Carlos

Reported herein is the rhodium-catalyzed enantioselective CH bond silylation of the cyclopentadiene rings in Fe and Ru metallocenes. Thus, in the presence of (S)-TMS-Segphos, the reactions took place under very mild conditions to afford metallocene-fused siloles in good to excellent yields and with ee values of up to 97 %. During this study it was observed that the steric hindrance of chiral ligands had a profound influence on the reactivity and enantioselectivity of the reaction, and might hold the key to accomplishing conventionally challenging asymmetric CH silylations.

New on the (metallo)cene: The title reaction of cyclopentadiene (Cp) rings in Fe and Ru metallocenes is reported. Fine-tuning the steric hindrance of diphosphine ligands led to the identification of (S)-TMS-Segphos [(S)-L], which enabled efficient, enantioselective CH silylation of the Cp rings in metallocenes under mild reaction conditions. cod=1,5-cyclooctadiene, TMS=trimethylsilyl.

The palladium-catalyzed coupling of a substituted o-diaminoanthracene and a substituted o-diaminophenazine to substituted 2,3-dichloroquinoxalines furnishes 10 differently substituted N,N′-dihydrotetraaza- or -hexaazahexacenes with the quinoxaline group of the azaacenes carrying fluorine, chlorine, or nitro groups. The N,N′-dihydrotetraazahexacenes with hydrogen, chlorine, and fluorine subtituents are oxidized to azaacenes, whereas only the parent N,N′-dihydrohexaazahexacenes, with hydrogen substituents, are oxidized by MnO₂. The resultant azaacenes are characterized by their optical and spectroscopic data. In addition, single-crystal X-ray structures have been obtained for the parent tetraazahexacenes and their difluoro-substituted derivatives. The di- and tetrachloro derivatives of the N,N′-dihydrohexaazahexacene have also been structurally characterized.

Making acene: A series of tetraaza- and hexaazahexacenes have been obtained by a coupling/oxidation strategy and the limit of stability of the structures has been extended, enabling the generation of stable azahexacenes (see figure).

A series of 2,5-distyrylfuran derivatives bearing pentafluorophenyl- and cyanovinyl units have been synthesized for aggregation-induced emission (AIE). The effect of the type and extent of the supramolecular connections on the AIE of the furan derivatives were examined and correlated with their X-ray crystal structures. It was found that the simultaneous presence of cyano and perfluorophenyl units strongly enhances the fluorescence upon aggregation. Single-crystal X-ray diffraction analysis confirmed that CH⋅⋅⋅F, F⋅⋅⋅F, CH⋅⋅⋅nitrile, Ar⋅⋅⋅Ar_F (Ar=aryl, Ar_F=fluoroaryl), and nitrile⋅⋅⋅Ar_F intra- and intermolecular interactions drive the topology of the molecule and that solid-state supramolecular contacts favor AIE of the furan derivatives.

Enhanced fluorescence: A series of 2,5-distyrylfuran derivatives bearing pentafluorophenyl- and cyanovinyl units have been synthesized for aggregation-induced emission (AIE). The simultaneous presence of cyano and perfluorophenyl units strongly enhances fluorescence upon aggregation. Single-crystal X-ray diffraction analysis confirmed that intra- and intermolecular interactions drive the topology of the molecule and that solid-state supramolecular contacts favor AIE of the furan derivatives (see figure).

A series of photoresponsive and full-colored fluorescent conjugated copolymers is synthesized by combining phenylene- and thienylene-based main chains with photochromic dithienylethene (DE) side chains. Solutions and cast films of the polymers exhibit various colored fluorescence in visible wavelengths of 400−700 nm corresponding to emissions of the conjugated main chain. The fluorescence is reversibly photoswitched between emission and quenching through DE photoisomerization using external stimuli from ultraviolet and visible light irradiation. The reprecipitation method with ultrasonication enables the polymers to form spherical aggregates with diameters of 20−70 nm in water. After investigating and comparing the optical properties, the resulting nanosphere solutions are assumed to exist in an intermediate state between an isolated state (i.e., in solution) and an aggregated state in cast film. The majority of the nanosphere solutions also exhibit the same photoswitchable fluorescence behavior as those in the solutions and the cast films. The results demonstrate that the visible fluorescence of the conjugated copolymers is reversibly switchable between emission and quenching using the photoisomerizing DE side chain regardless of the fluorescent colors and the polymer chain aggregation.

A series of photoresponsive and full-colored fluorescent conjugated polymers are synthesized by combining phenylene- and thienylene-based main chains with photochromic dithienylethene side chains. In chloroform solution, nanosphere solution, and solid film, the full-colored fluorescence is reversibly switchable between emission and quenching through photoisomerization of dithienylethene side chains regardless of the fluorescent colors and the polymer chain aggregation.

A highly soluble pyrene-fused undecacene is realized by end-capping the rectilinear aromatic π-plane with triptycenylene units. Besides the good solubility, the compound shows a high tendency to crystallize. Two polymorphs from dichlorobenzene and chloroform are described. In the polymorph from chloroform, half of the molecules are strongly bent out of the π-plane by 26.4°.

Acenes eleven: A highly soluble pyrene-fused undecacene is prepared by adding end-capping triptycenylene units to the linear π system (see structure, N blue). The new compound shows a high tendency to crystallize; two polymorphs from dichlorobenzene and chloroform solutions could be obtained.

A series of dithienylethene-containing phosphole derivatives has been designed, synthesized and characterized. One of the compounds has been characterized by X-ray crystallography. Upon photoexcitation, the compounds exhibit drastic color changes, ascribed to the reversible photochromic behavior. Their photochromic, photophysical and electrochemical properties have been studied. They show photochromic reactivities with high photocyclization quantum yields. Their photophysical and photochromic properties are found to be facilely tuned in this system by substitution at the phosphole backbone, as well as variation on the extent of π-conjugation of the phosphole backbone. Some selected compounds have been demonstrated to exhibit photochromic properties in polymethylmethacrylate (PMMA) films.

Robust photoswitch: A new series of robust dithienylethene-containing phosphole derivatives has been synthesized (see figure); their photophysical and photochromic properties are found to be readily tuned by simple modifications at the phosphorus center, substitution at the phosphole backbone, as well as variation on the extent of π-conjugation of the phosphole backbone. Both the open and closed forms of the phosphole compounds have good thermal stability in benzene solution and in PMMA film.

General synthetic access to expanded π-acidic surfaces of variable size, topology, chirality, and π acidity is reported. The availability of π surfaces with these characteristics is essential to develop the functional relevance of anion–π interactions with regard to molecular recognition, translocation, and transformation. The problem is that, with expanded π surfaces, the impact of electron-withdrawing substituents decreases and the high π acidity needed for strong anion–π interactions can be more difficult to obtain. To overcome this problem, it is herein proposed to build large surfaces from smaller fragments and connect these fragments with bridges that are composed only of single atoms. Two central surfaces for powerful anion–π interactions, namely, perfluoroarenes and naphthalenediimides (NDIs), were selected as fragments and coupled with through sulfide bridges. Their oxidation to sulfoxides and sulfones, as well as fluorine substitution in the peripheral rings, provides access to the full chemical space of relevant π acidities. According to cyclic voltammetry, LUMO levels range from −3.96 to −4.72 eV. With sulfoxide bridges, stereogenic centers are introduced to further enrich the intrinsic planar chirality of the expanded surfaces. The stereoisomers were separated by chiral HPLC and characterized by X-ray crystallography. Their topologies range from chairs to π boats, and the latter are reminiscent of the cation–π boxes in operational neuronal receptors. With pentafluorophenyl acceptors, the π acidity of NDIs with two sulfoxide groups in the core reaches −4.45 eV, whereas two sulfone moieties give a value of −4.72 eV, which is as low as with four ethyl sulfone groups, that is, a π superacid near the limit of existence. Beyond anion–π interactions, these conceptually innovative π-acidic surfaces are also of interest as electron transporters in conductive materials.

Little wings: Single-atom sulfur bridges between the classical π acids naphthalene-diimides and perfluoroarenes on the sulfide, the sulfoxide, and the sulfone levels open access to expanded π acids and π-acidity gradients (see figure; blue=π-acidic, red=π-basic) up to DADADAD (D: donor, A: acceptor) patterns, LUMO levels from −3.96 to −4.72 eV, and chiral topologies from chairs to boats.

We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P-containing PAHs exhibit properties expected for an emitter in white organic light-emitting diodes (WOLEDs).

Getting it white: The synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge are described (see figure). The impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P-containing PAHs exhibit the properties expected for an emitter in white organic light-emitting diodes (WOLEDs).