Polycyclic Molecules Research Articles

Aromaticity in Fully π-Conjugated Open-Cage Molecules.

Although aromaticity in 2D π-conjugated monocyclic and polycyclic molecules has been intensively studied, aromaticity in 3D fully π-conjugated molecular cages remains largely unexplored mainly due to the synthetic challenges. Herein, we report the facile synthesis of a π-conjugated molecular cage (1) containing four dimethylmethylene-bridged triphenylamine (DTPA) units via platinum-mediated assembly of four molecules of a pinacol borate trisubstituted DTPA derivative, followed by reductive elimination. 1 has an open-cage structure, consisting of two isomeric trimers in trans- and cis-configurations, and an additional macrocycle across four DTPA units. Accordingly, the trans- (2) and cis- (3) macrocyclic trimers were also synthesized for comparison. 1-3 can be facilely oxidized into their respective cations in which electrons are effectively delocalized at two or three dimensions. The detailed experimental measurements and theoretical calculations reveal that (1) the neutral cage 1 shows localized aromaticity in individual benzene rings; (2) the dication 12+·2SbF6- displays bicyclic (anti)aromaticity with one macrocycle being aromatic (38π) and another macrocycle being antiaromatic (28π); on the other hand, the dications of the model compounds 2 and 3 are globally antiaromatic and nonaromatic, respectively; (3) the tetracation 14+·4SbF6- exhibits dominant 2D Hückel antiaromaticity in one of the macrocycles (36π). In addition, 12+·2SbF6-, 14+·4SbF6-, and 22+·2SbF6- possess open-shell singlet ground state with significant diradical character, while 32+·2SbF6- adopts a triplet ground state to release strain.

Cascade cycloadditions of N‐aromatic zwitterions and allylic sulfonium ylides: Dual roles of the allylic sulfonium ylide in the cascade reaction

AbstractDearomative cycloadditions of N‐aromatic zwitterions have been performed to synthesize diverse N‐containing cyclic compounds. However, few practical syntheses of polycyclic molecules are reported, and thus, a novel methodology is necessary. We describe cascade reactions of N‐aromatic zwitterions and allylic sulfonium ylides to furnish fused N‐heterocyclic compounds. Unprecedentedly, molecules of the allylic sulfonium ylide react with the corresponding zwitterion as C1 and C3 synthons in the same reaction.

Optimizing band structure of CoP nanoparticles via rich‐defect carbon shell toward bifunctional electrocatalysts for overall water splitting

AbstractTransition‐metal phosphides (TMPs) with high catalytic activity are widely used in the design of electrodes for water splitting. However, a major challenge is how to achieve the trade‐off between activity and stability of TMPs. Herein, a novel method for synthesizing CoP nanoparticles encapsulated in a rich‐defect carbon shell (CoP/DCS) is developed through the self‐assembly of modified polycyclic aromatic molecules. The graft and removal of high‐activity C–N bonds of aromatic molecules render the controllable design of crystallite defects of carbon shell. The density functional theory calculation indicates that the carbon defects with unpaired electrons could effectively tailor the band structure of CoP. Benefiting from the improved activity and corrosion resistance, the CoP/DCS delivers outstanding difunctional hydrogen evolution reaction (88 mV) and oxygen evolution reaction (251 mV) performances at 10 mA cm−2 current density. Furthermore, the coupled water electrolyzer with CoP/DCS as both the cathode and anode presents ultralow cell voltages of 1.49 V to achieve 10 mA cm−2 with long‐time stability. This strategy to improve TMPs electrocatalyst with rich‐DCS and heterogeneous structure will inspire the design of other transition metal compound electrocatalysts for water splitting.

Facile synthesis of red-emissive carbon dots with theoretical understanding for cellular imaging

Recently, red emissive carbon dots (R-CDs) have drawn widespread attention on account of their desirable fluorescence properties and good biocompatibility. Despite great efforts, facile synthesis of R-CDs for cellular imaging remains challenging and the fluorescence mechanism of R-CDs is still elusive. Herein, p-phenylenediamine-derived R-CDs with excitation-independency were successfully obtained through a facile solvothermal approach together with proportional precipitation. The fluorescent solvatochromism of R-CDs is realized, while high polarity leads to higher degree of dipole interaction between R-CDs and different solvents, favoring for emissive red-shift. Furthermore, density functional theory is adopted to explore the optical and electronic characteristics of some polycyclic aromatic molecules. Among different configurations, pyridine nitrogen and carbonyl bonds could relatively increase the charge density and significantly narrow the band gap, which can provide a crucial theoretical basis for the precise preparation of R-CDs. Moreover, R-CDs possess favorable cellular imaging ability, which indicates their potential for a promising candidate as fluorescence probes in bioimaging.

The First Example of Photogeneration of a Pyrrole Molecule on the Basis of 6π-Electrocyclization of 2-Arylbenzofurans Containing a Pyrazole Fragment

The photochemical behavior of terarylenes containing benzofuran and aminopyrazole fragments was studied. It was found that the presence of an amino group in the structure of the studied terarylenes blocks photocyclization. At the same time, the transformation of the amino group into a pyrrole fragment allows one to remove the aforementioned blocking effect. As a result, UV-irradiation of pyrrole-containing compounds leads to 6π-electrocyclization of the 1,3,5-hexatriene system with the formation of polycyclic molecules. For the first time an efficient method for the photogeneration of pyrrole molecule using the phototransformation of substituted 2-arylbenzofurans was proposed. The structure of one of the target products was established by X-ray diffraction.

S-Shaped Fused Azacorannulene Dimer: Structural and Redox Properties

S-Shaped Fused Azacorannulene Dimer: Structural and Redox Properties

Energy-Transfer-Enabled Dearomative Cycloaddition Reactions of Indoles/Pyrroles via Excited-State Aromatics.

Exploring the enormous chemical space through an expedient building-up of molecular diversity is an important goal of organic chemistry. The development of synthetic methods toward molecules with unprecedented structural motifs lays the foundation for wide applications ranging from pharmaceutical chemistry to materials science. In this regard, the dearomatization of arenes has been recognized as a unique strategy since it provides novel retrosynthetic disconnections for various spiro or fused polycyclic molecules with increased saturation and stereoisomerism. However, inherent thermodynamic challenges are associated with dearomatization processes. The disruption of the aromaticity of arene substrates usually requires large energy inputs, which makes harsh conditions necessary for many ground-state dearomatization reactions. Therefore, further expansion of the scope of dearomatization reactions remains a major problem not fully solved in organic chemistry.The past decade has witnessed tremendous progress on photocatalytic reactions under visible light. Particularly, reactions via an energy transfer mechanism have unlocked new opportunities for dearomatization reactions. Mediated by appropriately chosen photosensitizers, aromatic substrates can be excited. This kind of precise energy input might make feasible some dearomatization reactions that are otherwise unfavorable under thermal conditions because of the significant energy increases of the substrates. Nevertheless, the lifetimes of key intermediates in energy-transfer-enabled reactions, such as excited-state aromatics and downstream biradical species, are quite short. How to regulate the reactivities of these transient intermediates to achieve exclusive selectivity toward a certain reaction pathway among many possibilities is a crucial issue to be addressed.Since 2019, our group has reported a series of visible-light-induced dearomative cycloaddition reactions for indole and pyrrole derivatives. It was found that the aromatic units in substrates can be excited under the irradiation of visible light in the presence of a suitable photosensitizer. These excited aromatics readily undergo various [m + n] cycloaddition reactions with appropriately tethered unsaturated functionalities including alkenes, alkynes, N-alkoxy oximes, (hetero)arenes, and vinylcyclopropanes. The reactions yield polycyclic indolines and pyrrolines with highly strained small- and/or medium-sized rings embedded, some of which possess unique bridge- or cagelike topologies. Systematic mechanistic studies confirmed the involvement of an energy transfer process. Density functional theory (DFT) calculations revealed the correlation between the substrate structure and the excitation efficiency, which accelerated the optimization of the reaction parameters. Meanwhile, DFT calculations demonstrated the competition between kinetically and thermodynamically controlled pathways for the open-shell singlet biradical intermediates, which allowed the complete switches from [2 + 2] cycloaddition to 1,5-hydrogen atom transfer in reactions with N-alkoxy oximes and to [4 + 2] cycloaddition in reactions with naphthalene. Furthermore, ab initio molecular dynamics (AIMD) simulations uncovered post-spin crossing dynamic effects, which determine the regioselectivity for the open-shell singlet biradical recombination step in the reactions of pyrrole-derived vinylcyclopropanes.An increasing number of scientists have joined in the research on visible-light-induced dearomative cycloaddition reactions and contributed to more elegant examples in this area. The visible-light-induced dearomatization reaction via energy transfer mechanism, although still in its infancy, has exhibited great potential in the synthesis of molecules that can hardly be accessed by other methods. We believe that future development will further push the boundary of organic chemistry and find applications in the synthesis of functional molecules and related disciplines.

7,12‐Dihydrobenzo[de]indolo[3,2‐b]quinoline: Unique Reactivity and Redox Interconversion

AbstractAcetyl‐substituted 7,12‐dihydrobenzo[de]indolo[3,2‐b]quinoline was developed as a N‐substituted polycyclic heteroaromatic molecule via Pd‐catalyzed cyclo‐isomerization of an alkyne precursor, followed by intramolecular Goldberg amination. This compound showed unique reactivity, notably, base‐mediated deacylative oxygenation and photo‐Fries rearrangement. A series of products exhibited characteristic electronic properties based on the redox state of the corresponding nitrogen atoms. The photo‐rearranged product, which possesses a 1,2‐diaminoethene substructure, akin to the redox functionality of the natural flavin adenine dinucleotide, underwent reversible interconversion with the corresponding oxidized form. The efficient stabilization of the highly electron‐rich 7,12‐dihydrobenzo[de]indolo[3,2‐b]quinoline skeleton was ascribed to the electron‐withdrawing effect, intramolecular hydrogen bonding of the acetyl group, and local aromatic stabilization in the indole moiety.

Multi-component analysis, molecular model construction, and thermodynamics performance prediction on various rejuvenators of aged bitumen

The molecular dynamics (MD) simulation method is proved as an efficient tool to explore the intermolecular interaction between rejuvenators and aged bitumen, but the simple “single-molecule” model of rejuvenator would bring the inaccuracy to simulation outputs due to a huge difference with its realistic multi-component chrematistic. This study aims to in-depth analyze the chemical components of four commonly-used rejuvenators with the Gas chromatography-mass spectrometry (GC–MS) method, and propose their multi-component molecular models for the first time. Further, MD simulations are performed on the multi-component models of various rejuvenators to anticipate and compare their atomic-level properties. The GC–MS results reveal that the chemical components of petroleum-based rejuvenators are more complicated than the bio-oil (BO). The alkane, naphthenic, and aromatic molecules are the main constituents of engine-oil (EO), naphthenic-oil (NO), and aromatic-oil (AO) rejuvenators. The experimental density results validate the reliability of these multi-component molecular models of four rejuvenators. From the MD simulations outputs, there is a significant difference in the energetic indices, cohesive energy density (CED), solubility parameter δ, volumetric parameters, dynamic behaviors, structural indicators, expansion coefficient (α and β), and isobaric heat capacity (Cp) between the multi-component models of four rejuvenators. However, the multi-component molecular model of aromatic-oil based on the GC–MS method is not accurate because the polycyclic aromatic molecules with heavy-weight are not detected and considered. This study detects the difference in chemical components and thermodynamics properties between four rejuvenators and proposes their more realistic multi-component molecular models for further MD simulations on the rejuvenation of aged bitumen.

Catalytic [2+2+2] Tandem Cyclization with Alkyl Substituted Methylene Malonate Enabling Concise Total Synthesis of Four Malagasy Alkaloids

Catalytic [2+2+2] Tandem Cyclization with Alkyl Substituted Methylene Malonate Enabling Concise Total Synthesis of Four Malagasy Alkaloids

Alkyne‐Based Syntheses of Carbo‐ and Heterohelicenes

Abstract[n]Helicenes are polycyclic aromatic molecules in which n ortho‐condensed benzene or other aromatic rings give rise to helical chiral and highly conjugated structures. The unique screw shape, helically extended π‐system and intriguing electronic and chirooptical properties of these molecules have attracted scientific interest for decades. The applications of helicenes have now expanded into several fields including material science, nanoscience, biochemistry, supramolecular and polymer chemistry. Despite the great theoretical and practical interest in helicenes, their synthesis remains a challenge. Among synthetic approaches to helicenes, alkyne cyclizations have great potential, since carbon‐rich high‐energy alkynes can form aromatic rings via cycloisomerizations. These processes are atom‐economic. In addition, alkyne reactions are highly favorable thermodynamically. This review focuses on alkyne‐based syntheses of carbo‐ and heterohelicenes (2000–2022). These syntheses are obviously multistage. In the review, they are systematized in terms of the key step leading to the formation of a helical shape. The methods are grouped into two categories: (a) metal‐free syntheses and (b) transition‐metal‐catalyzed syntheses. This division is very arbitrary, since catalytic Sonogashira and Suzuki‐Miyaura reactions and others are often used to prepare starting materials in the syntheses of the first group. Most of the publications on the topic are related to transition‐metal‐catalyzed syntheses of helicenes.magnified image

Desorption of polycyclic aromatic hydrocarbons by cosmic rays

Context. The rate of sputtering and release of condensed species is an important aspect of interstellar chemistry, as is photodesorption for the most volatile species, because in the absence of such mechanisms the whole gas phase would have to condense in times often shorter than the lifetime of the considered medium, in particular for dense clouds. The recent detection of cyclic aromatic molecules by radioastronomy requires an understanding of the potential mechanisms supporting the rather high abundances observed. Aims. We perform experiments to advance our understanding of the sputtering yield due to cosmic rays for very large carbonaceous species in the solid phase. Methods. Thin films of perylene and coronene were deposited on a quartz cell microbalance and exposed to a 1.5 MeV N+ ion beam at the Laboratoire de Physique des 2 Infinis Irène Joliot-Curie (IJCLab, Orsay, France) and a 230 MeV 48Ca10+ ion beam at the GSI Helmholtzzentrum für Schwerionenforschung (GSI, Darmstadt, Germany). The mass loss was recorded as a function of the fluence for the N+ beam. The microbalance response was calibrated using Fourier transform infrared (FTIR) reflectance measurements of the produced films. In addition, the destruction cross-section of the same species was measured with the 48Ca10+ ion beam by in situ monitoring of the evolution of the infrared spectra of the bombarded films. Results. We deduced the sputtering yield for perylene and coronene and their radiolysis destruction cross-sections. Combining these results with a cosmic ray astrophysical spectrum, we discuss the impact on the possible abundance that may originate from the sputtering of dust grains with these molecules as well as from polycyclic aromatic molecules when they are trapped in ice mantles.

Atogepant (Qulipta®) for migraine prevention

STRUCTURE: Atogepant (MK-8031/AGN-241689) is a heavily polycyclic molecule, containing four chiral centers, three aromatic and three aliphatic rings. An intriguing feature is the 2-azaspiro [4.4]nonan-1-one (spiroazaindane) motif in an S configuration, which is also present in earlier preclinical leads from Merck. The azospiro bispyridine unit is linked via an amide bond to a piperidine-2-one ring; the amide linkage is reversed to that seen in earlier leads to avoid potential release of a toxic aniline.

Gas-Phase Infrared Spectra of the C7H5 Radical and Its Bimolecular Reaction Products.

Resonance-stabilized radicals are considered as possible intermediates in the formation of polycyclic aromatic hydrocarbons (PAHs) in interstellar space. Here, we investigate the fulvenallenyl radical, the most stable C7H5 isomer by IR/UV ion dip spectroscopy employing free electron laser radiation in the mid-infrared region between 550 and 1750 cm-1. The radical is generated by pyrolysis from phthalide. Various jet-cooled reaction products are identified by their mass-selective IR spectra in the fingerprint region, based on a comparison with computed spectra. Interestingly, benzyl is present as a second resonance-stabilized radical. It is connected to fulvenallenyl by a sequence of two H atom losses or additions. Among the identified aromatic hydrocarbons are toluene and styrene, as well as polycyclic molecules, such as indene, naphthalene, fluorene and phenanthrene. Mechanisms for the formation of PAH from C7H5 have already been suggested in previous computational work. In particular, the radical/radical reaction of two fulvenallenyl radicals provides an efficient route to phenanthrene in one bimolecular step and might be relevant for PAH formation under astrochemical conditions.

Construction of dual-functional membrane with novel structured β-cyclodextrin hybridization for simultaneous oily wastewater separation and hazardous aromatics removal

During the separation of water-insoluble oil droplets in the oily wastewater by the membrane treatment process, the simultaneous removal of organic pollutants dissolved in the aqueous phase remains a challenge. Herein, we demonstrate an effective strategy for preparing dual-functional membranes with hybridization of novel β-cyclodextrin (β-CD) derivatives to achieve complete cleansing of oily sewage. Alkylenedioxy bridged bis(p-difluoro-p-dicyano) phenyl substituted β-CDs (R3-2T-2β-CD and R6-2T-2β-CD) are first synthesized and incorporated into three frequently used membranes (polyethersulfone (PES), poly(p-phenylene terephthalamide) (PPTA) and poly(m-phenylene isophthalamide) (PMIA)) casting solutions to fabricate hybrid membranes, respectively. The hydrophilicity of the prepared membrane can be improved greatly for the separation of oil-in-water emulsions. The PMIA/R3-2T-2β-CD membrane exhibited pure water permeances over 760.50 L·m−2·h−1·bar−1 with separation efficiency of the tween 80 stabilized diesel-in-water emulsion above 98.62% under cross-flow filtration. Significantly, the hybrid membranes could concurrently remove naphthalene and methylene blue dissolved in water during oil-in-water separation. This study proves the application potential of cyclodextrins in designing membrane materials and these one-step hybrid membranes can thoroughly decontaminate oil-in-water emulsions by eliminating the dissolved polycyclic aromatic molecules.

High-resolution vibronic spectroscopy of a single molecule embedded in a crystal.

Vibrational levels of the electronic ground states in dye molecules have not been previously explored at a high resolution in solid matrices. We present new spectroscopic measurements on single polycyclic aromatic molecules of dibenzoterrylene embedded in an organic crystal made of para-dichlorobenzene. To do this, we use narrow-band continuous-wave lasers and combine spectroscopy methods based on fluorescence excitation and stimulated emission depletion to assess individual vibrational linewidths in the electronic ground state at a resolution of ∼30MHz dictated by the linewidth of the electronic excited state. In this fashion, we identify several exceptionally narrow vibronic levels with linewidths down to values around 2GHz. Additionally, we sample the distribution of vibronic wavenumbers, relaxation rates, and Franck-Condon factors, in both the electronic ground and excited states for a handful of individual molecules. We discuss various noteworthy experimental findings and compare them with the outcome of density functional theory calculations. The highly detailed vibronic spectra obtained in our work pave the way for studying the nanoscopic local environment of single molecules. The approach also provides an improved understanding of the vibrational relaxation mechanisms in the electronic ground state, which may help create long-lived vibrational states for applications in quantum technology.

Dibenzodiazapyracylenes: Doubly N-Doped Cyclopenta-Fused Polycyclic Molecules That Exhibit High Carrier Mobility.

Pyracylene is a unique cyclopenta-fused polycyclic aromatic hydrocarbon (CP-PAH) that exhibits dual aromatic characteristics. Herein we report the synthesis of doubly N-doped benzannulated pyracylenes, namely dibenzodiazapyracylenes, by oxidative N-N linking reaction of [2.2](2,5)pyrrolophane-type precursors. Dibenzodiazapyracylenes displayed well-ordered π-stacked molecular packing in the solid state, which were feasible for effective hole-transporting along the stacking direction. High carrier mobility was estimated by microwave conductivity measurements as compared to dibenzoullazine. The high HOMO level of dibenzodiazapyracylene was verified by electrochemistry and its persistent radical cation species has been detected.

Total synthesis of nine longiborneol sesquiterpenoids using a functionalized camphor strategy.

Natural product total synthesis inspires the development of synthesis strategies to access important classes of molecules. In the 1960s, Corey and coworkers demonstrated a visionary preparation of the terpenoid longifolene, using 'strategic bond analysis' to craft a synthesis route. This approach proposes that efficient synthesis routes to bridged, polycyclic structures should be formulated to introduce the bulk of the target's topological complexity at a late stage. Subsequently, similar strategies have proved general for the syntheses of a wide variety of bridged, polycyclic molecules. Here, we demonstrate that an orthogonal strategy where topological complexity is introduced at the outset leads to the short synthesis of the longifolene-related terpenoid longiborneol. To implement this strategy, we access a bicyclo[2.2.1] starting material through scaffold remodelling of readily available (S)-carvone. We also employ a variety of late-stage C-H functionalization tactics in divergent syntheses of many longiborneol congeners. Our strategy may prove effective for the preparation of other topologically complex natural products that contain the bicyclo[2.2.1] framework.

Crystal structures of the solvate and two tetralkylammonium inclusion compounds of [1, 2, 4, 5-tetra(4'-carboxyphenyl) - benzene

This article reports [1, 2, 4, 5-tetra(4'-carboxyphenyl)-benzene] (1) and its tetraethyl ammonium and tetrabutylammonium inclusion compounds (C34H21O8 −·N+(C2H5)4·H2O (2) C34H21O8 −·N+(n-C3H7)4·H2O (3). Compound one eventually forms a "molecular column" along the direction of [110], and the solvent molecules are filled by two adjacent columns to form a stable crystal structure. In compound 2, the tetravalent host anion forms rectangular three-dimensional pores with water molecules by O-H… O hydrogen bonds, two tetraethyl ammonium ions are neatly arranged in the pores to form a tighter structure, In structure 3, the formation of the main skeleton mainly relies on O…H…O hydrogen bond formed by the contact between the proton H shared between the two host anions and the O-H…O generated by the water molecule and one of the two anions. In the three crystal structures, [1, 2, 4, 5-tetra(4'-carboxyphenyl)-benzene], as an “X” polycyclic polycarboxylate aromatic molecule, constructs a large 3 D hole by using its configuration feature. Corresponding solvent molecules and different guest molecules are contained in the 3 D pores, forming various stable crystal structures.

Synthesis of corn straw-based graphene quantum dots (GQDs) and their application in PO43- detection

Phosphate (PO43-) can cause eutrophication of water bodies due to soil erosion and agricultural fertilization, increasing toxic substances in water, therefore detecting PO43- is vital in water eutrophication. Graphene quantum dots (GQDs), zero-dimensional nanometer-sized graphene pieces, are made of a few graphene lattices and exhibit outstanding optical properties. The traditional synthesis precursors are limited by large carbon domains or toxic polycyclic aromatic molecules. Consequently, synthesis of GQDs from renewable biomass has attracted broad interests. Herein corn straw was used to directly prepare GQDs via a one-pot hydrothermal strategy. The as-prepared GQDs, with an average size of 2.67 nm, presented high quantum yield (15.67%), high crystallinity and dispersibility. The as-prepared non-doped GQDs had a special selectivity to Ce4+/Fe3+, causing the fluorescence (FL) quenching of GQDs and the formation of GQDs-Ce4+/GQDs-Fe3+ aggregation. In the presence of PO43-, a strong affinity between PO43- and Ce4+/Fe3+ can destroy GQDs-Ce4+/GQDs-Fe3+ aggregation, resulting in the FL recovery of GQDs. The GQDs-Ce4+ probe system can selectively detect PO43- with a detection limit of 0.06 μM in a linear range from 0.1 to 20.0 μM. Based on this, GQDs-Ce4+ paper-based sensors were also prepared for the visual detection of PO43-, which showed good responses to PO43-. This development is expected to be a promising strategy for convenient and rapid phosphate detection.