Shape-persistant macrocycles with terpyridine units: synthesis, characterization, and structure in the crystal

Transition-Metal-Free Oxidative C(sp2 )-H Hydroxylation of Terpyridines: A HOMO-Raising Strategy for the Construction of a New Super-Stable Terpyridine Chromophores

Direct functionalization of terpyridines is an increasingly important topic in the field of dyes and catalysis as well as supramolecular chemistry, but its synthesis and transformation is usually challenging. Herein, a HOMO-raising strategy is reported for the construction of a super-stable novel terpyridine chromophores, in which the selective oxidation of terpyridines at its 3-position was determined successfully to the synthesis of phenol-functionalization of terpyridines (TPyOHs) bearing a hydrogen bonding group. The corresponding TPyOHs displayed strong aggregation-induced emission and exhibited highly selective and visual detection of Zn^II cation with a record green terpyridine-based luminophore with nanomolar sensitivity (125 nm).

Crystal structure of 4'-{[4-(2,2':6',2''-terpyrid-yl-4'-yl)phen-yl]ethyn-yl}biphenyl-4-yl (2,2,5,5-tetra-methyl-1-oxyl-3-pyrrolin-3-yl)formate benzene 2.5-solvate

The title compound, C44H35N4O3·2.5C6H6 (1), consists of a terpyridine and a N-oxylpyrroline-3-formate group separated by an aromatic spacer, viz. 4-(phenyl-ethyn-yl)-1,1'-biphenyl. It crystallized in the triclinic space group P-1 with two and a half benzene solvate mol-ecules (one benzene mol-ecule is located about an inversion center), while the di-chloro-methane solvate (2) of the same mol-ecule [Ackermann et al. (2015 ▸). Chem. Commun. 51, 5257-5260] crystallized in the tetra-gonal space group P42/n, with considerable disorder in the mol-ecule. In (1), the terpyridine (terpy) group assumes an all-trans conformation typical for terpyridines. It is essentially planar with the two outer pyridine rings (B and C) inclined to the central pyridine ring (A) by 8.70 (15) and 14.55 (14)°, respectively. The planes of the aromatic spacer (D, E and F) are nearly coplanar with dihedral angles D/E, D/F and E/F being 3.42 (15), 5.80 (15) and 4.00 (16)°, respectively. It is twisted with respect to the terpy group with, for example, dihedral angle A/D being 24.48 (14)°. The mean plane of the N-oxylpyrroline is almost normal to the biphenyl ring F, making a dihedral angle of 86.57 (16)°, and it is inclined to pyridine ring A by 72.61 (15)°. The intra-molecular separation between the O atom of the nitroxyl group and the N atom of the central pyridine ring of the terpyridine group is 25.044 (3) Å. In the crystal, mol-ecules are linked by pairs of C-H⋯O hydrogen bonds, forming inversion dimers. The dimers stack along the c axis forming columns. Within and between the columns, the spaces are occupied by benzene mol-ecules. The shortest oxygen-oxygen separation between nitroxyl groups is 4.004 (4) Å. The details of the title compound are compared with those of the di-chloro-methane solvate (2) and with the structure of a related mol-ecule, 4'-{4-[(2,2,5,5-tetra-methyl-N-oxyl-3-pyrrolin-3-yl)ethyn-yl]phen-yl}-2,2':6',2''-terpyridine (3), which has an ethynylphenyl spacer [Meyer et al. (2015). Acta Cryst. E71, 870-874].

The crystal structure of 4'-{4-[(2,2,5,5-tetra-methyl-N-oxyl-3-pyrrolin-3-yl)ethyn-yl]phen-yl}-2,2':6',2''-terpyridine

The terpyridine group of the title compound, C31H27N4O, assumes an all-transoid conformation and is essentially planar with the dihedral angles between the mean planes of the central pyridine and the two outer rings amounting to 3.87 (5) and 1.98 (5)°. The pyrroline-N-oxyl group commonly seen in such nitroxyls is found in the title structure and the mean plane of the pyrroline ring subtends a dihedral angle of 88.44 (7)° to the mean plane of the central pyridine ring. The intra-molecular separation between the nitrogen atom of the central pyridine unit of the terpyridine group and the nitroxyl group is 14.120 (2) Å. In the crystal, the mol-ecules are arranged in layers stacked along [001]. Slipped face-to-face π-π inter-actions between the pyridine rings are observed along this direction with the shortest centroid-centroid distances amounting to 3.700 (1) and 3.781 (1) Å. Furthermore, edge-on C-H⋯π inter-actions between the phenyl-ene rings of neighbouring mol-ecules are observed along this direction. A two-dimensional C-H⋯O hydrogen-bonded network is formed within the (010) plane. The shortest O⋯O separation between neighbouring mol-ecules is 5.412 (3) Å.

Benzodithiophene based π-conjugated macrocycles: synthesis, morphology and electrochemical characterization

A 7,8-didodecyloxybenzo[1,2-b:4,3-b']dithiophene (BdT-Dod) containing a macrocycle was synthesized from a thiophene capped BdT-Dod comonomer through a Ti(iv) mediated McMurry reaction and characterized by (1)H NMR, (13)C NMR and MALDI-TOF mass spectrometry. Additionally, the morphological characterization was performed by AFM and SEM to investigate the self-aggregation properties. The macrocycle underwent self-assembly in the solid state to form fibers on the Si/SiO2 surface with a length in the μm range and a thickness of about 400 nm.

Arylene ethynylene macrocycles: from molecular hosts to components of high-performance supramolecular architectures

This perspective highlights the recent utilization of arylene ethynylene macrocycles as supramolecular synthons—and speculates on what future may hold.

Programmed assembly of 4,2′:6′,4′′-terpyridine derivatives into porous, on-surface networks

4,2′:6′,4′′-Terpyridine building blocks self-assemble into hydrogen-bonded domains; addition of copper atoms results in an on-surface transformation into a coordination network.

macrocycle embrace: encapsulation of fluoroarenes by m-phenylene ethynylene host

We report structural characterization of a new member of m-phenylene ethynylene ring family. This shape-persistent macrocycle also co-crystallizes with hexafluoro-, 1,2,4,5-tetrafluoro-, 1,3,5-trifluoro, and 1,4-difluorobenzene. The four complexes are almost isostructural, and all show the fluoroarene included into the central cavity of the macrocycle. Characterized by multiple short C - H⋅⋅⋅F - C contacts, these inclusion complexes further dimerize in the solid state into a 2+2 assembly, in which the two macrocycles embrace each other by their large hydrophobic groups that are rotated by 60° relative to one another.

Solution-phase dimerization of an oblong shape-persistent macrocycle

A new shape-persistent macrocycle comprising two 2,3-triphenylene moieties bridged by m-phenylene ethynylenes has been synthesized. UV-vis and fluorescence spectroscopies indicate limited interaction between the two triphenylene units. The compound, which has a pronounced oblong shape (the core measures approximately 2.2 × 1.0 nm), aggregates in CDCl3 and toluene-d8 to give stacked dimers, as indicated by the (1)H NMR signals corresponding to protons on or near the core, which shift upfield with increasing concentration. These changes in NMR shielding were modeled using DFT calculations on candidate dimer geometries. The best match to the experimental data was obtained for a dimer consisting of arene-arene stacking by 3.6 Å (on average) with a displacement along the molecular long axis of 3.5-4.0 Å. This displacement is larger than can be explained by the electronic effects of aromatic stacking interactions. Instead, the minimization of steric interactions between the side chains appears to control the dimer geometry, with the alkoxy groups of one molecule sliding into registry with the gaps along the periphery of the other. Such lateral displacement (as opposed to rotation) is a direct consequence of the extended oval shape of the compound.

Synthesis and photophysical properties of biphenyl and terphenyl arylene-ethynylene macrocycles

A series of single-walled carbon nanotube precursors, C3h-symmetric cyclotri(ethynylene)(biphenyl-2,4'-diyl) and cyclotri(ethynylene)(p-terphenyl-2,4″-diyl), have been prepared by a linear stepwise oligomerization-cyclization route and by statistical intermolecular cyclooligomerization. In addition to producing these members of a novel class of arylene ethynylene macrocycles, 1 and 2, the latter statistical process produces the smaller cyclic dimer, cyclodi(ethynylene)(p-terphenyl-2,4″-diyl) and the larger cyclic tetramer cyclotetra(ethynylene)(biphenyl-2,4'-diyl). These macrocycles display large Stokes shifts in their fluorescence spectra. Their biphenyl or terphenyl connectivity prevents these macrocycles from achieving full planarity in the ground state, and the ethynylene moieties could provide synthetic access to cyclic arylene oligomers and discrete carbon nanotube segments.

Multifunctional π-expanded macrocyclic oligothiophene 6-mers and related macrocyclic oligomers

Multifunctional π-expanded macrocyclic oligothiophene 6-mer 1, as well as 9- (2) and 12-mers (3), was synthesized using a McMurry coupling reaction as the key step. The 6-mer 1 was converted to cyclo[6](2,5-thienylene-ethynylene) (4) by using a bromination-dehydrobromination procedure. From X-ray analysis, the crystal structures of nonplanar 1 and round-shaped 2 and 4 were elucidated. STM showed that 4 formed a self-assembled monolayer at the liquid/solid interface to produce a hexagonal porous network. Chemical oxidation of 1, 2, and 4 with 1 and 2 equiv of Fe(ClO4)3 produced 1(•+) and 1(2+), 2(•+) and 2(2+), and 4(•+) and 4(2+), respectively. Although oligothiophene radical cations containing β,β-disubstituted thiophenes usually do not form π-dimers, 4(•+) clearly formed a π-dimer owing to its planar, round shape. As for the dications of 1, 2, and 4, 1(2+), which has 34π-electrons, exhibited a large diatropic ring current effect, whereas 34π dication 4(2+) only showed a medium diatropic ring current effect. In contrast to 1(2+) and 4(2+), 52π dication 2(2+) had biradical cationic character instead of Hückel-type cyclic conjugation. Interestingly, 6-mer 1 showed polymorphism and unusual melting point behavior due to the number of stable conformations in the solid state. Single crystals of 1 melted at 176 °C, whereas an amorphous film of 1 crystallized in the temperature range of 80-83 °C to form a lamellarly stacked microcrystalline film, which melted at 139 °C. The polymorphism of 1 was applied to either fluorescence switching or switching of field effect transistor (FET) activity and electrical conductivity.

Tetraiodoethynyl resorcinarene cavitands as multivalent halogen bond donors

The first examples of iodoethynyl resorcinarene cavitands as rigid 3D halogen bond (XB) donor molecules are presented. These concave macrocycles form strong, R_XB = 0.78–0.83, halogen bonds with dioxane oxygen, pyridine nitrogen and a bromide anion in tetraproropyl ammonium bromide resulting in deep cavity cavitand structures.

Preparation of shape-persistent macrocycles with a single pyridine unit by double cross-coupling reactions of aryl bromides and alkynes

A double Sonogashira-type coupling reaction between aryl bromides and alkynes using a catalytic Pd/XPhos (2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl) system was introduced as an efficient method for the synthesis of shape-persistent macrocycles (SPMs). This approach is advantageous in the synthesis of SPMs with a single pyridine unit.

Selective binding of D2h-symmetrical, acetylene-linked pyridine/pyridone macrocycles to maltoside

A macrocyclic host molecule having pyridine-pyridone-pyridine modules for saccharide recognition was prepared by Cu(II)-mediated oxidative homocoupling of a tandem diethynyl precursor. In CH(2)Cl(2), the host molecule associated with dodecyl β-maltoside much more strongly (K(a) = 1.4 × 10(6) M(-1)) than with octyl monohexosides (K(a) = ca. 2 × 10(3) to 1 × 10(4) M(-1)), accompanied with induced CDs. An all-pyridine macrocyclic host was also studied, and its binding strength with saccharides was weaker than that for the pyridine-pyridone-pyridine host.

Supramolecular surface-confined architectures created by self-assembly of triangular phenylene-ethynylene macrocycles via van der Waals interaction

At the liquid/graphite interface triangular and rhombic phenylene-ethynylene macrocycles substituted by alkyl chains self-assemble to form porous two-dimensional (2D) molecular networks of honeycomb and Kagomé types, respectively, or close-packed non-porous structures via alkyl chain interdigitation as the directional intermolecular linkages. Factors that affect the formation of the 2D molecular networks, such as alkyl chain length, solvent, solute concentration, and co-adsorption of guest molecules, were elucidated through a systematic study. For the porous networks, various molecules and molecular clusters were adsorbed in the pores reflecting the size and shape complementarity, exploring a new field of 2D host-guest chemistry.

Nanometer-scale water-soluble macrocycles from nanometer-sized amino acids

This paper introduces the unnatural amino acids m-Abc(2K) and o-Abc(2K) as nanometer-sized building blocks for the creation of water-soluble macrocycles with well-defined shapes. m-Abc(2K) and o-Abc(2K) are homologues of the nanometer-sized amino acid Abc(2K), which we recently introduced for the synthesis of water-soluble molecular rods of precise length (J. Am. Chem. Soc. 2007, 129, 7272). Abc(2K) is linear (180 degrees), m-Abc(2K) creates a 120 degree angle, and o-Abc(2K) creates a 60 degree angle. m-Abc(2K) and o-Abc(2K) are derivatives of 3'-amino-(1,1'-biphenyl)-4-carboxylic acid and 2'-amino-(1,1'-biphenyl)-4-carboxylic acid, with two propyloxyammonium side chains for water solubility. m-Abc(2K) and o-Abc(2K) are prepared as Fmoc-protected derivatives Fmoc-m-Abc(2K(Boc))-OH (1a) and Fmoc-o-Abc(2K(Boc))-OH (1b). These derivatives can be used alone or in conjunction with Fmoc-Abc(2K(Boc))-OH (1c) as ordinary amino acids in Fmoc-based solid-phase peptide synthesis. Building blocks 1a-c were used to synthesize macrocyclic "triangles" 9a-c, "parallelograms" 10a,b, and hexagonal "rings" 11a-d. The macrocycles range from a trimer to a dodecamer, with ring sizes from 24 to 114 atoms, and are 1-4 nm in size. Molecular modeling studies suggest that all the macrocycles except 10b should have well-defined triangle, parallelogram, and ring shapes if all of the amide linkages are trans and the o-alkoxy substituents are intramolecularly hydrogen bonded to the amide NH groups. The macrocycles have good water solubility and are readily characterized by standard analytical techniques, such as RP-HPLC, ESI-MS, and NMR spectroscopy. (1)H and (13)C NMR studies suggest that the macrocycles adopt conformations with all trans-amide linkages in CD(3)OD, that the "triangles" and "parallelograms" maintain these conformations in D(2)O, and that the "rings" collapse to form conformations with cis-amide linkages in D(2)O.

Self-association and electron transfer in donor-acceptor dyads connected by meta-substituted oligomers

The synthesis of a new series of electron donor-acceptor conjugates (5, 10, 13, and 16) in which the electron acceptor--C(60)--and the electron donor--pi-extended tetrathiafulvalene (exTTF)--are bridged by means of m-phenyleneethynylene spacers of variable length is reported. The unexpected self-association of these hybrids was first detected to occur in the gas phase by means of MALDI-TOF spectrometry and subsequently corroborated in solution by utilizing concentration-dependent and variable-temperature (1)H NMR experiments. Furthermore, the ability of these new conjugates to form wirelike structures upon deposition onto a mica surface has been demonstrated by AFM spectroscopy. In light of their photoactivity and redoxactivity, 5, 10, 13, and 16 were probed in concentration-dependent photophysical experiments. Importantly, absorption and fluorescence revealed subtle dissimilarities for the association constants, that is, a dependence on the length of the m-phenylene spacers. The binding strength is in 5 greatly reduced when compared with those in 10, 13, and 16. Not only that, the spacer length also plays a decisive role in governing excited-state interactions in the corresponding electron donor-acceptor conjugates (5, 10, 13, and 16). To this end, 5, in which the photo- and electroactive constituents are bridged by just one aromatic ring, displays--exclusively and independent of the concentration (10(-6) to 10(-4) M)--efficient intramolecular electron transfer events on the basis of a "through-bond" mechanism. On the contrary, the lack of conjugation throughout the bridges in 10 (two m-phenyleneethynylene rings), 13 (three m-phenyleneethynylene rings), and 16 (four m-phenyleneethynylene rings) favors at low concentration (10(-6) M) "through space" intramolecular electron transfer events. These are, however, quite ineffective and, in turn, lead to excited-state deactivations that are at high concentrations (10(-4) M) dominated by intracomplex electron transfer events, namely, between exTTF of one molecule and C(60) of another molecule, and that stabilize the resulting radical ion pair state with lifetimes reaching 4.0 micros.