Benzophenones as Generic Host Materials for Phosphorescent Organic Light-Emitting Diodes

A Review of Benzophenone-Based Derivatives for Organic Light-Emitting Diodes

Organic light-emitting diodes (OLEDs) have garnered considerable attention in academic and industrial circles due to their potential applications in flat-panel displays and solid-state lighting technologies, leveraging the advantages offered by organic electroactive derivatives over their inorganic counterparts. The thin and flexible design of OLEDs enables the development of innovative lighting solutions, facilitating the creation of customizable and contoured lighting panels. Among the diverse electroactive components employed in the molecular design of OLED materials, the benzophenone core has attracted much attention as a fragment for the synthesis of organic semiconductors. On the other hand, benzophenone also functions as a classical phosphor with high intersystem crossing efficiency. This characteristic makes it a compelling candidate for effective reverse intersystem crossing, with potential in leading to the development of thermally activated delayed fluorescent (TADF) emitters. These emitting materials witnessed a pronounced interest in recent years due to their incorporation in metal-free electroactive frameworks and the capability to convert triplet excitons into emissive singlet excitons through reverse intersystem crossing (RISC), consequently achieving exceptionally high external quantum efficiencies (EQEs). This review article comprehensively overviews the synthetic pathways, thermal characteristics, electrochemical behaviour, and photophysical properties of derivatives based on benzophenone. Furthermore, we explore their applications in OLED devices, both as host materials and emitters, shedding light on the promising opportunities that benzophenone-based compounds present in advancing OLED technology.

De Novo Synthesis of Acridone-Based Zn-Metal-Organic Framework (Zn-MOF) as a Photocatalyst: Application for Visible Light-Mediated Oxidation of Sulfides and Enaminones

Acridone, a cyclic analogue of benzophenone that undergoes efficient intersystem crossing (ISC) to the triplet-excited state with near-unity quantum yield, was elaborated as a 3-connecting triacid linker, i.e., H3AcTA, to develop a photocatalytic metal-organic framework (MOF) for energy transfer applications; the triacid linker inherently features concave shapes, an attribute that is important for the construction of MOFs with significant porosity. Metal ion (Zn2+)-assisted self-assembly of the triacid yielded a Zn-MOF, i.e., Zn-AcTA, with a solvent-accessible volume of ca. 31%. The protection of the acridone chromophore in the MOF in conjunction with a wider cross-section of its absorption in the visible region renders the MOF an excellent heterogeneous photosensitizer for singlet oxygen (1O2) generation by energy transfer to the ground-state triplet oxygen (3O2). It is shown that the Zn-MOF can be applied as a photosensitizing catalyst for visible light-mediated oxidation of various sulfides to sulfoxides and enaminones to amino-esters via 1,2-acyl migration. It is further demonstrated that the photocatalyst can be easily recycled without any loss of catalytic activity and structural integrity. Based on mechanistic investigations, 1O2 is established as the reactive oxygen species in photocatalytic oxidation reactions. The results constitute the first demonstration of rational development of a photocatalytic MOF based on acridone for heterogeneous oxidations mediated by 1O2.

Novel carbazole- and dioxino[2,3-b]pyrazine-based bipolar hosts for red PhOLEDs with a high brightness

The target compounds offer new synthetic ideas for red bipolar host materials.

Photophysical and semiconducting properties of isomeric triphenylimidazole derivatives with a benzophenone moiety

New isomeric compounds with imidazole and benzophenone moieties were synthesized and their thermal, photophysical, electrochemical and carrier mobilities have been analyzed.

Insight into Water-Soluble Highly Fluorescent Low-Dimensional Host-Guest Supramolecular Polymers: Structure and Energy-Transfer Dynamics Revealed by Polarized Fluorescence Spectroscopy

Water-soluble, highly fluorescent host-guest chromophore-cucurbit[8]uril supramolecular polymer bundles are investigated by polarized time-resolved photoluminescence spectroscopy, structural methods, and quantum chemistry to fully reveal structural organization and heterogeneity but, in particular, energy-transfer dynamics, being of crucial importance for the design of supramolecular artificial light-harvesting systems.

Multifunctional Materials for High-Performance Double-Layer Organic Light-Emitting Diodes: Comparison of Isomers with and without Thermally Activated Delayed Fluorescence

Organic light-emitting diodes (OLEDs) with simple structures are attracting a lot of attention nowadays, though their performances are always inferior to those of the more complicated structures as multifunctional materials are rare. Here, we have designed and synthesized multifunctional isomers by combining electron-donating carbazole (Cz) and triphenylamine (TPA) units with electron-accepting triazine (Trz), namely, N-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-[1,1'-biphenyl]-4-amine (CzTPA-p-Trz) and N-[3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-[1,1'-biphenyl]-4-amine (CzTPA-m-Trz). The use of multiple electron-donating groups gives them suitable highest occupied molecular orbitals for hole injection and high mobilities for hole transport. Hole-only devices with CzTPA-m-Trz or CzTPA-p-Trz as the hole injection layers and hole transport layers show a higher hole current than the widely used 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile/4,4'-N,N'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl system. Interestingly, CzTPA-p-Trz is a fluorescent material with a high photoluminescence quantum yield (PLQY), while CzTPA-m-Trz shows weak thermally activated delayed fluorescence (TADF). As expected, a CzTPA-p-Trz-based undoped double-layer green device achieved a higher external quantum efficiency (EQE) of 4.4% and a higher power efficiency (PE) of 11.8 lm/W. On the other hand, among double-layer devices doped with an orange phosphorescent dopant, a device based on TADF material, CzTPA-m-Trz, achieved higher peak EQE (23.5%) and PE (68.3 lm/W) than those of CzTPA-p-Trz (20.8% and 60.2 lm/W). Even at a high luminance of 5000 cd m^-2, a high EQE of 21.8% was retained for CzTPA-m-Trz-based devices. These results are even comparable to those for the state-of-the-art phosphorescent devices based on the same dopant with more complicated structures. The above results indicate that well-designed multifunctional materials are promising for high-performance OLEDs with simple structures.

Carbo[5]helicene versus planar phenanthrene as a scaffold for organic materials in OLEDs: the electroluminescence of anthracene-functionalized emissive materials

Rigid and twisted carbo[5]helicene imparts better physical and electroluminescence properties than planar phenantherene for phenylanthracene-functionalized emissive materials.

Tri- and tetraarylanthracenes with novel λ, χ and ψ topologies as blue-emissive and fluorescent host materials in organic light-emitting diodes (OLEDs)

Aryl-anthracene derivatives with λ, χ and ψ topologies serve as materials in OLEDs with intriguingly similar physical and electroluminescence properties.

Benzophenone-imbedded benzoyltriptycene with high triplet energy for application as a universal host material in phosphorescent organic light-emitting diodes (PhOLEDs)

Benzoyltriptycene functions as a very good host material for blue, green, yellow and red dopants in PhOLED devices.