Polycyclic Aromatic Ligands Research Articles

Flexible ligand for Metal-Organic frameworks with simultaneous Large-Pore and antenna effect emission

Polycyclic aromatic ligands improve the pore size of metal–organic frameworks (MOFs), but their big π-conjugation structure forbids energy transfer for antenna effect emission. Thus, large-pore and antenna effect are a dilemma even their combination could improve the efficiency of MOFs. Herein, we construct a flexible ligand, 1,3,5-tris(5-methoxy-1,3-benzene dicarboxylic acid)benzene (L1) by attaching three isophthalic acids (L2) to a benzene ring through flexible –CH2-O- bonds. L1 retains the optical properties of L2 for antenna effect and expands the molecular size for MOFs with large pore. Single-crystal result of the MOFs obtained with L1 and Eu3+, Tb3+, or Gd3+ reveals the aperture of 18 Å and the density of 1.2 g/mL. L1 excites Eu3+ and Tb3+ ions for their antenna effect emission. The –CH2-O- group tunes the energy transfer for dual-emission at 360 and 623 nm from L1-Eu MOF under single excitation of 290 nm. The dual-emission is used for ratiometric fluorescence detection of phosphate (PO43-) and adenosine-5′-triphosphate (ATP). We reveal the effect of porous structure of MOFs on the response speed and range. The pore size affects the target entrance as L1-Eu MOF shows faster response to PO43- and ATP than L2-Eu MOF. Moreover, fast diffusion dynamics of a target is observed in large-pore MOFs for good linear response. The relative specific surface area affects the linear range as a narrower range was observed for ATP than PO43-. Thus, flexible ligand is effective to expand the aperture, improve optical properties, and study the response mechanism for the extensive applications of MOFs.

Bright red emission with high color purity from Eu(iii) complexes with π-conjugated polycyclic aromatic ligands and their sensing applications.

Eu(iii) complexes emit red light with a high color purity and have consequently attracted attention for development toward display and physical sensing applications. The characteristic pure color emission originates from the intra-4f–4f transition, and the brightness strongly depends on the electronic and steric structures of organic ligands. A large π-conjugated ligand design with a large absorption coefficient has been actively studied for achieving bright emission. The π-conjugated Eu(iii) luminophores also provide oxygen and temperature sensing properties by controlling their excited state dynamics based on π-electron systems. A comprehensive understanding of the design strategy of large π-conjugated ligands is crucial for the further development of luminescent Eu(iii) complexes. In this review, we summarize the research progress on π-conjugated Eu(iii) luminophores exhibiting bright emission and their physical sensing applications.

Designing Rh(I)-Half-Sandwich Catalysts for Alkyne [2+2+2] Cycloadditions

AbstractMetal-mediated [2+2+2] cycloadditions of unsaturated molecules to cyclic and polycyclic organic compounds are a versatile synthetic route affording good yields and selectivity under mild conditions. In the last two decades, in silico investigations have unveiled important details about the mechanism and the energetics of the whole catalytic cycle. Particularly, a number of computational studies address the topic of half-sandwich catalysts which, due to their structural fluxionality, have been widely employed, since the 1980s. In these organometallic species, the metal is coordinated to an aromatic ring, typically the ubiquitous cyclopentadienyl anion, C5H5 –(Cp) or to the Cp moiety of a larger polycyclic aromatic ligand (Cp′). During the catalytic process, the metal continuously ‘slips’ on the ring, changing its hapticity. This phenomenon of metal slippage and its implications for the catalyst’s performance are discussed in this work, referring to the most important computational mechanistic studies reported in literature for Rh(I) half-metallocenes, with the purpose of providing hints for a rational design of this class of compounds.1 Introduction2 Mechanism of Metal-Catalyzed Acetylene [2+2+2] Cycloaddition to Benzene and the Problem of the Indenyl Effect2.1 Acetylene-Acetonitrile [2+2+2] Co-cycloaddition to 2-Methylpyridine: Evidence of the Indenyl Effect2.2 Heteroaromatic Catalysts and the Evidence of a Reverse Indenyl Effect2.3 Booth’s Mechanistic Hypothesis and the Evidence of the Indenyl Effect3 Structure–Reactivity Correlation: The Slippage-Span Model4 Conclusions and Perspectives

Ligand Design for Site-Selective Metal Coordination: Synthesis of Transition-Metal Complexes with η6 -Coordination of the Central Ring of Anthracene.

A polycyclic aromatic ligand for site-selective metal coordination was designed by using DFT calculations. The computational prediction was confirmed by experiments: 2,3,6,7-tetramethoxy-9,10-dimethylanthracene initially reacts with [(C5 H5 )Ru(MeCN)3 ]BF4 to give the kinetic product with a [(C5 H5 )Ru]+ fragment coordinated at the terminal ring, which is then transformed into the thermodynamic product with coordination through the central ring. These isomeric complexes have markedly different UV/Vis spectra, which was explained by analysis of the frontier orbitals. At the same time, the calculations suggest that electrostatic interactions are mainly responsible for the site selectivity of the coordination.

Ligand Design for Site‐Selective Metal Coordination: Synthesis of Transition‐Metal Complexes with η6‐Coordination of the Central Ring of Anthracene

AbstractA polycyclic aromatic ligand for site‐selective metal coordination was designed by using DFT calculations. The computational prediction was confirmed by experiments: 2,3,6,7‐tetramethoxy‐9,10‐dimethylanthracene initially reacts with [(C5H5)Ru(MeCN)3]BF4 to give the kinetic product with a [(C5H5)Ru]+ fragment coordinated at the terminal ring, which is then transformed into the thermodynamic product with coordination through the central ring. These isomeric complexes have markedly different UV/Vis spectra, which was explained by analysis of the frontier orbitals. At the same time, the calculations suggest that electrostatic interactions are mainly responsible for the site selectivity of the coordination.

Catalyst‐Free Polyhydroboration of Dodecaborate Yields Highly Photoluminescent Ionic Polyarylated Clusters

AbstractThe incorporation of polyhedral boranes into novel photoluminescent materials is an area with increasing interest. While the neutral carboranes have been widely investigated for this purpose, the dodecaborate ion has received much less attention. Herein we report a significant expansion to the scope of substitution reactions for the dodecaborate ion, whereby this cluster was observed to react directly with a wide range of arenes in a step‐wise and controlled manner. In the products of these reactions, the dodecaborate ion serves as a core upon which up to nine mono‐ or polycyclic aromatic hydrocarbon ligands are exohedrally bonded. Spectroscopic evidence suggests the presence of conjugation between the π systems of the aryl ligands and the dodecaborate core, resulting in materials which exhibit high solution‐phase photoluminescence, as well as molar absorptivities and Stokes shifts that are significantly larger than those of the free arenes from which they were derived. We propose that this broad reactivity is a valuable synthetic tool for the incorporation of polyhedral boron into novel organic structures.

Catalyst-Free Polyhydroboration of Dodecaborate Yields Highly Photoluminescent Ionic Polyarylated Clusters.

The incorporation of polyhedral boranes into novel photoluminescent materials is an area with increasing interest. While the neutral carboranes have been widely investigated for this purpose, the dodecaborate ion has received much less attention. Herein we report a significant expansion to the scope of substitution reactions for the dodecaborate ion, whereby this cluster was observed to react directly with a wide range of arenes in a step-wise and controlled manner. In the products of these reactions, the dodecaborate ion serves as a core upon which up to nine mono- or polycyclic aromatic hydrocarbon ligands are exohedrally bonded. Spectroscopic evidence suggests the presence of conjugation between the π systems of the aryl ligands and the dodecaborate core, resulting in materials which exhibit high solution-phase photoluminescence, as well as molar absorptivities and Stokes shifts that are significantly larger than those of the free arenes from which they were derived. We propose that this broad reactivity is a valuable synthetic tool for the incorporation of polyhedral boron into novel organic structures.

Antitumor and antiparasitic activity of novel ruthenium compounds with polycyclic aromatic ligands

Five novel ruthenium(II)–arene complexes with polycyclic aromatic ligands were synthesized, comprising three compounds of the formula [RuCl(η6-p-cym)(L)][PF6], where p-cym=1-isopropyl-4-methylbenzene and L are the bidentate aromatic ligands 1,10-phenanthroline-5,6-dione, 1, 5-amine-1,10-phenanthroline, 4, or 5,6-epoxy-5,6-dihydro-phenanthroline, 5. In the other two complexes [RuCl2(η6-p-cym)(L′)], the metal is coordinated to a monodentate ligand L′, where L′ is phenanthridine, 2, or 9-carbonylanthracene, 3. All compounds were fully characterized by mass spectrometry and elemental analysis, as well as NMR and IR spectroscopic techniques. Obtained ruthenium compounds as well as their respective ligands were tested for their antiparasitic and antitumoral activities. Even though all compounds showed lower Trypanosoma brucei activity than the free ligands, they also resulted less toxic on mammalian cells. Cytotoxicity assays on HL60 cells showed a moderate antitumoral activity for all ruthenium compounds. Compound 1 was the most potent antitumoral (IC50=1.26±0.78μM) and antiparasitic (IC50=0.19 ± 0.05μM) agent, showing high selectivity towards the parasites (selectivity index >100). As complex 1 was the most promising antitumoral compound, its interaction with ubiquitin as potential target was also studied. In addition, obtained ruthenium compounds were found to bind DNA, and they are thought to interact with this macromolecule mainly through intercalation of the aromatic ligand.

ChemInform Abstract: Cyclopentadienyl Ruthenium Complexes with Naphthalene and Other Polycyclic Aromatic Ligands

AbstractReview: synthesis, reactivity and applications; 137 refs.

Synthesis and OLED Properties of Zinc Complexes Based on Quinaldic Acid

Metal-chelate materials based on polycyclic aromatic ligands are attractive for tuning emission colors of organic light-emitting diodes (OLED). In this work, quinaldic acid (QA) and 8-hydroxyquinoline (HQ) were employed as organic ligands and the corresponding zinc complexes (Zn(HQA), Zn(QA), Zn(HQ)) were synthesized. The structures of Zn(HQA), Zn(QA), and Zn(HQ) were determined by 1H-NMR, 13C-NMR, FT-IR, UV-Vis and XPS. Zinc complexes showed thermal stability up to 350°C under nitrogen flow by TGA. The photoluminescence (PL) was measured from DMSO solution. The Zn(HQA) emitted a yellow light around 550 nm, while Zn(HQ) emitted a green light around 500 nm. Electroluminescence (EL) device having the structure of ITO/NPB/Zn(HQA)/Liq/Al was fabricated. The device emitted a yellow light around 550 nm. The maximum luminance of 190 cd/m2 and current of 50 mA/cm2 were observed at 15 V in the Zn(HQA)-containing device.

DFT and TD‐DFT Study of Structure and Properties of Semiconductive Hybrid Networks Formed by Bismuth Halides and Different Polycyclic Aromatic Ligands

The structure and spectroscopic properties of polycyclic aromatic ligands of 2,3,6,7,10,11‐hexakis (alkylthio) triphenylene (alkyl: methyl, ethyl, and isopropyl; corresponding to the abbreviations of the molecules: HMTT, HETT and HiPTT) were studied using density functional theory (DFT) and time dependent density functional theory (TD‐DFT) methods with triple‐zeta valence polarization (TZVP) basis set. It was shown that the type of functional theory used, Becke‐Perdew (BP) and Leeuwen‐Baerends (LB94) implemented in Amsterdam Density functional (ADF) program package, does not have essential influence on the geometry of studied compounds in both ground and excited states. However, significant differences were obtained for the band gap values with relativistic effects of the zero order regular approximation scalar corrections (ZORA) and LB94 functional seems to reproduce better the experimental optical band gap of these systems.

Theoretical DFT studies of chromium tricarbonyl complexes with polycyclic aromatic ligands

This paper presents a theoretical analysis of the structures of tricarbonyl chromium complexes of carbo- and heterocyclic polyaromatic ligands (PAL) and the mechanisms of interring haptotropic rearrangement in such complexes performed by using density functional theory (DFT) with the nonempirically constructed PBE functional and extended split basis sets. The reaction paths were calculated for interring haptotropic rearrangements and rotations of the metalcarbonyl fragment in the regioisomeric complexes. The structures and energy characteristics of stationary points of the systems were determined. The migration of the Cr(CO) 3 group was shown to occur at the periphery of the ligand via transition states with the structure of η 3-allylic or η 4-trimethylmethane complexes. Calculated geometries of the complexes and the activation barriers were in a close agreement with the experimental data. The reaction of η 6-tricarbonylchromium complexes of PAL with n-BuLi ( lithiation) was also studied by the DFT. The kinetic and thermodynamic factors that control the direction and selectivity of metallation were calculated for the model η 6-biphenylenetricarbonylchromium complex. Both approaches indicate that lithiation occurs exclusively at the aromatic ring bonded to the transition metal, which agrees with the experimental data. The selectivity inside this ring is governed by a thermodynamic factor. The solvation effects were simulated for the lithium salt of the model η 6-naphthalenechromium tricarbonyl complex in which lithium is localized at the α(1)-position of coordinated ring. The simulation showed the most stable coordination of the lithium atom with two THF molecules. Addition of extra THF molecules is thermodynamically unfavorable. The tricarbonylchromium complexes of naphthalene, biphenyl, biphenylene and dibenzothiophene calculated relative energies for all solvated by two THF molecules lithium salts indicate that the difference in energies ΔE ⩽ 1 kcal mol −1 corresponds to the experimentally observed absence of selectivity, while the difference more than 2.5 kcal mol −1 corresponds to the selectivity of the reaction. No additional coordination of lithium to heteroatom was observed for the sulfur-containing dibenzothiophene complex. Similar calculation shows that double metallation in the dibenzothiophene complex occurs at positions 1 and 4. The developed approach enables one to predict the direction and selectivity of metallation reactions of transition metal complexes with different arenes and thus to synthesize labeled complexes for the investigation of degenerate IRHR.

Configurationally Stable Longitudinally Twisted Polycyclic Aromatic Compounds

Two strategies for the synthesis of configurationally stable twisted polycyclic aromatic compounds (PACs) were pursued. The first approach employed dissymmetrically positioned 1-naphthyl substituents to bias the direction of twist in highly substituted PACs. 2,3-Bis(1-naphthyl)-1,4-diphenyltriphenylene (7) was prepared, and its meso cis-dinaphthyl and enantiomeric trans-dinaphthyl isomers were resolved by preparative supercritical fluid chromatography (SFC) on chiral supports. Similarly, several naphthyl-substituted derivatives of the more highly twisted 9,10,11,12,13,14-hexaphenylbenzo[b]triphenylene (2) were prepared. Of these, 10-(1-naphthyl)-9,11,12,14-tetraphenylbenzo[b]triphenylene (13) was resolved by SFC on a chiral support. The pure enantiomers of trans-7 showed moderately large specific rotations ([alpha]D(25) = -330 and +320 degrees), but the specific rotations for the enantiomers of 13 were unexpectedly small ([alpha]D(25) = -23 and +23 degrees). Computational studies suggest that the latter result is due to presence of a minor conformation of 13 possessing a larger rotation of opposite sign than the major conformation. Both 7 and 13 showed strong circular dichroism and moderately strong circularly polarized luminescence. A byproduct of these syntheses was 9,10,19,21-tetraphenyldiphenanthro[9,10-b:9,10-h]carbazole (15), a very crowded carbazole that exhibits an 81 degree end-to-end twist but is not resolvable. In the second approach, the large, twisted, polycyclic aromatic ligand 9,10,11,12,13,14-hexaphenylbenzo[h]naphtho[2,3-f]quinoline (21, an aza-2) was used to prepare the chiral, cyclometallated iridium(III) complex 4. The ligand 21 was prepared via an unusually stable benzannulated norbornadienone, for which the free energy of activation for decarbonylation was a remarkable 33.5 kcal/mol. The iridium complex 4 proved to be configurationally stable and resolvable by analytical HPLC on chiral supports, but the low solubility of 4 prevented its resolution on a preparative scale. A much more soluble dibutyl analogue of 4 (complex 28) was then prepared, but it was not resolvable on any of the available media.

Distinct host–guest interaction and subdued fluorescence in a coordination network of 2,3,6,7,10,11-hexakis(phenylthio)triphenylene and silver(I) triflate

This paper reports our recent efforts in using host–guest interactions to control the fluorescent properties of coordination networks containing polycyclic aromatic units. The polycyclic aromatic ligand 2,3,6,7,10,11-hexakis(phenylthio)triphenylene (HPhTT) coordinates with AgTf (Tf: trifluoromethanesulfonate) in nitrobenzene to form single crystals of a 2-D host network consisting of octameric (i.e., containing eight AgTf units) and dimeric AgTf moieties linked to the HPhTT molecules through the Ag-thioether coordination bonds. The HPhTT adopts a starburst and rather irregular conformation, which apparently contributes to the formation of empty space between the 2-D coordination networks. Such voids are occupied by the nitrobenzene guest molecules, resulting in distinct aromatic–aromatic stacking interactions with the triphenylene units (interplanar distances: 3.46 and 3.60 Å). In comparison to a previous Ag-HPhTT network with toluene as weaker-interacting guests, the current system shows a significantly suppressed fluorescent emission from the triphenylene core, apparently due to the quenching effect from the nitrobenzene guests.

Semiconductive Coordination Networks from 2,3,6,7,10,11-Hexakis(alkylthio)triphenylenes and Bismuth(III) Halides: Synthesis, Structure−Property Relations, and Solution Processing

This paper reports our initial efforts to promote electronic communications across polycyclic aromatic molecules through intervening metal halide moieties. Such efforts stand as part of the larger scheme to overcome the limitation of the van der Waals barrier in molecular semiconductors. In particular, the polycyclic aromatic ligands of 2,3,6,7,10,11-hexakis(alkylthio)triphenylene (alkyl: methyl, ethyl, and isopropyl; corresponding abbreviations for the molecules, HMTT, HETT, and HiPTT) were synthesized in an improved method, and interacted with bismuth(III) bromide and chloride to produce in high yields of a series of semiconductive hybrid networks featuring flexible network dimensionalities and electronic properties, as well as promising solution processing properties. Enlarging the side group from methyl to ethyl and to isopropyl groups effectively reduces the dimensionality of the bismuth halide components (and consequently the dimensionality of the overall coordination framework). Solid-state optical absorption measurements indicate effective electronic interactions between the organic π-system and the bismuth trihalide component, and the electronic band gap decreases monotonically with increasing dimensionality of the coordination network. As compared to molecular semiconductors, these integrated hybrid networks feature stronger electronic communication across the organic molecules, and point to potentially higher charge carrier mobilities.

Fluorescent Coordination Networks of 2,3,6,7,10,11-Hexakis(phenylthio)triphenylene and Silver(I) Triflate

The polycyclic aromatic ligand 2,3,6,7,10,11-hexakis(phenylthio)triphenylene (HPhTT) coordinates with AgTf (Tf = trifluoromethylsulfonate) to form 1D networks with various solvent molecules included. In particular, the crystal structures and photoluminescent properties of compound 1 (formula = 2HPhTT.3AgTf.3toluene) and compound 2 (formula = 2HPhTT.3AgTf.2THF) are described. Both 1 and 2 feature similar network connectivity as well as similar local coordination environments around the silver(I) atoms. The organizations of the guest molecules in the two structures are, however, quite different: In 1, the toluene molecules are enclathrated in isolated cavities by the host network; in 2, the THF molecules are confined in continuous 1D channels. Because of the large aromatic system of the triphenylene moiety, strong fluorescent bands (room temperature) are observed for HPhTT, 1 and 2, with lambda(F,max) = 447 nm for HPhTT and lambda(F,max) = 440 nm for both 1 and 2.

Strained silver(i) coordination polymers of 1,4-diazatriphenylene

Two-dimensional coordination polymers of AgX (X = BF4−, ClO4−) and 1,4-diazatriphenylene show significant distortions of the polycyclic aromatic ligand and a new unsymmetrical η2-μ-η2 bonding mode for BF4− and ClO4−.

High-resolution and cross-polarization magic angle spinning NMR studies of tricarbonylchromium complexes with polycyclic aromatic ligands

The strategy of investigation of the structures and transformations of organometallic compounds by high-resolution NMR spectroscopy in solutions and in the solid state (cross-polarization magic angle spinning NMR) was considered in relation to tricarbonylchromium complexes with polycyclic aromatic ligands.

Aromatic Hydrocarbon Receptor (AhR)·AhR Nuclear Translocator- and p53-mediated Induction of the Murine Multidrug Resistance mdr1 Gene by 3-Methylcholanthrene and Benzo(a)pyrene in Hepatoma Cells

The mouse multidrug resistance gene family consists of three genes (mdr1, mdr2, and mdr3) encoding P-glycoprotein. We show that the expression of mdr1 is increased at the transcriptional level upon treatment of the hepatoma cell line Hepa-1c1c7 with the polycyclic aromatic hydrocarbon 3-methylcholanthrene (3-MC). This increase is not observed in the aromatic hydrocarbon receptor (AhR)-defective TAOc1BP(r)c1 and the AhR nuclear translocator (Arnt)-defective BP(r)c1 variants, demonstrating that the induction of mdr1 by 3-MC requires AhR.Arnt. We show that the mdr1 promoter (-1165 to +84) is able to activate the expression of a reporter gene in response to 3-MC in Hepa-1c1c7 but not in BP(r)c1 cells. Deletion analysis indicated that the region from -245 to -141 contains cis-acting sequences mediating the induction, including a potential p53 binding sequence. 3-MC treatment of the cells increased the levels of p53 and induced p53 binding to the mdr1 promoter in an AhR.Arnt-dependent manner. Mutations in the p53 binding site abrogated induction of mdr1 by 3-MC, indicating that p53 binding to the mdr1 promoter is essential for the induction. Benzo(a)pyrene, a polycyclic aromatic hydrocarbon and AhR ligand, which, like 3-MC, is oxidized by metabolizing enzymes regulated by AhR.Arnt, also activated p53 and induced mdr1 transcription. 2,3,7,8-Tetrachlorodibenzo-p-dioxin, an AhR ligand resistant to metabolic breakdown, had no effect. These results indicate that the transcriptional induction of mdr1 by 3-MC and benzo(a)pyrene is directly mediated by p53 but that the metabolic activation of these compounds into reactive species is necessary to trigger p53 activation. The ability of the anticancer drug and potent genotoxic agent daunorubicin to induce mdr1 independently of AhR.Arnt further supports the proposition that mdr1 is transcriptionally up-regulated by p53 in response to DNA damage.

Organic light-emitting diodes using novel metal–chelate complexes

Electroluminescent (EL) properties of novel metal–chelate complexes have been investigated in the organic light-emitting diodes (OLEDs) comprised of the hole transport layer (HTL) and emitting layer (EML). The metal–chelate complexes have either polycyclic aromatic or fused ring ligands, which coordinate to zinc or aluminum. Various EL emission colors over the range of blue to yellow were obtained. The OLEDs using the complexes with polycyclic aromatic ligands showed desirable blue emission with a quantum efficiency of 1.5–1.7% at a luminance of 300 cd/m 2 and CIE color coordinates of around (0.17, 0.16). By perylene-doping into the blue-emitting complex, the improvement of EL efficiency was observed. On the other hand, the complex with fused ring ligands gave a quantum efficiency of 0.8% at yellow emission.