Cyclic Hexamer Research Articles

Synthesis, Structure, and Optical Property of [6]Cyclo-1,2-naphthylene.

A one-pot procedure with cobalt-mediated oxidation of 2,2'-dilithio-1,1'-binaphthyl by ferrocenium salts afforded the chiral cyclic hexamer of naphthylene, [6]cyclo-1,2-naphthylene (1). The molecular structure of 1 was determined by single crystal X-ray crystallography and NMR analyses, revealing its cyclic structure with an approximate D3 symmetry. Compound 1 exhibits blue emission at 383 nm with high photoluminescence quantum yield of 97 %, which can be attributed to its rigid twelve-membered ring structure. Optical resolution of 1 by chiral HPLC allowed for the evaluation of its chiroptical properties. Each enantiomer exhibits circular dichroism with complex Cotton effects, which are grouped into three positive or three negative couplets. Circularly polarized luminescence is observed at 383 nm with an anisotropy factor |glum| on the order of 10-4. The high photoluminescence quantum yield and the CPL properties of 1 indicate its potential application as a CPL emitter.

Synthesis and characterization of a chiral spirobifluorene cyclic hexamer

Abstract A new chiral macrocycle 1-[6], consisting of six chiral spirobifluorene units linked in a cyclic arrangement, was successfully synthesized via a homo-coupling of the corresponding acyclic trimer. Notably, this chiral cyclic hexamer exhibited flexibility in solution, and both low-temperature nuclear magnetic resonance (NMR) experiments and density functional theory (DFT) calculations suggest that its stable structure is not the hexagonal D6-symmetric structure but rather the figure-eight-shaped D2-symmetric structure. In this D2-symmetric structure, the opposing bifluorenyl units are π-stacked, and it is suggested that this π-stacked region undergoes rapid dissociation and reformation at room temperature. The HOMO is distributed over the π-stacked region, with a HOMO-LUMO gap of 4.02 eV. The macrocycle exhibited strong violet fluorescence. The absorption dissymmetry factor |gabs| was 7.4 × 10−3, which is larger compared to the series of chiral smaller macrocycles 1-[n] (n = 3 to 5). Additionally, the CPL efficiency, indicated by a BCPL value of 189 M−1 cm−1, is relatively high among chiral organic luminescent molecules.

All-body concept and quantified limits of cooperativity and related effects in homodromic cyclic water clusters from a molecular-wide and electron density-based approach.

We strongly advocate distinguishing cooperativity from cooperativity-induced effects. From the MOWeD-based approach, the origin of all-body cooperativity is synonymous with physics- and quantum-based processes of electron (e) delocalization throughout water clusters. To this effect, over 10 atom-pairs contribute to the total e-density at a BCP(H,O) between water molecules in a tetramer. Intermolecular all-body e-delocalization, that is, cooperativity, is an energy-minimizing process that fully explains non-additive increase in stability of a water molecule in clusters with an increase in their size. A non-linear change in cooperativity and cooperativity-induced effects, such as (i) structural (e.g., a change in d(O,O)) or topological intra- and intermolecular properties in water clusters (e.g., electron density or potential energy density at bond critical points) is theoretically reproduced by the proposed expression. It predicted the limiting value of delocalized electrons by a H2O molecule in homodromic cyclic clusters to be 1.58e. O-atoms provide the vast majority of electrons that "travel throughout a cluster predominantly on a privileged exchange quantum density highway" (⋅⋅⋅O-H⋅⋅⋅O-H⋅⋅⋅O-H⋅⋅⋅) using Bader's classical bond paths as density bridges linking water molecules. There are, however, additional electron exchange channels that are not seen on molecular graphs as bond paths. A 3D visual representation of the "privileged" and "additional" exchange channels as well as detailed intra- and inter-molecular patterns of e-sharing and (de)localizing is presented. The energy stabilizing contribution made by three O-atoms of neighboring water molecules was found to be large (-597 kcal/mol in cyclic hexamer) and 5 times more significant than that of a classical O-H⋅⋅⋅O intermolecular H-bond.

Solid-State Self-Assembly: Exclusive Formation and Dynamic Interconversion of Discrete Cyclic Assemblies Based on Molecular Tweezers.

In contrast to self-assembly in solution systems, the construction of well-defined assemblies in the solid state has long been identified as a challenging task. Herein, we report the formation of tweezers-shaped molecules into various assemblies through a solid-state self-assembly strategy. The relatively flexible molecular tweezers undergo exclusive and quantitative assembly into either cyclic hexamers or a porous network through classical recrystallization or the exposure of powders to solvent vapor, despite the fact that they form only dimers in solution. The cyclic hexamers have high thermal stability and exhibit moderate solid-state fluorescence. The formation of heterologous assemblies consisting of different tweezers allows for tuning these solid-state properties of the cyclic hexamer. Furthermore, (trimethylsilyl)ethynyl-substituted tweezers demonstrate solvent-vapor-induced dynamic interconversion between the cyclic hexamer and a pseudocyclic dimer in the solid state. This assembly behavior, which has been studied extensively in solution-based supramolecular chemistry, had not been accomplished in the solid state so far.

DFT and TD‐DFT Study of Many‐Body and Hydrogen Bonding Interactions: Nitrosamine Oligomers

AbstractThis study focuses on the properties and intermolecular interactions of nitrosamine oligomers, which are important in both semiconductor manufacturing and nuclear waste management. The study explores various configurations of nitrosamine oligomers, ranging from monomers to pentamers in linear, ladder, and cyclic clusters, with the finding that dimer cyclic forms and hexamers and above are unstable. Many‐body analysis revealed that two‐body interaction energies made remarkable contributions to the binding energy, while the sum of 3‐, 4‐, and 5‐body energy contributed less, indicating the decrease in stability of nitrosamine from dimer to pentamer clusters. Using advanced computational techniques, such as dispersion‐corrected B3LYP‐D3 and TD‐DFT, the study investigates the vibrational modes and electronic absorption spectra of nitrosamine oligomers. The results reveal that different configurations can significantly affect the vibrational modes and electronic properties of nitrosamine oligomers. The NH2 symmetric and asymmetric modes were particularly intense in various forms of nitrosamine oligomers. The wavelengths of electronic transition, oscillator strength, and HOMO to LUMO gap were reported. Additionally, the study reports on nitrosamine oligomers’ hydrogen‐bonded cooperativity and binding energy contributions. Overall, these findings offer valuable insights into the stability and properties of nitrosamine oligomers, with potential applications in materials science and chemical engineering.

Phenothiazine cyclic hexamers: synthesis, properties, and complexation behavior with C60.

Phenothiazine cyclic hexamers linked at the 3,7-positions were synthesized. Effects of the cyclic structure as well as substituent effects of the nitrogen atom were disclosed. Furthermore, the cyclic hexamer encapsulated C60 inside the ring in a 1 : 1 ratio giving a Saturn-type complex in solution. The structure and interactions were discussed based on DFT calculations.

Formation of Supramolecular Heterostacks at the Liquid-Solid Interface: Impact of Symmetry Mismatching on Structural Growth.

The construction of intricate three-dimensional (3D) nanoarchitectures on surfaces through molecular self-assembly attracts attention not only from a crystal engineering viewpoint but also because of its potential in a range of applications, given the current interest in van der Waals heterostructures. We herein report the formation of porous structures on alkane buffer layers on graphite. A dehydrobenzo[12]annulene (DBA) derivative having six decyloxy chains forms hexagonal structures on n-pentacontane and n-hexacontane buffer layers through van der Waals interactions at the 1-octanoic acid/graphite interface. The structural features are very similar to those on the graphite surface, except for the slight structural distortion, which is attributed to the p2 symmetry of the buffer layer underneath. Moreover, based on the observation of small clusters of the DBA molecules, we discussed the nucleation and structural growth of the DBA network on a buffer layer. Finally, a hierarchical multicomponent structure was formed through the coadsorption of a heteromolecular cluster formed by a hydrogen-bonded isophthalic acid cyclic hexamer hosting a coronene molecule on the buffer layer. This study on supramolecular heterostacks provides insights into the construction of intricate 3D nanoarchitectures using self-assembly at interfaces.

An Atropisomerism Study of Large Cycloarylenes: [n]Cyclo-4,10-Pyrenylenes' Case.

An atropisomerism of large cycloarylenes was studied using [n]cyclo-4,10-pyrenylenes (n=6-21) as an illustrative example with two simple assumptions: (1) alternating configurations (R,S,R,S,…) are thermodynamically most stable, and (2) three consecutive identical configurations (R,R,R or S,S,S) are prevented. Ni-mediated coupling of a 5,9-diiodopyrene gave a series of directly-linked cyclic pyrene oligomers in one-pot reaction. As-synthesized cyclic hexamer was assigned as an (R,S,S,R,R,S) structure, converted into an (R,S,R,S,R,S)-form upon heating. Cyclic heptamer consists of two types of C2 symmetric structures predicted from assumption (2), one of which was convergent to one another by heating. Three atropisomers of cyclic octamer were analyzed from the possible five candidates by means of 1 H nuclear magnetic resonance (NMR) spectroscopy, and the conversion process to (R,S,R,S,R,S,R,S) configurations upon heating was investigated. In total, according to two simple rules, the analysis of atropisomerism could be performed smoothly.

Plasmonic Cyclic Au Nanosphere Hexamers (Small 7/2023)

Au Nanosphere Hexamers Plasmonic cyclic Au nanosphere hexamers (PCHs) are synthesized by a template-assisted colloidal reaction. PCHs exhibit unique combinatorial plasmonic features, showing individual spherical NPs and in-plane coupling of entire nanorings. These plasmonic colloidal structures have hot-spots that are suitable for near-field focusing in a single particle level and can be applied for quantitative SERS-based immunoassay. More details can be found in article number 2205956 by Jwa-Min Nam, Sungho Park, and co-workers.

EstG is a novel esterase required for cell envelope integrity in Caulobacter

Proper regulation of the bacterial cell envelope is critical for cell survival. Identification and characterization of enzymes that maintain cell envelope homeostasis is crucial, as they can be targets for effective antibiotics. In this study, we have identified a novel enzyme, called EstG, whose activity protects cells from a variety of lethal assaults in the ⍺-proteobacterium Caulobacter crescentus. Despite homology to transpeptidase family cell wall enzymes and an ability to protect against cell-wall-targeting antibiotics, EstG does not demonstrate biochemical activity toward cell wall substrates. Instead, EstG is genetically connected to the periplasmic enzymes OpgH and BglX, responsible for synthesis and hydrolysis of osmoregulated periplasmic glucans (OPGs), respectively. The crystal structure of EstG revealed similarities to esterases and transesterases, and we demonstrated esterase activity of EstG invitro. Using biochemical fractionation, we identified a cyclic hexamer of glucose as a likely substrate of EstG. This molecule is the first OPG described in Caulobacter and establishes a novel class of OPGs, the regulation and modification of which are important for stress survival and adaptation to fluctuating environments. Our data indicate that EstG, BglX, and OpgH comprise a previously unknown OPG pathway in Caulobacter. Ultimately, we propose that EstG is a novel enzyme that instead of acting on the cell wall, acts on cyclic OPGs to provide resistance to a variety of cellular stresses.

Plasmonic Cyclic Au Nanosphere Hexamers.

Rational design of plasmonic colloidal assemblies via bottom-up synthesis is challenging but would show unprecedented optical properties that strongly relate to the assembly's shape and spatial arrangement. Herein, the synthesis of plasmonic cyclic Au nanosphere hexamers (PCHs) is reported, wherein six Au nanospheres (Au NSs) are connected via thin metal ligaments. By tuning Au reduction, six dangling Au NSs are interconnected with a core hexagon nanoplate (NPL). Then, Pt atoms are selectively deposited on the edges of thespheres. After etching of the core, necklace-like nanostructures of Pt framework are obtained. Deposition of Au is followed, leading to PCHs in high yield (≈90%). Notably, PCHs exhibit the combinatorial plasmonic characteristics of individual Au NSs and the in-plane coupling of the six linked Au NSs. They yield highly uniform, reproducible, and polarization-independent single-particle surface-enhanced Raman scattering signals, which are attributed to the 2-dimensional isotropic alignment of the Au NSs. Those are applied to a SERS-based immunoassay as quantitative and qualitative single particle SERS nanoprobes. This assay shows a low limit-of-detection, down to 100pm, which is orders of magnitude lower than those based on Au NSs, and one order of magnitude lower than an assay using analogous particles of smooth Au nanorings.

Iterative synthesis, structures, and properties of acyclic and cyclic acridone oligomers

AbstractAcyclic and cyclic acridone‐2,7‐diyl oligomers were synthesized by an iterative procedure from 10‐mesitylacridone as heteroatom containing π‐conjugated compounds. The oligomeric chain was elongated by a combination of regioselective bromination, borylation, Ni(0)‐mediated homocoupling, and Suzuki‐Miyaura coupling up to acyclic hexamer. Subsequently, the cyclic hexamer was synthesized by the bromination and intramolecular coupling of the acyclic hexamer. The DFT calculations revealed that the acyclic oligomers preferred to take extended structures with anti conformations, whereas the cyclic hexamer took a macrocyclic structure with syn conformations. The UV/Vis and fluorescence spectra of the series of oligomers were measured, and the effects of the chain length and the cyclization are discussed in terms of π‐conjugation.

A self-complementary macrocycle by a dual interaction system.

Self-complementary assembly is one of the most promising phenomena for the formation of discrete assemblies, e.g., proteins and capsids. However, self-complementary assembly based on multiple host-guest systems has been scarcely reported due to the difficulty in controlling each assembly. Herein, we report a dual interaction system in which the key assembly direction is well regulated by both π-π stacking and hydrogen bonding to construct a self-complementary macrocycle. Continuous host-guest behavior of anthracene-based molecular tweezers during crystallization leads to successful construction of a cyclic hexamer, which is reminiscent of Kekulé’s monkey model. Furthermore, the cyclic hexamer in a tight and triple-layered fashion shows hierarchical assembly into cuboctahedron and rhombohedral assemblies in the presence of trifluoroacetic acid. Our findings would be potentially one of metal-free strategies for constructing anthracene-based supramolecular assemblies with higher-order structure.

Self-Assembly of Alkylamido Isophthalic Acids toward the Design of a Supergelator: Phase-Selective Gelation and Dye Adsorption.

A new series of 5-alkylamido isophthalic acid (ISA) derivatives with varying single and twin alkyl chain lengths were designed and synthesized as potential supramolecular organogelators. 5-alkylamido ISAs with linear or branched alkyl tail-groups of different lengths were effective gelators for low polarity solvents. In particular, among the presented series, a derivative with a branched, 24 carbon atom tail-group behaves as a “supergelator” with up to twenty organic solvents forming gels that are highly stable over time. The gelation behavior was analyzed using Hansen solubility parameters, and the thermal stability and viscoelastic properties of select gels were characterized. Microscopy, spectroscopy, powder X-ray diffraction, and computer modeling studies were consistent with a hierarchical self-assembly process involving the formation of cyclic H-bonded hexamers via the ISA carboxylic acid groups, which stack into elementary fibers stabilized by H-bonding of the amide linker groups and π–π stacking of the aromatic groups. These new nanomaterials exhibited potential for the phase-selective gelation of oil from oil–water mixtures and dye uptake from contaminated water. The work expands upon the design and synthesis of supramolecular self-assembled nanomaterials and their application in water purification/remediation.

Characteristics of Cyclic Triarylamine Hexamers and Application to Organic Field Effect Transistor

Characteristics of Cyclic Triarylamine Hexamers and Application to Organic Field Effect Transistor

Electron-donating curved π-electronic systems that complex with buckyballs.

Modifications in curved π-electronic systems, dipyrrolylbenzodiazepines, resulted in various derivatives with modulated electronic properties and assembly behaviour. The electron-rich pyrrole-based curved π-system exhibited C60 complexation in the form of a hydrogen-bonding cyclic hexamer, giving rise to solid-state photo-induced electron transfer as elucidated by transient absorption spectroscopy.

Toward the Synthesis of a Belt-Shaped Cyclic π-Conjugated System Comprising para-Phenylene Framework and Amide Bridging Unit

Abstract Belt-shaped π-conjugated systems have been attracting more and more attention in recent years from the synthetic interest as well as their mysterious properties that linear counterparts do not have. In this paper, the stepwise condensation of 2-bromo-4-(octylamino)benzoic acid and subsequent macrocyclization was carried out to obtain a cyclic hexamer (c6mer). The palladium-catalyzed direct arylation was then performed to get the target belt-shaped molecule (b6mer) although the isolation of b6mer did not meet with success because of the contamination of structural defects. Theoretical calculation of b6mer indicated the strain energy of ca. 100.9 kcal·mol−1 and revealed the electronic transition from degenerate HOMO-1 and HOMO-2 orbitals to LUMO similar to that of parent cycloparaphenylene derivatives.

On‐Surface Synthesis and Collective Spin Excitations of a Triangulene‐Based Nanostar

AbstractTriangulene nanographenes are open‐shell molecules with predicted high spin state due to the frustration of their conjugated network. Their long‐sought synthesis became recently possible over a metal surface. Here, we present a macrocycle formed by six [3]triangulenes, which was obtained by combining the solution synthesis of a dimethylphenyl‐anthracene cyclic hexamer and the on‐surface cyclodehydrogenation of this precursor over a gold substrate. The resulting triangulene nanostar exhibits a collective spin state generated by the interaction of its 12 unpaired π‐electrons along the conjugated lattice, corresponding to the antiferromagnetic ordering of six S=1 sites (one per triangulene unit). Inelastic electron tunneling spectroscopy resolved three spin excitations connecting the singlet ground state with triplet states. The nanostar behaves close to predictions from the Heisenberg model of an S=1 spin ring, representing a unique system to test collective spin modes in cyclic systems.

On-Surface Synthesis and Collective Spin Excitations of a Triangulene-Based Nanostar.

Triangulene nanographenes are open‐shell molecules with predicted high spin state due to the frustration of their conjugated network. Their long‐sought synthesis became recently possible over a metal surface. Here, we present a macrocycle formed by six [3]triangulenes, which was obtained by combining the solution synthesis of a dimethylphenyl‐anthracene cyclic hexamer and the on‐surface cyclodehydrogenation of this precursor over a gold substrate. The resulting triangulene nanostar exhibits a collective spin state generated by the interaction of its 12 unpaired π‐electrons along the conjugated lattice, corresponding to the antiferromagnetic ordering of six S=1 sites (one per triangulene unit). Inelastic electron tunneling spectroscopy resolved three spin excitations connecting the singlet ground state with triplet states. The nanostar behaves close to predictions from the Heisenberg model of an S=1 spin ring, representing a unique system to test collective spin modes in cyclic systems.

Scholl Reaction of ortho-Phenylene-Bridged Cyclic Pyrrole-Thiophene Hybrid Hexamer

AbstractThe Scholl reaction of ortho-phenylene-bridged cyclic pyrrole-thiophene hybrid hexamer gave cyclophane-type [5]heterohelicene exclusively in 45% yield. The structure was unambiguously revealed by X-ray diffraction analysis. This helicenophane-type compound showed sharp absorption and fluorescence spectra, reflecting its rigid structure. The reaction path was analyzed on the basis of DFT calculations, and it was found that the formation of the [5]helicene-dimer is thermodynamically favored and further oxidation is prohibited due to the increased strain energy.