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2017 Volume 75 Issue 5
2017, 75(5): 419-438
doi: 10.6023/A17020049
Abstract:
Homogeneous gold catalysis has experienced rapid development since 2004 and generally exhibited high efficiency and good functional group tolerance. On the other hand, catalytic dearomatization reactions provide a unique and straight approach to the construction of highly functionalized molecules with diverse three-dimensional structures from simple aromatic compounds. In this perspective, recent examples on gold-catalyzed dearomatization reactions are summarized in two main categories: gold-catalyzed rearrangements and gold-catalyzed hydrofunctionalizations of alkynes and allenes. In the first category, intra-and inter-molecular dearomatization reactions were achieved via gold-catalyzed rearrangements of propargylic ester and its derivatives. Although this area is still at its early stage, several outstanding asymmetric examples have been reported by Shi and Toste. In the second category, an array of dearomatization reactions via gold-catalyzed hydrofunctionalizations of alkynes and allenes were presented. All these cases have shown great potentials for convenient and straightforward construction of spiro and/or bridged polycyclic molecules, and some of them have exhibited excellent enantioselectivity. In addition, salient features and proposed mechanisms for these two types of reactions are also described.
Homogeneous gold catalysis has experienced rapid development since 2004 and generally exhibited high efficiency and good functional group tolerance. On the other hand, catalytic dearomatization reactions provide a unique and straight approach to the construction of highly functionalized molecules with diverse three-dimensional structures from simple aromatic compounds. In this perspective, recent examples on gold-catalyzed dearomatization reactions are summarized in two main categories: gold-catalyzed rearrangements and gold-catalyzed hydrofunctionalizations of alkynes and allenes. In the first category, intra-and inter-molecular dearomatization reactions were achieved via gold-catalyzed rearrangements of propargylic ester and its derivatives. Although this area is still at its early stage, several outstanding asymmetric examples have been reported by Shi and Toste. In the second category, an array of dearomatization reactions via gold-catalyzed hydrofunctionalizations of alkynes and allenes were presented. All these cases have shown great potentials for convenient and straightforward construction of spiro and/or bridged polycyclic molecules, and some of them have exhibited excellent enantioselectivity. In addition, salient features and proposed mechanisms for these two types of reactions are also described.
2017, 75(5): 439-447
doi: 10.6023/A17020061
Abstract:
With the increasing needs for transportable fuels and the growing concerns on environmental pollution, significant attention has been paid to the conversion of renewable lignocellulosic biomass to liquid fuels. As a major component of bio-oil from biomass depolymerization, organic carboxylic acids make the bio-oil acidic, corrosive and unstable, which are harmful for storage, transportation, and upgrading of bio-oil. Therefore, the removal of carboxylic acids is very important. Ketonization reaction, also called ketonic decarboxylation, converts two moles carboxylic acids to ketone (symmetrical or asymmetrical ketones), carbon dioxide and water, which removes oxygen efficiently and increases the carbon chain length without using hydrogen. In addition, ketones are important chemicals and have been widely used in chemical industry as organic solvent. The mechanism and active site for ketonization are still under debate. Various mechanisms have been proposed for the ketonization, based on different reaction intermediates evolved (i.e., β-keto-acids, ketene, carboxylates and acyl carbonium ions). Ketonization reaction is a surface-structure-sensitive reaction, thus reaction activity depends on surface-structure of the metal oxides (such as crystal surfaces and particle size). The concerted function of oxygen anions (Brønsted bases) and unsaturated metal cations (Lewis acids) is crucial for ketonization. The amphoteric oxides show better catalytic activity than pure acidic or basic oxides. Oxygen vacancy formed on the surface of metal oxides is a key factor for high ketonization activity, which can stabilize the reaction product and reduce the activation energy. This paper reviews the progress in ketonization from the aspects of reaction mechanism, and the effects of surface structure, acidity and basicity, and reducibility of metal oxides on ketonization. The β-keto-acids based mechanism and ketene based mechanism will be discussed in detail to understand how does the C—C coupling happen and the fundamental role of α-H. Finally, the importance of surface structure and properties of metal oxides on the carboxylic acids ketonization reaction is explained.
With the increasing needs for transportable fuels and the growing concerns on environmental pollution, significant attention has been paid to the conversion of renewable lignocellulosic biomass to liquid fuels. As a major component of bio-oil from biomass depolymerization, organic carboxylic acids make the bio-oil acidic, corrosive and unstable, which are harmful for storage, transportation, and upgrading of bio-oil. Therefore, the removal of carboxylic acids is very important. Ketonization reaction, also called ketonic decarboxylation, converts two moles carboxylic acids to ketone (symmetrical or asymmetrical ketones), carbon dioxide and water, which removes oxygen efficiently and increases the carbon chain length without using hydrogen. In addition, ketones are important chemicals and have been widely used in chemical industry as organic solvent. The mechanism and active site for ketonization are still under debate. Various mechanisms have been proposed for the ketonization, based on different reaction intermediates evolved (i.e., β-keto-acids, ketene, carboxylates and acyl carbonium ions). Ketonization reaction is a surface-structure-sensitive reaction, thus reaction activity depends on surface-structure of the metal oxides (such as crystal surfaces and particle size). The concerted function of oxygen anions (Brønsted bases) and unsaturated metal cations (Lewis acids) is crucial for ketonization. The amphoteric oxides show better catalytic activity than pure acidic or basic oxides. Oxygen vacancy formed on the surface of metal oxides is a key factor for high ketonization activity, which can stabilize the reaction product and reduce the activation energy. This paper reviews the progress in ketonization from the aspects of reaction mechanism, and the effects of surface structure, acidity and basicity, and reducibility of metal oxides on ketonization. The β-keto-acids based mechanism and ketene based mechanism will be discussed in detail to understand how does the C—C coupling happen and the fundamental role of α-H. Finally, the importance of surface structure and properties of metal oxides on the carboxylic acids ketonization reaction is explained.
2017, 75(5): 448-452
doi: 10.6023/A17020080
Abstract:
Transition-metal-catalyzed α-vinylation of carbonyl compounds represents one of the most important carbon-carbon bond forming approaches to the synthesis of β, γ-unsaturated ketones, which are versatile synthetic building blocks and key structural motifs appearing in biologically active molecules. For this purpose, a number of methods have been developed by utilizing palladium-catalyzed cross-coupling of vinyl halide with C—H bond α-to carbonyl group. However, the elimination of vinyl halides in the presence of strong base would afford alkynes, which remained inert and therefore resulted in lower yields in the cross-coupling reaction. In recent years, cooperative catalysis merging transition metals and organic molecules represents a powerful strategy and renders numerous efficient transformations successful. Among which, palladium/enamine catalysis has emerged as an efficient method for the direct α-functionalization of ketones or aldehydes. We therefore envisaged that a direct cross-coupling of ketones and vinyl halides in the presence of Pd(0)/amine co-catalyst; the need of weak base would avoid the formation of alkynes through elimination of vinyl halides. Herein, we report a palladium/chiral amino acid co-catalyzed intramolecular α-vinylation reaction of cyclohexanones, which delivers a series of bridged ring compounds under mild reaction conditions in good to excellent yields. The resulting unique bridged ring system is analogous to the important morphan scaffold (2-azabicyclo[3.3.1]nonane), which is core structure existing in many important bioactive natural products. In the meantime, asymmetric version of this reaction was also tested and a number of desired products were achieved in moderate enantioselectivities. A representative procedure for this reaction is as following: To a dried Schlenk tube were added compound 1 (0.2 mmol), chiral amines (0.04 mmol, 20 mol%), K3PO4 (0.3 mmol, 1.5 equiv.), Pd(OAc)2 (0.01 mmol, 5 mol%) and PPh3 (0.024 mmol, 12 mol%) under N2, 2.0 mL THF was then introduced via a syringe. The resulting mixture was stirred at 85 ℃ (oil bath) for 72 h until the reaction was complete (monitored by TLC). The solvent was then removed under vacuum and the residue was purified by flash chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (V/V) to afford the desired product.
Transition-metal-catalyzed α-vinylation of carbonyl compounds represents one of the most important carbon-carbon bond forming approaches to the synthesis of β, γ-unsaturated ketones, which are versatile synthetic building blocks and key structural motifs appearing in biologically active molecules. For this purpose, a number of methods have been developed by utilizing palladium-catalyzed cross-coupling of vinyl halide with C—H bond α-to carbonyl group. However, the elimination of vinyl halides in the presence of strong base would afford alkynes, which remained inert and therefore resulted in lower yields in the cross-coupling reaction. In recent years, cooperative catalysis merging transition metals and organic molecules represents a powerful strategy and renders numerous efficient transformations successful. Among which, palladium/enamine catalysis has emerged as an efficient method for the direct α-functionalization of ketones or aldehydes. We therefore envisaged that a direct cross-coupling of ketones and vinyl halides in the presence of Pd(0)/amine co-catalyst; the need of weak base would avoid the formation of alkynes through elimination of vinyl halides. Herein, we report a palladium/chiral amino acid co-catalyzed intramolecular α-vinylation reaction of cyclohexanones, which delivers a series of bridged ring compounds under mild reaction conditions in good to excellent yields. The resulting unique bridged ring system is analogous to the important morphan scaffold (2-azabicyclo[3.3.1]nonane), which is core structure existing in many important bioactive natural products. In the meantime, asymmetric version of this reaction was also tested and a number of desired products were achieved in moderate enantioselectivities. A representative procedure for this reaction is as following: To a dried Schlenk tube were added compound 1 (0.2 mmol), chiral amines (0.04 mmol, 20 mol%), K3PO4 (0.3 mmol, 1.5 equiv.), Pd(OAc)2 (0.01 mmol, 5 mol%) and PPh3 (0.024 mmol, 12 mol%) under N2, 2.0 mL THF was then introduced via a syringe. The resulting mixture was stirred at 85 ℃ (oil bath) for 72 h until the reaction was complete (monitored by TLC). The solvent was then removed under vacuum and the residue was purified by flash chromatography on silica gel, eluting with ethyl acetate/petroleum ether 1:10 (V/V) to afford the desired product.
2017, 75(5): 453-456
doi: 10.6023/A17030090
Abstract:
Carbon soot containing terbium endohedral fullerenes was prepared by vaporizing a graphite rod filled with Tb4O7 and graphite powder in an electric arc-discharge chamber. After reflux extraction with 1, 2, 4-trichlorobenzene and rotary evaporation of solvent, the residue was ultrasonically dissolved in toluene. The obtained solution was filtered with a 0.2 μm PTFE film, and then subjected to a three-stage high-performance liquid chromatographic (HPLC) isolation process to achieve two individual isomers of Tb@C82. The successful isolation of Tb@C82 isomers was confirmed by matrix-assisted laser desorption time-of-flight mass spectrometry and analytical HPLC. According to their UV-Vis-NIR absorption spectra, the carbon cages of the isolated Tb@C82 isomers are estimated to be of C2v and Cs symmetry, respectively, and Tb atom is encapsulated in carbon cage at a valence state of +3. The cyclic voltammetry (CV) of the two Tb@C82 isomers was recorded in a 0.1 mol/L ortho-dichlorobenzene (o-DCB) solution of tetrabutylammonium hexafluorophosphate (TBAPF6) by referring the ferrocene/ferrocenium couple (Fc/Fc+). The working electrode and the counter electrode were platinum wires, and the reference one was a Ag/AgCl electrode. Tb@C82 (Ⅰ) exhibits two pairs of reversible oxidative and five pairs of reversible reductive peaks, and Tb@C82 (Ⅱ) shows one reversible oxidative and six reversible reductive ones. It is found that the symmetry of C82 cage has little effect on the reduction potentials but great effect on the oxidation potentials of Tb@C82 isomers. Moreover, the first reduction potential of both Tb@C82 isomers is relatively high, indicating that they are good electron accepting materials. Additionally, the corresponding redox potentials of Tb@C82 (Ⅱ) are relatively higher than those of Tb@C82 (Ⅰ), therefore it is concluded that Tb@C82 (Ⅱ) is of better electron accepting ability than Tb@C82 (Ⅰ). In comparison with those reported previously, three pairs of reversible reductive and one pair of reversible oxidative peaks were initially detected for Tb@C82 (Ⅰ), offering more information on the electrochemistry of metallofullerene.
Carbon soot containing terbium endohedral fullerenes was prepared by vaporizing a graphite rod filled with Tb4O7 and graphite powder in an electric arc-discharge chamber. After reflux extraction with 1, 2, 4-trichlorobenzene and rotary evaporation of solvent, the residue was ultrasonically dissolved in toluene. The obtained solution was filtered with a 0.2 μm PTFE film, and then subjected to a three-stage high-performance liquid chromatographic (HPLC) isolation process to achieve two individual isomers of Tb@C82. The successful isolation of Tb@C82 isomers was confirmed by matrix-assisted laser desorption time-of-flight mass spectrometry and analytical HPLC. According to their UV-Vis-NIR absorption spectra, the carbon cages of the isolated Tb@C82 isomers are estimated to be of C2v and Cs symmetry, respectively, and Tb atom is encapsulated in carbon cage at a valence state of +3. The cyclic voltammetry (CV) of the two Tb@C82 isomers was recorded in a 0.1 mol/L ortho-dichlorobenzene (o-DCB) solution of tetrabutylammonium hexafluorophosphate (TBAPF6) by referring the ferrocene/ferrocenium couple (Fc/Fc+). The working electrode and the counter electrode were platinum wires, and the reference one was a Ag/AgCl electrode. Tb@C82 (Ⅰ) exhibits two pairs of reversible oxidative and five pairs of reversible reductive peaks, and Tb@C82 (Ⅱ) shows one reversible oxidative and six reversible reductive ones. It is found that the symmetry of C82 cage has little effect on the reduction potentials but great effect on the oxidation potentials of Tb@C82 isomers. Moreover, the first reduction potential of both Tb@C82 isomers is relatively high, indicating that they are good electron accepting materials. Additionally, the corresponding redox potentials of Tb@C82 (Ⅱ) are relatively higher than those of Tb@C82 (Ⅰ), therefore it is concluded that Tb@C82 (Ⅱ) is of better electron accepting ability than Tb@C82 (Ⅰ). In comparison with those reported previously, three pairs of reversible reductive and one pair of reversible oxidative peaks were initially detected for Tb@C82 (Ⅰ), offering more information on the electrochemistry of metallofullerene.
2017, 75(5): 457-463
doi: 10.6023/A17010008
Abstract:
Although attempts to synthesize divalent uranium molecules were begun three decades ago, molecular U(Ⅱ) species isolable in solution have been not achieved until recent years. In 2013, Evans and co-workers synthesized the first U(Ⅱ) complex, [U(Cp')3]·[K(2, 2, 2-cryptand)] (Cp'=C5H4SiMe3) via flash reduction, that was suitable for X-ray crystal diffraction characterization. A year later, the group of Meyer obtained another divalent uranium complex, [U((Ad, MeArO)3mes)]·[K(2, 2, 2-cryptand)] employing their particularly interesting tris(aryloxide) arene ligand. The 5f36d1 and 5f4 ground states were assigned to these two complexes, respectively, by the jointed experimental/theoretical studies. It was demonstrated that the ligand significantly affect the nature of the ground state of divalent uranium complex by tuning the energetic separation of the 5f and 6d orbitals. Therefore, careful selection of ligand makes it possible to have access to +Ⅱ oxidation state of uranium and prepare new UⅡ complex. A flexible octadentate polypyrrollic Schiff-base macrocycle (H4L) has been developed to complex a variety of metals such as actinides, rare earth and transition metals that show a wide range of size and diverse oxidation states. Both mono-and bimetallic complexes featured with an intriguing "Pacman-like" structure were obtained. For example, the reaction of H4L with a trivalent uranium precursor [(UⅢ)Ⅰ3(THF)4] yielded a neutral [(UⅣ)(L)] complex, where the uranium ion was determined by the single crystal X-ray diffraction to be situated inside the ligand mouth and held by eight nitrogen atoms together. The +Ⅳ oxidation state was assigned to the uranium by presuming dihydrogen elimination. Considering the flexibility, tetravalent-anion nature as well as capability of accommodating bimetallic ions and stabilizing various oxidation states of uranium (e.g. Ⅲ~Ⅵ complexes have been found so far) that the polypyrrolic ligand has exhibited in previously synthesized complexes, two divalent uranium ions would be likely complexated by the ligand to generate a complex, [(UⅡ)2(L)]. In addition to enriching the coordination chemistry of U(Ⅱ), it is also a good example to explore electronic structures of the low-valent uranium complex and unravel the uranium-uranium multiple bonding nature. Although many theoretical studies have explored uranium complexes, the study focusing on the divalent diuranium complex of a single macrocyclic ligand remains rare. In the work, a relativistic density functional theory has been employed to investigate [(UⅡ)2(L)]. The structures in electron spin states (singlet, triplet, quintet, septet and nonet) were optimized. Short distances of U—U (2.32~2.67 Å), large bond order (2.95~3.90) and high stretching vibrational frequencies (180~263 cm-1) were calculated. Energetic calculations find that its triplet state is the ground state. It has the electronic configuration of π4σ2δ2, primarily contributed by U(5f) character. Structural and molecular-orbital analyses suggest a slightly weak uranium-uranium quadruple bond, which is confirmed by the quantum theory of atoms in molecule (QTAIM) calculations. Further comparison with analogues [(UⅢ)2(L)]2+ and [(UⅣ)2(L)]4+ was also addressed. It is found that the uranium oxidation state is able to tune the energetic matching between the highest-energy occupied orbital of ligand and the adjacent low-energy metal-based orbital, as well as correlates with the electron transfer between metal and ligand and the diuranium multiple bond number.
Although attempts to synthesize divalent uranium molecules were begun three decades ago, molecular U(Ⅱ) species isolable in solution have been not achieved until recent years. In 2013, Evans and co-workers synthesized the first U(Ⅱ) complex, [U(Cp')3]·[K(2, 2, 2-cryptand)] (Cp'=C5H4SiMe3) via flash reduction, that was suitable for X-ray crystal diffraction characterization. A year later, the group of Meyer obtained another divalent uranium complex, [U((Ad, MeArO)3mes)]·[K(2, 2, 2-cryptand)] employing their particularly interesting tris(aryloxide) arene ligand. The 5f36d1 and 5f4 ground states were assigned to these two complexes, respectively, by the jointed experimental/theoretical studies. It was demonstrated that the ligand significantly affect the nature of the ground state of divalent uranium complex by tuning the energetic separation of the 5f and 6d orbitals. Therefore, careful selection of ligand makes it possible to have access to +Ⅱ oxidation state of uranium and prepare new UⅡ complex. A flexible octadentate polypyrrollic Schiff-base macrocycle (H4L) has been developed to complex a variety of metals such as actinides, rare earth and transition metals that show a wide range of size and diverse oxidation states. Both mono-and bimetallic complexes featured with an intriguing "Pacman-like" structure were obtained. For example, the reaction of H4L with a trivalent uranium precursor [(UⅢ)Ⅰ3(THF)4] yielded a neutral [(UⅣ)(L)] complex, where the uranium ion was determined by the single crystal X-ray diffraction to be situated inside the ligand mouth and held by eight nitrogen atoms together. The +Ⅳ oxidation state was assigned to the uranium by presuming dihydrogen elimination. Considering the flexibility, tetravalent-anion nature as well as capability of accommodating bimetallic ions and stabilizing various oxidation states of uranium (e.g. Ⅲ~Ⅵ complexes have been found so far) that the polypyrrolic ligand has exhibited in previously synthesized complexes, two divalent uranium ions would be likely complexated by the ligand to generate a complex, [(UⅡ)2(L)]. In addition to enriching the coordination chemistry of U(Ⅱ), it is also a good example to explore electronic structures of the low-valent uranium complex and unravel the uranium-uranium multiple bonding nature. Although many theoretical studies have explored uranium complexes, the study focusing on the divalent diuranium complex of a single macrocyclic ligand remains rare. In the work, a relativistic density functional theory has been employed to investigate [(UⅡ)2(L)]. The structures in electron spin states (singlet, triplet, quintet, septet and nonet) were optimized. Short distances of U—U (2.32~2.67 Å), large bond order (2.95~3.90) and high stretching vibrational frequencies (180~263 cm-1) were calculated. Energetic calculations find that its triplet state is the ground state. It has the electronic configuration of π4σ2δ2, primarily contributed by U(5f) character. Structural and molecular-orbital analyses suggest a slightly weak uranium-uranium quadruple bond, which is confirmed by the quantum theory of atoms in molecule (QTAIM) calculations. Further comparison with analogues [(UⅢ)2(L)]2+ and [(UⅣ)2(L)]4+ was also addressed. It is found that the uranium oxidation state is able to tune the energetic matching between the highest-energy occupied orbital of ligand and the adjacent low-energy metal-based orbital, as well as correlates with the electron transfer between metal and ligand and the diuranium multiple bond number.
2017, 75(5): 473-478
doi: 10.6023/A17020068
Abstract:
Microporous organic polymers (MOPs) have drawn much attention because of their potential applications such as gas storage, separation and heterogeneous catalysis. There is great interest in the design, synthesis and property evaluation of poly(arylene ethynylenes) (PAEs) with intrinsic microporosity. In addition to Sonogashira coupling reaction between terminal alkynes and halides, the oxidative dimerization of terminal alkynes is an alternating strategy for the buildup of the microporous PAE frameworks. In this paper, a series of MOPs were synthesized by the oxidative dimerization of terminal alkynes using triethynyl monomers such as tris(4-ethynylphenyl)amine, tris(4-ethynylphenyl)methylsilane and polytris(4-ethynylphenyl)phenylsilane. The resulting MOPs were characterized by FT-IR spectra, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD) measurements. FT-IR spectra indicate the success of the homocoupling reaction for constructing the dialkyne-bridged polymer frameworks. These polymer frameworks exhibit high thermal stability with onset of decomposition temperature above 350 ℃ at 5% mass loss under nitrogen flow. PXRD and TEM measurements revealed that all the polymer frameworks are amorphous solid in nature. These dialkyne-bridged MOPs exhibit moderate surface areas ranging from 602 to 715 m2·g-1. The incorporation of triphenylamine moieties into the polymer skeleton increases the number of electron donating basic nitrogen sites in the porous frameworks. Thus, the triphenylamine-based polymer polytris(4-ethynylphenyl)amine (TEPA-MOP) with the highest Brunauer-Emmett-Teller (BET) surface area shows the highest CO2 uptake capacity of 1.59 mmol·g-1 at 273 K and 1.13 bar among the resulting polymer frameworks. In addition, TEPA-MOP showed the highest H2 adsorption up to 1.04 wt% at 1.13 bar and 77 K and polytris(4-ethynylphenyl)phenylsilane (TEPP-MOP) displayed the lowest H2 adsorption of 0.64 wt% at the same conditions. As for separation of CO2, both TEPA-MOP and TEPP-MOP exhibit relatively high CO2-over-N2 selectivities of 69.9 and 73.2 at 273 K, respectively. The above results show that TEPA-MOP might be the good candidate for the balanced CO2 uptake capacity with impressive CO2/N2 selectivity among the microporous PAE frameworks.
Microporous organic polymers (MOPs) have drawn much attention because of their potential applications such as gas storage, separation and heterogeneous catalysis. There is great interest in the design, synthesis and property evaluation of poly(arylene ethynylenes) (PAEs) with intrinsic microporosity. In addition to Sonogashira coupling reaction between terminal alkynes and halides, the oxidative dimerization of terminal alkynes is an alternating strategy for the buildup of the microporous PAE frameworks. In this paper, a series of MOPs were synthesized by the oxidative dimerization of terminal alkynes using triethynyl monomers such as tris(4-ethynylphenyl)amine, tris(4-ethynylphenyl)methylsilane and polytris(4-ethynylphenyl)phenylsilane. The resulting MOPs were characterized by FT-IR spectra, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD) measurements. FT-IR spectra indicate the success of the homocoupling reaction for constructing the dialkyne-bridged polymer frameworks. These polymer frameworks exhibit high thermal stability with onset of decomposition temperature above 350 ℃ at 5% mass loss under nitrogen flow. PXRD and TEM measurements revealed that all the polymer frameworks are amorphous solid in nature. These dialkyne-bridged MOPs exhibit moderate surface areas ranging from 602 to 715 m2·g-1. The incorporation of triphenylamine moieties into the polymer skeleton increases the number of electron donating basic nitrogen sites in the porous frameworks. Thus, the triphenylamine-based polymer polytris(4-ethynylphenyl)amine (TEPA-MOP) with the highest Brunauer-Emmett-Teller (BET) surface area shows the highest CO2 uptake capacity of 1.59 mmol·g-1 at 273 K and 1.13 bar among the resulting polymer frameworks. In addition, TEPA-MOP showed the highest H2 adsorption up to 1.04 wt% at 1.13 bar and 77 K and polytris(4-ethynylphenyl)phenylsilane (TEPP-MOP) displayed the lowest H2 adsorption of 0.64 wt% at the same conditions. As for separation of CO2, both TEPA-MOP and TEPP-MOP exhibit relatively high CO2-over-N2 selectivities of 69.9 and 73.2 at 273 K, respectively. The above results show that TEPA-MOP might be the good candidate for the balanced CO2 uptake capacity with impressive CO2/N2 selectivity among the microporous PAE frameworks.
2017, 75(5): 479-484
doi: 10.6023/A17010031
Abstract:
Siliceous MCM-41 (Si-MCM-41), two micro-mesoporous materials obtained either by physically mixing Si-MCM-41 with HZSM-5 zeolite (Z-MCM-41-M) or by coating Si-MCM-41 over HZSM-5 zeolite particles (Z-MCM-41), were prepared and characterized by means of XRD, N2 adsorption-desorption, pyridine adsorbed FT-IR. The hydrodesulfurization (HDS) performances of the supported Pd catalysts thereof, were evaluated with dibenzothiophene (DBT) as the model sulfur-containing molecule. The close relationship between the surface area of the support and the HDS performance for the supported Pd catalysts was not observed. The result indicated that the surface area of the support or the dispersion of the catalyst might not be the key parameter affecting the HDS performance of the supported Pd catalyst. However, the HDS performances of Pd catalysts were significantly influenced by the pore structures and acid properties of the supports. Pd catalysts supported on the acidic supports showed the enhancement of HDS and hydrogenation activities that was thought to be the effect of hydrogen spillover. Among the catalysts studied, Pd/Z-MCM-41 exhibited the highest HDS activity and excellent hydrogenation activities. The results demonstrated that mesoporous materials introducing to microporous zeolite was beneficial to the improvement of HDS activities, but only physically mixing Si-MCM-41 with HZSM-5 zeolite couldn't show the combination advantage of pore of mesoporous materials and acid properties of microporous zeolite, and further generate better synergistic catalytic action. Z-MCM-41 composite material with the regular structure and uniform distribution acidity was potential carriers for precious metal catalysts.
Siliceous MCM-41 (Si-MCM-41), two micro-mesoporous materials obtained either by physically mixing Si-MCM-41 with HZSM-5 zeolite (Z-MCM-41-M) or by coating Si-MCM-41 over HZSM-5 zeolite particles (Z-MCM-41), were prepared and characterized by means of XRD, N2 adsorption-desorption, pyridine adsorbed FT-IR. The hydrodesulfurization (HDS) performances of the supported Pd catalysts thereof, were evaluated with dibenzothiophene (DBT) as the model sulfur-containing molecule. The close relationship between the surface area of the support and the HDS performance for the supported Pd catalysts was not observed. The result indicated that the surface area of the support or the dispersion of the catalyst might not be the key parameter affecting the HDS performance of the supported Pd catalyst. However, the HDS performances of Pd catalysts were significantly influenced by the pore structures and acid properties of the supports. Pd catalysts supported on the acidic supports showed the enhancement of HDS and hydrogenation activities that was thought to be the effect of hydrogen spillover. Among the catalysts studied, Pd/Z-MCM-41 exhibited the highest HDS activity and excellent hydrogenation activities. The results demonstrated that mesoporous materials introducing to microporous zeolite was beneficial to the improvement of HDS activities, but only physically mixing Si-MCM-41 with HZSM-5 zeolite couldn't show the combination advantage of pore of mesoporous materials and acid properties of microporous zeolite, and further generate better synergistic catalytic action. Z-MCM-41 composite material with the regular structure and uniform distribution acidity was potential carriers for precious metal catalysts.
2017, 75(5): 485-493
doi: 10.6023/A17010012
Abstract:
With the renewable biopolymer chitosan (CTS) as a structure directing agent and organic precursor, facile coprecipitation method was applied for the cobalt and iron nitrates in solution to prepare CTS/cobalt iron layered double hydroxides composite. The LDHs sample was calcinated in a tubular furnace under Ar atmosphere via heating ramps of 5 ℃· min-1 from room temperature to 200 ℃ and kept for 1 h, then heated to 600 ℃ and remained for 2 h. After the sample was cooled naturally to room temperature, it was heated again to 250 ℃ under air atmosphere and kept for 12 h to oxidize the transition metal elements. As a result, nitrogen-doped partially graphitized carbon/cobalt iron transition metal oxides nanocomposite (N-PGC/CoFe-TMOs) was obtained. X-ray diffraction, Raman spectroscopy, N2 adsorption-desorption analysis, scanning electron microscopy, high resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy were carried out to characterize the structure, morphology and elemental composition of the product. Cyclic voltammetry and galvanostatic charge-discharge measurements were conducted to evaluate the electrochemical properties of N-PGC/CoFe-TMOs. Experimental results showed that the CTS precursor was converted into partially graphitized carbon by pyrolysis with the help of catalysis graphitization action of transition metal elements. At the same time, the derived carbon material was successfully doped with nitrogen in situ and the N/C atomic ratio was about 1/18. N-PGC/CoFe-TMOs possessed bimodal porous texture including macropores and mesopores, exhibited combined characters of electrical double-layer supercapacitor and pseudocapacitor when used as supercapacitor electrode material. At the current density of 2 A·g-1, N-PGC/CoFe-TMOs composite delivered a large discharge capacity of 671.1 F·g-1, far higher than 283.3 F·g-1 of pure cobalt iron oxides, indicating the typical synergistic effect between nitrogen-doped partially graphitized carbon and transition metal oxides. Even at the high current density of 10 A·g-1, N-PGC/CoFe-TMOs composite still remained a specific capacity of 573.3 F·g-1. After 5000 charge-discharge cycles at 10 A·g-1, the capacitance retention was 66.4%. The reported synthesis method in this work is simple and universal, and calcination process combines the nitrogen-doping, partially graphitized carbon formation with redox-active transition metal oxides synthesis in one step, endowing the product with excellent electrochemical properties.
With the renewable biopolymer chitosan (CTS) as a structure directing agent and organic precursor, facile coprecipitation method was applied for the cobalt and iron nitrates in solution to prepare CTS/cobalt iron layered double hydroxides composite. The LDHs sample was calcinated in a tubular furnace under Ar atmosphere via heating ramps of 5 ℃· min-1 from room temperature to 200 ℃ and kept for 1 h, then heated to 600 ℃ and remained for 2 h. After the sample was cooled naturally to room temperature, it was heated again to 250 ℃ under air atmosphere and kept for 12 h to oxidize the transition metal elements. As a result, nitrogen-doped partially graphitized carbon/cobalt iron transition metal oxides nanocomposite (N-PGC/CoFe-TMOs) was obtained. X-ray diffraction, Raman spectroscopy, N2 adsorption-desorption analysis, scanning electron microscopy, high resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy were carried out to characterize the structure, morphology and elemental composition of the product. Cyclic voltammetry and galvanostatic charge-discharge measurements were conducted to evaluate the electrochemical properties of N-PGC/CoFe-TMOs. Experimental results showed that the CTS precursor was converted into partially graphitized carbon by pyrolysis with the help of catalysis graphitization action of transition metal elements. At the same time, the derived carbon material was successfully doped with nitrogen in situ and the N/C atomic ratio was about 1/18. N-PGC/CoFe-TMOs possessed bimodal porous texture including macropores and mesopores, exhibited combined characters of electrical double-layer supercapacitor and pseudocapacitor when used as supercapacitor electrode material. At the current density of 2 A·g-1, N-PGC/CoFe-TMOs composite delivered a large discharge capacity of 671.1 F·g-1, far higher than 283.3 F·g-1 of pure cobalt iron oxides, indicating the typical synergistic effect between nitrogen-doped partially graphitized carbon and transition metal oxides. Even at the high current density of 10 A·g-1, N-PGC/CoFe-TMOs composite still remained a specific capacity of 573.3 F·g-1. After 5000 charge-discharge cycles at 10 A·g-1, the capacitance retention was 66.4%. The reported synthesis method in this work is simple and universal, and calcination process combines the nitrogen-doping, partially graphitized carbon formation with redox-active transition metal oxides synthesis in one step, endowing the product with excellent electrochemical properties.
2017, 75(5): 494-500
doi: 10.6023/A16100559
Abstract:
Enoyl-CoA hydratase (ECH), which is also known as crotonase, is the second requisite enzyme in the β-oxidation pathway of fatty acid that catalyzes the syn hydration of α, β-unsaturated thiolester substrates. In this work, ECH-catalyzed hydration mechanisms of DAC-CoA and Crotonyl-CoA were investigated using density functional theory (DFT) methods. Geometrical structures were optimized using Gaussian 03 program at the B3LYP/6-31G(d, p) level of theory. Frequency calculations were performed with the 6-31G(d, p) basis set to obtain zero-point vibrational energies (ZPEs) and to confirm the nature of all the stationary points that have no imaginary frequency for the local minima and have only one imaginary frequency for the saddle points. The single-point calculations on the optimized geometries were further performed with 6-311++G(2d, 2p) basis set to obtain more accurate energies. The polarizable-continuum model (PCM) with the dielectric constant of 4 was used to calculate the single point energies at 6-311++G(2d, p) level on all the optimized geometries to consider the effects of enzymatic environment that was not included in the computational model. Considering that B3LYP functional lacks the proper description of the long-range dispersion interactions, we further used the DFT-D3 program to calculate the empirical dispersion correction to correct the B3LYP energies. The final energies reported in this work are the single-point energies corrected for ZPEs, solvation and dispersion effects. The calculated results suggested that hydration proceeds through a stepwise mechanism, involving an enolate intermediate. Glu164 functions as the sole base/acid for catalysis. Although Glu144 is not directly involved in hydration, it induces the catalytic water molecule to locate an ideal orientation to attack the double bond of substrate by the hydrogen-bonding interaction. Crotonyl-CoA shows higher hydration activity than DAC-CoA. The backbone NH groups of Ala98 and Gly141 form an oxyanion hole with substrate carbonyl oxygen, which play key roles in binding substrate and stabilizing the generated transition states and intermediates. In addition, the hydrogen-bonding networks surrounding Glu144 and Glu164 are of great importance for active site arrangement.
Enoyl-CoA hydratase (ECH), which is also known as crotonase, is the second requisite enzyme in the β-oxidation pathway of fatty acid that catalyzes the syn hydration of α, β-unsaturated thiolester substrates. In this work, ECH-catalyzed hydration mechanisms of DAC-CoA and Crotonyl-CoA were investigated using density functional theory (DFT) methods. Geometrical structures were optimized using Gaussian 03 program at the B3LYP/6-31G(d, p) level of theory. Frequency calculations were performed with the 6-31G(d, p) basis set to obtain zero-point vibrational energies (ZPEs) and to confirm the nature of all the stationary points that have no imaginary frequency for the local minima and have only one imaginary frequency for the saddle points. The single-point calculations on the optimized geometries were further performed with 6-311++G(2d, 2p) basis set to obtain more accurate energies. The polarizable-continuum model (PCM) with the dielectric constant of 4 was used to calculate the single point energies at 6-311++G(2d, p) level on all the optimized geometries to consider the effects of enzymatic environment that was not included in the computational model. Considering that B3LYP functional lacks the proper description of the long-range dispersion interactions, we further used the DFT-D3 program to calculate the empirical dispersion correction to correct the B3LYP energies. The final energies reported in this work are the single-point energies corrected for ZPEs, solvation and dispersion effects. The calculated results suggested that hydration proceeds through a stepwise mechanism, involving an enolate intermediate. Glu164 functions as the sole base/acid for catalysis. Although Glu144 is not directly involved in hydration, it induces the catalytic water molecule to locate an ideal orientation to attack the double bond of substrate by the hydrogen-bonding interaction. Crotonyl-CoA shows higher hydration activity than DAC-CoA. The backbone NH groups of Ala98 and Gly141 form an oxyanion hole with substrate carbonyl oxygen, which play key roles in binding substrate and stabilizing the generated transition states and intermediates. In addition, the hydrogen-bonding networks surrounding Glu144 and Glu164 are of great importance for active site arrangement.
2017, 75(5): 501-507
doi: 10.6023/A16110594
Abstract:
Layered Ni-rich compound LiNi0.5Co0.2Mn0.3O2 has drawn considerable attention recently because high Ni content contributes to the improvement of specific capacity and the reduction of cost. However, it is a challenge to obtain the Ni-rich LiNi0.5Co0.2Mn0.3O2 cathode with both high rate performance and high tap density because the rate capability is often improved at the expense of volumetric energy density, which is mostly dependent on the tap density. In our work, an uniform Ni-rich LiNi0.5Co0.2Mn0.3O2 microsphere with an average diameter of ca. 5 μm and tap density of 2.1 g·cm-3 was successfully prepared using carbonate co-precipitation method, which can meet the commercial requirement for lithium-ion batteries (tap density≥2.1 g·cm-3, Lithium Nickel Cobalt Manganese Oxides from CETC International Co., Ltd). In this synthetic route, the 2 mol·L-1 mixture of NiSO4·6H2O, MnSO4·H2O and CoSO4·7H2O (Ni:Co:Mn=5:2:3, molar ratio) are the starting materials, 2 mol·L-1 Na2CO3 and 4 mol·L-1 NH3·H2O are the precipitant and chelating agent, respectively. In order to achieve high tap density, the stirring speed of continuous stirred tank reactor (CSTR) is as high as 1500 r/min, and the powder was preheated at 550 ℃ for 6 h and then calcined at 850 ℃ for 14 h in flowing oxygen. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) results indicate that the microsphere LiNi0.5Co0.2Mn0.3O2 material has a well-ordered α-NaFeO2 structure with stable in-plane [\begin{document}$ \sqrt 3 $\end{document} \begin{document}$ \sqrt 3 $\end{document}
Layered Ni-rich compound LiNi0.5Co0.2Mn0.3O2 has drawn considerable attention recently because high Ni content contributes to the improvement of specific capacity and the reduction of cost. However, it is a challenge to obtain the Ni-rich LiNi0.5Co0.2Mn0.3O2 cathode with both high rate performance and high tap density because the rate capability is often improved at the expense of volumetric energy density, which is mostly dependent on the tap density. In our work, an uniform Ni-rich LiNi0.5Co0.2Mn0.3O2 microsphere with an average diameter of ca. 5 μm and tap density of 2.1 g·cm-3 was successfully prepared using carbonate co-precipitation method, which can meet the commercial requirement for lithium-ion batteries (tap density≥2.1 g·cm-3, Lithium Nickel Cobalt Manganese Oxides from CETC International Co., Ltd). In this synthetic route, the 2 mol·L-1 mixture of NiSO4·6H2O, MnSO4·H2O and CoSO4·7H2O (Ni:Co:Mn=5:2:3, molar ratio) are the starting materials, 2 mol·L-1 Na2CO3 and 4 mol·L-1 NH3·H2O are the precipitant and chelating agent, respectively. In order to achieve high tap density, the stirring speed of continuous stirred tank reactor (CSTR) is as high as 1500 r/min, and the powder was preheated at 550 ℃ for 6 h and then calcined at 850 ℃ for 14 h in flowing oxygen. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) results indicate that the microsphere LiNi0.5Co0.2Mn0.3O2 material has a well-ordered α-NaFeO2 structure with stable in-plane [
2017, 75(5): 508-513
doi: 10.6023/A16110641
Abstract:
In this work, the reaction mechanism of photocatalytic oxidation of sacrificial ethanol during water-splitting process by titanium dioxide (TiO2) has been studied. The pure rutile TiO2 or mixed-phase structure titania (P25) was employed as the typical photocatalyst in ethanol oxidation. The as-obtained results showed that the formation of 2, 3-butanediol over TiO2 in heterogeneous systems is mainly due to the photochemical reaction proceeded between acetaldehyde molecule and ethanol molecule instead of the direct coupling of α-hydroxyethyl radicals. This is different from the early work claimed that the fundamental process to produce 2, 3-butanediol is based on the direct coupling of α-hydroxyethyl radicals generated by TiO2 oxidation. The photochemical reaction between acetaldehyde molecule and ethanol molecule to form 2, 3-butanediol can also occur when the concentration of the solid catalyst was reduced to certain degree if using P25 as catalyst in heterogeneous model, and the selectivity of 2, 3-butanediol would change from ca. 60% to 0% when enlarging the concentration of P25 step by step. However, the selectivity of 2, 3-butanediol is relatively invariable when the concentration of catalyst was changed if using rutile as photocatalyst. We thought that the distinct diffusing behaviors for mobile ·OHf and surface bound ·OHs generated on different titania can explain the varied selectivity when the solid concentration of TiO2 changed. The generation and diffusion of ·OH from the surface of P25 (80% anatase) to bulk solution is a key process to inhibit the direct coupling of α-hydroxyethyl radicals to produce acetaldehyde or further overoxidation products, and the reaction zone of ·OHf depends on the concentration of P25. For the case of rutile TiO2 promoted reaction, the lack of mobile ·OHf on rutile TiO2 makes the photochemical reaction between acetaldehyde molecule and ethanol molecule more facile to occur in bulk solution since the surface bound ·OHs can only have chance to attack the surface adsorbed substrates. This may be an important reason to explain why the selectivity of 2, 3-butanediol in ethanol oxidation was not influenced significantly by the variation of rutile TiO2 concentration. All the results regarding ethanol transformation during photocatalytic process achieved here cast some light on the mechanistic understanding of the reactions proceeded on the surface of solid catalyst in heterogeneous model and in the bulk solution when both catalytic step and photochemical step existed simultaneously.
In this work, the reaction mechanism of photocatalytic oxidation of sacrificial ethanol during water-splitting process by titanium dioxide (TiO2) has been studied. The pure rutile TiO2 or mixed-phase structure titania (P25) was employed as the typical photocatalyst in ethanol oxidation. The as-obtained results showed that the formation of 2, 3-butanediol over TiO2 in heterogeneous systems is mainly due to the photochemical reaction proceeded between acetaldehyde molecule and ethanol molecule instead of the direct coupling of α-hydroxyethyl radicals. This is different from the early work claimed that the fundamental process to produce 2, 3-butanediol is based on the direct coupling of α-hydroxyethyl radicals generated by TiO2 oxidation. The photochemical reaction between acetaldehyde molecule and ethanol molecule to form 2, 3-butanediol can also occur when the concentration of the solid catalyst was reduced to certain degree if using P25 as catalyst in heterogeneous model, and the selectivity of 2, 3-butanediol would change from ca. 60% to 0% when enlarging the concentration of P25 step by step. However, the selectivity of 2, 3-butanediol is relatively invariable when the concentration of catalyst was changed if using rutile as photocatalyst. We thought that the distinct diffusing behaviors for mobile ·OHf and surface bound ·OHs generated on different titania can explain the varied selectivity when the solid concentration of TiO2 changed. The generation and diffusion of ·OH from the surface of P25 (80% anatase) to bulk solution is a key process to inhibit the direct coupling of α-hydroxyethyl radicals to produce acetaldehyde or further overoxidation products, and the reaction zone of ·OHf depends on the concentration of P25. For the case of rutile TiO2 promoted reaction, the lack of mobile ·OHf on rutile TiO2 makes the photochemical reaction between acetaldehyde molecule and ethanol molecule more facile to occur in bulk solution since the surface bound ·OHs can only have chance to attack the surface adsorbed substrates. This may be an important reason to explain why the selectivity of 2, 3-butanediol in ethanol oxidation was not influenced significantly by the variation of rutile TiO2 concentration. All the results regarding ethanol transformation during photocatalytic process achieved here cast some light on the mechanistic understanding of the reactions proceeded on the surface of solid catalyst in heterogeneous model and in the bulk solution when both catalytic step and photochemical step existed simultaneously.
2017, 75(5): 464-472
doi: 10.6023/A17020074
Abstract:
Three donor-acceptor polymers PBT2F-TT-a, PBT2F-TT and PBT2F-Se were synthesized via Stille cross-coupling reaction with 5, 6-difluoro-benzo[1, 2, 5]thiadiazole as the acceptor, and 2, 5-bis-(2-octyl-dodecyloxy)-1, 4-di(thieno[3, 2-b]thiophen-2-yl)-benzene and 2, 5-bis-(2-octyl-dodecyloxy)-1, 4-di(selenophen-2-yl)-benzene as the donors. The conjugated backbones of these polymers were decorated with alkoxyl groups to achieve the chain planarity through S…O and Se…O intramolecular interactions. Furthermore, the intramolecular F…H interaction was helpful to minimize the torsional angles. These three polymers were characterized by UV-vis absorption spectroscopy, thermal gravimetric analysis, cyclic voltammetry, gel permeation chromatography and elemental analysis. All the polymers showed intense absorption in the visible range and demonstrated suitable ELUMO and EHOMO, which match well with the fullerene-based acceptor. Thus these three polymers were applied as donors and incorporated with PC71BM as active materials in bulk heterojunction polymer solar cells (PSCs). Polymers PBT2F-TT-a and PBT2F-TT are constructed with the same monomers and the latter has a high molecular weight. A notable enhancement in PCE from 3.48% to 4.22% was observed as the molecular weight was increased from 6.79 kDa (PBT2F-TT-a) to 10.36 kDa (PBT2F-TT). The effect of diphenyl ether (DPE) additive on photovoltaic performance of PSCs based on these polymers has been comprehensively investigated by means of atomic force microscopy (AFM), transmission electron microscopy (TEM), alternating current impedance spectrometry (ACIS), space-charge-limited current (SCLC) analysis and short circuit current density -light intensity (JSC-Plight) measurement. As revealed by AFM and TEM measurement, PBT2F-Se:PC71BM blend with DPE exhibited a nanoscale phase separation dominated with fibrillar structures. On the other hand, the charge carrier mobilities of these blend films were greatly increased after the addition of DPE, giving rise to enhanced photovoltaic performances. Furthermore, the dramatic increase in JSC of PBT2F-Se-based devices should also benefit from the well-balanced hole and electron mobilities as revealed by SCLC results. Interestingly, JSC-Plight measurement suggested the weak bimolecular recombination for these devices without and with the addition of DPE. PSCs based on PBT2F-TT-a, PBT2F-TT, and PBT2F-Se showed good power conversion efficiency. Particularly, PBT2F-Se: PC71BM blend with DPE exhibited a good device performance with JSC of 10.75 mA/cm2, VOC of 0.72 V and PCE of 4.18%.
Three donor-acceptor polymers PBT2F-TT-a, PBT2F-TT and PBT2F-Se were synthesized via Stille cross-coupling reaction with 5, 6-difluoro-benzo[1, 2, 5]thiadiazole as the acceptor, and 2, 5-bis-(2-octyl-dodecyloxy)-1, 4-di(thieno[3, 2-b]thiophen-2-yl)-benzene and 2, 5-bis-(2-octyl-dodecyloxy)-1, 4-di(selenophen-2-yl)-benzene as the donors. The conjugated backbones of these polymers were decorated with alkoxyl groups to achieve the chain planarity through S…O and Se…O intramolecular interactions. Furthermore, the intramolecular F…H interaction was helpful to minimize the torsional angles. These three polymers were characterized by UV-vis absorption spectroscopy, thermal gravimetric analysis, cyclic voltammetry, gel permeation chromatography and elemental analysis. All the polymers showed intense absorption in the visible range and demonstrated suitable ELUMO and EHOMO, which match well with the fullerene-based acceptor. Thus these three polymers were applied as donors and incorporated with PC71BM as active materials in bulk heterojunction polymer solar cells (PSCs). Polymers PBT2F-TT-a and PBT2F-TT are constructed with the same monomers and the latter has a high molecular weight. A notable enhancement in PCE from 3.48% to 4.22% was observed as the molecular weight was increased from 6.79 kDa (PBT2F-TT-a) to 10.36 kDa (PBT2F-TT). The effect of diphenyl ether (DPE) additive on photovoltaic performance of PSCs based on these polymers has been comprehensively investigated by means of atomic force microscopy (AFM), transmission electron microscopy (TEM), alternating current impedance spectrometry (ACIS), space-charge-limited current (SCLC) analysis and short circuit current density -light intensity (JSC-Plight) measurement. As revealed by AFM and TEM measurement, PBT2F-Se:PC71BM blend with DPE exhibited a nanoscale phase separation dominated with fibrillar structures. On the other hand, the charge carrier mobilities of these blend films were greatly increased after the addition of DPE, giving rise to enhanced photovoltaic performances. Furthermore, the dramatic increase in JSC of PBT2F-Se-based devices should also benefit from the well-balanced hole and electron mobilities as revealed by SCLC results. Interestingly, JSC-Plight measurement suggested the weak bimolecular recombination for these devices without and with the addition of DPE. PSCs based on PBT2F-TT-a, PBT2F-TT, and PBT2F-Se showed good power conversion efficiency. Particularly, PBT2F-Se: PC71BM blend with DPE exhibited a good device performance with JSC of 10.75 mA/cm2, VOC of 0.72 V and PCE of 4.18%.
