Anthracenyl Groups Research Articles

Highly Efficient N‐Heterocyclic Carbene Precursor from Sterically Hindered Benzimidazolium Salt for Benzoin Condensation

AbstractA diverse array of simple benzoin compounds featuring aryl and heteroaryl substituents were prepared from corresponding aldehydes, achieving moderate to excellent yields. To achieve this, a library of NHC precursors was designed and synthesized from imidazole and benzimidazole. Our custom‐designed NHC precursors (L1–L10) varied in size and structure. Built on imidazolinium and benzimidazolinium salts, these catalysts sported substituents at the N1 and N3 positions ranging from compact groups like butyl or benzyl to the much bulkier anthracenyl group. Treatment with a base transforms these salts into highly effective NHC precursors. After being activated, these NHCs become highly effective catalysts for the benzoin condensation reaction. We tested all the NHC precursors we made and found that L10, the one containing the large and bulky anthracenyl group attached to a benzimidazolium ring, worked the best for making benzoin derivatives.

π-Extended ligands with dual-binding behavior: hindered rotation unlocks unexpected reactivity in cyclometalated Pt complexes.

Cyclometalated platinum complexes play a crucial role in catalysis, bioimaging, and optoelectronics. Phenylpyridines are widespread cyclometalating ligands that generate stable and highly emissive Pt complexes. While it is common practice to modify these ligands to fine-tune their photophysical properties, the incorporation of polycyclic aromatic hydrocarbons into the ligand's structure has been largely overlooked. This report describes the cyclometalation of naphthalenyl- and anthracenylpyridine ligands, which has resulted in ten new luminescent PtII and PtIV complexes. These species are enabled by a dual-binding behavior discovered in our polyaromatic-containing ligands. The introduction of naphthalenyl and anthracenyl groups unlocks dual binding modes, with the Pt center bonding to either of two distant carbon atoms within the ligand. These complexes exhibit both symmetric structures with two 5-membered metallacycles and asymmetric structures with 5- and 6-membered metallacycles. This work presents a strategy for the regioselective synthesis of Pt complexes with bespoke structures and photophysical properties. Our findings offer new opportunities in platinum chemistry and beyond, with potential implications for materials and technologies.

π-Stacking among the Anthracenyl Groups of a Copper Complex Resulted in Doubling of Unit Cell Volume To Provide New Polymorphs.

Two polymorphs of the 9-N-(3-imidazolylpropylamino)methylanthracene (Hanthraimmida) containing hydrated copper(II)-2,6-pyridinedicarboxylate complex are reported. The two polymorphs have either lamellar or Herringbone arrangements of π-stacks among the anthracenyl groups of organocation. The difference between the two polymorphs originated from having face-to-face stacking arrangements between the two anthracenyl groups of the symmetry independent cations within the unit cell in one of the polymorphs. The π-stacked anthracenyl groups in consecutive layers of the polymorphs are oriented in one direction in the polymorph designated as P1, whereas the polymorph designated as P2 has such orientations in opposite directions. The unit cell volume of the polymorph P2 (Z = 4) has approximately twice the volume of the polymorph P1 (Z = 2); it happend due to coalescence of two unit cells of P1 in the ab-crystallographic plane. A mixed methanol/water solvate of the copper complex is also reported. It has a channel-like arrangement of the cations; has the anions and the solvents within the cation embraced channel-like enclosures. This complex is unstable, once taken out from the methanol solvent, it transforms in real time to P2 by replacements of the methanol molecules by water molecules.

Fluorescent protein chromophore-based photosensitizer modified with anthracenyl for lysosome-targeted photodynamic therapy and two-photon fluorescence imaging

In this work, two cis-anthracenyl fluorescent protein chromophore analogs, AnFP-1 and AnFP-2 were synthesized by [2 + 3] cycloaddition for photodynamic therapy and two-photon fluorescence imaging. We combine the anthracenyl group and fluorescent core imidazolinone to form the dye AnFP-1, and then the morpholine indole structure was introduced via Knoevenagel reaction to obtain the dye AnFP-2. The heavy-atom-free photosensitizing dyes AnFP-1 and AnFP-2 have satisfied yields of singlet oxygen, measured to be 30% and 21% in methanol solution, respectively. The tetrazolium blue (MTT) experiment showed that the survival rate of A549 cells was over 92% without light exposure and under 460 nm light exposure for 10 min, the half-inhibitory concentrations (IC50) of the photosensitizing dyes AnFP-1 and AnFP-2 were 3.7 μmol•L−1 and 4.1 μmol•L−1, respectively. Acridine orange (AO)/Ethidium bromide (EB) double staining experiments showed that the two photosensitizing dyes could generate singlet oxygen and induce apoptosis in cancerous cells under irradiation. In addition, the photosensitizing dye AnFP-2 has high specificity to lysosomes which improve the photodynamic effect. Its Pearson co-localization correlation coefficient is 93%. In biological imaging, AnFP-1 and AnFP-2 showed satisfactory two-photon fluorescence imaging in zebrafish with 800 nm femtosecond laser excitation. According to these results, AnFP-1 and AnFP-2 can be used in photodynamic therapy and two-photon fluorescence imaging, which lays the foundation for developing new photosensitizing dyes.

A novel heavy-atom-free lysosome-targeted BODIPY as triplet photosensitizer based on SOCT-ISC mechanism for photodynamic therapy

As important organelles in biological cells, lysosomes are closely associated with cell signaling, necrosis and apoptosis. Herein, we report a novel lysosome-targeted boron dipyrromethene (BODIPY) photosensitizer, Lyso-BDP, which has the advantage of lower side effects and higher phototoxicity for 4T1 cells in photodynamic therapy (PDT). Lyso-BDP possesses the lysosomal targeting treatment through the production of the singlet oxygen under the light excitation at 600 nm. We combine the anthracenyl group and BODIPY to form a D-A binary compound. The orthogonal configuration is confirmed by density functional theory (DFT) and time-dependent density functional theory (TDDFT). The molecular orbitals and the energies of the triplet state explain the spin-orbit charge transfer inter-system crossing (SOCT-ISC) mechanism. Due to SOCT-ISC mechanism, Lyso-BDP has the high singlet oxygen (1O2) quantum yield of 62% in DCM without heavy atoms. In this way, the dark toxicity of photosensitizer can be reduced. Meanwhile, the 1O2 ″afterglow” can be achieved to enhance the phototherapeutic effect because of the anthracene group. Compared to classical photosensitizers, Lyso-BDP shows the low half maximum inhibitory concentration (IC50) of 2.5 μM for 4T1 cells in vitro cytotoxicity assays. Therefore, this work provides a strategy to solve the problem of high cellular dark toxicity and no organelle targeting of classical photosensitizers.

A Theoretical Study on Rate Constants of Excited State Proton Transfer Reaction in Anthracene-Urea Derivatives

Abstract We elucidate the origin of the two types of observed fluorescence in a complex consisting of nPUA (1-anthracen-n-yl-3-phenylurea; n = 1, 2, 9) and an acetate ion. By calculating the molecular properties related to the proton transfer reaction in the excited state, we clarified a correlation between the acid dissociation constant in the excited state (pKa) in the urea moiety and the rate constant of the excited state proton transfer reaction. The computed pKa suggests that the proton on the anthracenyl group side is transferred in the case of 1PUA and 2PUA, whereas the proton on the phenyl group side is transferred in 9PUA. Low pKa and activation barriers were calculated for 9PUA, which causes the stability of 9PUA due to the absence of the planarity after the proton transfer reaction.

Synthesis of helically π-stacked poly(quinolylene-2,3-methylene)s with anthracene derivatives at the chain end: intramolecular energy transfer based on the π-stacked architecture

Synthesis of π-stacked poly(quinolylene-2,3-methylene)s with anthracene derivatives at the α-chain-end, exhibiting intramolecular-energy-transfer to the terminal anthracenyl group.

Suppressing Water Uptake and Increasing Hydroxide Conductivity in Ring-Opened Polynorbornene Ion-Exchange Materials via Backbone Design

In this study, we aimed to decrease segmental mobility in ring-opened polynorbornene anion-exchange membranes (AEMs) as a strategy to suppress swelling. This was accomplished by copolymerization of a norbornene-anthracene cycloadduct with cationic tetraaminophosphonium norbornene monomers to afford AEMs with glass transition temperatures above 100 °C. The anthracenyl side groups appended to the poly(vinylene-1,3-cyclopentylene) chain resulted in lower water uptake for the phosphonium-functionalized AEM when compared to an analogue without the arene moiety. Though chemical aging of these AEMs was noted over time, the benefits of rigidifying the polymer backbone were clear. Additionally, we have noted that the choice of dialkylamino groups around the phosphorus center plays a key role in alkaline stability of these phosphonium-based AEMs.

Triazolyl- vs Pyridyl-Functionalized N-Heterocyclic Carbene Complexes: Impact of the Pendant N-Donor Ligand on Intramolecular C-C Bond Formation.

Organometallic Rh(Cp*) (Cp* = η5-pentamethylcyclopentadienyl) complexes with monodentate N-heterocyclic carbene (NHC) ligands bearing a pendant anthracenyl substituent have been shown to undergo intramolecular C-C coupling reactions. Herein, two bidentate NHC ligands substituted with pyridyl or triazolyl donor groups were prepared along with the corresponding MII/III (M = RuII, OsII, RhIII, IrIII) complexes. While the Rh(Cp*) complex featuring an NHC-triazole bidentate ligand underwent the equivalent reaction as the monodentate Rh(NHC) complex, i.e., it formed a polydentate ligand, the pyridyl-pendant derivative was unequivocally shown to be unreactive. This contrasting behavior was further investigated by density functional theory (DFT) calculations that highlighted significant differences between the two types of Rh(III) complexes with pendant pyridyl or triazolyl N-coordinating groups. Modeling of the reaction pathways suggests that the initial formation of a dicationic Rh(III) species is unfavorable and that the internal ligand transformation proceeds first by dissociation of the coordinated N atom of the pendant group from the Rh center. After the formation of a neutral η4-fulvene ligand via combined proton/single electron transfer, a cycloaddition occurs between the exo-ene bond of fulvene and the 9' and 10' positions on the pendant anthracenyl group. The resulting experimental UV-visible spectrum recorded in methanol of the polydentate triazolyl-based Rh species revealed the loss of the vibronic coupling typically associated with an anthracenyl functional group. Moreover, TD-DFT modeling indicates the presence of an equilibrium process whereby the N-coordination of the pendant triazolyl group to the RhIII center appears to be highly labile. Charge decomposition analysis (CDA) of the DFT-modeled species with the dissociated triazolyl group revealed a pseudo-η3-allylic interaction between the π-type MOs of the transformed anthracenyl group and the RhIII center; thus, the singly attached chelating ligand is classified as having rare nonadenticity.

Proton-conducting metal–organic frameworks with linkers containing anthracenyl and sulfonate groups

Co(dia)1.5(Hsip)(H2O)·H2O (1) and Zn2(μ-OH)(dia)2(sip)·2H2O (2) were prepared from the same set of ligand precursors. They exhibited bnn and dia topologies, respectively. Factors that contributed to the higher proton conductivity of 1 were presented.

Synthesis, Spectroscopic, and 1O2 Sensitization Characteristics of Extended Pd(II) 10,10-Dimethylbiladiene Complexes Bearing Alkynyl-Aryl Appendages.

Photodynamic therapy (PDT), which involves the photoinduced sensitization of singlet oxygen, is an attractive treatment for certain types of cancer. The development of new photochemotherapeutic agents remains an important area of research. Macrocyclic tetrapyrrole compounds including porphyrins, phthalocyanines, chlorins, and bacteriochlorins have been pursued as sensitizers of singlet oxygen for PDT applications but historically are difficult to prepare/purify and can also suffer from high nonspecific dark toxicity, poor solubility in biological media, and/or slow clearance from biological tissues. In response to these shortcomings, we have developed a series of novel linear tetrapyrrole architectures complexed to late transition metals as potential PDT agents. We find that these dimethylbiladiene (DMBil1) tetrapyrrole complexes can efficiently photosensitize generation of 1O2 oxygen upon irradiation with visible light. To extend the absorption profile of the DMBil1 platform, alkynyl-aryl groups have been conjugated to the periphery of the tetrapyrrole using Sonogashira methods. Derivatives of this type containing ancillary phenyl (DMBil-PE), naphthyl (DMBil-NE), and anthracenyl (DMBil-AE) groups have been prepared and characterized. In addition to structurally characterizing Pd[DMBil-NE] and Pd[DMBil-AE], we find that extension of the tetrapyrrole conjugation successfully red-shifts the absorption of the DMBil-Ar family of biladienes further into the phototherapeutic window (i.e., 600-900 nm). Photochemical sensitization studies demonstrate that our series of new palladium biladiene complexes (Pd[DMBil-Ar]) can sensitize the formation of 1O2 with quantum yields in the range ΦΔ = 0.59-0.73 upon irradiation with light of λ ≥ 650 nm. The improved absorption properties of the Pd[DMBil-Ar] complexes in the phototherapeutic window, together with their high 1O2 quantum yields, highlight the promise of these compounds as potential agents for PDT.

Supramolecular Nanofibers from Collagen-Mimetic Peptides Bearing Various Aromatic Groups at N-Termini via Hierarchical Self-Assembly.

Self-assembly of artificial peptides has been widely studied for constructing nanostructured materials, with numerous potential applications in the nanobiotechnology field. Herein, we report the synthesis and hierarchical self-assembly of collagen-mimetic peptides (CMPs) bearing various aromatic groups at the N-termini, including 2-naphthyl, 1-naphtyl, anthracenyl, and pyrenyl groups, into nanofibers. The CMPs (R-(GPO)n: n > 4) formed a triple helix structure in water at 4 °C, as confirmed via CD analyses, and their conformations were more stable with increasing hydrophobicity of the terminal aromatic group and peptide chain length. The resulting pre-organized triple helical CMPs showed diverse self-assembly into highly ordered nanofibers, reflecting their slight differences in hydrophobic/hydrophilic balance and configuration of aromatic templates. TEM analysis demonstrated that 2Np-CMPn (n = 6 and 7) and Py-CMP6 provided well-developed natural collagen-like nanofibers and An-CMPn (n = 5–7) self-assembled into rod-like micelle fibers. On the other hand, 2Np-CMP5 and 1Np-CMP6 were unable to form nanofibers under the same conditions. Furthermore, the Py-CMP6 nanofiber was found to encapsulate a guest hydrophobic molecule, Nile red, and exhibited unique emission behavior based on the specific nanostructure. In addition to the ability of CMPs to bind small molecules, their controlled self-assembly enables their versatile utilization in drug delivery and wavelength-conversion nanomaterials.

Solvent Influence in Obtaining Diverse Coordination Symmetries of Dy(III) Metal Centers in Coordination Polymers: Synthesis, Characterization, and Luminescent Properties

Six new Dy(III)-containing coordination polymers (CPs) have been synthesized emphasizing the role of solvent molecules in directing the formation of the Dy(III) coordination sphere which in turn influences the dimensionality of the coordination polymer, thermal stability, and emission properties. An isophthalate-based flexible ligand 5-[(anthracen-9-ylmethyl)-amino]-isophthalic acid (H2L) with different solvents such as dimethylformamide (DMF), dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), diethylformamide (DEF), and N-donor linkers phen (1,10-phenanothroline) and pyridine (py) was employed to obtain six different coordination polymers, viz., [Dy2(L)2(HCOO)3(DMF)·Me2NH2·H2O]n (1), [Dy4(L)6(DMA)2(H2O)4·4DMA·4H2O]n (2), [Dy2(L)3(DMSO)3(H2O)2·2DMSO·2H2O]n (3), [{Dy(L)(DEF)}2(μ2-OH)]n (4), [Dy2(L)3(phen)2·DMA·7H2O]n (5), and [Dy(L)(NO3)(py)2·py]n (6), respectively. All the compounds were characterized by IR spectroscopy and thermogravimetric analysis, and unambiguously characterized by single crystal X-ray crystallography. The bulky anthracenyl group of the linker H2L in combination with the solvent molecules significantly alters the coordination symmetry of the Dy(III) coordination sphere in the polymers in the manner: D2d in 1, C2v and D4d in 2, C4v and Cs in 3, C5v in 4, D4d in 5, and D2d in 6. The coordination symmetry plays an interesting role in sensitization of lanthanide emission. The emission maxima of compounds 1–6 vary from the blue region to the yellow region significantly due to coordination symmetry expressed by the Dy(III) centers, which in turn depends upon the coordinated solvent molecule. The thermogravimetric profile indicates the thermal stability of the solvent free compounds up to 300 °C.

Triarylisocyanurate-Based Fluorescent Two-Photon Absorbers.

The synthesis and characterization of six triarylisocyanurates, featuring 2,7-fluorenyl or 9,10-anthracenyl groups incorporated in their peripheral arms are reported. Photophysical studies reveal that these new octupolar derivatives are more fluorescent (ΦF ≥0.60 for all new compounds except for 1,3,5-tri(9H-fluoren-2-yl)-1,3,5-triazinane-2,4,6-trione 3) and present a red-shifted lowest absorption and emission compared to their known phenyl analogues of comparable size. Depending on the nature of the terminal substituent, fast intramolecular energy transfer among the three arms or localization of the excitation on a single branch occurs after population of their first singlet excited state. The latter effect was only observed in the presence of strongly electron-releasing substituents in polar media. These new chromophores are also better two-photon absorbers than the 1,4-phenylene-based isocyanurates reported so far, with cross sections σ2 ≥500 GM at 770 nm for 4-NPh2 the fluorenyl group containing (13) and the anthracenyl group containing (14) chromophores. All these spectroscopic features, analyzed with the help of quantum chemical calculations, are crucial for the design of new biphotonic fluorescent dyes.

Early Metal Di(pyridyl) Pyrrolide Complexes with Second Coordination Sphere Arene-π Interactions: Ligand Binding and Ethylene Polymerization.

Early metal complexes supported by hemilabile, monoanionic di(pyridyl) pyrrolide ligands substituted with mesityl and anthracenyl groups were synthesized to probe the possibility of second coordination sphere arene−π interactions with ligands with potential for allosteric control in coordination chemistry, substrate activation, and olefin polymerization. Yttrium alkyl, indolide, and amide complexes were prepared and structurally characterized; close contacts between the anthracenyl substituents and Y-bound ligands are observed in the solid state. Titanium, zirconium, and hafnium tris(dimethylamido) complexes were synthesized, and their ethylene polymerization activity was tested. In the solid state structure of one of the Ti tris(dimethylamido) complexes, coordination of Ti to only one of the pyridine donors is observed pointing to the hemilabile character of the di(pyridyl) pyrrolide ligands.

Photoreaction of anthracenyl phosphine oxides: Usual reversible photo- and heat-induced emission switching, and unusual oxidative P[sbnd]C bond cleavage

Anthracenyl(diphenyl)phosphine oxide and dianthracenylphenylphosphine oxide as photoactive compounds have been synthesized. Anthracenyl group of these compounds indicate the multi-functional roles such as an emission component, a photodimerization component, and a leaving group. When the light irradiation was performed under an oxygen atmosphere, photo-oxidative PC bond cleavage to leave the antharacenyl group was observed. Moreover, phosphonyl radical was produced and then PP bond formation to form diphosphane was observed.

Structural, Magnetic, and Optical Studies of the Polymorphic 9'-Anthracenyl Dithiadiazolyl Radical.

The fluorescent 9'-anthracenyl-functionalized dithiadiazolyl radical (3) exhibits four structurally determined crystalline phases, all of which are monomeric in the solid state. Polymorph 3α (monoclinic P21/ c, Z' = 2) is isolated when the radical is condensed onto a cold substrate (enthalpically favored polymorph), whereas 3β (orthorhombic P21 21 21, Z' = 3) is collected on a warm substrate (entropically favored polymorph). The α and β polymorphs exhibit chemically distinct structures with 3α exhibiting face-to-face π-π interactions between anthracenyl groups, while 3β exhibits edge-to-face π-π interactions. 3α undergoes an irreversible conversion to 3β on warming to 120 °C (393 K). The β-phase undergoes a series of reversible solid-state transformations on cooling; below 300 K a phase transition occurs to form 3γ (monoclinic P21/ c, Z' = 1), and on further cooling below 165 K, a further transition is observed to 3δ (monoclinic P21/ n, Z' = 2). Both 3β → 3γ and 3γ → 3δ transitions are reversible (single-crystal X-ray diffraction), and the 3γ → 3δ process exhibits thermal hysteresis with a clear feature observed by heat capacity measurements. Heating 3β above 160 °C generates a fifth polymorph (3ε) which is distinct from 3α-3δ based on powder X-ray diffraction data. The magnetic behavior of both 3α and the 3β/3γ/3δ system reflect an S = 1/2 paramagnet with weak antiferromagnetic coupling. The reversible 3δ ↔ 3γ phase transition exhibits thermal hysteresis of 20 K. Below 50 K, the value of χm T for 3δ approaches 0 emu·K·mol-1 consistent with formation of a gapped state with an S = 0 ground-state configuration. In solution, both paramagnetic 3 and diamagnetic [3][GaCl4] exhibit similar absorption and emission profiles reflecting similar absorption and emission mechanisms for paramagnetic and diamagnetic forms. Both emit in the deep-blue region of the visible spectrum (λem ∼ 440 nm) upon excitation at 255 nm with quantum yields of 4% (3) and 30% ([3][GaCl4]) affording a switching ratio [ΦF(3+)/ΦF(3)] of 7.5 in quantum efficiency with oxidation state. Solid-state films of both 3 and [3][GaCl4] exhibit emission bands at a longer wavelength (490 nm) attributed to excimer emission.

Tetrahydrobenzo[5]helicenediol derivatives as additives for efficient proline-catalyzed asymmetric List-Lerner-Barbas aldol reactions of bulky aldehyde substrates

Tetrahydrobenzo[5]helicenediol (THB-[5]HDIOL) derivatives as additives for the efficient proline-catalyzed asymmetric List-Lerner-Barbas (LLB) aldol reactions of bulky aldehyde substrates was described. It was found that with dibromo-substituted helical diols P-4a/M-4aas additives, the proline-catalyzed LLB aldol reaction of 9-anthraldehyde and acetone gave the product in 83% yield and 99% ee. Transition state models revealed an edge-to-face π-π stacking between the anthracenyl group in TS(R) and the phenyl group of the additive, which might result in the high enantioselectivity.

Threading fluorescent calixarene-wheels with ammonium axles

The synthesis of new calix[6]arene derivatives bearing anthracenyl and naphthyl fluorescent units at the lower rim is here reported. The threading abilities of these new derivatives toward dialkylammonium and bis(benzylalkylammonium) axles were investigated by NMR and fluorescence spectroscopy. A quenching of the fluorescence of the calix-wheels was observed upon threading with ammonium axles. Finally, DFT calculations evidenced that stabilizing C–H···π interactions are present between the axle and the anthracenyl or naphthyl group of the wheel, in addition to the usual H-bond interactions between the ammonium group of the axle and the oxygen atoms of the calix-wheel.

Metal ion binding properties of a bimodal triazolyl-functionalized calix[4]arene on a multi-array microcantilever system. Synthesis, fluorescence and DFT computation studies

A bimodal calix[4]arene functionalized with triazolyl-linked anthracenyl and 3-propylthioacetate groups is described.