Polycyclic Units Research Articles

Cobalt-Catalyzed Cascade C-H Activation/Annulation Polymerizations toward Diversified and Multifunctional Sulfur-Containing Fused Heterocyclic Polymers.

Transition-metal-catalyzed C-H activation has greatly benefited the synthesis and development of functional polymer materials, and the construction of multifunctional fused (hetero)cyclic polymers via novel C-H activation-based polyannulations has emerged as a charming but challenging area in recent years. Herein, we report the first cobalt(III)-catalyzed cascade C-H activation/annulation polymerization (CAAP) approach that can efficiently transform readily available aryl thioamides and internal diynes into multifunctional sulfur-containing fused heterocyclic (SFH) polymers. Within merely 3 h, a series of SFH polymers bearing complex and multisubstituted S,N-doped polycyclic units are facilely and efficiently produced with high molecular weights (absolute Mn up to 220400) in excellent yields (up to 99%), which are hard to achieve by traditional methods. The intermediate-terminated SFH polymer can be used as a reactive macromonomer to controllably extend or modify polymer main chains. The structural diversity can be further enriched through facile S-oxidation and N-methylation reactions of the SFH polymers. Benefiting from the unique structures, the obtained polymers exhibit excellent solution processability, high thermal and morphological stability, efficient and readily tunable aggregate-state fluorescence, stimuli-responsive properties, and high and UV-modulatable refractive indices of up to 1.8464 at 632.8 nm. These properties allow the SFH polymers to be potentially applied in diverse fields, including metal ion detection, photodynamic killing of cancer cells, fluorescent photopatterning, and gradient-index optical materials.

Polarity and viscosity-sensitive fluorescence probes for lipid droplet imaging in cancer cells

Fluorescent probes sensitive to microenvironments have constantly been attractive, due to their significant benefits in monitoring changes in the pathophysiological microenvironment and their use in the early detection of associated disorders. In this work, we explored three new molecular rotors that could be potential candidates for detecting lipid droplets (LDs) in cancer cells based on coumarin derivatives connected with electron-donating polycyclic units including, tetraphenylethylene (LD-TPE), pyrene (LD-PYR), and 4,5-diphenylimidazole (LD-DIP). Gratifyingly, LD-PYR showed exceptional polarity and viscosity sensitivity and demonstrated bright fluorescence in highly viscous environments due to the suppression of the twisted intramolecular charge transfer (TICT) phenomenon and intramolecular rotation. Moreover, microenvironment-guided specific LD bioimaging by LD-PYR exhibited a reasonable ability to distinguish between cancer and noncancer cells. These data suggested that LD-PYR has interesting clinical diagnostic and microenvironment-related biological applications.

Atomic-scale mechanism of carbon nucleation from a deep crustal fluid by replica exchange reactive molecular dynamics simulation

We present a mechanistic model of carbon nucleation and growth from a fluid at elevated temperature (T) and pressure conditions, typical of those found in the shallow Earth’s lithosphere. Our model uses a replica exchange reactive molecular dynamics framework in which molecular configurations are swapped between adjacent T replica at regular intervals according to underlying statistical mechanics. This framework allows predicting complex molecular structures and thermodynamics while remaining computationally efficient. Here we simulate the reactivity of an unstable mixture of CO2 and CH4 at 1000 K and 1 GPa. We find that the path to thermodynamic equilibrium is initially entropy-driven, producing a diversity of short-lived species, including various alcohols with intermediate carbon oxidation states. Cyclic and polycyclic radicals that are sometimes resonance-stabilized form next and set the stage for carbon nucleation. The carbon exsolution process releases abundant water, is exothermic and starts with the nucleation of a large aggregate of hydrogenated graphene flakes from covalently bonded polycyclic units. The carbon backbone of this nucleus subsequently grows into a hydrogen-depleted fullerene-like structure, before evolving toward a partially bilayered graphene layer. Overall, our results show that the mechanism of graphitic C formation is certainly not bimolecular, and that it may involve a combination of key condensation and radical chain reactions. This will help understand the isotopic, and reactive characteristics of carbon-bearing fluids during their upward transit through the Earth’s mantle and crust. Moreover, the mechanistic insights outlined here present intriguing similarities with the process of soot and interstellar dust formation, which suggests that the widespread distribution of abiotic polyaromatic and graphitic material on Earth and beyond may reflect the prevalence of a fundamental chemical pathway.

Selenium-Containing Organic Photovoltaic Materials.

ConspectusOrganic photovoltaics (OPVs) with a photoactive layer containing a blend of organic donor and acceptor species are considered to be a promising technology for clean energy owing to their unique flexible form factor and good solution processability that can potentially address the scalability challenges. The delicate designs of both donors and acceptors have significantly enhanced the power conversion efficiency of OPVs to more than 18%. Nonfullerene small-molecule acceptors (NFAs) have played a critical role in enhancing the short-circuit current density (JSC) by efficiently harvesting near-infrared (NIR) sunlight. To take full advantage of the abundant NIR photons, the optical band gap of NFAs should be further reduced to improve the performance of OPVs. Incorporating highly polarizable selenium atoms onto the backbone of organic conjugated materials has been proven to be an effective way to decrease their optical band gap. For example, a selenium-substituted NFA recently developed by our group has attained a JSC of approximate 27.5 mA cm-2 in OPV devices, surpassing those of most emerging photovoltaic systems. Inspired by this advance, we concentrate on the topic of selenium-containing materials in this Account to incite readers' interest in further exploring this series of materials.In this Account, we first compare the differences among chalcogen heterocycles and discuss the influence of fundamental electronic behavior on the collective photoelectrical properties of the resulting materials. The superior features of selenium-substituted materials are summarized as follows: (1) The large covalent radius of selenium can diminish the π-orbital overlap, rendering enhanced quinoidal resonance character and a narrowed optical band gap of resulting materials. (2) The selenium atom is more polarizable than sulfur owing to its larger and looser outermost electron cloud, enabling enhanced intermolecular Se-Se interaction and increased charge carrier mobility of relevant materials in the solid state. We then focus on summarizing the design rules for various categories of selenium-containing materials including polymer donors, small-molecule acceptors, and polymer acceptors, especially those composed of ladder-type polycyclic units. The motivation for incorporating selenium atoms into these materials and the structure-property relationships were thoroughly elucidated. Specifically, we discuss the changes in the optical band gap, charge carrier mobility, and molecular packing induced by selenium substitution and correlate the effects of these changes with the exciton behaviors, energy loss, and nanoscale film morphology of corresponding OPV devices. Furthermore, we point out the intrinsic stability of selenium-containing materials under maximum-power-point tracking and long-term photo- or thermostress and indicate their potential use in semitransparent and tandem solar cells. At the end, the prospect of future research focuses and the possible applications of selenium-containing materials in the OPV field are discussed.

Polycyclic Arene-Fused Selenophenes via Site Selective Selenocyclization of Arylethynyl Substituted Polycyclic Arenes.

Arene-fused selenophenes were synthesized by a redox neutral process from arylethynyl substituted polycyclic arenes using selenium powder in refluxing N-methyl-2-pyrrolidone (NMP) with the assistance of the residual water in NMP as a catalytic proton source. The site-selective nature of this selenocyclization produces trans-alkenes as a competitive product, which is dependent on the π-electron donation ability of polycyclic arenes and the kind of arylethynyl group attached to it. DFT calculations were performed to understand the site selectivity in the selenophene formation reaction. The HOMO coefficient on the carbon adjacent to carbon having arylalkyne substituent of the polycyclic arene correlates with the selenocyclization tendency of the substrate. The wavelength of absorption and emission and quantum yield of emission increase with increasing the number of fused benzene rings in the polycyclic unit (from naphthalene to pyrene).

Tuning the Photophysical and Excited State Properties of Phosphorescent Iridium(III) Complexes by Polycyclic Unit Substitution.

Two novel N‐embedded polycyclic units functionalized phosphorescent iridium(III) complexes (Ir‐1 and Ir‐2) with substituents in different positions have been prepared. Complex Ir‐1 bearing the substituent at the 3‐position shows a distinct blue shift single‐peak emission (524 nm) with a higher luminescence efficiency (ΦPL=42 %) and shorter emission lifetime (τ=282 ns) by comparison with 4‐position substitution based complex Ir‐2 (ΦPL=23 %, τ=562 ns), which exhibits a dual‐peak emission (564 nm and 602 nm), and phosphorescence color can be tuned from green to yellow. In addition, DFT calculations demonstrate that unusual ligand‐to‐metal charge transfer (3LMCT) excited state property can be found in Ir‐2, which is in contrast to metal‐to‐ligand charge transfer (3MLCT) excited state character in Ir‐1. This result can be attribute to strong electron‐donating character and 4‐position substitution effect of the unit.

Comparison of Structural and Optical Properties for N‐Embedded Polycyclic and Non‐Embedded Cationic Phosphorescent Iridium(III) Complexes

We designed and synthesized N‐embedded polycyclic based cationic iridium(III) complex Ir‐NO and non‐embedded complexes Ir‐N and Ir‐O. Single crystal structures indicate that the N‐embedded polycyclic unit in Ir‐NO exhibits a certain planarity and induces two interesting π–π‐stackings between 2,2′‐bipyridine moieties of one molecule and two polycyclic units of the other molecule, and their shortest intermolecular distances are both 3.24 Å, which results in a stronger structural distortion of the 2,2′‐bipyridine ligand with a larger torsion angle (12.70°) in comparison with those of Ir‐N (5.51°) and Ir‐O (8.11°). Unpredictably, both Ir‐N and Ir‐O show deep red emission in solution, whereas Ir‐NO exhibits no emission. However, all complexes show significant luminescence in their respective polystyrene (PS) films, and Ir‐NO displays a longer emission lifetime than those of Ir‐N and Ir‐O. DFT calculations reveal that unusual ligand‐to‐metal charge transfer (3LMCT) excited state character can be found in Ir‐NO and Ir‐N, which is in contrast to the metal‐to‐ligand charge transfer (3MLCT) excited state observed in Ir‐O.

B- and N-embedded color-tunable phosphorescent iridium complexes and B-N Lewis adducts with intriguing structural and optical changes.

A novel family of B- and N-embedded phosphorescent iridium complexes has been prepared. Single crystal structures indicate that the B-embedded polycyclic unit exhibits better planarity than the N-embedded polycyclic unit, which leads to different π-π-stacking and electrical characteristics. More importantly, by controlling the number of boron or nitrogen atoms embedded, solution-processed OLED devices incorporating these emitters as emitting layers can achieve a phosphorescence color variation from green to deep red (638 nm) and show low-efficiency roll-off and turn-on voltage. In particular, the B-embedded complex Ir-BB shows good color purity with a narrow full width at half maximum (1211 cm-1) and CIE coordinates (0.67, 0.31) in the deep red light region. Notably, B-embedded iridium complexes can also react with two different Lewis bases (pyridine and DMAP) to form intriguing B-N Lewis adducts through different coordination modes. During this process, significantly different structural and optical changes are triggered by the structure and electronic properties of Lewis bases, as confirmed by X-ray crystallographic, 1H NMR and spectral analysis.

An oxygen-bridged triarylamine polycyclic unit based tris-cyclometalated heteroleptic iridium(iii) complex: correlation between the structure and photophysical properties.

A novel oxygen-bridged triarylamine polycyclic unit based tris-cyclometalated heteroleptic iridium(iii) complex (Ir-NO) has been designed and prepared. Similar iridium(iii) complexes (Ir-N and Ir-O) have also been prepared for comparison. The single crystal structure indicates that the oxygen-bridged triarylamine polycyclic unit of Ir-NO shows certain planarity, resulting in obvious rigidity and interesting π-π stacking. Additionally, Ir-NO shows a larger redshift emission (586 nm) and a longer emission lifetime (628 ns) than Ir-N (525 nm, 344 ns) and Ir-O (543 nm, 436 ns), and the phosphorescence color can be tuned from green to orange. Electrochemical experiments and DFT calculations reveal that Ir-NO exhibits a high HOMO energy level and intraligand charge transfer (3ILCT) excited state properties, which is in contrast to the low HOMO energy level and metal-to-ligand charge transfer (3MLCT) excited state properties in Ir-N and Ir-O. This result can be attributed to the strong electron-donating ability of the unit.

Highly sensitive detection of nitroaromatic explosives using an electrospun nanofibrous sensor based on a novel fluorescent conjugated polymer

An electrospun nanofibrous explosive sensor was first constructed based on a newly developed fluorescent conjugated polymer P containing heteroatom polycyclic units. Electrospinning by doping polymer P as a fluorescent probe in a polystyrene supporting matrix afforded a fluorescence nanofibrous film with unique porous structures, and effectively avoided the aggregation of polymer P. The novel explosive sensor exhibited stable fluorescence property, satisfactory reversibility with less than 5% loss of signal intensity after four quenching–regeneration cycles, and good reproducibility among three batches with a relative standard deviation of 2.8%. Such fabricated sensor also showed remarkable sensitivity toward a series of trace nitroaromatic explosive vapors, including picric acid (parts-per-trillion level) and 2,4,6-trinitrotoluene vapor (parts-per-billion level), as well as good selectivity with less than 10% response to typical interferents. Therefore, the present strategy extends the application of different kinds of conjugated polymers for the construction of optical chemosensors.

Designing Magnetic Organic Lattices from High‐Spin Polycyclic Units

This work addresses the conception of purely organic magnetic materials by properly bridging high-spin polycyclic hydrocarbons A and B, through covalent ligands L. The strategy varies two degrees of freedom that govern the magnetic character of the A-L--B sequence, namely, the bridge response to spin polarization and the relative signs of spin density on carbon atoms to which the bridge is attached. Topological prescriptions based on Ovchinnikov's rule are proposed to predict ground-state spin multiplicities of various A-L-B sets. The relevance of these guiding principles is essentially confirmed through DFT calculations on dimers connected by conjugated bridges. The transferability of interunit magnetic couplings to larger assemblies is further checked, the building blocks tending to maintain their high-spin character whatever the environment. Such local designs open the way to periodic lattices of ferromagnetic, antiferromagnetic, ferrimagnetic, or paramagnetic materials.

Role of Pyridine in Wyodak−Pyridine Adducts

When pyridine (PYR) is added to powdered Wyodak subbituminous coal (WYO), the sample is converted to a paste, and the molecular-level adduct which is formed is stable for months. After the excess pyridine has evaporated from the WYO−PYR sample, the stoichiometry of the adduct is ca. two pyridine molecules per bilayer of WYO polycyclic units; this adduct exists even after mild vacuum treatment of the sample. The pyridine molecules in this adduct appear to be located between the bilayer lamellae and to be H-bonded to either H−O or H−N moieties attached to the poly-cyclic aromatic units of WYO. An H-bonded N- - -H−X distance of 2.6 Å has been calculated from a structural model of the WYO−PYR adduct.

Stable Free‐Radical Polymerization of Styrene in Combination with 2‐Vinylnaphthalene Initiation

AbstractThe elevated temperatures required for the stable free‐radical polymerization (SFRP) process lead to thermal initiation of styrene via the classic Mayo mechanism. Studies have shown the utility of styrene thermal initiation in controlled autopolymerization processes. In addition, the thermal polymerization of 2‐vinylnaphthalene (2VN), a styrenic derivative with an additional fused ring, was examined. An Arrhenius analysis of the 2VN thermal polymerization process using in‐situ FT‐IR spectroscopy demonstrated a greater propensity for 2VN thermal polymerization compared to styrene. A modified Mayo mechanism was proposed based on additional resonance stabilization in 2VN derived radicals compared to a single ring of resonance stabilization for styrene. The utility of 2VN as an initiator in the SFRP of styrene was investigated. 2VN initiation resulted in polymers that are end‐functionalized with a single 2VN unit or a polycyclic unit that results from Diels‐Alder reaction in the initiation mechanism. Variation of the styrene/2VN molar ratio in the presence of 2,2,6,6‐tetramethylpiperdinyl‐1‐oxyl enabled molecular weight control and narrow molecular weight distributions (ca. 1.1–1.2). The integrity of the polymer end groups was confirmed using 1H NMR and UV‐vis spectroscopy. In addition, the UV‐vis absorbance of the 2VN initiating unit was used for construction of a calibration curve for molecular weight prediction based on the intensity of the absorbance at 312 nm associated with 2VN initiation. The observed rate constant for the polymerization initiated with 2VN (1.73 × 10−5 s−1) was comparable to that of benzoyl peroxide (kobs = 1.99 × 10−5 s−1) initiation. SFRP of styrene thermally initiated with 2VN.imageSFRP of styrene thermally initiated with 2VN.

On the Molecular-Level Interactions Between Pyridine and Pittsburgh No. 8 Coal

The poly-cyclic units of Pittsburgh No. 8 coal (PIT), on the average, lie in short-range structural domains of ca. three layers. The species C14H9 is consistent with the average PCA unit in PIT, and its radius is ∼2.9 A. The average distance between the PCA layers in the short-range domains of PIT is ∼3.9 A. The addition of pyridine molecules to PIT does not alter structuring within the PCA units to an extent measured by wide-angle X-ray scattering experiments, and it appears that the interlayer structuring within the short-range structural domains in PIT is also not altered to a measurable extent. Rather, the quasi-stable adduct is formed between the three-layer domains of PIT and the pyridine molecules.

X-ray Analysis of Coals Treated with Organic Liquids. Detailed Study of the Adduct Formed between Pyridine Molecules and Beulah Zap Lignite

Wide-angle X-ray scattering methods indicate that, almost instantly, pyridine molecules penetrate between the nearest layers of the poly-cyclic units of Beulah Zap lignite to form a quasi-stable adduct. The lifetime of this adduct is several hours, and even after most of the pyridine has evaporated from the BZ/PYR gel, the expanded interlayer distance characteristic of the gel is retained.

Interlayer Structural Models of Beulah Zap Lignite Based on Its Wide Angle X-ray Scattering

Wide-angle X-ray scattering (WAXRS) in the 0.5-2.5 A -1 region of the intensity curve of Beulah Zap (BZ) lignite indicates that the average distance between adjacent layers is ca. 3.5 A. The resulting interlayer structural curve, calculated by Fourier transform from the WAXRS intensity, indicates that only two layers occur in the average short-range structural domain of BZ with the distances between atoms in the adjacent layers occurring between 3.4 and 5.7 A. Both the WAXRS intensity curve (in reciprocal space) and the interlayer structure curve (in molecular space) are consistent with an average short-range structural domain in which the flexible spacers (attachments) between the polycyclic units are important contributors and where the PC units in the adjacent chains are not eclipsed.

Structural Characterization of Asphaltene Fraction from Vacuum Residue of Arabian Crude Mixture by Spectroscopic and Pyrolytic Methods.

The structural properties of the n-C5 insoluble asphaltene isolated from the vacuum residue of Arabian crude mixture have been investigated by referring to the data obtained from pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), 1H/13C NMR, gel permeation chromatography (GPC), and matrix assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometry methods. Assignments of NMR signals have been discussed in detail. The average size of aromatic fused ring systems within the asphaltene has been determined to be 4-5. Pyrolysis experiments implied that the asphaltene sample is constructed with relatively large polycyclic units connected by relatively strong bonds. Our results also support the view that asphaltene is a mixture of complex polydispersed molecules with large variation in molecular sizes.

A theoretical study of the molecular and electronic structure of benzoannulated tetracyanoquinodimethanes

The molecular and electronic structure of a series of TCNQ derivatives with laterally extended π-systems is investigated using quantum-chemical methods. The steric hindrance introduced by lateral benzoannulation determines the loss of planarity of the molecular system which adopts a butterfly-type structure with the TCNQ ring folded in a boat conformation. PM3-optimized geometries are in good agreement with experimental X-ray data and show that the structural identity of the polyacenic units laterally fused to TCNQ is preserved. The evolution of the acceptor properties is rationalized with the help of VEH calculations. For the more extended TCNQs, these calculations show that the lateral naphthalene or anthracene units act as donors and determine the appearance of low-energy charge-transfer absorption bands. The geometries of negatively charged TCNQs up to the trianion are optimized at the PM3 level. The anions are calculated to be non-planar, thus explaining their low stability. For the dianions, the polycyclic skeleton is planar and the dicyanomethylene groups are rotated out of the molecular plane. While the first two extra electrons are mostly incorporated into the dicyanomethylene groups, the third electron added to form the trianion is shown to enter the central polycyclic unit. This result explains the formation of relatively stable trianions and tetra-anions for π-extended TCNQs.

Stickstoffverbindungen von elementen der dritten hauptgruppe mit intra- und intermolekularen donor—akzeptor-bindungen: II. Strukturelle untersuchungen

The crystal and molecular structures of the three compounds Me 2Si(N tBu) 2(AlPh 2) 2 (I), Me 2Si(N tBu)(N tBuH)AlCl 2 (II) and [Me 2Si(N tBu) 2InMe] 2 (III) have been obtained by X-ray structure determinations. Compound I represents a bicyclic organometallic molecule, in which two four-membered cycles share a common AlN edge (197.5(6) pm). One of the rings consists of a tetravalent silicon atom, a three-valent nitrogen atom, and an aluminum and nitrogen atom with a four-fold coordination, the other ring unites the two latter atoms together with a tetrahedral aluminum and carbon atom. The carbon atom is a member of a phenyl group and is in a special binding position. One of the aluminum atoms in I is thus stabilized by a donor—acceptor bond, the other by a two-electron-three-center-bond (AlC 214.5(8) and 220.7(5) pm). By temperature dependent NMR techniques it can be shown that molecules such as I show fluctional behaviour in non-polar solvents. In molecule II an intramolecular nitrogen—aluminum bond (199.4(2) pm) is responsible for the formation of a cycle, which contains a tetrahedral silicon atom, two nitrogen atoms (four- and three-fold coordination) and an aluminum atom with four ligands. In the crystal of II hydrogen bonds of the type NH ⋯ Cl can be recognized. The indium compound III (point symmetry, C i ( 1 )) may be described as a polycyclic unit built up of three four-membered rings standing orthogonally against each other and sharing common edges. It originates from two SiN 2In cycles which are held together by two Nin donor—acceptor bonds (225.6(4) pm), forming an almost square central N 2In 2 cycle. As a general feature, intramolecular (II), intermolecular donor—acceptor (III) bonds as well as two-electrons-three-center bonds (I), are used to stabilize the electron-deficiency at the aluminum and indium atoms. The synthesis and the properties of the compound Me 2Si(N tBu)(N iProp)(AlMe 2) 2 (IV) are described.

Synthesis of organo-silicon block copolymers by hetero-functional polycondensation

A study was made of hetero-functional polycondensation of bifunctional bi-, tri- and tetracyclosiloxanes containing organocyclotri-, organocyclotetra- and organo-cyclohexasiloxanes with α, ω-dihydroxypolydimethylsiloxanes in the polycyclic unit. It was found that by the interaction of bis-(chlorodimethylsiloxy) organobicyclopentasiloxanes with α, gw-dihydroxypolydimethylsiloxanes linear block copolymers are formed. Cross-linked polymers are obtained by the replacement of bis-(chlorodimethylsiloxy) functional groups by bis-[diethylamino(dimethyl)siloxy] derivatives. The use of hydrogen chloride acceptors in polycondensation results in a more intensive intermolecular reaction, consequently, polymer yield increases to 85%. The hydrodynamic parameters derived for synthetic block copolymers did not show any marked increase in macromolecular chain rigidity. X-ray shows that a polycyclic structure is responsible for the variation of interplanar distances in block copolymers: with an increase of the content of this structure inter-chain distances increase to 10·4 Å. With short single chain segments inter-chain distance may correspond to the distance between polycyclic units.