Herein, we demonstrate that the strategic implementation of electron-accepting tricoordinate boron and electron-donating carbazole subunits into polycyclic aromatic hydrocarbons (PAHs) produces a family of attractive full-color luminophores that can emit narrowband and efficient thermally activated delayed fluorescence (TADF). A versatile modular design for these boron- and carbazole-embedded PAHs can facilitate the systematic modulation of their photophysical and optoelectronic properties. Organic light-emitting diodes that utilize these PAHs as TADF emitters demonstrate narrowband electroluminescence from blue to red, achieving high maximum external quantum efficiencies of 29.3%, 31.8%, and 22.0% for blue, green, and red, respectively.

Full-Color, Narrowband, and High-Efficiency Electroluminescence from Boron and Carbazole Embedded Polycyclic Heteroaromatics.

We thank the Leverhulme Trust (RPG-2016-047) for the financial support. S.S. acknowledges sup-port from the Marie Sklodowska-Curie Individual Fellowship (NarrowbandSSL EC Grant Agree-ment No: 838885). Computational resources have been provided by the Consortium des Equipements de Calcul Inten-sif (CECI), funded by the Fonds de la Recherche Scientifiques de Belgique (F.R.S.-FNRS) under Grant No. 2.5020.11, as well as the Tier-1 supercomputer of the Federation Wallonie-Bruxelles, infrastructure funded by the Walloon Region under the grant agreement n1117545. DB is a FNRS Research Director.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/adfm.201908677

Multiresonant Thermally Activated Delayed Fluorescence Emitters Based on Heteroatom-Doped Nanographenes: Recent Advances and Prospects for Organic Light-Emitting Diodes

Thermally activated delayed fluorescence (TADF) materials based on the multiple resonance (MR) effect are applied in organic light-emitting diodes (OLEDs), combining high color purity and efficiency. However, they are not fabricated via solution-processing, which is an economical approach toward the mass production of OLED displays. Here, a solution-processable MR-TADF material (OAB-ABP-1), with an extended π-skeleton and bulky substituents, is designed. OAB-ABP-1 is synthesized from commercially available starting materials via a four-step process involving one-shot double borylation. OAB-ABP-1 presents attractive photophysical properties, a narrow emission band, a high photoluminescence quantum yield, a small energy gap between S1 and T1 , and low activation energy for reverse intersystem crossing. These properties are attributed to the alternating localization of the highest occupied and lowest unoccupied molecular orbitals induced by the boron, nitrogen, and oxygen atoms. Furthermore, to facilitate charge recombination, two novel semiconducting polymers with similar ionization potentials to that of OAB-ABP-1 are synthesized for use as interlayer and emissive layer materials. A solution-processed OLED device is fabricated using OAB-ABP-1 and the aforementioned polymers; it exhibits pure green electroluminescence with a small full-width at half-maximum and a high external quantum efficiency with minimum efficiency roll-off.

Solution-Processable Pure Green Thermally Activated Delayed Fluorescence Emitter Based on the Multiple Resonance Effect.

The design and synthesis of organic materials with a narrow emission band in the longer wavelength region beyond 510 nm remain a great challenge. For constructing narrowband green emitters, we propose a unique molecular design strategy based on frontier molecular orbital engineering (FMOE), which can integrate the advantages of a twisted donor-acceptor (D-A) structure and a multiple resonance (MR) delayed fluorescence skeleton. Attaching an auxiliary donor to a MR skeleton leads to a novel molecule with twisted D-A and MR structure characteristics. Importantly, a remarkable red-shift of the emission maximum and a narrowband spectrum are achieved simultaneously. The target molecule has been employed as an emitter to fabricate green organic light-emitting diodes (OLEDs) with Commission Internationale de L'Eclairage (CIE) coordinates of (0.23, 0.69) and a maximum external quantum efficiency (EQE) of 27.0 %.

Constructing Charge‐Transfer Excited States Based on Frontier Molecular Orbital Engineering: Narrowband Green Electroluminescence with High Color Purity and Efficiency

Efficient organic emitters in the deep-red region are rare due to the "energy gap law". Herein, multiple boron (B)- and nitrogen (N)-atoms embedded polycyclic heteroaromatics featuring hybridized π-bonding/ non-bonding molecular orbitals are constructed, providing a way to overcome the above luminescent boundary. The introduction of B-phenyl-B and N-phenyl-N structures enhances the electronic coupling of those para-positioned atoms, forming restricted π-bonds on the phenyl-core for delocalized excited states and thus a narrow energy gap. The mutually ortho-positioned B- and N-atoms also induce a multi-resonance effect on the peripheral skeleton for the non-bonding orbitals, creating shallow potential energy surfaces to eliminate the high-frequency vibrational quenching. The corresponding deep-red emitters with peaks at 662 and 692 nm exhibit narrow full-width at half-maximums of 38 nm, high radiative decay rates of ca. 108  s-1 , ≈100 % photo-luminescence quantum yields and record-high maximum external quantum efficiencies of ca. 28 % in a normal planar organic light-emitting diode structure, simultaneously.

Multi-Resonance Deep-Red Emitters with Shallow Potential-Energy Surfaces to Surpass Energy-Gap Law**

Isomeric Bright Sky-Blue TADF Emitters Based on Bisacridine Decorated DBNA: Impact of Donor Locations on Luminescent and Electroluminescent Properties

New symmetric and unsymmetric B,N,B-doped benzo[4]helicenes 3-6 a/b have been achieved in good yields, using a three-step process, starting from N(tolyl)3 in a highly divergent manner (7 examples). A borinic acid functionalized 1,4-B,N-anthracene 1 was found to display unprecedented reactivity, acting as a convenient and highly effective precursor for selective formation of bromo-substituted B,N,B-benzo[4]helicenes 2 a/2 b via intramolecular borylation and sequential B-Mes bond cleavage in the presence of BBr3 . Subsequent reaction of 2 a/2 b with Ar-Li provided a highly effective toolbox for the preparation of symmetrically/unsymmetrically functionalized B,N,B-helicenes. Their high photoluminescence quantum yields along with the small ΔEST suggest their potential as thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs).

/pdf/intramolecular-borylation-via-sequential-b-mes-bond-cleavage-tvnf95c7j4.pdf

Intramolecular Borylation via Sequential B-Mes Bond Cleavage for the Divergent Synthesis of B,N,B-Doped Benzo[4]helicenes.

Enantiopure molecules based on macrocyclic architecture are unique for applications in enantioselective host-guest recognition, chiral sensing and asymmetric catalysis. Taking advantage of the chiral transfer from the intrinsically planar chirality of pillar[5]arenes, we herein present an efficient and straightforward approach to achieve early examples of highly luminescent chiral systems (P5NN and P5BN). The optical resolution of their enantiomers has been carried out via preparative chiral HPLC, which was ascribed to the molecular functionalization of pillar[5]arenes with π-conjugated, sterically bulky triarylamine (Ar3 N) as an electron donor and triarylborane (Ar3 B) as an acceptor. This crucial design enabled investigations of the chiroptical properties, including circular dichroism (CD) and circularly polarized luminescence (CPL) in the solid state. The intramolecular charge transfer (ICT) nature in P5BN afforded an interesting thermochromic shift of the emission over a wide temperature range.

/pdf/planar-chiral-organoboranes-with-thermoresponsive-emission-2t1qdwkapp.pdf

Planar Chiral Organoboranes with Thermoresponsive Emission and Circularly Polarized Luminescence: Integration of Pillar[5]arenes with Boron Chemistry

Herein, we report on an unusual light-emitting behavior of the homo- and copillar[5]arenes (MeP5, EtP5, PrP5, BuP5, DBuP5 and DBP5) with combinations of alkoxy functionalities. Our investigations revealed that the emission of these pillar[5]arenes was highly enhanced in the aggregate state. This turn-on fluorescence could be ascribed to the well-known aggregation-induced-emission (AIE) mechanism, which was confirmed by SEM imaging and the dynamic light scattering (DLS) technique. The current work may open another avenue to the chemistry of pillararenes as new AIEgen macrocycles for luminescence sensing of guest species including organic molecules, and metal ions as herein tested for Fe(III).

Pillar[5]arenes: a new class of AIEgen macrocycles used for luminescence sensing of Fe3+ ions

A new class of benchtop-stable boron-doped pentacenes, ie, 5,14-dimesityl-5,14-dihydro-5,14-diborapentacene (3H) and its 2,3-dihalogenated derivatives, 3F and 3Cl, have been successfully applied as emitters in fluorescent organic light-emitting diodes (OLEDs) The best performance was achieved with 2% of the blue emitter 3H doped in 9,10-di-(2-naphthyl)anthracene (ADN) as the emitting layer (turn-on voltage Von = 33 V, λem = 476 nm, maximum external quantum efficiency ηext = 34% with a negligible roll-off up to 10 000 cd m−2, maximum luminance Lmax = 39 180 cd m−2) Contrary to the blue-emitting 3H-based device, 3F- and 3Cl-containing OLEDs produced turquoise (484 nm) and green (492 nm) light, respectively

Guoyun Meng

Papers

Isomeric Bright Sky-Blue TADF Emitters Based on Bisacridine Decorated DBNA: Impact of Donor Locations on Luminescent and Electroluminescent Properties

Intramolecular Borylation via Sequential B-Mes Bond Cleavage for the Divergent Synthesis of B,N,B-Doped Benzo[4]helicenes.

Planar Chiral Organoboranes with Thermoresponsive Emission and Circularly Polarized Luminescence: Integration of Pillar[5]arenes with Boron Chemistry

Pillar[5]arenes: a new class of AIEgen macrocycles used for luminescence sensing of Fe3+ ions

Doubly boron-doped pentacenes as emitters for OLEDs