Simultaneously obtaining high efficiency and deep blue emission inorganic light emitting diodes (OLEDs) remains a challenge. To overcome the demands associated with deep blue thermally activated delayed fluorescence (TADF) emitters, two deep blue TADF materials namely, DBA-BFICz and DBA-BTICz, are designed and synthesized by incorporating oxygenbridged boron (DBA) acceptor with heteroatoms, oxygen and sulphur-based donors, BFICz and BTICz, respectively. Both TADF materials show deep blue photoluminescence emissions below 450 nm by enhancing the optical band gap over 2.8 eV through deeper highest occupied molecular orbital (HOMO) level of heteroatom based donor moieties. At the same time, the photoluminescence quantum yields (PLQYs) of both TADF materials remain over 94%. The TADF device with DBA-BFICz as an emitter exhibits a good external quantum efficiency (EQE) of 33.2%. Since both new TADF materials show deep blue emissions and high efficiencies, hyperfluorescence (HF) OLED devices are fabricated using ν-DABNA as a fluorescence dopant. DBA-BFICz as a TADF sensitized host in HF-OLED reveals an outstanding EQE of 38.8% along with narrow full width at half maximum of 19 nm in the bottom emission pure blue OLEDs. This study provides an approach to develop deep blue TADF emitters for highly efficient OLEDs.

Recently, the exploration of boron (B)/heteroatom-embedded polycyclic nanographites featuring multiresonance thermally activated delayed fluorescence (MR-TADF) garners astonishing attention to promote the advancement of organic light-emitting diodes (OLEDs). Contrary to the traditional donor-acceptor (D-A)-type TADF emitters, the MR-TADF emitters manifest narrowband emission with full width at half maximum (FWHM ≤ 40 nm) and superior photoluminescence quantum yield (PLQY) coupled with the small singlet-triplet energy splitting, which appeal their potential as promising candidates in fabricating efficient OLEDs. Growingly, MR-TADF emitters deliver benchmark device performance comparable to the conventional TADF/phosphorescent emitters. However, they are suffering from the major drawbacks such as difficult to realize full-color emitters, slow exciton upconversion dynamics, aggregationcaused emission quenching, severe efficiency roll-off, and poor operational lifetime, which jeopardizes their practical applicability. Herein, a comprehensive review on B-based MR-TADF emitters reported till date is presented, focusing on the different design strategies documented for circumventing the aforementioned shortcomings. This review is divided into several subgroups based on the emission color of the materials to draw the attention of organic electronics community toward constructing efficient full-color MR-OLEDs. Finally, challenges and opportunities in the MR-TADF emitters are discussed.

In the field of organic light emitting diodes (OLEDs), organo-boron based thermally activated delayed fluorescence (TADF) emitters have reached great achievement. However, it is still challenging to achieve pure blue color (CIE y <0.20) along with high efficiencies. To overcome these hurdles, hyperfluorescence (HF) suggest a key strategy in future OLED applications. Here, we report two TADF materials, pMDBA-DI and mMDBA-DI. Further, a pure blue multi resonance type tert-butyl substituted fluorescence emitter, t-Bu-ν-DABNA was also synthesized. Among our synthesized TADF materials based pure blue HF devices, mMDBA-DI as TADF sensitized host with t-Bu-ν-DABNA fluorescence emitter exhibited a high external quantum efficiency of 40.7% (Lambertian assumption) along with narrow emission with full width at half maximum of 19 nm (CIE y=0.15). Moreover, we analyzed that such high device efficiency is mainly attributed to the high orientation factor, enhanced photoluminescence quantum yield, and a good TADF characteristic of t-Bu-ν-DABNA with high Förster resonance energy transfer.

The subclass of multi resonant thermally activated delayed fluorescent emitters (MR-TADF) containing boron atoms has garnered significant attention in the field of organic light emitting diode (OLED) research. Among boron-based MR-TADF emitters, double boron-embedded MR-TADF (DB-MR-TADF) emitters show excellent electroluminescence performances with high photoluminescence quantum yields, narrow band emission, and beneficially small singlet-triplet energy levels in all the full-color gamut regions. This article reviews recent progress in DB-MR-TADF emitters, with particular attention to molecular design concepts, synthetic routes, optoelectronic properties, and OLED performance, giving future prospects for real-world applications.

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Pure organic molecules based thermally activated delayed fluorescence (TADF) emitters have been successfully developed in recent years for their propitious application in highly efficient organic light emitting diodes (OLEDs). In the case of orange red emitters, the non-radiative process is known to be a serious issue due to its lower lying singlet energy level. However, recent studies indicate that there are tremendous efforts put to develop efficient orange red TADF emitters. In addition, the external quantum efficiency (EQE) of heteroaromatic based orange red TADF OLEDs surpassed 30 %. Such heteroaromatic type emitters showed wide emission spectra; therefore, more attention is being paid to develop highly efficient orange red TADF emitters along with good color purity. Herein, the recent progress of orange red TADF emitters based on molecular structures, such as cyanobenzene, heteroaromatic, naphthalimide, and boronbased acceptors, are reviewed. Further, our insight on these acceptors has been provided by their photophysical studies and device performances. Future perspectives of orange red TADF emitters for real practical applications are discussed.[a] K.

microcavities are used to decrease the fullwidth half maximum (FWHM) of the EL spectra in the latest OLEDs, the development of high efficient luminescent materials with narrowband emissions to realize high color purity displays is highly desired. [11] Recently, In 2016, Hatakeyama et al. reported boron-based emitter 5,9-diphenyl-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracene (DABNA-1) exhibiting multiple resonance effect (MR effect) with alternative highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). [12] In addition, the DABNA-1 showed the pure narrow spectral width of 28 nm and blue emission with high photoluminescence (PL) quantum yield (PLQY) and good color purity. [12] Even though this MR effect is suitable for narrow FWHM emission, the emission color in MR moieties is mainly limited to blue and green region. There are fewer reports based on the MR effect using boron and nitrogen atoms in the red emission region. [13,14] Recently Yasuda et al. developed BBCz-R by considering the B-π-B and N-π-N strategy for narrow red emission with a yield of just 5%. [15] By viewing the same design, Duan et al. reported more bathochromic shifted emitters (R-BN and R-TBN) with high PLQY and pure color in the deep-red region (over 650 nm). [14] Even though these two works show a narrow emission spectrum, the synthesis is complex due to double borylation, which includes double lithiation on the para position of the benzene ring, which is challenging for scale the reactions and utilize in display industries. Moreover in red region with high PLQY and narrow spectrum, there are reports like BODIPY emitters. [16][17][18][19][20][21] But this type of emitter shows a deep LUMO energy level, which could provide difficulty in selecting a host and other layer materials for OLED device fabrication. In particular, the development of narrow red emission for optoelectronic applications presents a unique set of challenges. Considering these limitations and the difficulty of material synthesis, it is an urgent requirement to develop a new design strategy for the narrow spectrum in bathochromic shifted emissions.Herein we propose a new novel molecular design for producing easy pure red color with a narrow spectral width. With the proposed design, the emitters (N, N, 9-triphenyl-9H-9-aza-13b-boratetrabenzo [a, de, kl, rst] pentaphen-7-amine) (BP-2DPA), and (5-(7-(diphenylamino)-9-phenyl-9H-9-aza-13b boratetrabenzo [a,de,kl,rst] pentaphen-18-yl)-N1,N1,N3,N3-tetraphenylbenzene-1,3-diamine) (DBP-4DPA) were developed and synthesized. Both the emitters show

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