In this contribution, a set of five differently substituted phenoxazines ( POA ) derived from a central terephthalonitrile core is investigated. Depending on incorporated electron‐donating groups ( ‐NH 2 , ‐NMe 2 , and ‐OMe ) or electron‐withdrawing groups ( ‐NO 2 and ‐CN ), distinctive luminescent behavior is observed, with preferred emission either in solution, in the solid‐state, or in both. An in‐depth assessment of the photophysical properties revealed a subtle influence of the substituents on the absorption and emission wavelengths, which correlate with the Hammett parameters, yet a strong sensitivity to the surrounding environment. Hence, solvatochromic response and aggregation studies were conducted to identify the optimal conditions for efficient emission. Absolute photoluminescence quantum yield values of up to 0.47 in tetrachloromethane and 0.33 in the solid state were determined, underscoring the impressive photophysical characteristics of the presented compounds. X‐ray diffractometric analyses in combination with Hirshfeld surface evaluation were employed to elucidate the packing effects and their possible relation to the photophysical performance. Finally, density functional theory calculations provided a detailed understanding of the occurring electronic transitions and spatial localization of the natural transition orbitals.

One new aminopyrazole, 1,3-di(pyridin-2-yl)-1H-pyrazol-5-amine (2), and three new thiourea-functionalized compounds, 1-(4-methoxyphenyl)-3-(3-phenyl-1-(pyridin-2-yl)-1H-pyrazol-5-yl)thiourea (3), 1-(4-methoxyphenyl)-3-(3-pyridinyl-1-(pyridin-2-yl)-1H-pyrazol-5-yl)thiourea (4), and 1-(3-methoxyphenyl)-3-(3-pyridinyl-1-(pyridin-2-yl)-1H-pyrazol-5-yl)thiourea (5) were synthesized and characterized. The crystal structures of all four aminopyrazole-based frameworks, as well as a minor side-product, O-ethyl(3-phenyl-1-(pyridin-2-yl)-1H-pyrazol-5-yl)carbamothioate (6), and the zinc(II) chloride complex with 4, were determined. For each pyrazolylthiourea, all strong hydrogen-bond donors are utilized, while the pyrazole nitrogen hydrogen-bond acceptors are unengaged. This is attributed in part due to the formation of intermolecular R 2 2(8) N-HS hydrogen-bonded rings that incorporate the weaker sulfur acceptor, leaving an open Lewis base site available for metal coordination. Excitation and emission properties were evaluated in both solution and solid-state for the three methoxyphenyl-substituted ligands (3, 4, and 5) revealing bright solid-state fluorescence for 3 and 4. Enhanced solid-state fluorescence was observed for 4 relative to 3 (Phi solid-state = 7.63 vs 4.28%) consistent with increased molecular rigidity and a higher proportion of NH/HN interactions (9.7 vs 5.0% of the Hirshfeld surfaces). Upon coordination to Zn(II), fluorescence from 4 was quenched, demonstrating its potential as a metal-responsive sensor. DFT and TD-DFT calculations indicate that quenching likely arises from a diminished transition dipole associated with the ligand-ligand charge-transfer S1 state of the Zn(II) complex.

The "magic methyl" effect is widely regarded as one of the most extraordinary features in small-molecule drug design and has recently been recognized as a subtle yet powerful tool for fine-tuning the photophysical properties of luminophores. In this context, we investigated how steric pressure influences the structural and photophysical attributes in a series of sequentially methylated phenoxazines. Structural elucidation using X-ray diffraction revealed that the steric strain of ortho-positioned methyl groups induces out-of-plane twisting of the N-arylated rings, which significantly alters the packing interactions by preventing dense pi stacking. Complementary quantum chemical calculations indicate changes in the antiaromatic character due to partial rehybridization of the bridging nitrogen atom from sp2 to a more trigonal pyramidal geometry. Steady-state and time-resolved spectroscopy further highlighted the correlations between out-of-plane bending and emissive behavior, as characterized by distinctly pronounced changes in molar absorptivity and Stokes shifts. Finally, an effective strategy to overcome steric hindrance was demonstrated by extending the overall molecular conjugation, resulting in intense emission with high absolute photoluminescence quantum yields in both solution and the solid state.

Quinoxalines are an important class of compounds that can exhibit properties such as luminescence and liquid crystal phases. The corresponding quinoxaline dimers and their cyclotrimers, in contrast, have received little attention. We report the synthesis and characterization of a novel tetrakis(dialkoxyphenyl)biquinoxaline derivative (1) and the corresponding novel hexakis(dialkoxyphenyl)-1,4,7,10,13,16-hexaazatrinaphthylene (2) using the nickel-mediated Yamamoto coupling as a key step. The resulting compounds show solvent-dependent emission spectra in solution, suggesting a donor–acceptor architecture with charge separation in the excited state. Preliminary mesophase characterization reveals that both compounds also exhibit columnar mesophases, as shown by polarized optical microscopy and differential scanning calorimetry, and form glasses upon cooling to room temperature.

We report a mechanistic investigation of an aromatic dithioimide (2SS) displaying puzzling yet efficient photochemistry in ether solvents. Perplexingly, 2SS dissolved in ether solvents in a sealed and degassed vial was photochemically converted to the corresponding diimide (2OO), as determined by 1H NMR following product extraction. With no external sources of oxygen in the sample, could the oxygen in 2OO be from the ether itself? To study this unprecedented proposition, we attempt to uncover the ether's involvement in this reaction. As seen by laser-flash photolysis, 2SS appears to first react with the solvent from its singlet excited state. Following the reaction by NMR under rigorously oxygen- and water-free conditions led to the identification of a photoreductive pathway that quantitatively transformed one thione into a methylene to yield 2SH2. Subsequent oxidation of 2SH2 or irradiation of 2SS under air proved that molecular oxygen was indeed necessary to observe an oxidative pathway leading to 2OO, ruling out the initially proposed involvement of an ether oxygen. An explanation of 2SS desulfurization was further revealed through the study of solvent by-products by GC-MS analysis. Supported by DFT calculations, a mechanism is proposed to involve a chain reaction initiated by photochemically generated ether radical.

We report the unexpected nucleophilic ring-opening reaction of electron deficient dioxins in the presence of carbazole under basic conditions. This nucleophilic ring-opening reaction is reversible under basic conditions in the absence of nucleophiles. Further, we demonstrate that this unexpected reactivity can be used to prepare novel donor-acceptor compounds that are emissive in solution and as thin films and exhibit thermally activated delayed fluorescence (TADF).

The incorporation of heteroatoms into polycyclic aromatic hydrocarbons can alter their optical and electronic properties. Here, we report the synthesis and characterization of a series of N,N′-diaryl diazadioxatetrahydropentacenes (4a–e) as well as related N-phenyl azatrioxatetrahydropentacene and triazatetrahydrotetracene derivatives (5, 6) to investigate their photophysical properties and solid-state organization. These compounds were prepared from readily available compounds via a concise approach involving copper-catalyzed aryl amination, followed by nucleophilic aromatic substitution. The compounds display bright luminescence in solution and in the solid state and strong solvatochromism. Single-crystal X-ray diffraction of N,N′-aryl diazadioxatetrahydropentacenes (4b–d) revealed that all the compounds possessed nearly planar polycyclic aromatic systems with the pendant aryl groups nearly orthogonal to the pentacyclic core. Nonetheless, different substituents on the pendant aryl groups resulted in differences in photophysical properties because of differences in molecular geometries and solid-state packing. Interestingly, the N,N′-aryl diazadioxatetrahydropentacene bearing 2,6-dimethylphenyl groups attached to the nitrogen atoms (4d) gave two different polymorphs from the same solvent system, constituting a relatively rare example of concomitant polymorphism for such a rigid structure.

Aromatic compounds are a diverse and fascinating class of compounds with wide-ranging importance. This book provides an overview of the synthesis and reactivity of aromatic compounds. The publication covers the many important reaction types, such as electrophilic and nucleophilic substitution, the reactivity of benzynes, aryllithium chemistry, and transition metal-mediated reactions. It also includes a discussion of the synthesis of heteroaromatic compounds, polycyclic aromatic compounds, and nonplanar aromatic systems. This book focusses on reaction mechanisms and numerous examples of applications in multistep synthesis of aromatic compounds.

Substituted triphenylenes show promise as organic semiconductors because of their ability to form columnar liquid crystalline phases featuring extended π-stacked arrays. While there are several methods for preparing triphenylenes, including oxidative cyclization reactions such as the Scholl reaction, as well as transition metal-catalyzed aryne cyclotrimerization, these methods are not effective for electron deficient triphenylenes. Here we demonstrate that the nickel-mediated Yamamoto coupling of o-dibromoarenes is a concise and efficient way to prepare substituted triphenylenes, including electron-deficient systems that are otherwise challenging to prepare. We also demonstrate the application of this approach to prepare electron deficient discotic mesogens composed of triphenylenes bearing imide and thioimide groups.

Biofilms are communities of self-enmeshed bacteria in a matrix of exopolysaccharides. The widely distributed human pathogen and commensal Escherichia coli produces a biofilm matrix composed of phosphoethanolamine (pEtN)-modified cellulose and amyloid protein fibers, termed curli. The addition of pEtN to the cellulose exopolysaccharide is accomplished by the action of the pEtN transferase, BcsG, and is essential for the overall integrity of the biofilm. Here, using the synthetic co-substrates p-nitrophenyl phosphoethanolamine and β-d-cellopentaose, we demonstrate using an in vitro pEtN transferase assay that full activity of the pEtN transferase domain of BcsG from E. coli (EcBcsGΔN) requires Zn2+ binding, a catalytic nucleophile/acid-base arrangement (Ser278/Cys243/His396), disulfide bond formation, and other newly uncovered essential residues. We further confirm that EcBcsGΔN catalysis proceeds by a ping-pong bisubstrate-biproduct reaction mechanism and displays inefficient kinetic behavior (kcat/KM = 1.81 × 10-4 ± 2.81 × 10-5 M-1 s-1), which is typical of exopolysaccharide-modifying enzymes in bacteria. Thus, the results presented, especially with respect to donor binding (as reflected by KM), have importantly broadened our understanding of the substrate profile and catalytic mechanism of this class of enzymes, which may aid in the development of inhibitors targeting BcsG or other characterized members of the pEtN transferase family, including the intrinsic and mobile colistin resistance factors.

Bacterial biofilms are cellular communities that produce an adherent matrix. Exopolysaccharides are key structural components of this matrix and are required for the assembly and architecture of biofilms produced by a wide variety of microorganisms. The human bacterial pathogens Escherichia coli and Salmonella enterica produce a biofilm matrix composed primarily of the exopolysaccharide phosphoethanolamine (pEtN) cellulose. Once thought to be composed of only underivatized cellulose, the pEtN modification present in these matrices has been implicated in the overall architecture and integrity of the biofilm. However, an understanding of the mechanism underlying pEtN derivatization of the cellulose exopolysaccharide remains elusive. The bacterial cellulose synthase subunit G (BcsG) is a predicted inner membrane–localized metalloenzyme that has been proposed to catalyze the transfer of the pEtN group from membrane phospholipids to cellulose. Here we present evidence that the C-terminal domain of BcsG from E. coli (EcBcsGΔN) functions as a phosphoethanolamine transferase in vitro with substrate preference for cellulosic materials. Structural characterization of EcBcsGΔN revealed that it belongs to the alkaline phosphatase superfamily, contains a Zn2+ ion at its active center, and is structurally similar to characterized enzymes that confer colistin resistance in Gram-negative bacteria. Informed by our structural studies, we present a functional complementation experiment in E. coli AR3110, indicating that the activity of the BcsG C-terminal domain is essential for integrity of the pellicular biofilm. Furthermore, our results established a similar but distinct active-site architecture and catalytic mechanism shared between BcsG and the colistin resistance enzymes.

Understanding and control of weak intermolecular interactions, including pi-interactions, is an element toward the strategic design of supramolecular materials. In this work, we describe an approach to promoting cofacial pi-stacking in the solid state by preparing polycyclic aromatic compounds that bear complementary electron-rich and electron-poor rings. Specifically, we describe the synthesis and single crystal structures of a series of six dissymmetric systems (three dibenzo-p-dioxins and three phenoxazines) comprised of one electron-rich and one electron-deficient ring. In all cases, antico-facial pi-pi interactions were observed, but no significant C-H...pi interactions. These observations were compared with similar structures in the Cambridge Structural Database, and it was found that the presence of bulky substituents, lattice solvent, and stronger intermolecular interactions interfere with efficient it-stacking. Both qualitative and quantitative evaluations of the newly reported structures, and database examples, are included.

We report the synthesis and properties of a series of novel triphenylenedicarboxyimides and thioimides (4-6) to probe the effect of thionation on the formation of columnar mesophases. These materials display broad columnar mesophases and high clearing points and self-associate in solution to form dimers. Overall, thionation improved the self-assembly in solution and led to a stabilization of the columnar mesophase. Furthermore, increasing the thionation of these materials led to a lowering of the lowest unoccupied molecular orbital (LUMO) energy level and a narrowing of the highest occupied molecular orbital-LUMO gap.

A synthetic approach for preparing a variety of heterocyclic tetrahydropentacene derivatives via nucleophilic aromatic substitution reactions of bidentate nucleophiles and tetrafluoroterephthalonitrile was developed. X-ray crystallography of several products revealed that the compounds containing oxygen and nitrogen heteroatoms are highly planar and engage in π-stacking, while the compounds containing sulfur are bent and do not stack as effectively. The compounds were also highly emissive, and the heteroatom had a significant impact on the emission and electrochemical properties.

We report the synthesis of novel polycatenar dibenzopentacenequinones 1 and 2 that are designed to form columnar liquid crystalline phases. The mesomorphic properties of these compounds were investigated by polarized optical microscopy, differential scanning calorimetry, and powder Xray diffraction. While compound 1 exhibits two distinct columnar mesophases between 148 and 177 degrees C, fluorinated 2 exhibits a columnar mesophase from 121 to 336 degrees C. This dramatic stabilization of the columnar mesophase of 2 can be attributed to improved pi-stacking as a result of arene perfluoroarene interactions.

The synthesis and single crystal structures of 3-phenyl-1-(pyridin-2-yl)-1H-pyrazol-5-amine (L1) and its complex with ZnCl2 are reported. L1 exhibits supercooling, with a difference in melting and solidification points of over 100 oC. The complex [L1ZnCl2] has a room-to-low temperature single crystal-to-crystal phase transition in the solid state, while a birefringent fluid phase mixed with crystalline domains is observed at high temperatures. Significant fluorescence enhancement is observed upon formation of the ZnCl2 complex.

A series of new tetrakis(dialkoxyphenyl) dicyanotetraoxapentacene derivatives (1 a-c) were prepared by reaction of the appropriate terphenyl diols with tetrafluoroterephthalonitrile in good yields. Compounds 1 b and 1 c, which bear hexyloxy and decyloxy side chains, exhibited columnar hexagonal mesophases, as shown by polarized optical microscopy, variable-temperature powder X-ray diffraction, and differential scanning calorimetry. Single-crystal X-ray diffraction of methoxy-substituted 1 a revealed that the dicyanotetraoxapentacene core is highly planar, consistent with the notion that these molecules are able to stack in columnar mesophases. A detailed photophysical characterization showed that these compounds exhibit aggregation-induced emission in solution, emission in nonpolar solvents, weak emission in polar solvents, and strong emission in the solid state both as powder and in thin films. These observations are consistent with a weakly emissive charge-transfer state in polar solvents and a more highly emissive locally excited state in nonpolar solvents.

The synthesis of novel materials for organic electronics is a growing field with potential end applications in energy storage, energy harvesting, displays, and more.Probing the characteristics and properties of novel aromatic and heteroaromatic structures, which increasingly appear in these devices, is a worthwhile pursuit in which we gain insight into the structure-function relationship of previously unknown substances.This in turn allows for more precise tuning of properties for future materials.In certain cases the intermolecular interactions can lead to interesting (and useful) properties such as aggregation-enhanced emission (AIE).Utilizing new materials in novel applications, however, requires a full understanding of their chemical behavior and characteristics.We report the synthesis of a series of dicyanoheteropentacenes 1-4 incorporating oxygen and/or nitrogen into the linear polycyclic core.These compounds display intense luminescence in solution and the solid state.Compound 4, bearing long alkoxy chains, displays a columnar liquid crystalline phase, as shown by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and single-crystal X-ray diffraction.The synthesis, photophysical, mesomorphic properties, and the solid state organization of these compounds will be described.

Crystals of a tetraoxapentacene derivative bearing two diaminotriazine groups exhibit hydrogen-bonded sheets formed by the characteristic hydrogen bonding patterns of the diaminotriazines. By virtue of the large tetraoxapentacene moieties that are oriented perpendicular to the diaminotriazines, these sheets are unable to pack closely, leading to the formation of open network structures with a considerable volume accessible to guest molecules.