exhibit weak spin-orbital coupling (SOC) effect because of the lack of noble heavy metals, and the generation and direct emission from the triplet state is spin-forbidden. This would lead to slow intersystem crossing, long triplet lifetime, and low phosphorescence quantum yield. Herein, strong spin-orbital coupling between singlet and triplet was observed in a "flexible" and twist thianthrene-pyrimidine-based purely organic compound in an amorphous film state, which shows a fast intersystem crossing process and a high phosphorescence rate of 1.1 × 10

Versatile host materials with good chemical stability and carrier-transporting ability are quite responsible for achieving stable solution-processed thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). Herein, we reported three bipolar dendritic hosts with or without the electron-withdrawing pyridine moiety via 6-site-linkages, namely, 3,3'-bis(3,3″,6,6″-tetra-tert-butyl-9'H-[9,3':6',9″-tercarbazol]-9'-yl)-1,1'-biphenyl (mCDtCBP), 3,3″,6,6″-tetra-tert-butyl-9'-(6-(3-(3,3″,6,6″-tetra-tert-butyl-9'H-[9,3':6',9″-tercarbazol]-9'-yl)phenyl)pyridine-2-yl)-9'H-9,3':6',9″-tercarbazole (mCDtCBPy), and 6,6'-bis(3,3″,6,6″-tetra-tert-butyl-9'H-[9,3':6',9″-tercarbazol]-9'-yl)-2,2'-bipyridine (mCDtCBDPy), exhibiting outstanding solubility, thermal stability as well as electrochemical stability. According to the calculation of bond dissociation energy (BDE), photodegradation results, and carrier dynamics evaluation, a significant relationship between device stability and the pyridine-based dendritic hosts was uncovered. Using mCDtCDPy with the highest electron mobility as the host, the solution-processed bluish-green TADF-OLED showed the shortest operational lifetime due to the unbalanced charge fluxes despite its highest anionic BDE for good chemical stability. However, the device based on mCDtCBPy exhibited twice longer lifetime than that based on mCDtCBP in spite of their similar balanced charge transportation, highlighting the importance of higher anionic BDE of the C-N bond in the device degradation process. Our findings unveiled a potential approach to achieve a subtle regulation of chemical stability and carrier transportation for realizing stable solution-processed TADF-OLEDs.

A new type of simple emissive organic cage consisting of diphenyl sulfone units and nitrogen atoms was developed via one-pot C–N coupling condensation or two-step reactions along with a series of sulfoxide cages obtained, which exhibited excellent chemical modifiability and structural stability. By precisely controlling the participation of donor and acceptor units, a highly soluble organic cage with delayed fluorescence was obtained for the first time. More interestingly, due to the restriction of intramolecular flipping by locking the building blocks within a rigid framework, this emissive organic cage further showed narrowband ultra-deep blue electroluminescence emission at 413 nm with a full-width at half-maximum of 35 nm. This finding not only expands the family of electroluminescent organic cages, but also opens up a new platform for delayed fluorescence materials with high solubility and color purity.

A series of novel hyper-structured molecular (HSM) thermally activated delayed fluorescent (TADF) emitters, in which the TADF units and host units are bound together into one inactive core through flexible linkages, were designed. Phenoxazine-triphenyltriazine (PXZ-Trz), 1,3-bis(9H-carbazol-9-yl)benzene (mCP) and calix[4]resorcinarene (CRA) were chosen as the TADF unit, the host unit and the core, respectively. A series of CRA-based HSM emitters, CRA-PXZ-Trz(X)-mCP(100−X) (X = 0, 12.5, 25, 50, 75, 87.5 or 100) were successfully synthesized by a two-step click reaction. Upon using non-doped CRA-PXZ-Trz(87.5)-mCP(12.5) as the light-emitting layer, the solution-processable OLEDs emitted yellow-green light, and displayed an external quantum efficiency of 16.7% at 100 cd m−2.

Multiple resonance thermally activated delayed fluorescence (MR-TADF) compounds have set off an upsurge of research because of their tremendous application prospects in the field of wide color gamut display. Herein, we propose a novel MR-TADF molecular construction paradigm based on polycyclization of the multiple resonance parent core, and construct a representative multiple resonance polycyclic aromatic hydrocarbon (MR-PAH) based on the para-alignment of boron and nitrogen atoms into a six-membered ring (p-BNR). Through the retrosynthesis analysis, a concise synthesis strategy with wide applicability has been proposed, encompassing programmed sequential boron esterification, Suzuki coupling and Scholl oxidative coupling. The target model molecule BN-TP shows green fluorescence with an emission peak at 523 nm and a narrow full-width at half-maximum (FWHM) of 34 nm. The organic light-emitting diode (OLED) employing BN-TP as an emitter exhibits ultrapure green emission with Commission Internationale de L'Eclairage (CIE) coordinates of (0.26, 0.70), and achieves a maximum external quantum efficiency (EQE) of 35.1 %.