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2016 Volume 74 Issue 8
2016, 74(8): 639-648
doi: 10.6023/A16040172
Abstract:
Metal-based photonic crystals (PCs), which provide a unique optic-electric properties based on its intrinsic characteristic, is of great significance for the applications in the field of new energy system, such as solar cells, water electrolysis, light emitting diode (LED), etc. This article reviews the research progress of the metal-based PC, including the fabrication method, property investigation and the relative applications. Metal-based PCs are generally fabricated from the building blocks of metal, metal oxide or their composites materials. The fabrication method refers to the bottom up and top down approach. Bottom up approach covers the self-assembly of the metal nanoparticles directly or infiltrating the nanoparticles into the opal template and the subsequent removal of the template toward the metal-based inverse opals. Top down approach refers to the lithography and deposition. The lithography approach includes laser lithography, reaction ion etching, etc. And the deposition method covers physical vapor deposition, atomic layer deposition, pulsed laser deposition, etc. Furthermore, the metal-based PCs demonstrate many excellent properties based on the combination of the light manipulation property of PCs and the intrinsic property of the metal materials. For example, the materials showed surface-enhanced Raman effect, which can provide special optic signal and demonstrate the application in high-sensitive detecting of organic molecules. The combination of Plasmon effect of metal particles and photonic stopband of the PCs can improve the emission intensity, which is significant for the application in high efficient detecting of special material. Otherwise, the stopband of metal-based PCs is beneficial for the improvement of the optic adsorbent property and photoluminescence property. Furthermore, the combination of metal materials and its suitable stopband can amplify its optic-electronic property, sensing property and the optic-catalytic behavior. Finally, the potential applications of metal-based PCs on the new energy system is put forward. Typically, it was used as optic-electric materials in solar cell, water electrolysis, and high efficient LED. This review will provide an important insight for the new energy development and potential utilization.
Metal-based photonic crystals (PCs), which provide a unique optic-electric properties based on its intrinsic characteristic, is of great significance for the applications in the field of new energy system, such as solar cells, water electrolysis, light emitting diode (LED), etc. This article reviews the research progress of the metal-based PC, including the fabrication method, property investigation and the relative applications. Metal-based PCs are generally fabricated from the building blocks of metal, metal oxide or their composites materials. The fabrication method refers to the bottom up and top down approach. Bottom up approach covers the self-assembly of the metal nanoparticles directly or infiltrating the nanoparticles into the opal template and the subsequent removal of the template toward the metal-based inverse opals. Top down approach refers to the lithography and deposition. The lithography approach includes laser lithography, reaction ion etching, etc. And the deposition method covers physical vapor deposition, atomic layer deposition, pulsed laser deposition, etc. Furthermore, the metal-based PCs demonstrate many excellent properties based on the combination of the light manipulation property of PCs and the intrinsic property of the metal materials. For example, the materials showed surface-enhanced Raman effect, which can provide special optic signal and demonstrate the application in high-sensitive detecting of organic molecules. The combination of Plasmon effect of metal particles and photonic stopband of the PCs can improve the emission intensity, which is significant for the application in high efficient detecting of special material. Otherwise, the stopband of metal-based PCs is beneficial for the improvement of the optic adsorbent property and photoluminescence property. Furthermore, the combination of metal materials and its suitable stopband can amplify its optic-electronic property, sensing property and the optic-catalytic behavior. Finally, the potential applications of metal-based PCs on the new energy system is put forward. Typically, it was used as optic-electric materials in solar cell, water electrolysis, and high efficient LED. This review will provide an important insight for the new energy development and potential utilization.
2016, 74(8): 649-656
doi: 10.6023/A16050252
Abstract:
Being an important part of polymer science, the single chain conformation and aggregation structure in polymer solution has been widely studied by many experiential exponential laws. In the review, several kinds of commonly used exponential laws were summarized, and the use in the study of shape characteristics of complex single chain and aggregation was introduced. The aggregation structure and morphology of films can be controlled by precursor solution, so deep understanding to the intrinsic properties of precursor solution is particularly important. Combined with the electron microscope, spectra, etc., the exponential law can be used to further study the single chain, aggregation size and morphology, structure evolution, and the law of the movement process of structure units at all levels in polymer solution, this will lay a theoretical foundation for the molecular designing, functional development and application of polymer materials.
Being an important part of polymer science, the single chain conformation and aggregation structure in polymer solution has been widely studied by many experiential exponential laws. In the review, several kinds of commonly used exponential laws were summarized, and the use in the study of shape characteristics of complex single chain and aggregation was introduced. The aggregation structure and morphology of films can be controlled by precursor solution, so deep understanding to the intrinsic properties of precursor solution is particularly important. Combined with the electron microscope, spectra, etc., the exponential law can be used to further study the single chain, aggregation size and morphology, structure evolution, and the law of the movement process of structure units at all levels in polymer solution, this will lay a theoretical foundation for the molecular designing, functional development and application of polymer materials.
2016, 74(8): 657-663
doi: 10.6023/A16050260
Abstract:
Uranium, one of typical actinide elements, has strong polarizing property. Using 5f orbitals for bonding with ligands, uranium(III) compounds have some unique reactivities including: migratory insertion, σ-bond metathesis and redox activity etc., which provides researchers with good opportunities to obtain organic uranium complexes or materials with unique structures and reactional properties. In the last 20 years, it has been found that trivalent uranium organic complexes exhibit a wide variety of activation towards small molecules. Due to the significant research and potential industrial value, this field has been well developed in recent years. Some research results for small molecules (such as N2, CO, CO2) activation promoted by trivalent uranium complexes were summarized in the paper.
Uranium, one of typical actinide elements, has strong polarizing property. Using 5f orbitals for bonding with ligands, uranium(III) compounds have some unique reactivities including: migratory insertion, σ-bond metathesis and redox activity etc., which provides researchers with good opportunities to obtain organic uranium complexes or materials with unique structures and reactional properties. In the last 20 years, it has been found that trivalent uranium organic complexes exhibit a wide variety of activation towards small molecules. Due to the significant research and potential industrial value, this field has been well developed in recent years. Some research results for small molecules (such as N2, CO, CO2) activation promoted by trivalent uranium complexes were summarized in the paper.
2016, 74(8): 664-668
doi: 10.6023/A16040205
Abstract:
Simple and sensitive detection of proteins is crucial in biological analysis and medical diagnosis. Conjugated polymers (CPs) with π-conjugated backbones were recognized as having excellent light-harvesting capability and high fluorescent quantum yield. They have been widely used as an energy donor to amplify fluorescence signal via high efficient Föster resonance energy transfer (FRET). In particular, conjugated polymer brush with high charge density provides more possibilities due to stronger electrostatic interactions with negatively charged biomolecules. Here, we developed a highly sensitive protein biosensor for thrombin detection based on a conjugated polymer brush (PFNI) and a fluorescein-labeled aptamer (FAM-apt15). PFNI is a water-soluble cationic polyfluorene derivate with extremely high charge density (78 positive charges per repeat unit). PFNI can attract negatively charged aptamer through strong electrostatic interactions. In this case, the energy donor (PFNI) and acceptor (FAM) are in a close proximity, which results in an efficient FRET process and a high FRET signal. However, when the FAM-apt15 combines with the target protein, a rigid and big-sized G-quadruplex/thrombin complex formed. Due to the steric hindrance from the densely brush of PFNI, the distance between the two fluorophores increased significantly, leading to an inefficient FRET process and a low FRET signal. The strategy exhibits excellent specificity and the limit of detection (LOD) for thrombin in buffer was estimated to be 0.05 nmol/L. It also works well in diluted serum and a LOD of 0.2 nmol/L can be obtained. Compared to the biosensors based on traditional linear conjugated polymers, the sensitivity was improved by one order of magnitude. In addition, our strategy also shows the merits of simple, label-free, and low-cost because labeled DNA is much more expensive than unlabeled one. Based on the specific binding of aptamer and protein, this novel method can be extended to a highly sensitive detection of more proteins.
Simple and sensitive detection of proteins is crucial in biological analysis and medical diagnosis. Conjugated polymers (CPs) with π-conjugated backbones were recognized as having excellent light-harvesting capability and high fluorescent quantum yield. They have been widely used as an energy donor to amplify fluorescence signal via high efficient Föster resonance energy transfer (FRET). In particular, conjugated polymer brush with high charge density provides more possibilities due to stronger electrostatic interactions with negatively charged biomolecules. Here, we developed a highly sensitive protein biosensor for thrombin detection based on a conjugated polymer brush (PFNI) and a fluorescein-labeled aptamer (FAM-apt15). PFNI is a water-soluble cationic polyfluorene derivate with extremely high charge density (78 positive charges per repeat unit). PFNI can attract negatively charged aptamer through strong electrostatic interactions. In this case, the energy donor (PFNI) and acceptor (FAM) are in a close proximity, which results in an efficient FRET process and a high FRET signal. However, when the FAM-apt15 combines with the target protein, a rigid and big-sized G-quadruplex/thrombin complex formed. Due to the steric hindrance from the densely brush of PFNI, the distance between the two fluorophores increased significantly, leading to an inefficient FRET process and a low FRET signal. The strategy exhibits excellent specificity and the limit of detection (LOD) for thrombin in buffer was estimated to be 0.05 nmol/L. It also works well in diluted serum and a LOD of 0.2 nmol/L can be obtained. Compared to the biosensors based on traditional linear conjugated polymers, the sensitivity was improved by one order of magnitude. In addition, our strategy also shows the merits of simple, label-free, and low-cost because labeled DNA is much more expensive than unlabeled one. Based on the specific binding of aptamer and protein, this novel method can be extended to a highly sensitive detection of more proteins.
2016, 74(8): 669-675
doi: 10.6023/A16040162
Abstract:
We designed a bispiropyran switchable molecule based on acridone. Using commercially available 3-bromoanisole and 2-amino-4-methoxybenzoic acid as starting materials, through a six-step synthetic route containing Ullmann biaryl amine condensation, Friedel-Crafts acylation, alkylation of the amine group in the resulting acridone core, regioselective double formylation at the ortho-position to the methoxy groups, demethylation of the two methoxy groups, double condensation with 1, 2, 3, 3-tetramethyl-3H-indolium iodide, the target bispiropyran switchable molecule was successfully synthesized. The UV/Vis spectra and fluorescence spectra of the target dual-switch molecule were studied. It was demonstrated that the bispiropyran molecule had obvious reversible photochromic behavior in dichloromethane solution. For more detail, the spiropyran unit of the designed molecule could be changed to the open-ring form upon UV light irradiation, and the open-ring form of the molecule could be changed to its closed-ring form again when it was placed in the dark. The molecule showed a high stability to acid in MeOH and CH2Cl2, and it had a slow acidichromic behaviour in MeCN. In addition, the molecule showed an acidichromic behaviour in MeCN/H2O solution only when the pH was below 4. However, in the above chromic process, through the UV/Vis spectra we have not found the two states containing single-ring-opened form followed by dual-ring-opened form of the designed molecule.Further study was performed through the computer simulation, and the optimal structures for the dual-ring-closed form (SP-Ac-SP), single-ring-opened form (SP-Ac-MC) and dual-ring-opened form (MC-Ac-MC) of the target molecule in the photochromic process were calculated using B3LYP/6-31g(d) in vacuum. It was found that the SP-Ac-SP was more easily directly transformed to MC-Ac-MC, because the Gibbs free energy change (ΔG1=7.2 kcal/mol) from SP-Ac-SP to SP-Ac-MC was much higher than that (ΔG2=3.5 kcal/mol) from SP-Ac-MC to MC-Ac-MC. The relevant frontier molecular orbitals for the SP-Ac-SP and MC-Ac-MC of the designed molecule calculated using B3LYP/6-31g(d) in vacuum could further explain the detail of the chromic process. Our study will give inspiration to design new type of dual-switch molecules based on conjugate structure.
We designed a bispiropyran switchable molecule based on acridone. Using commercially available 3-bromoanisole and 2-amino-4-methoxybenzoic acid as starting materials, through a six-step synthetic route containing Ullmann biaryl amine condensation, Friedel-Crafts acylation, alkylation of the amine group in the resulting acridone core, regioselective double formylation at the ortho-position to the methoxy groups, demethylation of the two methoxy groups, double condensation with 1, 2, 3, 3-tetramethyl-3H-indolium iodide, the target bispiropyran switchable molecule was successfully synthesized. The UV/Vis spectra and fluorescence spectra of the target dual-switch molecule were studied. It was demonstrated that the bispiropyran molecule had obvious reversible photochromic behavior in dichloromethane solution. For more detail, the spiropyran unit of the designed molecule could be changed to the open-ring form upon UV light irradiation, and the open-ring form of the molecule could be changed to its closed-ring form again when it was placed in the dark. The molecule showed a high stability to acid in MeOH and CH2Cl2, and it had a slow acidichromic behaviour in MeCN. In addition, the molecule showed an acidichromic behaviour in MeCN/H2O solution only when the pH was below 4. However, in the above chromic process, through the UV/Vis spectra we have not found the two states containing single-ring-opened form followed by dual-ring-opened form of the designed molecule.Further study was performed through the computer simulation, and the optimal structures for the dual-ring-closed form (SP-Ac-SP), single-ring-opened form (SP-Ac-MC) and dual-ring-opened form (MC-Ac-MC) of the target molecule in the photochromic process were calculated using B3LYP/6-31g(d) in vacuum. It was found that the SP-Ac-SP was more easily directly transformed to MC-Ac-MC, because the Gibbs free energy change (ΔG1=7.2 kcal/mol) from SP-Ac-SP to SP-Ac-MC was much higher than that (ΔG2=3.5 kcal/mol) from SP-Ac-MC to MC-Ac-MC. The relevant frontier molecular orbitals for the SP-Ac-SP and MC-Ac-MC of the designed molecule calculated using B3LYP/6-31g(d) in vacuum could further explain the detail of the chromic process. Our study will give inspiration to design new type of dual-switch molecules based on conjugate structure.
2016, 74(8): 676-682
doi: 10.6023/A16050268
Abstract:
To better understand the relationships between the microstructure and the optoelectronic characteristics of the electron acceptor and to meet the needs of donor-acceptor materials with excellent optical properties for solar cell, a series of acceptor molecules with A'-π-A-π-A' type are designed. In these molecules, the core framework of benzothiadiazole is used as an acceptor (A), three kinds of conjugated heterocyclics (A') with different abilities of electron-withdrawing and steric effects are applied as the terminals, and various conjugated structures, such as the double bond, thiophene, benzothiophene and vinyl thiophene, are utilized as π-bridge, respectively. Their geometric configurations, the characteristics of frontier molecular orbital, optical properties, as well as the electronic reorganization energy are predicted by DFT-B3LYP and TD-DFT-CAM-B3LYP. Solvent effects from acetone and chlorobenzene on molecular properties are studied. Furthermore, the Donor-Acceptor (D-A) interfaces are respectively constructed by combining the excellent acceptors with the selected two donors. The DFT-D3 method is used to scan the binding energy of D-A complex, in order to determine the stacked displacement of the interface. The degree of interface recombination is evaluated by calculating electronic coupling (Vif) between HOMO of donors and LUMO of acceptors. The results show that modifying benzothiadiazole with a reasonable substituent is an effective way to adjust LUMO energy levels and lead to the noticeable variation of the energy gap. Combining planar electron acceptor materials (A'-π-A-π-A' type) with non-planar electron donor materials (D), to form the optical active layer is a practical approach for preventing interface recombination and achieving high open-circuit voltage (Voc). Considering ΔEL, Vif, light absorption efficiency, and solvation effect, D1-1aγ and D1-2aγ combinations are the most promising candidates of optical active layer materials in organic solar cell.
To better understand the relationships between the microstructure and the optoelectronic characteristics of the electron acceptor and to meet the needs of donor-acceptor materials with excellent optical properties for solar cell, a series of acceptor molecules with A'-π-A-π-A' type are designed. In these molecules, the core framework of benzothiadiazole is used as an acceptor (A), three kinds of conjugated heterocyclics (A') with different abilities of electron-withdrawing and steric effects are applied as the terminals, and various conjugated structures, such as the double bond, thiophene, benzothiophene and vinyl thiophene, are utilized as π-bridge, respectively. Their geometric configurations, the characteristics of frontier molecular orbital, optical properties, as well as the electronic reorganization energy are predicted by DFT-B3LYP and TD-DFT-CAM-B3LYP. Solvent effects from acetone and chlorobenzene on molecular properties are studied. Furthermore, the Donor-Acceptor (D-A) interfaces are respectively constructed by combining the excellent acceptors with the selected two donors. The DFT-D3 method is used to scan the binding energy of D-A complex, in order to determine the stacked displacement of the interface. The degree of interface recombination is evaluated by calculating electronic coupling (Vif) between HOMO of donors and LUMO of acceptors. The results show that modifying benzothiadiazole with a reasonable substituent is an effective way to adjust LUMO energy levels and lead to the noticeable variation of the energy gap. Combining planar electron acceptor materials (A'-π-A-π-A' type) with non-planar electron donor materials (D), to form the optical active layer is a practical approach for preventing interface recombination and achieving high open-circuit voltage (Voc). Considering ΔEL, Vif, light absorption efficiency, and solvation effect, D1-1aγ and D1-2aγ combinations are the most promising candidates of optical active layer materials in organic solar cell.
2016, 74(8): 683-688
doi: 10.6023/A16060294
Abstract:
Uranium complexes play an increasingly important role in the fields of power resource, environment and medical science. As the most stable and the most prevalent formation of uranium, hexavalent uranyl species (UO22+) are widely present in the natural water system and the nuclear fuel cycle. Since 2005, the isoelectronic analogue of the uranyl, U(NR)22+, (R=alkyl and aryl) has been a burgeoning area of research. Many bis-imido uranium complexes have been synthesized and investigated for their structural, reactivity and spectroscopic properties. It is found that the bis-imido uranium(VI) complex is capable of undergoing imido exchange reaction with oxo group, but the contrary reaction can not occur. Recently, a flexible polypyrrolic macrocycle (H4L) has been widely used to complexate hexavalent UO2+. An interesting Pacman-like complex, [(THF)(UVIO2)(H2L)], was obtained, where the uranyl ion is accommodated by one N4-donor compartment and the other compartment remains vacant. In the equatorial plane of linear uranyl ion, one THF solvent serves as the fifth coordination. Notably, two hydrogen bonds are formed between the endo-oxo of uranyl and remaining hydrogen atoms of two pyrrolides in the second compartment of macrocycle. In this work, a series of uranium complexes of the polypyrrolic macrocycle with the mixed oxo and imido groups, [(THF)(OUE)(A2L)] (E=NH, NMe and NPh; A=H and Li; labeled as UE-A) were designed, on the basis of their dioxo analogues UO-A (E=O) where the UO-H was experimentally synthesized and characterized. Their structures, Infrared (IR) vibrational spectra and oxo-imido exchange reaction were examined by the scalar relativistic density functional theory (DFT). The U=Oendo bond lengths of UE-A were optimized to be within 1.84～1.89 Å, longer than those of known uranyl complexes which possess regular pentagonal dipyramidal structure. This is related to the interaction between the A and endo-oxo atoms. The calculated U=N distances range from 1.87 to 1.90 Å, which are affected by various R substituent (direct effect) and different A atom that is bonding to endo-oxo atom (indirect effect). All the calculated U=O/U=N distances fall well within the range of experimental values. The partial triple character is unraveled for U=Oexo and U=N bonds, but a modest one between single and double is assigned to U=Oendo of UE-Li. Frequency calculations find the close bonding properties for O=U=NH and O=U=O, both of which show symmetrical and asymmetrical stretching vibrational bands between 700 and 900 cm-1. The introduction of steric substituents of Me and Ph leads to two greatly separate peaks of U=O and U=N-C. The strong coupling of Me and Ph with U=N bonding makes the U=N-C vibrations present in the high-frequency region from 1166 to 1266 cm-1, which are comparable to experimental values of 1170～1270 cm-1 for U=N-R (R=tBu and Ph). The variation of the A atom from H to Li significantly redshifts the U=O and U=N-C stretches. When carefully selecting the A atom and the R substituent, the Pacman-like complex UO-A would be easier to undergo the oxo exchange with the imido group, compared with regular pentagonal dipyrimid complex. This study is expected to provide theoretical support for experimental study of mixed oxo-imido uranium complex.
Uranium complexes play an increasingly important role in the fields of power resource, environment and medical science. As the most stable and the most prevalent formation of uranium, hexavalent uranyl species (UO22+) are widely present in the natural water system and the nuclear fuel cycle. Since 2005, the isoelectronic analogue of the uranyl, U(NR)22+, (R=alkyl and aryl) has been a burgeoning area of research. Many bis-imido uranium complexes have been synthesized and investigated for their structural, reactivity and spectroscopic properties. It is found that the bis-imido uranium(VI) complex is capable of undergoing imido exchange reaction with oxo group, but the contrary reaction can not occur. Recently, a flexible polypyrrolic macrocycle (H4L) has been widely used to complexate hexavalent UO2+. An interesting Pacman-like complex, [(THF)(UVIO2)(H2L)], was obtained, where the uranyl ion is accommodated by one N4-donor compartment and the other compartment remains vacant. In the equatorial plane of linear uranyl ion, one THF solvent serves as the fifth coordination. Notably, two hydrogen bonds are formed between the endo-oxo of uranyl and remaining hydrogen atoms of two pyrrolides in the second compartment of macrocycle. In this work, a series of uranium complexes of the polypyrrolic macrocycle with the mixed oxo and imido groups, [(THF)(OUE)(A2L)] (E=NH, NMe and NPh; A=H and Li; labeled as UE-A) were designed, on the basis of their dioxo analogues UO-A (E=O) where the UO-H was experimentally synthesized and characterized. Their structures, Infrared (IR) vibrational spectra and oxo-imido exchange reaction were examined by the scalar relativistic density functional theory (DFT). The U=Oendo bond lengths of UE-A were optimized to be within 1.84～1.89 Å, longer than those of known uranyl complexes which possess regular pentagonal dipyramidal structure. This is related to the interaction between the A and endo-oxo atoms. The calculated U=N distances range from 1.87 to 1.90 Å, which are affected by various R substituent (direct effect) and different A atom that is bonding to endo-oxo atom (indirect effect). All the calculated U=O/U=N distances fall well within the range of experimental values. The partial triple character is unraveled for U=Oexo and U=N bonds, but a modest one between single and double is assigned to U=Oendo of UE-Li. Frequency calculations find the close bonding properties for O=U=NH and O=U=O, both of which show symmetrical and asymmetrical stretching vibrational bands between 700 and 900 cm-1. The introduction of steric substituents of Me and Ph leads to two greatly separate peaks of U=O and U=N-C. The strong coupling of Me and Ph with U=N bonding makes the U=N-C vibrations present in the high-frequency region from 1166 to 1266 cm-1, which are comparable to experimental values of 1170～1270 cm-1 for U=N-R (R=tBu and Ph). The variation of the A atom from H to Li significantly redshifts the U=O and U=N-C stretches. When carefully selecting the A atom and the R substituent, the Pacman-like complex UO-A would be easier to undergo the oxo exchange with the imido group, compared with regular pentagonal dipyrimid complex. This study is expected to provide theoretical support for experimental study of mixed oxo-imido uranium complex.
2016, 74(8): 689-693
doi: 10.6023/A16050245
Abstract:
Formamidinium lead halide perovskites have attracted wide attention as photoelectronic conversion materials due to the high photoelectronic conversion efficiency (PCE), low cost and simple synthetic process. The structural, electronic and optical properties of mixed formamidinium lead halide perovskites FAPbIxCl3-x (FA=NH2CH=NH2+, x=0～3) have been investigated by the first-principles theory. Our results show that FA cations lie along [001] direction in the trigonal FAPbX3 (X=Cl, Br, I). However, the direction is slightly shifted owing to the distortion of PbX6 (X=Cl, I) octahedrons in the mixed FAPbIxCl3-x. The Pb-I bond distances (0.315～0.334 nm) are larger than Pb-Cl bond distances (0.282～0.302 nm). With the increase of I/Cl ratio, the lattice parameters and volumes of FAPbIxCl3-x increase. The FA cations play a crucial role in balancing the crystal structure, but they do not participate into the process of frontier orbital transition directly. They just play the role of charge donors to contribute ca. 0.76 e to PbI3 framework. FAPbIxCl3-x are direct band-gap semiconductors, with the direct bandgap nature at Z (0, 0, 0.5) symmetry point. The valence band maximum (VBM) is composed of antibonding orbitals of I 5p (Cl 3p) and a few Pb 6s orbitals, and the conduction band minimum (CBM) is composed of Pb 6p orbital. There exists a combined covalent and ionic bonding mechanism between Pb and I (Cl) ions. As the I/Cl ratio increases, the band gaps decrease and the absorption spectra are red shifted. FAPbI3 has an ideal band gap of 1.53 eV. It exhibits the superior absorption spectrum especially in the range of 300 nm to 500 nm, which elucidates that FAPbI3 has great potential as the photoelectronic conversion material. Our results could provide theoretical guidance for the experimental design and synthesis of perovskite solar cells.
Formamidinium lead halide perovskites have attracted wide attention as photoelectronic conversion materials due to the high photoelectronic conversion efficiency (PCE), low cost and simple synthetic process. The structural, electronic and optical properties of mixed formamidinium lead halide perovskites FAPbIxCl3-x (FA=NH2CH=NH2+, x=0～3) have been investigated by the first-principles theory. Our results show that FA cations lie along [001] direction in the trigonal FAPbX3 (X=Cl, Br, I). However, the direction is slightly shifted owing to the distortion of PbX6 (X=Cl, I) octahedrons in the mixed FAPbIxCl3-x. The Pb-I bond distances (0.315～0.334 nm) are larger than Pb-Cl bond distances (0.282～0.302 nm). With the increase of I/Cl ratio, the lattice parameters and volumes of FAPbIxCl3-x increase. The FA cations play a crucial role in balancing the crystal structure, but they do not participate into the process of frontier orbital transition directly. They just play the role of charge donors to contribute ca. 0.76 e to PbI3 framework. FAPbIxCl3-x are direct band-gap semiconductors, with the direct bandgap nature at Z (0, 0, 0.5) symmetry point. The valence band maximum (VBM) is composed of antibonding orbitals of I 5p (Cl 3p) and a few Pb 6s orbitals, and the conduction band minimum (CBM) is composed of Pb 6p orbital. There exists a combined covalent and ionic bonding mechanism between Pb and I (Cl) ions. As the I/Cl ratio increases, the band gaps decrease and the absorption spectra are red shifted. FAPbI3 has an ideal band gap of 1.53 eV. It exhibits the superior absorption spectrum especially in the range of 300 nm to 500 nm, which elucidates that FAPbI3 has great potential as the photoelectronic conversion material. Our results could provide theoretical guidance for the experimental design and synthesis of perovskite solar cells.
2016, 74(8): 694-702
doi: 10.6023/A16050216
Abstract:
Air pollution is a common phenomenon in developing countries, and pollutants are suggested to be essential reasons to produce various diseases, such as cancers, neuro-degenerative diseases and so on. In present work, the effects of sulfur dioxide on the dissociation of Aβ17～42 peptides from core region of Aβ fibril were studied with umbrella sampling method. It is found that the free energy penalty related to the dissociation processes would decrease for larger concentrations of sulfur dioxide. The detailed interactions between peptides and sulfur dioxide are analyzed based on contact statistics. It is suggested that the destabilization of the Aβ fibril is realized by the binding of sulfur dioxide with the peptide backbone as well as the side chains of charged residues, which results in the decrease of hydrophobic interaction and blockage of the electrostatic interactions between charged residues. Furthermore, the positive contribution of such a marginal destabilization on the growth of fibril is also discussed with a nonlinear master equation, which is consistent with the medical knowledge. Through these computations, we disclose the characteristics of the interactions between air pollutants and protein molecules. We expect that these results could help to assess the effect of air pollutants on human health.
Air pollution is a common phenomenon in developing countries, and pollutants are suggested to be essential reasons to produce various diseases, such as cancers, neuro-degenerative diseases and so on. In present work, the effects of sulfur dioxide on the dissociation of Aβ17～42 peptides from core region of Aβ fibril were studied with umbrella sampling method. It is found that the free energy penalty related to the dissociation processes would decrease for larger concentrations of sulfur dioxide. The detailed interactions between peptides and sulfur dioxide are analyzed based on contact statistics. It is suggested that the destabilization of the Aβ fibril is realized by the binding of sulfur dioxide with the peptide backbone as well as the side chains of charged residues, which results in the decrease of hydrophobic interaction and blockage of the electrostatic interactions between charged residues. Furthermore, the positive contribution of such a marginal destabilization on the growth of fibril is also discussed with a nonlinear master equation, which is consistent with the medical knowledge. Through these computations, we disclose the characteristics of the interactions between air pollutants and protein molecules. We expect that these results could help to assess the effect of air pollutants on human health.
