Anthracene Units Research Articles

Regioisomeric dipyrazolyl−anthracene luminophores: mechanochromic luminescence switch and mercury ion detection with ‘turn-off’ response

A series of regioisomeric luminophores L1–L8 with 1H-pyrazol-3-yl or 1H-pyrazol-4-yl substituents at the different positions of anthracene core have been synthesised and characterised. According to the photophysical properties and related frontier orbital features of these compounds, the ‘site-effect’ of pyrazolyl substituent on an anthracene unit can be found, demonstrating the dependence of the properties of the compound on the position of substitution of the pyrazolyl moieties connecting to the anthracene core. Moreover, the target luminophores present reversible mechanochromism properties. The most significant mechanochromism luminescence is achieved for luminophores L1 and L2 with pyrazolyl substituents at the 9-and 10-positions of the anthracene unit. Upon grinding the pristine powder sample, a colour change from light yellow to yellow-green is observed. In addition, the target luminophores L2, L4, L6 and L8 demonstrate sensing properties of Hg2+ ions with high selectivity and exceptional sensitivity. These findings suggest that these anthracene-centred luminophores are promising functional platforms with fluorescence and selective heavy metal sensor arrays.

Photooxidase Mimicking with Adaptive Coordination Molecular Capsules.

One important feature of enzyme catalysis is the induced-fit conformational change after binding substrates. Herein, we report a biomimetic water-soluble molecular capsule featuring adaptive structural change toward substrate binding, which offers an ideal platform for efficient photocatalysis. The molecular capsule was coordination-assembled from three anthracene-bridged bis-TPT [TPT = 2,4,6-tris(4-pyridyl)-1,3,5-triazine] ligands and six (bpy)Pd(NO3)2 (bpy = 2,2'-bipyridine). Once substrates bind to its hydrophobic cavity, this capsule would undergo quantitative capsule-to-bowl transformation. Visible-light absorption brought about by both the anthracene units and the charge-transfer absorption on the late-formed quintuple π-π stacked host-guest complex efficiently facilitates aerobic photooxidation for the sulfide guests by visible-light irradiation under mild conditions. Desired turnover numbers and product selectivity (sulfoxide over sulfone) have been achieved by the transformable nature of the catalyst and the hydrophilicity of the sulfoxide product. Such a photocatalytic process enabled by an adaptive coordination capsule and substrates as the allosteric effector paves the way for constructing artificial systems to mimic enzyme catalysis.

Donor-Acceptor Pairs in Covalent Organic Frameworks Promoting Electron Transfer for Metal-Free Photocatalytic Organic Synthesis.

The donor-acceptor-type covalent organic frameworks (COFs) have recently gained increasing interest in photocatalysis, but the photoinduced electron-transfer regimes in the COFs are underexplored. Herein, we demonstrate a designed porphyrinic COF possessing a donor-acceptor structure together with its photocatalytic performance in aerobic coupling of primary amines. The COF could be photoexcited by the full range of visible light to generate electron-hole pairs that could be separated by donor-acceptor pairs. Electron transfer as the mechanism of the reaction from anthracene unit to porphyrin unit was revealed by natural transition orbitals analyses. The electrons migrate to the adsorbed O2 to generate reactive oxidative species. The COF displays remarkable photocatalytic activities in the coupling of amines to imines, which can be explained mainly by the sufficient charge separation and mobility, benefiting from the donor-acceptor pairs in the COF and their interactions to the reactants and intermediates.

Synthesis, structures and luminescence properties of N^C^N-coordinated platinum(II) complexes based on an anthracene core: A red shift and a twist

1,8-Bis(2-pyridyl)anthracene HL2 is shown to act as a tridentate, N^C^N-coordinating ligand to platinum(II), undergoing metallation at position 9 of the anthracene. The structures of Pt(N^C^N-L2)Cl and of HL2 have been determined by X-ray diffraction. The complex features two 6-membered chelate rings and an N-Pt-N bite angle of 178.16(7)°, close to the “ideal” value of 180°. The attainment of this angle necessitates not only a twisting of the pyridyl rings relative to the anthracene, but also a remarkable twisting distortion of the anthracene unit itself. The complex is isomeric with the previously reported Pt(d8qb)Cl {d8qb = 1,3-di(8-quinolyl)benzene}. A new derivative of the latter has been prepared, PtL3Cl, featuring methyl substituents in the central benzene ring ortho to the quinolines. Like PtL2Cl, its structure shows twisting of the coordinated heterocycles relative to the plane of the central aromatic ring. The Pt(II) complex PtL1Cl of a related N^C^N-coordinating ligand featuring extended conjugation, benzo[1,2-h: 5,4 = h’]diquinoline HL1, has also been prepared following a previously described procedure. PtL1Cl is brightly phosphorescent in deoxygenated solution at ambient temperature, in the red region of the spectrum. The impressive photoluminescence quantum yield of 0.30 and long emission lifetime of 38 μs are indicative of a rigid structure with little excited state distortion. In contrast, PtL2Cl shows no detectable emission, probably due to the distorted nature of the structure leading to rapid non-radiative decay of the excited state. This result contrasts with the weak red emission displayed by the isomeric Pt(d8qb)Cl and its dimethylated derivative PtL3Cl.

Pyridinium Modified Anthracenes and Their Endoperoxides Provide a Tunable Scaffold with Activity against Gram-Positive and Gram-Negative Bacteria.

Due to the emergence of multidrug resistant bacteria, the development of new antibiotics is required. We introduce here asymmetrically modified positively charged bis(methylpyridinium) anthracenes as a novel tunable scaffold, in which the two positive charges can be placed at a defined distance and angle. Our structure-activity relationship reveals that coupling the methylpyridiniums with alkynyl linkers to the central anthracene unit yields antibacterial compounds against a wide range of bacteria, including Escherichia coli, Staphylococcus aureus, and Staphylococcus epidermidis. Also, different mycobacteria, such as Mycobacterium smegmatis and Mycobacterium tuberculosis, are efficiently targeted by these compounds. The antibacterial activity depends on the number of alkynyl linkers and consequently also on the distance of the positive charges in the rigid anthracene scaffold. Additionally, the formation of an anthracene endoperoxide further increases the antibacterial activity, likely due to the release of toxic singlet oxygen that converts the endoperoxide back to the antibacterial anthracene scaffold with half-lives of several hours.

Crystal structures of 9-[bis-(benzyl-sulfan-yl)meth-yl]anthracene and of cyclo-dodeca-kis-(μ2-phenyl-methane-thiol-ato-κ2 S:S)hexa-palladium(6 Pd-Pd)-anthracene-9,10-dione (1/1).

The first title compound, C29H24S2, L1, represents an example of an anthracene-based functionalized di-thio-ether, which may be useful as a potential chelating or terminal ligand for coordination chemistry. This di-thio-acetal L1 crystallizes in the monoclinic space group P21/c. The phenyl rings of the benzyl groups and that of the anthracene unit form dihedral angles of 49.21 (4) and 58.79 (5)° and the crystal structure displays short C-H⋯π contacts. Surprisingly, when attempting to coordinate L1 to [PdCl2(PhCN)2], instead of the targeted chelate complex [PdCl2(κ2-L1)], a cleavage reaction leads to the formation of the centrosymmetric hexa-nuclear cyclic cluster of composition [Pd6(μ2-SCH2Ph)12] Pd6, or [Pd6(C7H7S)12]·C14H8O2. This tiara-shaped hexa-mer crystallizing in the triclinic space group P consists of six approximately square planar Pd(II)S4 centers, which are inter-connected through twelve μ2-bridging benzyl thiol-ate groups. The Pd⋯Pd contacts range from 3.0892 (2) to 3.1609 (2) Å and can be considered as weakly bonding. The unit cell of Pd6 contains also a co-crystallized anthracene-9,10-dione mol-ecule.

Reductive Coupling Synthesis of a Soluble Poly(9,10-anthrylene ethynylene)

A fully soluble poly(9,10-anthrylene ethynylene), poly[2,6-(2-octyldecyl)-9,10-anthrylene ethynylene] PAAE, with moderate degrees of polymerization Pn of ca. 10 is generated in a reductive, dehalogenative homocoupling scheme, starting from a 2,6-dialkylated 9,10-bis(dibromomethylene)-9,10-dihydroanthracene monomer and n-BuLi/CuCN as the reducing agent. PAAE shows surprisingly broad and unstructured absorption and photoluminescence emission bands with peaks at 506 nm and 611 nm, respectively, both in chloroform solution. The long absorption tail ranging into the 600–700 nm region and the large Stokes shift points to a high degree of geometrical disorder in the arrangement of the 9,10-anthrylene chromophores along the distorted polymer backbone. This disorder is borne out in the unusually strong wavelength dependence of fluorescence depolarisation, both with regards to the excitation and the emission wavelengths. Picosecond fluorescence depolarisation spectroscopy provides clear evidence for the presence of orthogonal transition dipole moments, presumably arising from the off-axis transition of the anthracene unit and the on-axis transition of the polymer backbone. Intramolecular energy relaxation then gives rise to the observed fluorescence depolarization dynamics.

Synthesis and Evaluation of Charge Transport Property of Ethynylene‐Bridged Anthracene Oligomers

AbstractA set of ethynylene‐bridged anthracene oligomers from monomer to tetramer is synthesized and characterized. The red‐shifts in the UV–vis absorption and fluorescence spectra indicate the π‐extension with elongation of the linear chain. Cyclic voltammetric measurements suggest that their highest occupied molecular orbitals are located lower than –5.0 eV, indicating high air stability. Single‐crystal X‐ray analysis of a trimer needle crystal indicates that anthracene units display a twisted arrangement, adopting a face‐to‐face packing structure. The dip‐coating method with a very slow pulling rate provides crystalline films of dimer and trimer. The top‐contact bottom‐gate organic field‐effect transistor devices reveal that trimer shows better charge transport property (8.0 × 10–3 cm2 V–1 s–1) than dimer (8.9 × 10–4 cm2 V–1 s–1). Furthermore, the single‐crystal field‐effect transistor of trimer shows mobility up to 0.14 cm2 V–1 s–1, which is higher than that of tetramer (3.3 × 10–2 cm2 V–1 s–1). This is likely due to the larger amount of defects in tetramer crystals that are caused by the free rotation of ethynylene units, while the trimer achieves a good balance between the effective π‐conjugation and defectless crystal formation.

Spin-Orbit Charge-Transfer Intersystem Crossing in Anthracene-Perylenebisimide Compact Electron Donor-Acceptor Dyads and Triads and Photochemical Dianion Formation.

Perylenebisimide (PBI)-anthracene (AN) donor-acceptor dyads/triad were prepared to investigate spin-orbit charge-transfer intersystem crossing (SOCT-ISC). Molecular conformation was controlled by connecting PBI units to the 2- or 9-position of the AN moiety. Steady-state, time-resolved transient absorption and emission spectroscopy revealed that chromophore orientation, electronic coupling, and dihedral angle between donor and acceptor exert a significant effect on the photophysical property. The dyad PBI-9-AN with orthogonal geometry shows weak ground-state coupling and efficient intersystem crossing (ISC, ΦΔ =86 %) as compared with PBI-2-AN (ΦΔ =57 %), which has a more coplanar geometry. By nanosecond transient absorption spectroscopy, a long-lived PBI localized triplet state was observed (τT =139 μs). Time-resolved EPR spectroscopy demonstrated that the electron spin polarization pattern of the triplet state is sensitive to the geometry and number of AN units attached to PBI. Reversible and stepwise generation of near-IR-absorbing PBI radical anion (PBI-⋅ ) and dianion (PBI2- ) was observed on photoexcitation in the presence of triethanolamine, and it was confirmed that selective photoexcitation at the near-IR absorption bands of PBI.- is unable to produce PBI2- .

Front Cover: Construction of Helical Structures with Multiple Fused Anthracenes: Structures and Properties of Long Expanded Helicenes (Chem. Eur. J. 14/2021)

Helical structures are constructed by successive fusion of anthracene units in a helicene-like manner like a dragon rising in a spiral. In the derivatives with four or more anthracene units, interlayer π⋅⋅⋅π interactions play an important role in the structures and properties of the polycyclic aromatic hydrocarbons. The helical inversion occurred via multistep mechanisms at relatively high barriers. This molecular design is valuable as a new helical motif based on the expanded and conjugated π systems. More information can be found in the Communication by S. Toyota et al. on page 4548.

Synthesis of Anthracene‐Based Cyclic π‐Clusters and Elucidation of their Properties Originating from Congested Aromatic Planes

AbstractSynthesis and properties of anthracene‐based cyclic π‐clusters which possess two and four anthracene units are discussed. The optimal cyclization conditions were determined based on a nickel(0)‐mediated reaction that afforded a cyclic anthracene dimer as the major product. Bringing two anthracene planes in close proximity in a face‐to‐face manner resulted in red‐shifted absorption owing to the narrowing of the HOMO–LUMO gap. The cyclic anthracene dimer exhibits multi‐stimuli responsiveness due to high π‐congestion. For example, photoirradiation on the anthracene dimer affords its photoisomer having C−C bonds that are longer than 1.65 Å, which can undergo thermal reversion under gentle heating. This enabled mechanochromism of the photoisomer (colorless) to the original anthracene dimer (red). Photoisomerization was also observed in the crystalline state, accompanied by crystal jumping or collapsing, that is, the photosalient effect.

Construction of Helical Structures with Multiple Fused Anthracenes: Structures and Properties of Long Expanded Helicenes.

Polycyclic aromatic compounds consisting of four or five fused anthracene units were synthesized by PtCl2 -catalyzed cycloisomerization as novel long expanded helicenes. These compounds have helical structures with significant stacking of the terminal anthracene moieties at 0.33 nm interlayer distance. In the UV-vis and fluorescence spectra, the absorption and emission bands were red-shifted as the number of fused anthracene units was increased. The characteristic broad and long-lived emission bands of the long analogues are explained by the excimer-like stabilization of the excited state. These photophysical data as well as their cyclic voltammetric data are discussed on the basis of the π-conjugation and interlayer π⋅⋅⋅π interactions in the molecular structures and the molecular orbitals. The barrier and mechanism of helical inversion are also reported.

Synthesis of Anthracene-Based Cyclic π-Clusters and Elucidation of their Properties Originating from Congested Aromatic Planes.

Synthesis and properties of anthracene-based cyclic π-clusters which possess two and four anthracene units are discussed. The optimal cyclization conditions were determined based on a nickel(0)-mediated reaction that afforded a cyclic anthracene dimer as the major product. Bringing two anthracene planes in close proximity in a face-to-face manner resulted in red-shifted absorption owing to the narrowing of the HOMO-LUMO gap. The cyclic anthracene dimer exhibits multi-stimuli responsiveness due to high π-congestion. For example, photoirradiation on the anthracene dimer affords its photoisomer having C-C bonds that are longer than 1.65 Å, which can undergo thermal reversion under gentle heating. This enabled mechanochromism of the photoisomer (colorless) to the original anthracene dimer (red). Photoisomerization was also observed in the crystalline state, accompanied by crystal jumping or collapsing, that is, the photosalient effect.

Flow Photochemistry for Single-Chain Polymer Nanoparticle Synthesis.

Single chain polymer nanoparticles (SCNP) are an attractive polymer architecture that provides functions seen in folded biomacromolecules. The generation of SCNPs, however, is limited by the requirement of a high dilution chemical step, necessitating the use of large reactors to produce processable quantities of material. Herein, the chemical folding of macromolecules into SCNPs is achieved in both batch and flow photochemical processes by the previously described photodimerization of anthracene units in polymethylmethacrylate (100 kDa) under UV irradiation at 366 nm. When employing flow chemistry, the irradiation time is readily controlled by tuning the flow rates, allowing for the precise control over the intramolecular collapse process. The flow system provides a route at least four times more efficient for SCNP formation, reaching higher intramolecular cross-linking ratios five times faster than batch operation.

Flow Photochemistry for Single‐Chain Polymer Nanoparticle Synthesis

AbstractSingle chain polymer nanoparticles (SCNP) are an attractive polymer architecture that provides functions seen in folded biomacromolecules. The generation of SCNPs, however, is limited by the requirement of a high dilution chemical step, necessitating the use of large reactors to produce processable quantities of material. Herein, the chemical folding of macromolecules into SCNPs is achieved in both batch and flow photochemical processes by the previously described photodimerization of anthracene units in polymethylmethacrylate (100 kDa) under UV irradiation at 366 nm. When employing flow chemistry, the irradiation time is readily controlled by tuning the flow rates, allowing for the precise control over the intramolecular collapse process. The flow system provides a route at least four times more efficient for SCNP formation, reaching higher intramolecular cross‐linking ratios five times faster than batch operation.

Synthesis and Properties of a Cyclohexa‐2,7‐anthrylene Ethynylene Derivative

AbstractThe synthesis of a cyclohexa‐2,7‐(4,5‐diaryl)anthrylene ethynylene (1) was achieved for the first time by using 1,8‐diaryl‐3,6‐diborylanthracene and 1,8‐diaryl‐3,6‐diiodoanthracene as key synthetic intermediates. Macrocycle 1 possesses a planar conformation of approximately D6h symmetry, because of the triple‐bond linker between the anthracene units at the 2,7‐positions. It was confirmed that macrocycle 1, bearing bulky substituents at the outer peripheral positions, behaves as a monomeric form in solution without π‐stacking self‐association. Macrocycle 1 has an inner‐cavity size that allows specific inclusion of [9]cycloparaphenylene ([9]CPP), but not [8]CPP or [10]CPP, through an aromatic edge‐to‐face CH‐π interaction.

Synthesis and Properties of a Cyclohexa-2,7-anthrylene Ethynylene Derivative.

The synthesis of a cyclohexa-2,7-(4,5-diaryl)anthrylene ethynylene (1) was achieved for the first time by using 1,8-diaryl-3,6-diborylanthracene and 1,8-diaryl-3,6-diiodoanthracene as key synthetic intermediates. Macrocycle 1 possesses a planar conformation of approximately D6h symmetry, because of the triple-bond linker between the anthracene units at the 2,7-positions. It was confirmed that macrocycle 1, bearing bulky substituents at the outer peripheral positions, behaves as a monomeric form in solution without π-stacking self-association. Macrocycle 1 has an inner-cavity size that allows specific inclusion of [9]cycloparaphenylene ([9]CPP), but not [8]CPP or [10]CPP, through an aromatic edge-to-face CH-π interaction.

Unsymmetrical Squaraine Dye-Based Organic Photodetector Exhibiting Enhanced Near-Infrared Sensitivity

An unsymmetrical squaraine (SQ) derivative containing anthracene and phenyl hydrazine (ANPHSQ) units linked to the central SQ was synthesized and used as electron donors in bulk heterojunction phot...

Efficient blue light-emitting polydibenzofluorenes through the integration of an anthracene unit

Series of light emitting polymers based on dibenzofluorene-acene have been synthesized through aromatic nucleophilic substitution reaction. The polymer displayed strong solubility in specific organic solvents with a polydispersity index of 1.5–2.0 and weight average molecular weight within the range from 25000 to 34000. At 420 nm the highest photoluminescence of the polymer solution was observed. The temperature of the thermal decomposition was determined by TGA and ranged from 300 to 446 °C while the value of Tg was between 120 and 140 °C. Cyclic voltammetry tests of polydibezofluorenes show that the compounds with HOMO and LUMO in the range 2.23–5.26 eV is stable under redox condition. The optical properties of these polydibenzofluorenes showed significant blue emissions in the polymers obtained.

Dual Functionalization of Electron Transport Layer via Tailoring Molecular Structure for High-Performance Perovskite Light-Emitting Diodes.

Great progress in modification and optimization of emission layer (EML) in perovskite light-emitting diodes (PeLEDs) results in a significant improvement in device efficiency. However, so far, less attention has been paid to the exploration of hole/electron injection and transporting layers to maximize the utilization of charge carriers for efficient and stable PeLEDs. At present, low electron mobility of electron transport layer (ETL) causes an unbalanced charge injection, and the defects at the ETL/perovskite interface limit the formation and utilization of generated excitons. Here, a series of compounds (BPBiTP, BPBiPN, and BPBiPA) flanked by diphenyl-1H-benzo[d]imidazole end groups have been developed as ETL materials, where the bridging units (benzene, naphthalene, anthracene) are manipulated to achieve dual functionality, namely, the high charge carrier mobility and effective passivation of perovskite surface. The coordinating end groups effectively reduce the trap state at the interface of ETL and EML due to their strong nucleophilic quality. H-aggregation of anthracene units and large transfer integral in BPBiPA lead to its superior electron mobility of 8.4 × 10-4 cm2 V-1 s-1 in the solid state, over 1 order of magnitude higher than that of the typical one (TPBi). Consequently, green PeLEDs with a maximum external quantum efficiency (EQE) of 19.7%, reduced efficiency roll-off, as well as extended operational lifetime have been achieved without any outcoupling technique. Our result demonstrated that optimization of ETL materials via improving both passivation capability and electron mobility is a powerful strategy for producing high-performance PeLEDs.