Polycyclic Aromatic Units Research Articles

Unit-Emitting Carbon Dots.

Understanding the photoluminescence mechanisms of carbon dots (C-dots) is of importance for both fundamental science and their corresponding applications. In this study, we verify the emitting-unit model of C-dots by an upgraded "contrastive analysis" research paradigm. Employing preparative thin-layer chromatography, we recently developed polyamide column chromatography separation techniques, and four kinds of highly correlative C-dots are obtained from a homologous sample made from ortho-aminophenol precursors. Combining comprehensive experimental characterizations, especially the direct evidence from electrospray ionization mass spectrometry, we demonstrate that the photoluminescence of the four C-dots comes from the same polycyclic aromatic hydrocarbon units (named as emitting units) indeed, although these C-dots have substantially different chemical compositions.

One-Step Catalyst-Transfer Macrocyclization: Expanding the Chemical Space of Azaparacyclophanes.

In this paper, we report on a one-step catalyst-transfer macrocyclization (CTM) reaction, based on the Pd-catalyzed Buchwald-Hartwig cross-coupling reaction, selectively affording only cyclic structures. This route offers a versatile and efficient approach to synthesize aza[1n]paracyclophanes (APCs) featuring diverse functionalities and lumens. The method operates at mild reaction temperatures (40 °C) and short reaction times (∼2 h), delivering excellent isolated yields (>75% macrocycles) and up to 30% of a 6-membered cyclophane, all under nonhigh-dilution concentrations (35-350 mM). Structural insights into APCs reveal variations in product distribution based on different endocyclic substituents, with steric properties of exocyclic substituents having minimal influence on the macrocyclization. Aryl-type endocyclic substituents predominantly yield 6-membered macrocycles, while polycyclic aromatic units such as fluorene and carbazole favor 4-membered species. Experimental and computational studies support a proposed mechanism of ring-walking catalyst transfer that promotes the macrocycle formation. It has been found that the macrocyclization is driven by the formation of cyclic conformers during the oligomerization step favoring an intramolecular C-N bond formation that, depending on the cycle size, hinges on either preorganization effect or kinetic increase of the reductive elimination step or a combination of the two. The CTM process exhibits a "living" behavior, facilitating sequential synthesis of other macrocycles by introducing relevant monomers, thus providing a practical synthetic platform for chemical libraries. Notably, CTM operates both under diluted and concentrated regimes, offering scalability potential, unlike typical macrocyclization reactions usually operating in the 0.1-1 mM range.

Structure and Chiroptical Properties of Anthra[1,2-a]anthracene-1-yl Dimers as New Biaryls.

Dimers of anthra[1,2-a]anthracene-1-yl units and its mesityl derivative were synthesized by Ni(0)-mediated coupling of the corresponding chloro derivatives as new biaryls. The X-ray analysis and DFT calculations revealed that two polycyclic aromatic units with nonplanar deformations took a twisted conformation about the single bond as a chiral axis. Enantiomers of the nonsubstituted compound were resolved by chiral HPLC, and the enantiopure samples showed intense Cotton effects at 321 nm in the circular dichroism (CD) spectra and emission bands at 449 nm in the circularly polarized luminescence (CPL) spectra with dissymmetry factor of |glum| 3.6×10-3. The absolute stereochemistry of this biaryl was determined by the theoretical calculation of CD spectrum by the time-dependent DFT method. The barrier to enantiomerization was determined to be 108 kJ mol-1 at 298 K. The dynamic process proceeded via a stepwise mechanism involving the helical inversion of each aromatic unit and the rotation about the biaryl axis as analyzed by the DFT calculations.

Crystalline Metallo-Organic Cage by Triphenylene-Cored Hexaterpyridine for Fast Iodine Capture.

In recent years, radioactive iodine capture has played an important role in nuclear waste treatment. However, most of the adsorbents possess low economic efficiency and undesirable reutilization in practical application. In this work, a terpyridine-based porous metallo-organic cage was assembled for iodine adsorption. Through synchrotron X-ray analysis, the metallo-cage was found to have a porous hierarchical packing mode with inherent cavity and packing channel. By taking advantage of polycyclic aromatic units and charged ⟨tpy-Zn2+-tpy⟩ (tpy = terpyridine) coordination sites in the structure, this nanocage exhibits an excellent ability to capture iodine in both the gas phase and aqueous medium, and the crystal state of the nanocage shows an ultrafast kinetic process of capturing I2 in aqueous solution within 5 min. The calculated maximum sorption capacities for I2 based on the Langmuir isotherm models are 1731 and 1487 mg g-1 for amorphous and crystalline nanocages, which is noticeably higher than most of the reported iodine sorbent materials in the aqueous phase. This work not only provides a rare example of iodine adsorption by a terpyridyl-based porous cage but also expands the applications of terpyridine coordination systems into iodine capture.

Comprehensive evaluation of polycyclic aromatic units in three liquefaction-derived heavy fractions from Zhunnan lignite

The structural characteristics of polycyclic aromatic units in three liquefaction-derived heavy fractions from Zhunnan lignite, including thermal dissolution (TD) in cyclohexane (HF C ), ethanolysis (HF E ), and two-step sequential TD in cyclohexane-ethanol (HF CE ), were investigated in depth. Combining multiple destructive tools, the intrinsic correlation among dissociated/degraded fragments and organic macromolecular networks, involving the types of alkyl side chain, methylene bridged bond, heteroatom, and aromatic nucleus, was also constructed. The results indicate that HF C with a smaller average molecular weight may be rich in -OH, >C-O-, and >C O units, while HF CE has higher aromaticity. In addition, abundant arenes and arenols were detected in the volatiles released from HF C flash pyrolysis, but macro/ultramolecular groups dominated in HF E and HF CE . Obviously, the differences in thermochemical reactions further confirmed that the component distribution of volatiles is mainly related to the direct gasification of small/medium molecules and the cleavage of weak/moderate strength covalent bonds. The analyses with quadrupole exactive orbitrap mass spectrometer and ruthenium ion-catalyzed oxidation show that HF C also contains abundant oxynitrides, while HF CE may be dominated by cata -condensed aromatics and polyaryl units, followed by few peri -condensed aromatics, long-chain saturated rings, aromatic rings with longer aliphatic side chains, and polymethylene linkage units. Comprehensive evaluation of these difficult-to-detect parts is beneficial to the resource and diversified utilization of such special soluble portions with potential environmental hazards. • HFCE has the highest aromaticity, while HFC is rich in O-containing FGs. • HFC also contains abundant >C-O- moieties and oxynitrides. • HFCE may be dominated by cata-condensed aromatics and polyaryl units. • The inner link among degraded fragments and organic structures was revealed.

Insight into biomass pyrolysis mechanism based on cellulose, hemicellulose, and lignin: Evolution of volatiles and kinetics, elucidation of reaction pathways, and characterization of gas, biochar and bio‐oil

Pyrolysis is the first step of gasification and combustion. The pyrolysis process of biomass is complicated, which is generally considered to consist of the pyrolysis of the three major components (i.e., cellulose, hemicellulose, and lignin). Understanding the pyrolysis behavior and product of each component holds a key to understanding the biomass pyrolysis mechanism. In this work, the pyrolysis behavior, pyrolysis kinetics, volatile evolution, and product characterization of the three major components are investigated. Results showed that pyrolysis characteristics and thermal stability of the three components were closely related to their unique chemical structures. During pyrolysis, the main pyrolytic volatiles of hemicellulose appeared first, followed by cellulose and then lignin volatiles in the 3D FTIR spectra. In term of pyrolysis products, gases were generated by the cracking of specific functional groups. Hemicellulose had the highest CO2 yield, whereas lignin had the highest CH4 yield due to the aromatic rings and methoxy groups in lignin structure. Whereas cellulose demonstrated the highest CO yield at high temperatures (above 550 °C). With increasing temperature, the carbon structures of carboxylic-C and O-alkyl-C in biochar decreased, while aryl-C was enhanced. This was due to the deoxygenation reactions such as dehydroxylation, decarboxylation, decarbonylation, and demethoxylation, resulting in a reduction in the number of oxygen-containing functional groups (such as –OH, –C=O, –COOH, and –OCH3), as well as the polycondensation reactions that formed more polycyclic aromatic hydrocarbon units during pyrolysis. The major components of cellulose bio-oil included anhydrosugars and furans. Whereas the bio-oils derived from hemicellulose and lignin showed the highest relative content of acids and phenols, respectively. Based on this analysis, the thermal decomposition pathways of cellulose, hemicellulose, and lignin were proposed.

Twins of Minimalistic Carbon Dots: Uniform Emitting‐Units and Molecular Level Repeatable Photoluminescence

AbstractUnderstanding the photoluminescence mechanism of carbon dots (C‐dots) is both of fundamental and technical significance. However, it has remained an extreme challenge due to C‐dots’ indeterminate constitution and complicated composition/structure. Herein, a combined processing system, namely extraction and subsequent preparative thin layer chromatography for C‐dots separation is presented. Benefiting from its powerful separation performances, two minimalistic C‐dots with almost identical structure and optical properties (named as “twin” C‐dots) are well separated. Then, by contrastive analysis, a photophysical picture for the C‐dots’ photoluminescence is presented: The C‐dots’ photoluminescence comes from uniform surface polycyclic aromatic hydrocarbon units instead of the whole particles, which is both size‐ and oxygen‐independent. The products not only are highly bright and stable against photobleaching, but possess repeatable photoluminescence with molecular level accuracy. So, the C‐dots favorably integrate the advantages from small molecule dyes to photoluminescent nanomaterials, which is unprecedented and desirable for property exploration and application expansion.

C 3-symmetric truxene discotic liquid crystals with mixed ether chains: synthesis, mesomorphism, and self-assembly properties

ABSTRACT Nine new C3-symmetric 2,7,12-tris(decanoxy)-3,8,13-tris(alkoxy)truxene discogens were synthesized, and all exhibited only one three-dimensionally ordered hexagonal columnar mesophase with a wide mesogenic temperature range, as characterized by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffractometry. Crucially, as the length of the alkoxy chain increased, the melting points first increased and then decreased, and, at the same time, the temperatures of the clearing point decreased gradually. In addition, these compounds were found to be highly thermally stable, having decomposition temperatures occurring well above 350°C, as determined by thermogravimetric analysis. The self-assembly behaviors in solution were studied using variable-concentration 1H-NMR, revealing that the truxenes self-aggregated in solution via the π–π facial interactions of the polycyclic aromatic units, and scanning tunneling microscopy results revealed that one of the discotic liquid crystal compounds periodically assembled in a hexagonal geometry at the liquid–solid interface of highly oriented pyrolytic graphite.

Conjugated Nanohoops Incorporating Donor, Acceptor, Hetero- or Polycyclic Aromatics.

In the last 13 years several synthetic strategies were developed that provide access to [n]cycloparaphenylenes ([n]CPPs) and related conjugated nanohoops. A number of potential applications emerged, including optoelectronic devices, and their use as templates for carbon nanomaterials and in supramolecular chemistry. To tune the structural or optoelectronic properties of carbon nanohoops beyond the size‐dependent effect known for [n]CPPs, a variety of aromatic rings other than benzene were introduced. In this Review, we provide an overview of the syntheses, properties, and applications of conjugated nanohoops beyond [n]CPPs with intrinsic donor/acceptor structure or such that contain acceptor, donor, heteroaromatic or polycyclic aromatic units within the hoop as well as conjugated nanobelts.

Conjugated Nanohoops Incorporating Donor, Acceptor, Hetero‐ or Polycyclic Aromatics

AbstractIn the last 13 years several synthetic strategies were developed that provide access to [n]cycloparaphenylenes ([n]CPPs) and related conjugated nanohoops. A number of potential applications emerged, including optoelectronic devices, and their use as templates for carbon nanomaterials and in supramolecular chemistry. To tune the structural or optoelectronic properties of carbon nanohoops beyond the size‐dependent effect known for [n]CPPs, a variety of aromatic rings other than benzene were introduced. In this Review, we provide an overview of the syntheses, properties, and applications of conjugated nanohoops beyond [n]CPPs with intrinsic donor/acceptor structure or such that contain acceptor, donor, heteroaromatic or polycyclic aromatic units within the hoop as well as conjugated nanobelts.

Enhanced Photocatalytic Performance of Donor–Acceptor-Type Polymers Based on a Thiophene-Contained Polycyclic Aromatic Unit

Donor–acceptor (D–A)-type photocatalysts containing the polycyclic aromatic donor (BTT-CPP) and nonpolycyclic aromatic donor (TTB-CPP) are designed and synthesized. Their physicochemical properties are thoroughly investigated. The photocatalytic hydrogen generation experiments show that both polymers exhibit distinct photocatalytic performance. BTT-CPP displays an attractive hydrogen evolution rate (HER) of 37,866 μmol g–¹ h–¹ without further addition of the metal co-catalyst, one of the highest values reported for organic photocatalysts. The optimal HER of TTB-CPP is 8466 μmol g–¹ h–¹. These results highlight the important role of the donor unit on the performance of D–A-type photocatalysts and demonstrate that thiophene-contained polycyclic aromatic unit BTT is an excellent donor unit for high HER photocatalysts.

Mild and Efficient Synthesis of Diverse Organo-AuI -L Complexes in Green Solvents.

An exceptionally mild and efficient method was developed for the preparation of (hetero)aryl‐AuI‐L complexes using ethanol or water as the reaction medium at room temperature and Ar‐B(triol)K boronates as the transmetalation partner. The reaction does not need an exogeneous base or other additives, and quantitative yields can be achieved through a simple filtration as the only required purification method, which obviates considerable waste associated with alternative workup methods. A broad reaction scope was demonstrated with respect to both the L and (hetero)aryl ligands on product Au complexes. Despite the polar reaction medium, large polycyclic aromatic hydrocarbon units can be incorporated on the Au complexes in very good to excellent yields. The approach was demonstrated for the chemoselective manipulation of orthogonally protected aryl boronates to afford a new class of N‐heterocyclic carbene‐Au‐aryl complexes. A mechanistic rationale was proposed.

Structure and Properties of Epoxy Resins Containing Polycyclic Aromatic Unit

Structure and Properties of Epoxy Resins Containing Polycyclic Aromatic Unit

Branched 2‐Ethylhexyl Substituted Indacenodithieno[3,2‐b]Thiophene Core Enabling Wide‐Bandgap Small Molecule for Fullerene‐Based Organic Solar Cells with 9.15% Efficiency: Effect of Length and Position of Fused Polycyclic Aromatic Units

A pair of 2‐ethylhexyl‐substituted indacenodithieno[3,2‐b]thiophene (EH‐IDTT) based tetrafluorinated substituted wide‐bandgap small molecular donor materials with different electron‐rich terminal units, DT4FIDTT and TT4FIDTT, has been synthesized for high efficiency fullerene‐based organic solar cells. The utilization of the EH‐IDTT center core increased the optical bandgap of DT4FIDTT (Eg of 1.86 eV) and decreased HOMO energy level in thin films in comparison with those of BIT‐4F‐T with indacenodithiophene core and thiophene π bridge. Compared to DT4FIDTT with 2,2′‐bithiophene terminal unit, TT4FIDTT with further fused thieno[3,2‐b]thiophene terminal units exhibited a larger optical bandgap and more straight conformation due to less effective conjugated length of thieno[3,2‐b]thiophene. Devices based on DT4FIDTT/PC71BM exhibited high power conversion efficiency (PCE) up to 9.15%, significantly higher than that of the device based on TT4FIDTT/PC71BM (PCE of 7.35%). The higher Jsc of the device based on DT4FIDTT/PC71BM can be attributed to its better charge transport properties and favorable phase separation features. Such high efficiency of 9.15% is the highest value reported for the fullerene‐based organic solar cells based on wide‐bandgap (Eg > 1.85 eV) small molecular donor, demonstrating the feasibility of branched alkylated‐indacenodithieno[3,2‐b]thiophene core in enhancing overall photovoltaic performance.

Precursor synthesis strategy for polycyclic aromatic conjugated polymers on the application of supercapacitors

Polycyclic aromatics (PCAs) possess excellent photoelectric properties, but the construction of such compounds has been a quite challenging subject of study, mainly due to very low solubility. Herein we report a precursor synthesis strategy for polycyclic aromatic conjugated polymers. A soluble precursor polymer, that containing fusible “double U-shaped aromatic” (DUA) and perylenetetracarboxydiimide (PDI) units, was firstly synthesized by Suzuki coupling. The stereo aromatic units in polymer backbone were found to be converted into polycyclic aromatic units, i.e. hexa-peri-hexabenzocoronene (HBC), by chemical or electrochemical oxidation, which resulted in a formation of insoluble polycyclic aromatic conjugated polymers. The electrochemical oxidations that occurred at the interface of electrode and solution exhibited higher cyclization reactivity and leads to the formation of high quality films on the electrode surface. Characterization by Raman and UV-visible (UV-Vis) spectroscopy validated the successful formation of this HBC structure. Some potential applications of such thin films are being explored, and here we focus on the characteristics of supercapacitors based on their excellent electrochemical properties.

Donor–Acceptor Conjugated Polymers Based on Dithieno[3,2-b:3′,2′-b′]naphtho[1,2-b:5,6-b′]dithiophene: Synthesis and Semiconducting Properties

A polycyclic aromatic unit comprising six rings, i.e., 5,11-bis(2-octyldodecyl)dithieno[3,2-b:3′,2′-b′]naphtho[1,2-b:5,6-b′]dithiophene (DTNDT), was developed. Four donor–acceptor (D–A) conjugated polymers, which are named P-BT, P-2FBT, P-IID, and P-DPP, were synthesized with DTNDT as the D-unit and 2,1,3-benzothiadiazole (BT), 5,6-difluorobenzo[c][1,2,5]thiadiazole (2FBT), isoindigo (IID), and diketopyrrolopyrrole (DPP) as the A-unit, respectively. All four polymers are thermally stable with decomposition temperature above 390 °C and show pseudo-straight-shaped backbones. Their ordered thin films were prepared via solution spin-casting, in which conjugated backbones mainly adopted edge-on alignment on the substrate. The semiconducting properties of the polymers were characterized with bottom gate and top contact (BGTC) organic thin film transistors (OTFTs). All four polymers showed p-type transport behavior, and the hole mobilities were 0.023, 0.078, 0.50, and 1.80 cm2/(V s) for P-BT, P-2FBT, P-IID, and ...

Electronic and Morphological Studies of Conjugated Polymers Incorporating a Disk-Shaped Polycyclic Aromatic Hydrocarbon Unit.

As more research findings have shown the correlation between ordering in organic semiconductor thin films and device performance, it is becoming more essential to exercise control of the ordering through structural tuning. Many recent studies have focused on the influence of side chain engineering on polymer packing orientation in thin films. However, the impact of the size and conformation of aromatic surfaces on thin film ordering has not been investigated in great detail. Here we introduce a disk-shaped polycyclic aromatic hydrocarbon building block with a large π surface, namely, thienoazacoronenes (TACs), as a donor monomer for conjugated polymers. A series of medium bandgap conjugated polymers have been synthesized by copolymerizing TAC with electron donating monomers of varying size. The incorporation of the TAC unit in such semiconducting polymers allows a systematic investigation, both experimentally and theoretically, of the relationships between polymer conformation, electronic structure, thin film morphology, and charge transport properties. Field effect transistors based on these polymers have shown good hole mobilities and photoresponses, proving that TAC is a promising building block for high performance optoelectronic materials.

MAZ-binding G4-decoy with locked nucleic acid and twisted intercalating nucleic acid modifications suppresses KRAS in pancreatic cancer cells and delays tumor growth in mice

KRAS mutations are primary genetic lesions leading to pancreatic cancer. The promoter of human KRAS contains a nuclease-hypersensitive element (NHE) that can fold in G4-DNA structures binding to nuclear proteins, including MAZ (myc-associated zinc-finger). Here, we report that MAZ activates KRAS transcription. To knockdown oncogenic KRAS in pancreatic cancer cells, we designed oligonucleotides that mimic one of the G-quadruplexes formed by NHE (G4-decoys). To increase their nuclease resistance, two locked nucleic acid (LNA) modifications were introduced at the 3′-end, whereas to enhance the folding and stability, two polycyclic aromatic hydrocarbon units (TINA or AMANY) were inserted internally, to cap the quadruplex. The most active G4-decoy (2998), which had two para-TINAs, strongly suppressed KRAS expression in Panc-1 cells. It also repressed their metabolic activity (IC50 = 520 nM), and it inhibited cell growth and colony formation by activating apoptosis. We finally injected 2998 and control oligonucleotides 5153, 5154 (2 nmol/mouse) intratumorally in SCID mice bearing a Panc-1 xenograft. After three treatments, 2998 reduced tumor xenograft growth by 64% compared with control and increased the Kaplan–Meier median survival time by 70%. Together, our data show that MAZ-specific G4-decoys mimicking a KRAS quadruplex are promising for pancreatic cancer therapy.

Highly Twisted Triarylamines for Photoinduced Intramolecular Charge Transfer

9-(N,N-Dianisylamino)anthracene (9DAAA), 9-(N,N-dianisylamino)dinaphth([1,2-a:2'-1'-j]-anthracene (9DAAH), and 9,10-bis(N,N-dianisylamino)anthracene (910BAA) were synthesized as highly twisted triarylamines with potential for photoexcited internal charge transfer. Crystallography of 9DAAA shows its dianisylamino group to be twisted nearly perpendicular to its anthracene unit, similar to a report for 910BAA. The solution fluorescence spectra show strong bathochromic shifts for each of the three molecular systems with strongly decreased quantum efficiency in higher polarity solvents. Solution-phase (ensemble) time-resolved photoluminescence measurements show up to 4-fold decreases in fluorescence lifetime in acetonitrile compared to hexane. The combined results are consistent with photoinduced, transient intramolecular charge-transfer from the bis-anisylamine unit to the polycyclic aromatic unit. Computational modeling is in accord with intramolecular transfer of electron density from the bis-anisylamino unit to the anthracene, based on in comparisons of HOMO and LUMO.

Synthesis and Photophysical Properties of Pyrrole/Polycyclic Aromatic Units Hybrid Fluorophores

A series of pyrrole/polycyclic aromatic unit hybrid fluorophores was developed by a two-stage synthetic strategy. Their central aryl-substituted pyrrole cores were constructed by a Paal-Knorr pyrrole synthesis reaction. The reaction conditions and mechanism are also discussed in detail. End-capping triflate onto the central pyrrole core enables the core to incorporate various polycyclic aromatic units. The Buchwald-Hartwig amination reaction and the Suzuki-Miyaura cross-coupling reaction were adopted to incorporate the triflate end-capping pyrrole with N-phenylnaphthalen-1-amine and various polycyclic aromatic units to form the hybrid fluorophores. The photophysical properties and thermal properties of the fluorophores were characterized. Most of the pyrrole fluorophores emitted blue light and exhibited high quantum efficiency. The fluorescence properties of these pyrrole fluorophores were induced by manipulating the surrounding polycyclic aromatic units. When the central pyrrole core was incorporated with amino or naphthalene moieties, the fluorescence efficiency and thermal stability of fluorophores 1 and 2 were low (phi(f) < 0.35, T(g) <140 degrees C). Rigid and highly fluorescent moieties (such as pyrenyl, 9,9-dimethylfluorenyl, 9,9-diphenylfluorenyl, and spirofluorenyl groups) were grafted onto the pyrrole. Fluorophores 3-6 had high fluorescence efficiency (phi(f) > 0.99) and stable glassy morphology (the T(g) value of the fluorophore 6 was as high as 220 degrees C). Results of this study demonstrate that the sterically induced fluorescence of crowded pyrrole and the fluorescent polycyclic aromatic units significantly affect the emission properties of the hybrid fluorophores.