Benzene Units Research Articles

Stable planar chirality of arylated pillar[6]arene and its thermal response

Macrocyclic molecules with chirality have been studied because of their wide applications in the field of chiral recognition, chiroptical materials, and asymmetric catalysis. Planar chirality of pillar[n]arenes also contributes to many applications. Without bulky substituents, racemization occurs between pillar[n]arene enantiomers. Pillar[5]arenes with stable planar chirality have been formed by introducing bulky substituents into the pillar[5]arene rims. However, pillar[6]arene enantiomers that show stable planar chirality by introducing bulky conjugated moieties have not been reported. Herein, we report stable planar chirality of pillar[6]arene by introducing biphenyl groups into one benzene unit of pillar[6]arene. The enantiomers show thermo-responsive circular dichroism signals without racemization.

Wavelength Selective Photocontrol of Hybrid Azobenzene‐Spiropyran Photoswitches with Overlapping Chromophores

AbstractCompounds with multiple photoswitching units are appealing for complex photochemical control of molecular materials and nanostructures. Herein, we synthesized novel meta‐ and para‐ connected (related to the nitrogen of the indoline) azobenzene‐spiropyran dyads, in which the central benzene unit is shared by both switches. We investigated their photochemistry using static and time‐resolved transient absorption spectroscopy as well as quantum chemical calculations. In the meta‐compound, the individual components are photochemically decoupled due to the meta‐pattern. In the para‐compound the spiro‐connectivity leads to a bifunctional photoswitchable system with a red‐shifted absorption. The azobenzene and the spiropyran can thus be addressed and switched independently by light of appropriate wavelength. Through the different connectivity patterns two different orthogonally photoswitchable systems have been obtained which are promising candidates for complex applications of light control.

Wavelength Selective Photocontrol of Hybrid Azobenzene-Spiropyran Photoswitches with Overlapping Chromophores.

Compounds with multiple photoswitching units are appealing for complex photochemical control of molecular materials and nanostructures. Herein, we synthesized novel meta- and para- connected (related to the nitrogen of the indoline) azobenzene-spiropyran dyads, in which the central benzene unit is shared by both switches. We investigated their photochemistry using static and time-resolved transient absorption spectroscopy as well as quantum chemical calculations. In the meta-compound, the individual components are photochemically decoupled due to the meta-pattern. In the para-compound the spiro-connectivity leads to a bifunctional photoswitchable system with a red-shifted absorption. The azobenzene and the spiropyran can thus be addressed and switched independently by light of appropriate wavelength. Through the different connectivity patterns two different orthogonally photoswitchable systems have been obtained which are promising candidates for complex applications of light control.

Intrinsic low‐dielectric‐constant polyimides based on a novel diamine having −CF3 groups and kinkable 1,4‐diisopropylbenzene units

AbstractPolyimides (PIs) with low dielectric constants and optical transparency are of great interest in 5G/6G communication applications and in the microelectronics industry, where they are used as interlayer dielectric materials, wearable display devices and so forth. In this study, we designed and synthesized a novel fluorinated diamine called 4,4′‐(1,4‐phenylenebis(propane‐2,2‐diyl))diphenoxybis(2‐(trifluoromethyl)‐4‐aminobenzene) (BPBTAB) monomer from bisphenol‐P having diisopropyl benzene units and fabricated four novel BPBTAB‐X PIs. These PI films possess excellent properties such as a low dielectric constant (1.13–1.84 at 1 MHz), high 5% loss temperature (395–491 °C), moderate glass transition temperature (223–254 °C), good tensile modulus (0.827–1.076 GPa), excellent optical properties (T450 up to 83.37%), low moisture absorption (<0.63%) and good solubility in organic solvents. Hence, the as‐synthesized PI films exhibit excellent comprehensive properties for high‐frequency 5G/6G communication applications. © 2023 Society of Chemical Industry.

Synthesis and physical properties of doubly-annulated [10]cycloparaphenylene

Abstract A doubly annulated cycloparaphenylene (CPP), in which two [N]paraphenylenes share one benzene unit by meta (m)-connection, m-,m-phenylene-[2N]CPP with N = 5 (2a), was synthesized by double annulation between a CPP precursor and 1,5-dibromo-2,4-diiodobenzene followed by reductive aromatization. The structure of 2a was confirmed by NMR, mass spectroscopy, and single crystal X-ray diffraction analysis. As 2a has a figure-eight structure, it can have a twisted Möbius topology. However, the X-ray analysis clearly reveals a non-twisted Hückel topology in a solid state. The photophysical and electrochemical properties of 2a were also clarified. The studies proved that, while 2a can also be seen as ortho (o)-,o- or para (p)-,p-connected [10]CPP, 2a has an meta (m)-,m-connected electronic structure. The theoretical calculations also support this conclusion.

Synthesis of Defective Wheel‐Shaped Nanographdiynes

AbstractThe synthesis and optical properties of wheel‐shaped nanographdiynes that has lost some butadiyne spokes were reported. These defective wheel‐shaped nanographdiynes possess butadiyne‐bridged metacyclophanes with para‐bis(phenylbutadiynyl)‐benzene units as the axis. The optimized geometries of the defective wheel‐shaped nanographdiynes along with their vibrational spectra, HOMO and LUMO orbitals were calculated at B3LYP/6‐311G(d,p) level. HOMO and LUMO orbitals are delocalized mainly over the para‐bis(phenylbutadiynyl)‐benzene axis, with weak contribution from the attached ethynyl units. The π‐conjugation extension and quantity increase of the para axis influenced the optical properties of these graphdiyne substructures, leading to the change of bandgap from 2.88 eV to 2.56 eV as reflected by optical spectroscopy. The defective wheel‐shaped nanographdiynes lost the characteristic intensive sharp absorption peak at low energy region, which indicated that the fusion of adjacent dehydrobenzo [18] annulenes are crucial for the bulk properties of graphdiyne.

Design, synthesis, and properties of soluble intrinsic black polyimide bearing tetraphenylcyclopentadienone units

AbstractBlack polyimides (BPIs) have gained increasing attention because of their growing demands in optoelectronic areas. However, the commonly used BPI containing carbon black suffers from the decreases of mechanical and electrical performances. In this work, a soluble intrinsic BPI (TPCPDFPPI) was prepared by the reaction of 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and a new diamine (TPCPDFPDA) bearing tetraphenylcyclopentadienone (TPCP) connected with benzene and fluorene units. TPCP grafted with benzene and fluorene units acted as a chromophore that shifted the absorption range of PI toward the long‐wave direction. The resulting TPCPDFPPI possessed whole visible‐light absorption characteristic and therefore exhibited high blackness and opacity. Additionally, TPCPDFPPI displayed superior solubility, mechanical and electrical performance. Theoretical calculations exhibited that the visible‐light absorption responsible for the blackness of TPCPDFPPI was chiefly ascribed to the HOMO to LUMO electron transition in the diamines, where the electrons were primarily migrated from the 2,5‐position aryl groups to the cyclopentadienone. This work offers a promising strategy for improving the overall properties of BPIs for photo‐electronic areas.

From (Sub)Porphyrin to (Sub)Phthalocyanine: Aromaticity Signatures in the UV-Vis Absorption Spectra

Understanding the structure-property relationship in (sub)porphyrin and (sub)phthalocyanine derivatives facilitates the design of new materials on demand. One of the main features of these systems are their optical properties, i.e. characteristic Soret and Q absorption bands, which depend on π-delocalization. A possible way to characterize differences in the π system is the theoretical description of the aromaticity, previously used to rationalize the non-optical properties of octaphyrins [1]. However, the high complexity given by the topological flexibility and the existence of multiple π-electron circuits makes it a challenging task [2]. In this work, we analyze the influence structural differences on the aromatic character and the UV/vis absorption spectra of eight (sub)porphyrinoids (Figure 1), including phthalocyanine and subpthalocyanine. We performed calculations at CAM-B3LYP/cc-pVTZ level of theory followed by global and local aromaticity descriptors, providing a qualitative relation between aromaticity and UV-vis absorption spectra. We found that the red shifts in Soret and Q bands observed for tetra/tri-isoindole systems compared to pyrrole analogs correlate with the decrease of global aromaticity due to the inclusion of the fused benzene units. Figure 1

A Rational Design of Isoindigo-Based Conjugated Microporous n-Type Semiconductors for High Electron Mobility and Conductivity.

The development of n-type organic semiconductors has evolved significantly slower in comparison to that of p-type organic semiconductors mainly due to the lack of electron-deficient building blocks with stability and processability. However, to realize a variety of organic optoelectronic devices, high-performance n-type polymer semiconductors are essential. Herein, conjugated microporous polymers (CMPs) comprising isoindigo acceptor units linked to benzene or pyrene donor units (BI and PI) showing n-type semiconducting behavior are reported. In addition, considering the challenges of deposition of a continuous and homogeneous thin film of CMPs for accurate Hall measurements, a plasma-assisted fabrication technique is developed to yield uniform thin films. The fully conjugated 2D networks in PI- and BI-CMP films display high electron mobility of 6.6 and 3.5cm2 V-1 s-1 , respectively. The higher carrier concentration in PI results in high conductivity (5.3mScm-1 ). Both experimental and computational studies are adequately combined to investigate structure-property relations for this intriguing class of materials in the context of organic electronics.

Manipulating the excited states from charge-transfer to hybridized local and charge-transfer towards high-performance blue electroluminescence

Manipulating the excited states of organic luminescent materials can efficiently improve the utilization of both singlet and triplet excitons for developing high-performance organic light-emitting diodes (OLEDs), but the issue remains difficult due to the lack of well-controlled ways. Here, we proposed a molecular design strategy of excited state manipulation from charge-transfer (CT) to hybridized local and charge-transfer (HLCT) via adjusting the cyano position on pyridine acceptor. The meta-substituted PyAn4CN is mainly composed of a CT component, while the para-substituted PyAn5CN is endowed with a HLCT component. On further extending the conjugation of PyAn5CN by inserting a benzene unit between the pyrene and anthracene core, the HLCT character is preserved in PyPhAn5CN, accompanied by a faster radiative decay. Consequently, the vacuum-evaporated OLEDs exhibit blue electroluminescence (EL) with the emission peaks in the range of 455–460 nm and high external quantum efficiency (EQE) up to 7.52%, together with well-suppressed efficiency roll-offs of 0.8% and 3.7% at the luminance of 100 and 1000 cd m-2, respectively. More importantly, the solution-processed device shows an excellent performance with EQE of 6.49%, which is one of the best results in the solution-processed HLCT OLEDs. Our results clearly indicate that the formation of HLCT state is an efficient way to realize high-efficiency blue electrofluorescence.

Color-tunable photoluminescent discotic liquid crystal based on perylene – Pentaalkynylbenzene triad

This article describes the design and development of a discotic triad, where perylene is sandwiched between two pentaalkynyl benzene units, linked via a flexible alkyl spacer. The thermotropic liquid crystalline properties of the compound were analyzed by differential scanning calorimetry (DSC), polarising optical microscopy (POM), and wide-angle X-ray diffraction (WXRD) techniques. The compound exhibits columnar oblique (Colob) mesophase that sustains over a significant temperature range. The corresponding electron density map was derived from the intensities observed in the diffraction pattern. The photophysical behaviour of the compound in various solvents of varying polarity has been studied. The compound shows positive solvatochromism with a significant increase in Stoke's shift of around 91 nm between toluene and ethanol. The compound shows high fluorescence quantum yield in non-polar solvents and the lowest in polar solvents. The presented luminescent material with positive solvatochromism will reveal its potential application in fluorescence imaging and the field of optoelectronic organic materials.

Catalytic Linkage Engineering of Covalent Organic Frameworks for the Oxygen Reduction Reaction

AbstractMetal‐free covalent organic frameworks (COFs) have been employed to catalyze the oxygen reduction reaction (ORR). To achieve high activity and selectivity, various building blocks containing heteroatoms and groups linked by imine bonds were used to create catalytic COFs. However, the roles of linkages of COFs in ORR have not been investigated. In this work, the catalytic linkage engineering has been employed to modulate the catalytic behaviors. To create single catalytic sites while avoiding other possible catalytic sites, we synthesized COFs from benzene units linked by various bonds, such as imine, amide, azine, and oxazole bonds. Among these COFs, the oxazole‐linkage in COFs enables to catalyze the ORR with the highest activity, which achieved a half‐wave potential of 0.75 V and a limited current density of 5.5 mA cm−2. Moreover, the oxazole‐linked COF achieved a conversion frequency (TOF) value of 0.0133 S−1, which were 1.9, 1.3, and 7.4‐times that of azine‐, amide‐ and imine‐COFs, respectively. The theoretical calculation showed that the carbon atoms in oxazole linkages facilitated the formation of OOH* and promoted protonation of O* to form the OH*, thus advancing the catalytic activity. This work guides us on which linkages in COFs are suitable for ORR.

Catalytic Linkage Engineering of Covalent Organic Frameworks for the Oxygen Reduction Reaction.

Metal-free covalent organic frameworks (COFs) have been employed to catalyze the oxygen reduction reaction (ORR). To achieve high activity and selectivity, various building blocks containing heteroatoms and groups linked by imine bonds were used to create catalytic COFs. However, the roles of linkages of COFs in ORR have not been investigated. In this work, catalytic linkage engineering has been employed to modulate the catalytic behaviors. To create single catalytic sites while avoiding other possible catalytic sites, we synthesized COFs from benzene units linked by various bonds, such as imine, amide, azine, and oxazole bonds. Among these COFs, the oxazole-linkage in COFs enables to catalyze the ORR with the highest activity, which achieved a half-wave potential of 0.75 V and a limited current density of 5.5 mA cm-2. Moreover, the oxazole-linked COF achieved a conversion frequency (TOF) value of 0.0133 S-1, which were 1.9, 1.3, and 7.4-times that of azine-, amide- and imine-COFs, respectively. The theoretical calculation showed that the carbon atoms in oxazole linkages facilitated the form of OOH* and promoted protonation of O* to form the OH*, thus advancing the catalytic activity. This work guides us on which linkages in COFs are suitable for ORR.

An Ortho-Bisalkyloxylated Benzene-Based Fully Non-fused Electron Acceptor for Efficient Organic Photovoltaic Cells.

To develop the low-cost nonfullerene acceptors (NFAs), two fully non-fused NFAs (TBT-2 and TBT-6) with ortho-bis((2-ethylhexyl)oxy)benzene unit and different side chains onto thiophene-bridges are synthesized through highly efficient synthetic procedures. Both acceptors show good planarity, low optical gaps (≈1.51eV), and deep highest occupied molecular orbital levels (≤-5.77eV). More importantly, the single-crystal structure of TBT-2 shows compact molecular arrangement due to the existence of intramolecular interactions between adjacent aromatic units and strong π-π stacking between intermolecular terminal groups. When the two acceptors are fabricated organic photovoltaic (OPV) cells by combining with a wide optical gap polymer donor, the TBT-6 with strong crystallization forms large domain sizes in bulk heterojunction (BHJ) blend. As a result, the TBT-6-based OPV cell shows a low power conversion efficiency (PCE) of 9.53%. In contrast, the TBT-2 with proper crystallization facilitates morphological optimization in the BHJ blend. Consequently, the TBT-2-based OPV cell gives an outstanding PCE of 13.25%, which is one of the best values among OPV cells with similar optical gaps. Overall, this work provides a practical molecular design strategy for developing high-performance and low-cost electron acceptors.

Pyrene‐Based Covalent Organic Frameworks for Photocatalytic Hydrogen Peroxide Production

AbstractFour highly porous covalent organic frameworks (COFs) containing pyrene units were prepared and explored for photocatalytic H2O2 production. The experimental studies are complemented by density functional theory calculations, proving that the pyrene unit is more active for H2O2 production than the bipyridine and (diarylamino)benzene units reported previously. H2O2 decomposition experiments verified that the distribution of pyrene units over a large surface area of COFs plays an important role in catalytic performance. The Py‐Py‐COF though contains more pyrene units than other COFs which induces a high H2O2 decomposition due to a dense concentration of pyrene in close proximity over a limited surface area. Therefore, a two‐phase reaction system (water‐benzyl alcohol) was employed to inhibit H2O2 decomposition. This is the first report on applying pyrene‐based COFs in a two‐phase system for photocatalytic H2O2 generation.

Pyrene-Based Covalent Organic Frameworks for Photocatalytic Hydrogen Peroxide Production.

Four highly porous covalent organic frameworks (COFs) containing pyrene units were prepared and explored for photocatalytic H2 O2 production. The experimental studies are complemented by density functional theory calculations, proving that the pyrene unit is more active for H2 O2 production than the bipyridine and (diarylamino)benzene units reported previously. H2 O2 decomposition experiments verified that the distribution of pyrene units over a large surface area of COFs plays an important role in catalytic performance. The Py-Py-COF though contains more pyrene units than other COFs which induces a high H2 O2 decomposition due to a dense concentration of pyrene in close proximity over a limited surface area. Therefore, a two-phase reaction system (water-benzyl alcohol) was employed to inhibit H2 O2 decomposition. This is the first report on applying pyrene-based COFs in a two-phase system for photocatalytic H2 O2 generation.

Topological, Spectroscopic and Energetic Properties of Cycloparaphenylene Series

Carbon nanorings are macrocyclic aromatic hydrocarbons that represent the segments of carbon nanotubes and have received considerable attention due to their novel nanoelectronic and photophysical capabilities. The cycloparaphenylene (CPP), a carbon nanoring with a ring-like structure comprising of only benzene units, has been the subject matter of several studies. The carbon nanoring structures bearing polycyclic aromatic hydrocarbons such as hexabenzocoronene and pyrene molecules are also found to exhibit exciting characteristics and applications. This in turn evolves a wide range of novel chemical structures whose behavior and attributes are to be studied and explored. Molecular descriptors help us to study such novel nanostructures by providing a greater understanding of their unique properties, whereas such characterization remains challenging due to their ring-shaped arrangement. In this study, we investigate cycloparaphenylene series and show that such structures are not bounded by the partial cube family. We also derive the exact analytic expressions of degree, distance and closeness-related descriptors. We have also computed the thermodynamic and kinetic stabilities of the three structures using the graph spectra, resonance energies, HOMO-LUMO gaps and Kekulé counts obtained from the graph spectra and combinatorial methods. Whereas the CPPhbc[5] structure is thermodynamically more stable, the CPPyr[9] is kinetically more stable. Furthermore, we have employed combinatorial generating function methods to compute the NMR and ESR spectra of the title compounds.

Terephthalaldehyde-based covalent organic frameworks as photocatalysts for CO2 reduction under visible light

As a new type of porous organic materials, two-dimensional covalent organic frameworks (2D COFs) show superior visible-light harvesting and effective separation and transport of the photogenerated charges, which ensures COFs to be promising platforms for photocatalysis. In the current work, two 2D imine-linked COFs (PDA-TAB and PDA-TTA), having the same framework with benzene and/or triazine units, were synthesized to investigate the effects of the introduced triazine units in the skeleton of COFs on photocatalytic CO2 reduction. Compared to PDA-TAB, PDA-TTA exhibits a much higher photocatalytic activity with a HCOOH yield of 65.7 μmol gcat-1h−1. Further studies indicate the introduction of triazine units in the skeleton of PDA-TTA not only can enhance the visible-light absorption due to the high conjugation degree, but also can promote the charge separation and migration, thus improving the photocatalytic performance. The current work facilitates to understand the roles of the key structural units in 2D COFs on photocatalysis and provides some insights to develop efficient photocatalysts for the conversion of CO2.

Efficient Small‐Molecule Organic Solar Cells by Modulating Fluorine Substitution Position of Donor Material

Comprehensive SummaryThe fluorine substitution position in organic semiconductors is critical in improving device performance for organic solar cells (OSCs). Herein, two similar small‐molecule donors, B3T‐PoF and B3T‐PmF, are designed and synthesized, which only differ on the fluorine substitution position on the pendent benzene unit. Although both small‐molecule donors exhibit similar absorption profiles and molecular energy levels, B3T‐PmF has stronger crystallinity and lower energetic disorder than B3T‐PoF. After blending with the non‐fullerene acceptor of BO‐4Cl, B3T‐PmF shows better phase separation and more ordered molecular packing in blend film. As a result, the B3T‐PoF:BO‐4Cl‐based OSC shows a power conversion efficiency (PCE) of 12.3%. In contrast, the B3T‐PmF:BO‐4Cl‐based cell demonstrates obviously increased JSC and FF values, thus yielding an excellent PCE of 14.7%. This study indicates that reasonable selection of fluorine atom substitution position in conjugated side chains is one of the promising strategies for achieving high‐performance SM‐OSCs.

Preparation and characterization of glucose-based covalent organic polymer coated silica as stationary phase for high-performance liquid chromatography

Carbohydrate is a renewable, sustainable, hydrophilic, and biodegradable natural product, which is widely used in the field of adsorption. In this study, a glucose-based covalent organic polymer (COP) coated silica was fabricated by facile solvent knitting reaction between tetrabenzylglucose and silica-phenyl with anhydrous aluminum trichloride as catalyst, forming a core-shell stationary phase (donated as SiO2@COPBn-glu) for high performance liquid chromatography. The prepared SiO2@COPBn-glu was characterized by scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectrometry, solid-state 13C nuclear magnetic resonance spectrometry, X-ray photoelectron spectroscopy, and N2 adsorption-desorption experiments. Owing to the coexistence of benzene units and alkyl, hydroxyl and ether groups in the skeleton of COPBn-glu shell, the developed chromatographic packing exhibited reversed-phase/hydrophilic interaction mixed-mode with multiple retention mechanisms, such as hydrophobic, π-π, hydrogen bonding, and electron donor-acceptor interactions. The results revealed that the SiO2@COPBn-glu column demonstrated excellent selectivity and retention behavior for both hydrophilic and hydrophobic compounds with good repeatability and stability. Meanwhile, the chromatographic performance of the prepared SiO2@COPBn-glu column was compared with a C18 column to assess the role of the coating COPBn-glu shell. Therefore, the development of the SiO2@COPBn-glu stationary phase expands the potential application of COPs in separation field.