Search

In photo‐induced olefin synthesis, the photocatalysts with high triplet energy could cause the isomerization of olefins. This study demonstrates a new quinoxalinone photocatalytic system for highly stereoselective alkenes preparation from alkenyl sulfones and alkyl boronic acids. Our photocatalyst could not convert the thermodynamically favored E‐olefin to Z‐olefin, guaranteeing the high E‐configuration selectivity of the reaction. There is weak interaction between boronic acids and quinoxalinone according to NMR experiments, probably decreasing the oxidation potential of boronic acids. This system can be further extended to the allyl and alkynyl sulfones to give corresponding alkenes and alkynes. [ABSTRACT FROM AUTHOR]

m‐Benziporphyrin(1.1.0.0) and m‐pyreniporphyrin(1.1.0.0) were prepared as ring‐contracted carbaporphyrins. While m‐Benziporphyrin(1.1.0.0) was unstable, m‐pyreniporphyrin(1.1.0.0) was fairly stable. Both of their PdII complexes showed distorted coordination structures with extremely short Pd−C bonds. As compared with the reported m‐benziporphyrin PdII complexes, these PdII complexes showed considerably small HOMO‐LUMO gaps, despite their smaller molecular size. PdII metalation of the m‐pyreniporphyrin(1.1.0.0) dimer gave the corresponding PdII complex, which showed similar distorted coordination and a smaller HOMO‐LUMO gap. Finally, PdII metalation of a pyrene‐sharing formal p‐benziporphyrin(1.1.1.1) dimer gave a nonaromatic PdII dimer, which rearranged to an aromatic PdII complex upon treatment with alumina. [ABSTRACT FROM AUTHOR]

Green‐to‐blue triplet–triplet annihilation photon upconversion with the well‐studied upconversion pair 9,10‐diphenylanthracene (DPA)/platinum octaethylporphyrin (PtOEP) was used to reversibly drive the photoisomerization of diarylethene (DAE) photoswitches by using visible light. By carefully selecting the kinetic and spectral properties of the molecular system as well as the experimental geometry, a single green light source can be used to selectively trigger both the ring‐opening and the ring‐closing reactions, whilst also inducing fluorescence from the colored closed isomer that can be used as a readout to monitor the isomerization process in situ. The upconversion solution and the DAE solution are kept physically separated, allowing them to be characterized both concomitantly and individually without further separation processes. The ring‐closing reaction using upconverted photons was quantified and compared to the efficiency of direct isomerization with ultraviolet light. [ABSTRACT FROM AUTHOR]

The triptycene scaffold has been ring‐opened by using a retro‐Friedel‐Crafts‐type reaction under acidic conditions to give its corresponding anthrone product. 9‐Hydroxytriptycenes and unsubstituted triptycene undergo ring‐opening reaction under strongly acidic conditions, such as with TfOH. An investigation of the substitution effect has revealed that the electron‐donating group on the arene moiety allows the reaction to proceed in the presence of a weaker acid, such as TFA. In addition, the reaction has been successfully applied toward the synthesis of tetracene. [ABSTRACT FROM AUTHOR]

Recent years have seen a marked increase in the occurrence of sulfoximines in the chemical sciences, often presented as valuable motifs for medicinal chemistry. This has been prompted by both pioneering works taking sulfoximine containing compounds into clinical trials and the concurrent development of powerful synthetic methods. This review covers recent developments in the synthesis of sulfoximines concentrating on developments since 2015. This includes extensive developments in both S−N and S−C bond formations. Flow chemistry processes for sulfoximine synthesis are also covered. Finally, subsequent transformations of sulfoximines, particularly in N‐functionalization are reviewed, including N−S, N−P, N−C bond forming processes and cyclization reactions. [ABSTRACT FROM AUTHOR]

Diarylethene (DTE) has been widely used in fluorescence probes, molecular logic gates, optical data‐storage devices owing to the excellent photochromic property, while constructing high‐performance photochromic DTE in aqueous media remains a big challenge. Herein we present several host‐guest systems formed between cucurbit[n]uril (CB[n], n=7, 8, 10) and two water‐soluble DTE derivatives 1 and 2. It was found that host‐guest interactions not only affect the photophysical properties of photochromic guests, but also make great differences on the photoreaction process. Different host‐guest binding behaviors also lead to different effects on the photochromic properties of guests. In the presence of CB[n], both 1 and 2 showed enhanced emission and higher fluorescence quenching ratio at photostationary state. Besides, CB[10]⋅1 exhibited faster response rate in cyclization reaction and better photofatigue resistance than free 1 in aqueous solution, while the supramolecular assembly of (CB[8])n⋅(2)n showed slower response rate in both directions of the reversible photoreaction. Besides, the photofatigue resistance of 2 can be greatly improved through binding with CB[7]. Our results suggest that host‐guest interactions could be an efficient way to improve photochromic properties of DTE in aqueous solution. [ABSTRACT FROM AUTHOR]

Acenes, polyaromatic hydrocarbons composed of linearly fused benzene rings have received immense attention due to their performance as semiconductors in organic optoelectronic applications. Their appealing physicochemical properties, such as extended delocalization, high charge carrier mobilities, narrow HOMO‐LOMO gaps and partially radical character in the ground state make them very attractive targets for many potential applications. However, the intrinsic synthetic challenges of unsubstituted members such as high reactivity and poor solubility are still limiting factors for their wider exploitation. Herein, we report a simple general synthesis of a new family of angularly fused acenoacenes with improved stability compared to their isoelectronic linear counterparts. The synthesis and comprehensive characterization of pentacenopentacene, pentacenohexacene and hexacenohexacene, with lengths between decacene and dodecacene, are disclosed. [ABSTRACT FROM AUTHOR]

The borondipyrromethene (BODIPY) chromophore is a versatile platform for the construction of photoresponsive dyes with unique properties. Specifically, its covalent connection to a photocleavable group can be exploited to engineer compounds with photoswitchable fluorescence. The resulting photoactivatable fluorophores can increase their emission intensity or shift their emission wavelengths in response to switching. Such changes permit the spatiotemporal control of fluorescence with optical stimulations and the implementation of imaging strategies that would be impossible to replicate with conventional fluorophores. Indeed, BODIPYs with photoactivatable fluorescence enable the selective highlighting of intracellular targets, the nanoscaled visualization of sub‐cellular components, the real‐time monitoring of dynamic events and the photochemical writing of optical barcodes. [ABSTRACT FROM AUTHOR]

Heptacene (1) has been produced via a monoketone precursor, 2, which was prepared from 1,2,4,5‐tetrabromobenzene in nine steps in a total yield of 10 %. Compound 2 was converted to 1 quantitatively by heating at 202 °C. Heptacene exhibited high thermal stability in the solid state without any observable change over two months. To investigate the potential value of 1 as a material for p‐type organic field‐effect transistors (OFETs), top‐contact OFET devices were fabricated by vacuum deposition of 1 onto a hexamethyldisilazane (HMDS)/SiO2/Si substrate. The best hole mobility performance was 2.2 cm2 V−1 s−1. This is the first report of stable heptacene being used in an effective device and examined for its charge carrier properties. [ABSTRACT FROM AUTHOR]

Super‐resolution microscopy (SRM) imaging of the finite subcellular structures and subtle bioactivities inside organelles delivers abundant cellular information with high fidelity to unravel the intricate biological processes. An ideal fluorescent probe with precise control of fluorescence is critical in SRM technique like stimulated emission depletion (STED). Si‐rhodamine was decorated with both targeting group and H+‐receptor, affording the dually fluorogenic Si‐rhodamine in which the NIR fluorescence was efficiently controlled by the coalescent of spirolactone‐zwitterion equilibrium and PeT mechanism. The dually fluorogenic characters of the probe offer a perfect mutual enhancement in sensitivity, specificity and spatial resolution. Strong fluorescence only released in the existence of targeting protein at acidic lysosomal pH, ensured precisely tracking the dynamic of lysosomal structure and pH in living cells by STED. [ABSTRACT FROM AUTHOR]

Many (poly‐)phenolic natural products, for example, curcumin and taxifolin, have been studied for their activity against specific hallmarks of neurodegeneration, such as amyloid‐β 42 (Aβ42) aggregation and neuroinflammation. Due to their drawbacks, arising from poor pharmacokinetics, rapid metabolism, and even instability in aqueous medium, the biological activity of azobenzene compounds carrying a pharmacophoric catechol group, which have been designed as bioisoteres of curcumin has been examined. Molecular simulations reveal the ability of these compounds to form a hydrophobic cluster with Aβ42, which adopts different folds, affecting the propensity to populate fibril‐like conformations. Furthermore, the curcumin bioisosteres exceeded the parent compound in activity against Aβ42 aggregation inhibition, glutamate‐induced intracellular oxidative stress in HT22 cells, and neuroinflammation in microglial BV‐2 cells. The most active compound prevented apoptosis of HT22 cells at a concentration of 2.5 μm (83 % cell survival), whereas curcumin only showed very low protection at 10 μm (21 % cell survival). [ABSTRACT FROM AUTHOR]

Ring/chain competition in oligomerization reactions represents a long‐standing topic of synthetic chemistry and was treated extensively for solution reactions but is not well‐understood for the two‐dimensional confinement of surface reactions. Here, the kinetic and thermodynamic principles of ring/chain competition in on‐surface synthesis are addressed by scanning tunneling microscopy, X‐ray photoelectron spectroscopy, and Monte Carlo simulations applied to azulene‐based organometallic oligomers on Cu(111). Analysis of experiments and simulations reveals how the ring/chain ratio can be controlled through variation of coverage and temperature. At room temperature, non‐equilibrium conditions prevail and kinetic control leads to preferential formation of the entropically favored chains. In contrast, high‐temperature equilibrium conditions are associated with thermodynamic control, resulting in increased yields of the energetically favored rings. The optimum conditions for ring formation include the lowest possible temperature within the regime of thermodynamic control and a low coverage. The general implications are discussed and compared to the solution case. [ABSTRACT FROM AUTHOR]

Alzheimer′s disease (AD) is a neurological disorder with still no preventive or curative treatment. Flavonoids are phytochemicals with potential therapeutic value. Previous studies described the flavanone sterubin isolated from the Californian plant Eriodictyon californicum as a potent neuroprotectant in several in vitro assays. Herein, the resolution of synthetic racemic sterubin (1) into its two enantiomers, (R)‐1 and (S)‐1, is described, which has been performed on a chiral chromatographic phase, and their stereochemical assignment online by HPLC‐ECD coupling. (R)‐1 and (S)‐1 showed comparable neuroprotection in vitro with no significant differences. While the pure stereoisomers were configurationally stable in methanol, fast racemization was observed in the presence of culture medium. We also established the occurrence of extracted sterubin as its pure (S)‐enantiomer. Moreover, the activity of sterubin (1) was investigated for the first time in vivo, in an AD mouse model. Sterubin (1) showed a significant positive impact on short‐ and long‐term memory at low dosages. [ABSTRACT FROM AUTHOR]

Graphite intercalation compounds (GICs) are often used to produce exfoliated or functionalised graphene related materials (GRMs) in a specific solvent. This study explores the formation of the Na‐tetrahydrofuran (THF)‐GIC and a new ternary system based on dimethylacetamide (DMAc). Detailed comparisons of in situ temperature dependent XRD with TGA‐MS and Raman measurements reveal a series of dynamic transformations during heating. Surprisingly, the bulk of the intercalation compound is stable under ambient conditions, trapped between the graphene sheets. The heating process drives a reorganisation of the solvent and Na molecules, then an evaporation of the solvent; however, the solvent loss is arrested by restacking of the graphene layers, leading to trapped solvent bubbles. Eventually, the bubbles rupture, releasing the remaining solvent and creating expanded graphite. These trapped dopants may provide useful property enhancements, but also potentially confound measurements of grafting efficiency in liquid‐phase covalent functionalization experiments on 2D materials. [ABSTRACT FROM AUTHOR]

Understanding of the aromatic properties and magnetically induced current densities of highly conjugated chromophores is important when designing molecules with strongly delocalized electronic structure. Linear extension of the triphyrin(2.1.1) skeleton with an annelated benzo[b]heterocycle fragment modifies the aromatic character by extending the electron delocalization pathway. Two‐electron reduction leads to an antiaromatic triphyrin(2.1.1) ring and an aromatic benzo[b]heterocycle subunit. Current‐density calculations provide detailed information about the observed pathways and their strengths. [ABSTRACT FROM AUTHOR]

An aromatic expanded triphyrin, [22]triphyrin(6.6.0) 2, containing a pyrrole unit, a bipyrrole moiety, and annulene links, was obtained from a tellurium‐containing precursor meso‐tetraaryl‐26,28‐ditellurasapphyrin 1. The reaction path proceeds through an acid‐promoted tellurium extrusion from 1 yielding directly 2, characterized in a dicationic form by X‐ray crystallography. In solution the neutral macrocycle 2 reveals flexibility typical for annulenes and it exists as a mixture of conformers that differ by the configuration of the annulene fragments, as proven by 1H NMR studies and analyzed by DFT methods. The conformation is controlled by protonation state, the nature of an interacting anion, solvent identity, and by interaction with water. [ABSTRACT FROM AUTHOR]

A metal‐ and oxidant‐free catalytic method for accessing structurally diverse thioesters from readily accessible, widespread aldehydes, is described. A strategy of a simple organic 9,10‐phenanthrenequinone‐promoted hydrogen atom transfer (HAT) with visible light was successfully implemented to selectively generate acyl radicals without inducing crossover reactivity of thioester products. The preparative power of the method was demonstrated by broad substrate scope and wide functional group tolerance, and enabled the late‐stage modification of complex structures, which are difficult to achieve with the existing protocols. [ABSTRACT FROM AUTHOR]

Diindeno‐fused dibenzo[a,h]anthracene 6 and diindeno‐fused dibenzo[c,l]chrysene 9 contain the key moieties 1,4‐quinodipropene (1,4‐QDP) and 2,6‐naphthoquinodipropene (2,6‐NQDP), respectively, and they both have an open‐shell singlet ground state. The latter compound exhibits a strong biradical character and interesting properties, including a low ΔET−S (2.44 kcal mol−1), a small HOMO–LUMO gap (1.06 eV), a wide photoabsorption range (250–1172 nm), and a large two‐photon absorption cross‐section (σ=1342±56 GM). This work verifies that 6 has a slightly larger HOMO–LUMO gap and ΔET−S than its helical isomer diindeno[2,1‐f:1′,2′‐j]picene (DIP), but is a much stronger two‐photon absorber, verifying the important effect of geometry on the photophysical properties. [ABSTRACT FROM AUTHOR]

(Hetero)aryl, benzylic, and alkyl zinc halides were thiolated with N‐thiophthalimides at 25 °C within 1 h in the presence of 5–10 % Cu(OAc)2⋅H2O to furnish the corresponding polyfunctionalized thioethers in good yields. This electrophilic thiolation was extended to the introduction of trifluoromethylthio (SCF3), thiocyanate (SCN), and selenophenyl (SePh) groups. The utility of this method was shown in a seven‐step synthesis of a potent cathepsin D inhibitor in 34 % overall yield. (Hetero)aryl, benzylic, and alkyl zinc halides were thiolated with N‐thiophthalimides at 25 °C in the presence of 5–10 % Cu(OAc)2⋅H2O to give polyfunctionalized thioethers in 55–98 % yields (see scheme). This electrophilic thiolation was extended to the introduction of trifluoromethylthio (SCF3), thiocyanate (SCN), and selenophenyl (SePh) groups. The utility of this method was shown in the seven‐step synthesis of a potent cathepsin D inhibitor in 34 % overall yield. [ABSTRACT FROM AUTHOR]

A rigid and planar ethynylene‐bridged pentacene dimer (PenD) was synthesized from pentacenequinone in two steps, skipping the conventional stepwise approach. A brickwork motif in the single crystal shows two‐dimensionally extended electronic interaction in the solid state. Highly crystalline dip‐coated films exhibited average hole mobility of 0.24 cm2 V−1 s−1, comparable to that of the single‐crystal organic field‐effect transistors. This discovery and understanding of the reaction for the facile synthesis of ethynylene‐bridged π‐conjugated systems enables to the synthesis of a wide range of organic semiconducting materials. A rigid and planar ethynylene‐bridged pentacene dimer was synthesized from pentacenequinone in two steps, skipping the conventional stepwise approach. A brickwork motif in the single crystal shows two‐dimensionally extended electronic interaction in the solid state. Highly crystalline dip‐coated films exhibited the comparable hole mobility to that of the single‐crystal organic field‐effect transistors. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of 23‐oxahemiporphycene, the first monooxa analogue of hemiporphycene, a structural isomer of porphyrin, is reported. Its generation under McMurry reaction conditions is surprisingly accompanied by the appearance of a formyl derivative of oxacorrole, 21‐oxacorrole‐5‐carbaldehyde. A mechanism for the formation of the latter is proposed, relying on pinacol rearrangement of titanium pinacolate. The structures of the most stable tautomeric forms are established for both compounds based on IR and NMR spectra combined with DFT calculations. Spectral and photophysical characteristics are compared with those of structurally similar macrocycles. Replacement of one nitrogen by oxygen in hemiporphycene has only a minor impact. In contrast, for corrole it leads to the enhancement of stability and to strongly reduced rates of nonradiative deactivation of the lowest excited singlet state. This is explained by the planarity of oxacorroles, achieved by removing one of the inner hydrogen atoms from the inner cavity. Unusual crystal packing is observed for the protonated form of 23‐oxahemiporphycene, which exhibits a π–π stacked columnar alignment of positively charged macrocycle units. [ABSTRACT FROM AUTHOR]

Abstract: Carbon based supercapacitors (CSCs), with high output power and long lifespan, are considered as promising power sources for modern electronic devices. The rush to find new approaches for optimizing their electrochemical behaviors is still vibrant, and particularly, widespread enthusiasm was focused on improving the energy density of CSCs through improving the specific capacitance and expanding the operating voltage. In this regard, this article provides a brief review about recent progress and new understanding about the assembly of CSCs with high energy density. Novel applied strategies were highlighted and discussed from the aspects of electrolyte, electrodes, and device modulation. Dynamic and mechanism factors associated with the energy storage process of CSCs are particularly emphasized. Finally, the opportunities and challenges are elaborated in the hope of guiding the promising direction for the design of high‐energy CSCs. [ABSTRACT FROM AUTHOR]

A new synthetic route to highly fluorescent benzofuranylmethylidenebenzoxasiloles through cationic rhodium(I)/binap complex‐catalyzed cascade cycloisomerization of bis(2‐ethynylphenol)silanes has been developed involving 1,2‐silicon and 1,3‐carbon (alkyne) migrations followed by oxycyclization. The present synthesis requires only three steps, starting from commercially available dichlorodiisopropylsilane, which is markedly shorter than our previous synthesis (eight steps starting from commercially available chlorodiisopropylsilane). Theoretical calculations elucidated the mechanism of the above cascade cycloisomerization. This reaction is initiated by the formation of a rhodium vinylidene not through direct 1,2‐silicon migration but rather through an unprecedented stepwise 1,5‐silicon migration followed by C−Si bond‐forming cyclization from a dearomatized allenylrhodium complex. Subsequent 1,3‐carbon (alkyne) migration leading to a η3‐allenyl/propargyl‐rhodium complex followed by oxycyclization through π‐bond (alkyne) activation with the cationic rhodium(I) complex affords the benzofuranylmethylidenebenzoxasilole product. The structure–fluorescence property relationships of the thus obtained benzofuranylmethylidenebenzoxasiloles were investigated, which revealed that good fluorescence quantum yields were generated in the solution state (φF=69–87 %) by introduction of electron‐donating alkyl and phenyl groups on two phenoxy groups. In the powder state, 4‐methyl‐ and 4‐methoxy‐phenoxy derivatives exhibited efficient blue fluorescence (φF=52 % and 46 %, respectively). Especially, the 4‐methylphenoxy derivative was thermally stable, and exhibited strong narrow‐band fluorescence in the film state (blue, φF=95 %) and redshifted strong narrow‐band fluorescence (green, φF=90 %) in the crystalline state as a result of the formation of an offset π‐stacked dimer; the latter was confirmed by X‐ray crystallographic analysis and by theoretical calculations. [ABSTRACT FROM AUTHOR]

While thioesters are common intermediates in biochemical processes, they are much less appreciated in organic synthesis, also compared to other carboxylic acid derivatives. However, their chemistry and reactivity is intriguing and diversified, reaching much further than the acyl substitution and aldol chemistry. Herein, we focus on metal-catalyzed reactions for the synthesis of thioesters as well as their transformations. Reactions such as thiocarbonylation, crosscoupling, decarbonylation, allylic substitution or dual photoredox/ metal catalysis are discussed. On one hand, new atom economic methods allow for convenient synthesis of thioesters from well available starting materials. On the other hand, various synthetically important compounds can by synthesized due to the multifaceted reactivity of thioesters that we aimed to depict. [ABSTRACT FROM AUTHOR]

Abstract: A novel helically twisted π‐extended corrorin derivative having two boron dipyrrin (BODIPY) moieties at the periphery, a BODIPY DYEmer (6‐BF2) cross‐bridged with π‐conjugated dipyrrinylidene unit, was synthesized and characterized. The neutral 6‐BF2 is nonfluorescent due to the internal photoinduced charge transfer (CT) character in the excited state as inferred from the femtosecond transient absorption spectroscopy. However, upon protonation, the CT process is suppressed and the species H6‐BF2+ becomes near infrared (IR) emissive. With the aid of rigid helical conformations in 6‐BF2, the helical isomers (P‐ and M‐forms) were resolved and their chiroptical property was investigated. The distinct circular dichroism (CD) spectral changes of the enantiomers were observed in the presence of acids, which demonstrates that 6‐BF2 can be utilized for potential acid‐responsive chiroptical materials. [ABSTRACT FROM AUTHOR]

We have designed a series of molecules and developed synthetic methodology that allows for the inclusion of structural diversity along both the lateral and vertical axes of the basic TCNQ skeleton. In the lateral direction, benzoannulation extends the π-system through (hetero)acene formation, whereas incorporation of a [3]cumulene increases delocalization vertically. The potential of these new molecules as semiconductors is explored through UV/Vis spectroscopy, cyclic voltammetry, X-ray crystallography, thin-film formation, and mobility measurements (using space charge limited current measurements). [ABSTRACT FROM AUTHOR]

Carbatriphyrin(3.1.1) is the structural isomer of biphenylcorrole and achieved by switching the bonding mode of biphenyl unit from 3,3′ to 2,3′ which turns the corrole into a triphyrin analogue. The presence of a m-arene unit in the framework restricts the overall conjugation and thus leads to a nonaromatic macrocycle. The protonation experiments afford a trifluoroacetate ion complex. The coordination chemistry reveals that the bottom approach of boron(III) ion forms weak C−H⋅⋅⋅B interactions, however a top approach stabilizes the organoborane complex and the product distribution relies on the basicity of the proton scavengers. These results are unambiguously confirmed by single-crystal X-ray analyses. [ABSTRACT FROM AUTHOR]

Photoswitchable probes are of great utility in fluorescence microscopy, permitting numerous determinations, including molecular localization for super-resolution, based on their modifiable emission intensity and spectra. We have coated a blue-emitting (425 nm) quantum dot (QD) with a diheteroarylethene photochrome (PCf), the closed form isomer of which has absorption and emission maxima at 440 and 520-530 nm, respectively, and thus functions as a fluorescent acceptor for the QD donor in Förster resonance energy transfer (FRET). The transition from the non-absorbing, non-fluorescent open state to the fluorescent closed state is achieved by irradiation in the near-UV and reversed by visible light. The PCf is coupled to an amphiphilic polymer that stably coats the QD, thereby creating a water-soluble color-switching QD (csQD) emitting in the blue after visible light irradiation and in the green after UV irradiation. Thus, csQDs photomodulate between two observable states, without the 'off' state of previous constructs. The resulting change in the emission ratios of the QD and PCf is up to 180 %, and the csQD can undergo multiple photocycles with minimal fatigue. [ABSTRACT FROM AUTHOR]

Ruthenocene-type hybrid complexes with N-fused porphyrinato ligands, [Ru(NFp)Cp] (NFp=N-fused porphyrin, Cp=cyclopentadienyl), have been prepared and characterized by NMR and UV/Vis/NIR spectroscopy, cyclovoltammetry, and X-ray crystallography. [Ru(NFp)Cp] is a common low-spin ruthenium(II) complex and shows strong aromaticity. The Ru-Cp distance (1.833 Å) in [Ru(NFp)Cp] is comparable to that in [RuCp2] (1.840 Å). DFT calculations on [Ru(NFp)Cp] showed the unequivocal contribution of the RuCp moiety as well as the NFp moiety to both the HOMO and LUMO, constructing a three-dimensional d-π conjugated system. The HOMO-LUMO gaps of [Ru(NFp)Cp] are insensitive to the substituents on the NFp ligand, which is illustrated spectroscopically as well as theoretically. This is in sharp contrast to the ligand precursor, the N-fused porphyrin, in which the HOMO-LUMO gap is affected by substituents in a similar manner to standard porphyrins and related macrocycles. [ABSTRACT FROM AUTHOR]

A catalyst-free multicomponent CDC reaction is rarely reported, especially for the intermolecular tandem CDC cyclization, which represents an important strategy for constructing cyclic compounds. Herein, a three-component tandem CDC cyclization by a Pummerer-type rearrangement to afford biologically relevant isoindolinones from aromatic acids, amides, and DMSO, is described. This intermolecular tandem reaction undergoes a C(sp2)−H/C(sp3)−H cross-dehydrogenative coupling, C−N bond formation, and intramolecular amidation. A notable feature of this novel protocol is avoiding a catalyst and additive (apart from oxidant). [ABSTRACT FROM AUTHOR]

The extent of electronic coupling between a boron dipyrromethene (BODIPY) fluorophore and a diarylethene (DAE) photoswitch has been modulated in a covalently linked molecular dyad by irradiation with either UV or visible light. In the open isomer, both moieties can be regarded as individual chromophores, while in the closed form the lowest electronic (S0→S1) transition of the dyad is slightly shifted, enabling photomodulation of its fluorescence. Transient spectroscopy confirms that the dyad behaves dramatically different in the two switching states: while in the open isomer it resembles an undisturbed BODIPY fluorophore, in the closed isomer no fluorescence occurs and instead a red-shifted DAE behavior prevails. [ABSTRACT FROM AUTHOR]

A series of 'turn-on' fluorescence diarylethenes derived from 2,3-bis(2-methylbenzo[ b]thiophen-3-yl)-5,6-dihydro-4 H-thieno[2,3- b]thiopyran-4-one ( 1) with alkyl and acetyl substituents were synthesized. The photochemical and photophysical properties of these derivatives, including the photoreaction of crystalline 1, were thoroughly investigated to reveal substituent effects on their properties. The results indicated that alkyl substituents did not significantly affect the absorption and emission spectra of the diarylethenes. However, large absorption and emission wavelength shifts were observed for the diarylethene with an acetyl substituent due to extension of π-π conjugation. Significantly, all of the fluorescent ring-closed forms of the compounds isomerized to their ring-open forms in the presence of Cu2+ in the dark. EPR results provide clear evidence for the formation of the compound 1 radical cation intermediate that might be generated in the reaction between c- 1 and Cu2+. DFT calculations found that the ground-state activation energy for ring-opening of 1.+ was approximately 9.2 kcal mol−1 lower than that of 1 without Cu2+, such that a Cu2+-catalyzed oxidative cycloreversion reaction at room temperature might be possible. [ABSTRACT FROM AUTHOR]

Graphical abstracts of papers in the current issue of "Chemistry: A European Journal," are presented with topics such as click reaction in a copper-containing polymeric membrane-installed microflow device, surface-enhanced Raman scattering technique and red-violet and blue transient intermediates of the Gmelin reaction.

Indaphyrins, pyrrole-modified porphyrins containing a cleaved pyrrole β,β'-bond and two annulated indanone moieties, possess unusually broadened and redshifted UV/Vis spectra because of their π-expanded chromophores. The parent free base indaphyrin has been crystallographically characterized, highlighting its strongly ruffled conformation incorporating a helimeric twist. It was shown to be susceptible to regiospecific derivatizations at the opposite side of the ring-cleaved pyrrole (dihydroxylation, followed by functional group transformations of the resulting diol functionality), generating indaphyrin-based chlorin analogues, indachlorins, that incorporate a dihydroxypyrroline, pyrrolindione, oxazolone, or a morpholine moiety. Structural modifications resulted in further broadening and hyper- and bathochromic shifts of the optical spectra, some of which possess a nearly panchromatic absorption between 300 to well above 900 nm. The extents to which these modifications affect their solid-state conformations were analyzed. [ABSTRACT FROM AUTHOR]

Five diarylethene photochromic derivatives, the structures of which incorporate a central benzothiophene unit, a left-hand thiazole group, and a right-hand benzothiophene group, have been prepared. The compound with a thiazole unit with no substituent on the reaction-center carbon atom reveals an unprecedented transformation upon light irradiation. When the 4-position of thiazole is protected by a methyl group, the compounds show high photosensitivity and photochromic properties. In this case, light irradiation affords new compounds with [5]helicene structures featuring the highest redshifted absorption maxima reported to date. [ABSTRACT FROM AUTHOR]

We here report the construction of an E. coli expression system able to manufacture an unnatural amino acid by artificial biosynthesis. This can be orchestrated with incorporation into protein by amber stop codon suppression inside a living cell. In our case an alkyne-bearing pyrrolysine amino acid was biosynthesized and incorporated site-specifically allowing orthogonal double protein labeling. [ABSTRACT FROM AUTHOR]

Ruthenium-catalyzed cycloisomerization of 2-ethynylbiaryls was investigated to identify an optimal ruthenium catalyst system. A combination of [η6-( p-cymene)RuCl2(PR3)] and two equivalents of AgPF6 effectively converted 2-ethynylbiphenyls into phenanthrenes in chlorobenzene at 120 °C over 20 h. Moreover, 2-ethynylheterobiaryls were found to be favorable substrates for this ruthenium catalysis, thus achieving the cycloisomerization of previously unused heterocyclic substrates. Moreover, several control experiments and DFT calculations of model complexes were performed to propose a plausible reaction mechanism. [ABSTRACT FROM AUTHOR]

Heteronuclear complexes FeCp2DTECCRu(dppe)2Cl ( 1 o; dppe=1,2-bis(diphenylphosphino)ethane, Cp=cyclopentadienyl, DTE=dithienylethene) and FeCp2DTECCRu(dppe)2CCDTEFeCp2 ( 2 oo), with redox-active ferrocenyl and ruthenium centers separated by a photochromic DTE moiety, were prepared to achieve photoswitchable charge delocalization and Fe⋅⋅⋅Ru electronic communication. Upon UV-light irradiation of 2 oo, the Fe⋅⋅⋅Ru heterometallic electronic interaction is increasingly facilitated with stepwise photocyclization, 2 oo→ 2 co→ 2 cc; this is ascribed to the gradual increase in π-conjugated systems. The near-infrared absorptions in mixed-valence species [ 2 oo]+/[ 2 co]+/[ 2 cc]+ are gradually intensified following the conversion of [ 2 oo]+→[ 2 co]+→[ 2 cc]+, which demonstrates that the extent of charge delocalization shows progressive enhancement with stepwise photocyclization. As revealed by electrochemical, spectroscopic, and theoretical studies, complex 2 exhibits nine switchable states through stepwise photochromic and reversible redox processes. [ABSTRACT FROM AUTHOR]

Metalation of 6,13,20,21-tetraaryl-22 H-[14]tribenzotriphyrins(2.1.1) (TriP, 1 a- d) with [Mn(CO)5Br] provided MnI tricarbonyl complexes of [14]tribenzotriphyrins(2.1.1) 2 a- d in 85-93 % yield. The complexes were characterized by mass spectrometry and UV/Vis absorption, IR, and NMR spectroscopy. Single-crystal X-ray analyses revealed that 2 b and 2 c adopt bowl-shaped conformations. The redox properties of [(TriP)MnI(CO)3] ( 2 a- d) were studied by cyclic voltammetry. Each compound undergoes two reversible one-electron reductions to form a porphyrin π anion radical and a dianion in CH2Cl2. Two oxidation waves were observed, the first of which corresponds to a metal-centered electron-transfer process. The redox potentials of 2 a- d are consistent with the optical spectroscopic data and the relatively narrow HOMO-LUMO gaps that were predicted in DFT calculations. The optical spectra can be assigned by using Michl's perimeter model. TDDFT calculations predict the presence of several metal-to-ligand charge-transfer bands in the L-band region between 500 and 700 nm. [ABSTRACT FROM AUTHOR]

Caged rhodamine dyes (Rhodamines NN) of five basic colors were synthesized and used as 'hidden' markers in subdiffractional and conventional light microscopy. These masked fluorophores with a 2-diazo-1-indanone group can be irreversibly photoactivated, either by irradiation with UV- or violet light (one-photon process), or by exposure to intense red light ( λ∼750 nm; two-photon mode). All dyes possess a very small 2-diazoketone caging group incorporated into the 2-diazo-1-indanone residue with a quaternary carbon atom (C-3) and a spiro-9 H-xanthene fragment. Initially they are non-colored (pale yellow), non-fluorescent, and absorb at λ=330-350 nm (molar extinction coefficient (ε)≈104 M−1 cm−1) with a band edge that extends to about λ=440 nm. The absorption and emission bands of the uncaged derivatives are tunable over a wide range ( λ=511-633 and 525-653 nm, respectively). The unmasked dyes are highly colored and fluorescent ( ε= 3-8×104 M−1 cm−1 and fluorescence quantum yields ( ϕ)=40-85 % in the unbound state and in methanol). By stepwise and orthogonal protection of carboxylic and sulfonic acid groups a highly water-soluble caged red-emitting dye with two sulfonic acid residues was prepared. Rhodamines NN were decorated with amino-reactive N-hydroxysuccinimidyl ester groups, applied in aqueous buffers, easily conjugated with proteins, and readily photoactivated (uncaged) with λ=375-420 nm light or intense red light ( λ=775 nm). Protein conjugates with optimal degrees of labeling (3-6) were prepared and uncaged with λ=405 nm light in aqueous buffer solutions ( ϕ=20-38 %). The photochemical cleavage of the masking group generates only molecular nitrogen. Some 10-40 % of the non-fluorescent (dark) byproducts are also formed. However, they have low absorbance and do not quench the fluorescence of the uncaged dyes. Photoactivation of the individual molecules of Rhodamines NN (e.g., due to reversible or irreversible transition to a 'dark' non-emitting state or photobleaching) provides multicolor images with subdiffractional optical resolution. The applicability of these novel caged fluorophores in super-resolution optical microscopy is exemplified. [ABSTRACT FROM AUTHOR]

The sulfoneamidohelicene tetramer in solution exhibits different molecular responses to the same cooling stimulus delivered once and twice under thermal hysteresis conditions. Its random-coil state at a high temperature was cooled and maintained at a given temperature for which its molecules remained in a random coil (first cooling); the resulting solution was heated and cooled, after which a helix dimer formed (second cooling). Such a property can be regarded as a molecular function of counting the numbers 1 and 2. [ABSTRACT FROM AUTHOR]

A tetrathiafulvalene (TTF)-conjugated bistetracene was synthesized and characterized in the molecular electronic structures based on the spectroscopic measurements and the single-crystal X-ray diffraction analysis. UV/Vis absorption and electrochemical measurements of 5 revealed the considerable electronic communication between two tetracenedithiole units by through-bond and/or through-space interactions. The difference in the crystal-packing structures of 5, showing polymorphism, results in a variety of intermolecular electronic-coupling pattern. Of these, the π-stacking structure of 5 A gave a large transfer integral of HOMOs (97 meV), which value is beyond hexacene and rubrene, thus, quite beneficial to achieve the high hole mobility. [ABSTRACT FROM AUTHOR]

Organocatalysis: A concise synthesis of L‐pyrrolysine has been accomplished in six steps from simple starting materials. The facile synthetic strategy relies on an organocatalytic Michael addition, an efficient amide coupling, and a challenging method for the imine‐bond construction (see scheme). [ABSTRACT FROM AUTHOR]

Congest and conjugate: The application of a sterically congested dipyrromethane in an acid‐catalyzed [2+2+2] building‐block approach was studied for the first time, resulting in the formation of two stable calix[6]phyrin(1.1.1.1.1.1) diastereomers (see scheme). The calix[n]phyrins were further functionalized at their pentafluorophenyl residues, allowing the first synthesis of a calix[4]phyrin(1.1.1.1) dimer. [ABSTRACT FROM AUTHOR]

The synthesis of a series of novel core-modified and fused-ring-expanded tetraphenylporphyrins is reported. Theoretical calculations and magnetic circular dichroism (MCD) and fluorescence spectroscopic measurements were used to analyze the effect of core modification with Group 16 oxygen, sulfur, selenium, and tellurium atoms on the optical properties and electronic structures of the porphyrins. Marked redshifts of the Q and B bands and accelerated intersystem-crossing rates were observed, thus making these compounds potentially suitable for use in a variety of applications. The scope for further fine-tuning of these optical properties based on additional structural modifications, such as the incorporation of fused benzene rings to form ABAB structures by using a thiophene precursor with a fused bicyclo[2.2.2]octadiene ring and the introduction of various substituents onto the meso-phenyl rings, is also examined. [ABSTRACT FROM AUTHOR]