Compared to efficient green and near‐infrared light‐emitting diodes (LEDs), less progress has been made on deep‐blue perovskite LEDs. They suffer from inefficient domain [various number of PbX6− layers (n)] control, resulting in a series of unfavorable issues such as unstable color, multipeak profile, and poor fluorescence yield. Here, a strategy involving a delicate spacer modulation for quasi‐2D perovskite films via an introduction of aromatic polyamine molecules into the perovskite precursor is reported. With low‐dimensional component engineering, the n1 domain, which shows nonradiative recombination and retarded exciton transfer, is significantly suppressed. Also, the n3 domain, which represents the population of emission species, is remarkably increased. The optimized quasi‐2D perovskite film presents blue emission from the n3 domain (peak at 465 nm) with a photoluminescence quantum yield (PLQY) as high as 77%. It enables the corresponding perovskite LEDs to deliver stable deep‐blue emission (CIE (0.145, 0.05)) with an external quantum efficiency (EQE) of 2.6%. The findings in this work provide further understanding on the structural and emission properties of quasi‐2D perovskites, which pave a new route to design deep‐blue‐emissive perovskite materials.

This work describes a strategy to produce circularly polarized thermally activated delayed fluorescence (CP-TADF). A set of two structurally similar organic emitters SFST and SFOT are constructed, whose spiro architectures containing asymmetric donors result in chirality. Upon grafting within the spiro frameworks, the donor and acceptor are fixed proximally in a face-to-face manner. This orientation allows intramolecular through-space charge transfer (TSCT) to occur in both emitters, leading to TADF properties. The donor units in SFST and SFOT have a sulfur and oxygen atom, respectively; such a subtle difference has great impacts on their photophysical, chiroptical, and electroluminescence (EL) properties. SFOT exhibits greatly enhanced EL performance in doped organic light-emitting diodes, with external quantum efficiency (EQE) up to 23.1%, owing to the concurrent manipulation of highly photoluminescent quantum efficiency (PLQY, ∼90%) and high exciton utilization. As a comparison, the relatively larger sulfur atom in SFST introduces heavy atom effects and leads to distortion of the molecular backbone that lengthens the donor–acceptor distance. SFST thus has lower PLQY and faster nonradiative decay rate. The collective consequence is that the EQE value of SFST, i.e., 12.5%, is much lower than that of SFOT. The chirality of these two spiro emitters results in circularly polarized luminescence. Because SFST has a more distorted molecular architecture than SFOT, the luminescence dissymmetry factor (|g lum|) of circularly polarized luminescence of one enantiomer of the former, namely, either (S)-SFST or (R)-SFST, is almost twice that of (S)-SFOT/(R)-SFOT. Moreover, the CP organic light-emitting diodes (CP-OLEDs) show obvious circularly polarized electroluminescence (CPEL) signals with g EL of 1.30 × 10–3 and 1.0 × 10–3 for (S)-SFST and (S)-SFOT, respectively.

basically limited to donor (D)-π-acceptor (A) molecular architecture. [2] This type of molecular design, first proposed by Adachi and co-workers for TADF, [1a] can tune their D or/and A groups, geometries, and steric hindrance between them to generate twisted induced charge-transfer-type emission. [3] The twisted dihedral angle between D and A units can minimize the singlettriplet splitting energy (ΔE ST) for fast RISC, [1c,4] but the resulted TADF OLEDs still need to be significantly improved, notably in terms of efficiency roll-off at high brightness and concentration quenching because of the ππ intermolecular interactions in the solid-state. [5] Another way to achieve TADF is to use D/A complex, in which the D/A blocks are spatially isolated, but their forming exciplexes are far less efficient than D-π-A analogs, and the resulting OLEDs also display severe efficiency roll-off. [6] Recently, researchers conceptually consider that the intramolecular noncovalent interaction between D/A units in faceto-face alignment could be a new option to realize TADF. [7] Constructing TADF materials in this unconjugated way has the potential to combine the small ΔE ST value with substantial transition dipole and achieve high luminescent efficiency. [8] These two electron-rich and electron-poor π-systems need to be held close in space to form homoconjugation. In this regard, The ORCID identification number(s) for the author(s) of this article can be found under

Rational manipulation of frontier orbital distribution and singlet‐triplet splitting is crucial to exploit the luminescent properties of organic molecules. To realize ultra‐blue luminescence, both blue‐shifted wavelength peak (λpeak) and narrow full‐width at half‐maximum (FWHM) are required. Herein, a new thermally activated delayed fluorescence (TADF) skeleton by inserting the diphenyl methylene intramolecular‐lock to adjust the torsion angles and restrict the intramolecular relaxation is developed. Two rigid emitters, incorporating phenoxazine (PXZN‐B) and acridine (DMACN‐B) as donors and mesitylboron as an acceptor, exhibit narrow FWHMs (<50 nm) with deep‐blue (0.133, 0.147) and violet‐blue emission (0.151, 0.045), respectively. In particular, the Commission Internationale de l'Eclairage (CIE) coordinates of a DMACN‐B‐based device closely approach the Rec.2020 standard (0.131, 0.046). Moreover, both of the organic light‐emitting diodes (OLEDs) based on PXZN‐B and DMACN‐B show TADF character, with high external quantum efficiencies (EQEs) exceeding 10%. Furthermore, owing to the large orbital overlap, these TADF emitters own a fast S1–S0 transition rate exceeding 108 s–1, thereby exhibiting marked amplified spontaneous emission (ASE) with low thresholds. Therefore, the intramolecular‐lock strategy provides not only innovation for realizing high‐efficiency deep‐blue TADF emission with high color purity but also an avenue for a TADF‐based ASE and lasing application.

which have great potential to replace phosphorescent materials based on rare metal (like iridium or platinum) complexes in organic light-emitting diodes (OLEDs). [2] In this kind of so-called D-π-A structures, the intramolecular charge transfer can take place through covalent bond (TBCT). [3] By carefully modulating the twisted angle between donor and acceptor as well as their relative intensities, the singlet-triplet splitting energy (DE ST ) of the D-π-A compounds can be reduced. [4] Then, the reverse intersystem crossing (RISC) process can promote the triplet excitons up to the singlet low-lying state at due to such small DE ST after photo-or electroexcitation. Therefore, 100% internal quantum efficiency (IQE) can be theoretically achieved in OLEDs. Following this strategy, the D-π-A type TADF emitters covering R-G-B even the near infrared regions have been extensively studied. [5] Another way for small DE ST in TADF materials is to separate D/A moieties in unconjugated structures because the isolated D and A would result in a small overlap of highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) for small electron exchange energy. [1d,6] Such D-σ-A type TADF emitters can be constructed by spiro junction, xanthene, triptycene, poly-styrene, etc., [7] and the relative intramolecular charge transfer process is through space (TSCT). [8] However, most of them exhibit mode rate photoluminescence quantum yield (PLQY) and relatively low electroluminescence especially in blue OLEDs. [9] Thus, the design paradigm of D-σ-A type TADF molecules still needs further investigations.In this work, we designed and synthesized a novel sky-blue spiro-type TADF emitter QAFCN, in which the donor and acceptor were not perpendicular to each other although they were connected through a spiro carbon. [5c,10] This was because the rigid donor moiety, 5,9-dihydroquinolino[3,2,1-de]acridine (QA), had a deformed conformation, which could bend the donor toward the acceptor moiety and thus shorten the D/A distance to facilitate the TSCT. [11] As compared to the classic spiro TADF emitter ACRFLCN, [9a] the QAFCN had blue-shifted emission, obviously higher PLQY and faster rate of RISC. Consequently, QAFCN-based device achieved an EQE of 17.9% Through-space charge transfer, which exists in nonconjugation linker based thermally activated delayed fluorescence (TADF) materials, excites chemists to explore more possibilities in organic light-emitting diodes (OLEDs). Herein, an sp 3 -hybrid carbon-centered donor-σ-acceptor type chromophore, QAFCN, is tentatively developed by exploring bi-acridine based electrondonor, i.e., 5,5-dimethyl-5,9-dihydroquinolino[3,2,1-de]acridine (QA). It is interesting to find that the QA moiety shows downshift in highest occupied molecular orbital because of its deformed geometry, which makes it qualified for sky-blue electroluminescence emission. Together with the blue-shift, enhanced photoluminescence quantum yield and faster reverse intersystem crossing rate are also o...