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Porous organic polymers (POPs) are emergent tailor‐made materials, which can be accessed by covalent polymerization of diligently designed molecular building blocks in a bottom‐up fashion. Acridone, a well‐known chromophore that undergoes intersystem crossing (ISC) with near‐unity quantum yield akin to benzophenone, was structurally elaborated into a building block and subjected to Friedel‐Crafts polyalkylation to afford a series of POPs, namely, Ac‐MePOP, Ac‐OMePOP, and Ac‐CBPOP. These POPs exhibit remarkable porosity and significant absorption in the visible region. Of the three polymers, Ac‐CBPOP with the highest BET surface area of ca. 1027 m2/g is shown to serve as an excellent heterogeneous photocatalyst for visible light‐mediated oxidative transformations, that is, oxidative coupling of benzylamines to imines and cyclocondensation of o‐phenylenediamines with aldehydes to benzimidazoles under oxygen atmosphere. It is further shown that Ac‐CBPOP can be reused for several reaction cycles without any loss of catalytic activity with its stability intact. Mechanistic studies show that 1O2 serves as the key reactive oxygen species, formed by the energy transfer from Ac‐CBPOP to 3O2, in the photocatalytic oxidation reactions. The results demonstrate the development of stable photocatalytic POP materials with tailor‐made properties by a bottom‐up covalent polymerization of programmed molecular building blocks. [ABSTRACT FROM AUTHOR]

The functionalization of small aromatic heterocycles is a straight and efficient method to access large polycyclic conjugated molecules. However, due to its unique reactivity, the derivatization of acridone usually gives the product in the angular shape and is difficult to obtain the linear ones. Here we report the direct functionalization of acridone to generate its linearly fused derivatives containing cyclobutadienoid via the palladium‐catalyzed arene‐(oxa)norbornene annulation followed by the dehydrated aromatization. The experimental characterizations demonstrate that the antiaromatic cyclobutadienoid ring can extend the molecular conjugation. Theoretical calculations reveal the weakened aromaticity of neighboring benzenoid rings of cyclobutadienoid with no influence on the electronic structure of central pyridone. The molecular stability is enhanced in comparison to that of linear acridone derivatives containing only six‐membered rings. [ABSTRACT FROM AUTHOR]

Electron‐deficient acridones and in situ generated acridinium salts are reported as potent, closed‐shell photooxidants that undergo surprising mechanisms. When bridging acyclic triarylamine catalysts with a carbonyl group (acridones), this completely diverts their behavior away from open‐shell, radical cationic, 'beyond diffusion' photocatalysis to closed‐shell, neutral, diffusion‐controlled photocatalysis. Brønsted acid activation of acridones dramatically increases excited state oxidation power (by +0.8 V). Upon reduction of protonated acridones, they transform to electron‐deficient acridinium salts as even more potent photooxidants (*E1/2=+2.56–3.05 V vs SCE). These oxidize even electron‐deficient arenes where conventional acridinium salt photooxidants have thusfar been limited to electron‐rich arenes. Surprisingly, upon photoexcitation these electron‐deficient acridinium salts appear to undergo two electron reductive quenching to form acridinide anions, spectroscopically‐detected as their protonated forms. This new behaviour is partly enabled by a catalyst preassembly with the arene, and contrasts to conventional SET reductive quenching of acridinium salts. Critically, this study illustrates how redox active chromophoric molecules initially considered photocatalysts can transform during the reaction to catalytically active species with completely different redox and spectroscopic properties. [ABSTRACT FROM AUTHOR]

Besides the peripheral modification, the introduction of heteroatoms to modulate the property of longer acenes with improved chemical stability has been extensively studied for their potential applications in organic electronics. However, the utilization of 4‐pyridone, a common unit in the air‐ and photo‐stable acridone and quinacridone, to decorate higher acenes with increased stability has not been realized yet. Here we present the synthesis of a series of monopyridone‐doped acenes up to heptacene via the palladium‐catalyzed Buchwald‐Hartwig amination of aniline and dibromo‐ketone. The effect of pyridone on the property of doped acenes were investigated experimentally and computationally. With the π‐extension of doped acenes, the pyridone ring shows the weakened conjugation and gradual loss of aromaticity. The doped acenes demonstrate enhanced stability in solution and maintain the electronic communication between the acene planes. [ABSTRACT FROM AUTHOR]

Paratrimerin C is a natural acridone antioxidant that is also potent as an anti‐UV agent. The photophysical process of Paratrimerin C, including the absorption and emission and the excited state intramolecular proton transfer (ESIPT) mechanism, is studied herein with time‐dependent density functional theory. The solvent effect on ESIPT is studied for polar (water) and non‐polar (benzene) solvents employing the Integral Equation Formalism Polarization Continuum Model and adding up to three explicit molecules of solvent. The normal and tautomer forms of the Paratrimerin C at the ground‐ and excited‐state structures are studied at the M06‐2X/6‐311++G(d,p) level of theory. The potential energy curves along the reaction coordinates indicate that the ESIPT is a barrier‐less reaction, and the variation of OdOa distance in the excited state shows significant molecular structure deformation along the proton transfer process following the normal‐to‐tautomerism pathway. The obtained results suggest using of acridone derivatives as efficient and tunable fluorescence molecules besides their biological activities. [ABSTRACT FROM AUTHOR]

Acridone units were incorporated into the arylene–ethynylene structure as polar arene units. Cyclic trimers consisting of three acridone‐2,7‐diyl units and three 1,3‐phenylene units were synthesized by Sonogashira couplings via stepwise or direct route. X‐ray analysis revealed that the trimer had a nearly planar macrocyclic framework with a cavity surrounded by three carbonyl groups. In contrast, the corresponding tetramer had a nonplanar macrocyclic framework. 1H NMR measurements showed that the trimer formed a 1 : 1 complex as a macrocyclic host with dihydric phenol guests, and the association constants were determined to be ca. 1.0×103 L mol−1 for hydroquinone or resorcinol guests in CDCl3 at 298 K. The calculated structures of these complexes by the DFT method supported the presence of two sets of OH⋅⋅⋅O=C hydrogen bonds between the host and guest molecules. The spectroscopic data of the cyclic trimers and tetramers are compared with those of reference acridone compounds. [ABSTRACT FROM AUTHOR]

By linking the carbazole unit to the nitrogen atom of acridone through phenyl or pyridyl, two compounds, named 10‐(4‐(9H‐carbazol‐9‐yl)phenyl)acridin‐9(10H)‐one (AC‐Ph‐Cz) and 10‐(5‐(9H‐carbazol‐9‐yl)pyridin‐2‐yl)acridin‐9(10H)‐one (AC‐Py‐Cz) were designed and synthesized. These two materials, characterized with highly twisted and rigid structure, good thermal stability, and balanced carrier‐transporting properties, were employed as host materials for green phosphorescent and thermally activated delayed fluorescent organic light‐emitting diodes (OLEDs). The carbazole group, despite its small contribution to the highest occupied molecular orbitals (HOMOs) of these two materials, plays an essential role as an intramolecular host in energy delivering and improving the hole transporting ability of these two hosts. The incorporation of the electron‐deficient pyridyl group as a linking group slightly improves the electron transporting capability of AC‐Py‐Cz. The green phosphorescent OLED (PhOLED) based on AC‐Py‐Cz exhibited excellent device performance with a turn‐on voltage of 2.5 V, a maximum power efficiency and an external quantum efficiency (ηext) of 89.8 lm W−1 and 25.2 %, respectively, benefitting from the better charge‐balancing ability of AC‐Py‐Cz host due to the presence of the pyridyl bridge. More importantly, all the devices based on these two hosts showed low efficiency roll‐off at high brightness due to the suppressed non‐radiative transition in the emitting layer. In particular, the AC‐Py‐Cz‐hosted green PhOLED exhibited an efficiency roll‐off of 1.6 % from the maximum next at a high brightness of 1000 cd m−2 and a roll‐off of 15.9 % at an extremely high brightness of 10000 cd m−2. This study manifests that acridone‐based host materials have great potential in fabricating OLEDs with low efficiency roll‐off. [ABSTRACT FROM AUTHOR]

Acyclic and cyclic acridone‐2,7‐diyl oligomers were synthesized by an iterative procedure from 10‐mesitylacridone as heteroatom containing π‐conjugated compounds. The oligomeric chain was elongated by a combination of regioselective bromination, borylation, Ni(0)‐mediated homocoupling, and Suzuki‐Miyaura coupling up to acyclic hexamer. Subsequently, the cyclic hexamer was synthesized by the bromination and intramolecular coupling of the acyclic hexamer. The DFT calculations revealed that the acyclic oligomers preferred to take extended structures with anti conformations, whereas the cyclic hexamer took a macrocyclic structure with syn conformations. The UV/Vis and fluorescence spectra of the series of oligomers were measured, and the effects of the chain length and the cyclization are discussed in terms of π‐conjugation. [ABSTRACT FROM AUTHOR]

Acridone as a new kind of visible light photocatalyst has been developed to catalyze metal free atom transfer radical polymerization (ATRP). The photocatalyst possess low excited state potential as can undergo an oxidative quenching pathway to initiate ATRP of vinyl monomers. Kinetic study and light on/off reaction demonstrate the "living"/controlled nature of the polymerization by light. Block copolymers can be achieved by using PMMA as macroinitiator to reinitiate polymerization of other vinyl monomers, which shows highly preserved Br chain‐end functionality in the synthesized polymers. Moreover, the polymerization can be conducted under air atmosphere as most photocatalysts need anaerobic condition, which may give inspiration of further application of this kind of photocatalyst. [ABSTRACT FROM AUTHOR]

N‐substituted acridine‐containing 1,2‐dioxetanes have been recently proposed as thermochemiluminescence (TCL) universal labels for bioanalytical applications. The TCL properties of these compounds markedly depend on the nature of substituents of the acridine ring. In the attempt to obtain new TCL probes with improved properties and stability, the push‐pull approach was adopted, in which both electron withdrawing and electron donating groups are present in the acridine moiety. The results have been useful to better understand the role of the different decorations at the acridine fluorophore in modulating the photophysical properties and the activation parameters of 1,2‐dioxetane labels. Moreover, the great versatility and innovation of these molecules make them extremely attractive for bioanalytical applications, in particular as labels for immune‐ and gene‐probe assays. [ABSTRACT FROM AUTHOR]

Two series of eight visible‐light‐absorbing redox active molecules derived from 9(10H)‐acridone and thioxanthen‐9‐one were designed and synthetized. The different dyes were characterized by UV‐vis absorption and fluorescent spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and cyclic voltammetry (CV) for their thermal, optical and electrochemical properties, respectively. Theoretical calculations DFT were also carried out to support the experimental results. These molecules are thermally stable with Td (decomposition temperature) range from 290 °C to 418 °C and have glass forming properties with Tg (glass transition temperature) varying from 44 °C to 134 °C. These chromophores strongly absorb and emit in the visible spectral range (400–550 nm for absorption and 450–650 for fluorescence). Their frontier orbitals' energy levels as well as optical bandgaps can be tuned by changing the nature and the number of the arylamine electron‐donating groups. These compounds have been found to be promising candidates for photo‐initiators for photo‐polymerization process applied in 3D printing technique. They could also be potentially applied as hole transporting materials for hybrid perovskite photovoltaics. [ABSTRACT FROM AUTHOR]

Benzene‐ and naphthalene‐fused acridone derivatives with hexyl and phenyl groups at the amino position were synthesized and their properties were investigated experimentally and computationally. All the structures of these fused π‐extended acridone derivatives were unambiguously confirmed by single‐crystal X‐ray analysis, which revealed the presence of face‐to‐face π–π stackings along the acridone moiety and the intermolecular hydrogen bond‐directed molecular packings of the phenyl‐substituted acridone derivatives in the crystals. Moreover, the dimerization of linearly fused acridone derivative was observed after storing the crystals over months. The benzene ring at the turning point of the angularly fused acridone derivatives contained relatively longer and shorter C–C bonds, which affected the molecular conjugation, as confirmed by the results of photophysical characterization and the study of the aromaticity. Mobility calculations based on the molecular packings in the single crystals showed that the linearly fused acridone derivatives bearing better electron and hole mobilities are good candidates of organic functional materials. [ABSTRACT FROM AUTHOR]

The surface extension of all‐carbon based bowl‐shaped molecules, such as corannulene and sumanene, to synthesize even larger buckybowls has been widely studied, leaving other concave compounds with heteroatoms less considered. Herein we present a highly curved molecule synthesized via stepwise cyclization of fjords of a bisacridone derivative. Crystallographic analysis unambiguously confirmed a boat‐shaped structure with deformed bottom benzene ring. Theoretical calculation unravels an inversion process with an S‐shaped transition structure rather than a planar one. The enlarged boat demonstrates interesting properties, such as red shifts in absorption and emission spectra, enhanced emission intensity, and convergent frontier molecular orbital energy levels, in comparison to the related concave N‐heterotriangulene. [ABSTRACT FROM AUTHOR]

This study describes the synthesis of an acridone through the directed lithiation of a diarylamine, and elaboration via the 4,5‐dibromoacridone. The bromo substituents are amenable to Suzuki‐Miyaura coupling. Conversion to a 9‐chloro‐4,5‐dibromoacridine, followed by bromine‐lithium exchange, allows the preparation of a 4,5‐bis (phosphino)‐9‐chloroacridine. The 9‐chloro moiety undergoes nucleophilic aromatic substitution by methoxide or an aryloxide. One‐electron reduction of a 9‐(aryloxy)‐4,5‐bis(phosphino)acridine affords a stable radical anion. [ABSTRACT FROM AUTHOR]

Acridone‐functionalized carbazole dendrimers were synthesized via copper‐catalyzed Ullmann amination and their properties were investigated by spectroscopic and electrochemical measurements, as well as theoretical calculations. The results reveal that the properties of the carbazole dendrimers vary according to the position of acridone. Intramolecular charge transfer between the acridone core and the outer carbazole dendron is observed, accompanying a red shift of the emission maximum and a decline of quantum yields with the rise of the dendrimer generation. Whereas the internal carbazole unit has little influences on the photoluminescence of dendrimers with acridone at the periphery in solution. The electrochemical analysis and theoretical calculations demonstrate a convergence in HOMO and LUMO energy levels in dendrimers bearing the acridone core and a decrease in both of these energy levels in dendrimers with the acridone at the periphery when the dendrimer generation increases. [ABSTRACT FROM AUTHOR]

A variety of N‐substituted acridone derivatives were synthesized to make a comparison of their properties according to the number of acridone unit and the nature of substituent. The spectroscopic and electrochemical investigations show that the properties of N‐substituted acridone derivatives are substituent‐dependent. With benzene, biphenyl, fluorene and carbazole as linkers, the acridone derivatives demonstrate the properties of acridone itself due to a very weak intramolecular charge transfer (ICT) between acridone and the linker. However, significant ICT process is observed when the electron withdrawing groups are involved to form the donor–acceptor systems with acridone as the electron donating groups, which is different from the previously reported results of which acridone is usually used as an electron acceptor. Moreover, thermally activated delayed fluorescence (TADF) is observed with anthraquinone as linker. The theoretical calculations reveal that the N‐substitutions have more influences on the locations and energy levels of the LUMOs than those of the HOMOs. [ABSTRACT FROM AUTHOR]

Length‐defined 2,7‐acridone oligomers were synthesized via a sequence of bromination, borylation and Suzuki–Miyaura cross‐coupling reaction. Both the single crystal structure analysis and the theoretical calculations demonstrate that the anti conformation is favored in the oligomer. The relationship of the properties and the number of acridone units in the oligomer was investigated. The UV/Vis absorption and fluorescence spectroscopy reveal that the absorption and emission of oligomers are red‐shifted and energy gaps narrow with the increase of acridone moieties, as well as a decline in the radiative decay rate. Cyclic voltammetry measurements and theoretical calculations elucidate that the quantity of acridone in the oligomer plays a greater effect on the HOMO energy levels than on the LUMO ones. [ABSTRACT FROM AUTHOR]

Abstract: Acridonylalanine (Acd) is a useful fluorophore for studying proteins by fluorescence spectroscopy, but it can potentially be improved by being made longer wavelength or brighter. Here, we report the synthesis of Acd core derivatives and their photophysical characterization. We also performed ab initio calculations of the absorption and emission spectra of Acd derivatives, which agree well with experimental measurements. The amino acid aminoacridonylalanine (Aad) was synthesized in forms appropriate for genetic incorporation and peptide synthesis. We show that Aad is a superior Förster resonance energy transfer acceptor to Acd in a peptide cleavage assay and that Aad can be activated by an aminoacyl tRNA synthetase for genetic incorporation. Together, these results show that we can use computation to design enhanced Acd derivatives, which can be used in peptides and proteins. [ABSTRACT FROM AUTHOR]

We have unfolded a convenient and mild protocol for the synthesis of diaryl ketones via Pd‐ NHC catalysed carbonylative Suzuki coupling reaction. Notably, this method offers advantages like no use of toxic CO gas, shorter reaction time, high yield, and broad substrate scope. Several sensitive functional groups (like‐COMe, ‐COOMe, ‐F, ‐Cl, ‐Br, ‐NH2, ‐CN) are well tolerated in this reaction. In addition, we have also demonstrated a new efficient route for the synthesis of biologically active and pharmaceutically important 2‐substituted 3‐Aroylquinolin‐4(1H)‐ones and acridone scaffolds. [ABSTRACT FROM AUTHOR]

A palladium-catalyzed regiodivergent C1 insertion multicomponent reaction involving aryne, CO, and 2-iodoaniline is established to construct the scaffolds of phenanthridinone and acridone alkaloids. Regioselective control is achieved under the guidance of selective ligands. The phenanthridinones are solely obtained under ligand-free condition. In comparison, application of the electron-abundant bidentate ligand dppm afforded the acridones with high efficiency. The release rate of the aryne from the precursor assists the regioselectivity of insertion as well, which was revealed through interval NMR tracking. A plausible mechanism was suggested based on the control experiments. Representative natural products and two types of natural product analogues were synthesized divergently through this tunable method. [ABSTRACT FROM AUTHOR]

Indirect release of fluorogenic phenols such as umbelliferone was used as a chemical principle to prepare fluorogenic substrates for a variety of enzymes in which the enzyme-reactive group is separated from the fluorescent reporter group, allowing structural and functional diversification. Fluorescent probes were obtained for enzymes useful for asymmetric synthesis including aldolase catalytic antibodies, transaldolases, alcohol dehydrogenases, lipases, epoxide hydrolases, proteases, and Bayer-Villiger monoxygenases. Arrays of structurally related substrates were prepared and used to record the activity of enzymes on multiple substrates simultaneously in parallel formats such as microtiter plates, microarrays, and substrate cocktails, leading to enzyme-specific activity patterns. Arrays of nonlabeled substrates were assayed using indirect product sensors such as the adrenaline-periodate back-titration assay for 1,2-diols or the copper–calcein assay for amino acids. Many of the fluorogenic substrates and sensors described here are either commercially available or accessible in one or two simple synthetic steps and can be used for high-throughput screening of enzyme activities. [ABSTRACT FROM AUTHOR]

A cDNA encoding a novel plant type III polyketide synthase was cloned and sequenced from the Chinese club moss Huperzia serrata (Huperziaceae). The deduced amino acid sequence of Hu. serrata polyketide synthase 1 showed 44–66% identity to those of other chalcone synthase superfamily enzymes of plant origin. Further, phylogenetic tree analysis revealed that Hu. serrata polyketide synthase 1 groups with other nonchalcone-producing type III polyketide synthases. Indeed, a recombinant enzyme expressed in Escherichia coli showed unusually versatile catalytic potential to produce various aromatic tetraketides, including chalcones, benzophenones, phloroglucinols, and acridones. In particular, it is remarkable that the enzyme accepted bulky starter substrates such as 4-methoxycinnamoyl-CoA and N-methylanthraniloyl-CoA, and carried out three condensations with malonyl-CoA to produce 4-methoxy-2′,4′,6′-trihydroxychalcone and 1,3-dihydroxy- N-methylacridone, respectively. In contrast, regular chalcone synthase does not accept these bulky substrates, suggesting that the enzyme has a larger starter substrate-binding pocket at the active site. Although acridone alkaloids have not been isolated from Hu. serrata, this is the first demonstration of the enzymatic production of acridone by a type III polyketide synthase from a non-Rutaceae plant. Interestingly, Hu. serrata polyketide synthase 1 lacks most of the consensus active site sequences with acridone synthase from Ruta graveolens (Rutaceae). [ABSTRACT FROM AUTHOR]

Polyketide synthase 1 (PKS1) from Huperzia serrata is a plant-specific type III polyketide synthase that shows an unusually versatile catalytic potential, producing various aromatic tetraketides, including chalcones, benzophenones, phlorogulucinols and acridones. Recombinant H. serrata PKS1 expressed in Escherichia coli was crystallized using the hanging-drop vapour-diffusion method. The crystals belonged to space group I222 or I212121, with unit-cell parameters a = 73.3, b = 85.0, c = 137.7 Å, α = β = γ = 90.0°. Diffraction data were collected to 2.0 Å resolution using synchrotron radiation at BL24XU of SPring-8. [ABSTRACT FROM AUTHOR]

Pot‐economic synthesis of N‐aryl acridones was performed with 2‐aminobenzophenones and aryl boronic acids as starting materials. Cu‐catalyzed chelation‐assisted oxidative C–N cross‐coupling reactions were well merged with the following intra‐molecular oxidative dehydrogenative C–H amination reactions under an air atmosphere. The use of reagent capsules can further resolve the compatibility problem of reagents and simplify the operational process, providing a more straightforward access to the target products. [ABSTRACT FROM AUTHOR]