An expression for energy transfer probability （η） between host （TPD） and guest （Ir（ppy）3） phosphorescent systems is proposed,and the energy transfer process in doped organic electrophosphorescent （EP） devic...An expression for energy transfer probability （η） between host （TPD） and guest （Ir（ppy）3） phosphorescent systems is proposed,and the energy transfer process in doped organic electrophosphorescent （EP） devices is discussed. The results show that （1） The rate of the triplet energy transfer （KHG and KGH） exponentially increases with the host-guest molecular distance （R）, and KHG decreases quickly as the intermolecular distance of the guest （RGG） increases. In addition,the KHG/KGH ratio of the dopant system increases when R or RGG is reduced; （2） The energy transfer probability approximately linearly decreases as R increases from 0.8 to 1.2nm,and the variation of RGG can be neglected when R〈1.1nm. For 1. 1nm〈R〈l. 2nm, RGG （〈1.6nm） plays an increasingly important role when 71 drops with the latter＇ （3） η increases when the Forster energy transfer rate increases or Gibb＇s energy declines.展开更多
The function of protein in long-range biological electron transfer is a question of debate. We report some preliminary results in femtosecond spectroscopic study of photosynthetic bacterial light-harvesting antenna co...The function of protein in long-range biological electron transfer is a question of debate. We report some preliminary results in femtosecond spectroscopic study of photosynthetic bacterial light-harvesting antenna complex assembled onto TiO2 nanoparticle with an average size of 8 nm in diameter. Crystal structure shows that photosynthetic bacterial antenna complex LH2 has a ring-like structure composed by alpha- and beta-apoprotein helices. The alpha- and beta-transmembrance helices construct two concentric cylinders with pigments bacteriochlorophyll a (Bchl a) and carotenoid (Car) buried inside the protein. We attempt to insert TiO2 nanoparticle into the cavity of the inner cylindrical hollow of LH2 to investigate the nature of the electron transfer between the excited-state Bchl a and the TiO2 nanoparticle. A significant decrease in the ground state bleaching recovery time constant for Bchl a at 850 run (B850) in respect to that of the Bchl a in free LH2 has been observed. By using the relation of distance-dependent long-range electron transfer rate in protein, the distance between the donor B850 and the acceptor TiO2 nanoparticle has been estimated, which is about 0.6 nm. The proposed method of assembling proteins onto wide-gap semiconductor nanoparticle can be a promising way to determine the role of the protein playing in biological electron transfer processes.展开更多
Accurately known energy level structure of the A＇∑u＋b3 IIu complex of states from a recent global de-perturbation of these states has enabled additional assignments of 140 perturbation facilitated infrared-infrared...Accurately known energy level structure of the A＇∑u＋b3 IIu complex of states from a recent global de-perturbation of these states has enabled additional assignments of 140 perturbation facilitated infrared-infrared double resonance （PFIIDR） transitions to the 2^3△1g state from collisionally populated intermediate 1 ＋ A Eu levels. Together with the 221 previously observed 2^3△1g←A1∑u＋←X1∑g＋ Eu X Eg double resonance lines [J. Chem. Phys. 128, 204313 （2008）], molecular constants and the Rydberg-Klein-Rees potential energy curve of the 23△1g state have been recalculated （excluding 54 perturbed levels）. The centrifugal distortion constant has been determined and agrees well with the value calculated based on standard empirical formulas. The hyperfine structure of the 23△1g state, which has not resolved in our sub-Doppler excitation spectra of the 23△1g state, has been interpreted with a preliminary simulation.展开更多
Metal-free indoline dyes for dye-sensitized solar cells were studied by employing quantum chemistry methods. Comparative study of the properties of both ground and excited states of metal-free indoline dyes for dye-se...Metal-free indoline dyes for dye-sensitized solar cells were studied by employing quantum chemistry methods. Comparative study of the properties of both ground and excited states of metal-free indoline dyes for dye-sensitized solar cells revealed： （i） as the number of rhodanine rings increases, the energy difference between HOMO and LUMO decreases and there is a red shift in the absorption spectrum with the binding energy increased, and the transition dipole moment decreased; （ii） Based on an analysis of charge differential density, we observed that the charge and energy are transfered from the phenylethenyl to the indoline and rhodanine rings; （iii） The electron-hole coherences are mainly on the indoline and rhodanine rings, and the exciton sizes are 30 and 40 atoms for indoline dyes with one and two rhodanline rings, respectively. These results serve as a good example of computer-aided design in metal-free indoline dyes for dye-sensitized solar cells.展开更多
In this work, we investigated the energy transfer (EnT) and electron transfer (ET) processes as well as their relationship in the carbon quantum dots/rhodamine B (CQDs/RhB) including o-CQDs/Rh B and m-CQDs/RhB systems...In this work, we investigated the energy transfer (EnT) and electron transfer (ET) processes as well as their relationship in the carbon quantum dots/rhodamine B (CQDs/RhB) including o-CQDs/Rh B and m-CQDs/RhB systems by using photoluminescence spectroscopy in combination with steady-state and transient absorption spectroscopy. We found that the ET process is negligible in the o-CQDs/RhB system with an EnT efficiency as high as 73.2%,while it becomes pronounced in the m-CQDs/RhB system whose EnT efficiency is lower than 33.5%. Such an interplay of En T and ET processes revealed in the prototypical composite system consisting of carbon quantum dots and dye molecules would provide helpful insights for applications of relevance to exciton quenching.展开更多
Based on the charge injection and recombination processes and the triplet-triplet annihilation process, a model to calculate the electroluminescent(EL) efficiency is presented. The influences of the applied electric f...Based on the charge injection and recombination processes and the triplet-triplet annihilation process, a model to calculate the electroluminescent(EL) efficiency is presented. The influences of the applied electric field on the injection efficiency, recombination efficiency and electroluminescent efficiency are discussed. It is found that: (1) The injection efficiency is increasing while the recombination efficiency is decreasing with the applied electric field increasing. (2) The EL efficiency is enhanced at low electric field slowly but is decreasing at high electric field with the increase of applied voltage. (3) The EL efficiency is decreasing with the increase of the host-guest molecular distance (R). So, it is concluded that the EL efficiency in single-layer organic electrophosphorescent devices is dominated by injection efficiency at lower electric field and recombination efficiency at higher electric field.展开更多
Molecular packing patterns are crucial factors determining electron/energy transfer processes that are critical for the optoelectronic properties of organic thin film devices.Herein,the polarization-selective ultravio...Molecular packing patterns are crucial factors determining electron/energy transfer processes that are critical for the optoelectronic properties of organic thin film devices.Herein,the polarization-selective ultraviolet/infrared(UV/IR)mixed frequency ultrafast spectroscopy is applied to investigate the relative molecular orientations in two organic thin films of 7-(diethylamino)coumarin-3-carboxylic acid(DEAC)and perylene.The signal anisotropy changes caused by intermolecular energy/electron transfers are utilized to calculate the cross angles between the electronic transition dipole moment of the donor and the vibrational transition dipole moments of the acceptor,yielding the relative orientation between two adjacent molecules.Using this method,the relative orientation angle in DEAC film is determined to be 53.4°,close to 60°of its single crystalline structure,and that of the perylene film is determined to be 6.2°,also close to-0.2°of its single crystalline structure.Besides experimental uncertainties,the small difference between the angles determined by this method and those of single crystals also results from the fact that the thin film samples are polycrystalline where some of the molecules are amorphous.展开更多
Iron-based single-atom catalysts with nitrogen-doped carbon as support(Fe-SA/NPC)are considered effective alternatives to replace Pt-group metals for scalable application in fuel cells.However,synthesizing high-loadin...Iron-based single-atom catalysts with nitrogen-doped carbon as support(Fe-SA/NPC)are considered effective alternatives to replace Pt-group metals for scalable application in fuel cells.However,synthesizing high-loading Fe-SA catalysts by a simple procedure remains challenging.Herein,we report a high-loading(7.5 wt%)Fe-SA/NPC catalyst prepared by carbon-assisted pyrolysis of metal complexes.Both the nitrogen-doped porous carbon(NPC)support with high specific surface area and ο-phenylenediamine(o-PD)play key roles role in the preparation of high-loading Fe-SA/NPC catalysts.The results of X-ray photoelectron spectroscopy,high-angle annular dark-field scanning transmission electron microscopy,and X-ray absorption fine structure spectroscopy experiments show that the Fe atoms are anchored on the carbon carriers in a single-atom site configuration and coordinated with four of the doped nitrogen atoms of the carbon substrates(Fe-N_(4)).The activities of the Fe-SA/NPC catalysts in the oxygen reduction reaction increased with increasing iron loading.The optimized 250Fe-SA/NPC-800 catalyst exhibited an onset potential 0.97 V of and a half-wave potential of 0.85 V.Our study provides a simple approach for the large-scale synthesis of high-loading single-atom catalysts.展开更多
A new functionalized heteroleptic iridium complex coordinated with 1-phenylisoquinoline （1-piq） and a functionalized fl-diketone （G1）, Ir（1-piq）2G1, was synthesized and characterized by 1H-NMR, mass spectrometry...A new functionalized heteroleptic iridium complex coordinated with 1-phenylisoquinoline （1-piq） and a functionalized fl-diketone （G1）, Ir（1-piq）2G1, was synthesized and characterized by 1H-NMR, mass spectrometry and elemental analysis. The larger conjugation of the replacement of acetylacetone （acac） by a functionalizedβ-diketonate ligand led to a significant decrease in the HOMO level toward vacuum level, while Ir（1-piq）2G1 and Ir（1-piq）2（acac） showed red phosphorescent emissions of about 620 nm in dichloromethane solution. The phosphorescent polymer light-emitting devices were achieved, with the complexes incorporated with polyfluorene （PFO） as a host polymer doped with 30% of 5-（4-biphenylyl）-2-（4-tert-butylphenyl）-1,3,4-oxadiazole （PBD） as electron transport material. The energy transfer mechanism of the devices was also discussed. The lower EL performance of Ir（1-piq）2G1 is ascribed to the inter-ligand energy transfer, indicating that it is important to control the energy level of the cyclometalated and ancillary ligands.展开更多
Platinum(Pt)is an efficient catalyst for hydrogen evolution reaction(HER)and oxygen reduction reaction(ORR),but the debate of the relevance between the Pt particle size and its electrocatalytic activity still exist.Th...Platinum(Pt)is an efficient catalyst for hydrogen evolution reaction(HER)and oxygen reduction reaction(ORR),but the debate of the relevance between the Pt particle size and its electrocatalytic activity still exist.The strong metal–support interaction(SMSI)between the metal and carrier causes the charge transfer and mass transport from the support to the metal.Herein,Pt species(0.5 wt.%)with various particle sizes supported on carbon nanotubes(CNTs)have been synthesized by a photo-reduction method.The^1.5 nm-sized Pt catalyst shows much higher HER performance than the counterparts in all pH solutions,and the mass activity of it is even 23–36 times that of Pt/C.While for ORR,the^3 nm-sized Pt catalyst exhibits the optimal performance,and the mass activity is 3 times and even 16 times that of Pt/C in acidic and alkaline media,respectively.The high HER and ORR performances of the^1.5 nm-and^3 nm-sized Pt catalysts benefit from the SMSI between Pt and the CNTs matrix and the higher ratio of face sites to edge sites,which is meaningful for the design of efficient electrocatalysts for renewable energy application.展开更多
A comprehensive performance evaluation of a solar assisted transcritical CO2-based Rankine cycle system is made with exergy analysis method. The actual thermal data taken from the all-day experiment of the system are ...A comprehensive performance evaluation of a solar assisted transcritical CO2-based Rankine cycle system is made with exergy analysis method. The actual thermal data taken from the all-day experiment of the system are utilized to determine energy transfer and the exergy destructions in each component of the system. In addition, a hypothetical carbon dioxide expansion turbine is introduced, then two thermodynamic models for solar transcritical carbon dioxide Rankine cycles with a throttling valve (experiment) and with an expansion turbine have been established with exergy analysis method. The obtained results clearly show that solar collector contributes the largest share to system irreversibility and entropy generation in the all-day working state, and the exergy improvement potential of solar collector is the maximum in the working state. So this component should be the optimization design focus to improve system exergy effectiveness. For the cycle with the turbine, the energy efficiency and the entropy generation are not much higher than the cycle with throttling valve, but the exergy efficiency of the cycle with turbine is twice of the cycle with throttling valve. It provides more guidance when the transcritical CO2-based Rankine system is in a large-scale solar application.展开更多
文摘An expression for energy transfer probability （η） between host （TPD） and guest （Ir（ppy）3） phosphorescent systems is proposed,and the energy transfer process in doped organic electrophosphorescent （EP） devices is discussed. The results show that （1） The rate of the triplet energy transfer （KHG and KGH） exponentially increases with the host-guest molecular distance （R）, and KHG decreases quickly as the intermolecular distance of the guest （RGG） increases. In addition,the KHG/KGH ratio of the dopant system increases when R or RGG is reduced; （2） The energy transfer probability approximately linearly decreases as R increases from 0.8 to 1.2nm,and the variation of RGG can be neglected when R〈1.1nm. For 1. 1nm〈R〈l. 2nm, RGG （〈1.6nm） plays an increasingly important role when 71 drops with the latter＇ （3） η increases when the Forster energy transfer rate increases or Gibb＇s energy declines.
文摘The function of protein in long-range biological electron transfer is a question of debate. We report some preliminary results in femtosecond spectroscopic study of photosynthetic bacterial light-harvesting antenna complex assembled onto TiO2 nanoparticle with an average size of 8 nm in diameter. Crystal structure shows that photosynthetic bacterial antenna complex LH2 has a ring-like structure composed by alpha- and beta-apoprotein helices. The alpha- and beta-transmembrance helices construct two concentric cylinders with pigments bacteriochlorophyll a (Bchl a) and carotenoid (Car) buried inside the protein. We attempt to insert TiO2 nanoparticle into the cavity of the inner cylindrical hollow of LH2 to investigate the nature of the electron transfer between the excited-state Bchl a and the TiO2 nanoparticle. A significant decrease in the ground state bleaching recovery time constant for Bchl a at 850 run (B850) in respect to that of the Bchl a in free LH2 has been observed. By using the relation of distance-dependent long-range electron transfer rate in protein, the distance between the donor B850 and the acceptor TiO2 nanoparticle has been estimated, which is about 0.6 nm. The proposed method of assembling proteins onto wide-gap semiconductor nanoparticle can be a promising way to determine the role of the protein playing in biological electron transfer processes.
文摘Accurately known energy level structure of the A＇∑u＋b3 IIu complex of states from a recent global de-perturbation of these states has enabled additional assignments of 140 perturbation facilitated infrared-infrared double resonance （PFIIDR） transitions to the 2^3△1g state from collisionally populated intermediate 1 ＋ A Eu levels. Together with the 221 previously observed 2^3△1g←A1∑u＋←X1∑g＋ Eu X Eg double resonance lines [J. Chem. Phys. 128, 204313 （2008）], molecular constants and the Rydberg-Klein-Rees potential energy curve of the 23△1g state have been recalculated （excluding 54 perturbed levels）. The centrifugal distortion constant has been determined and agrees well with the value calculated based on standard empirical formulas. The hyperfine structure of the 23△1g state, which has not resolved in our sub-Doppler excitation spectra of the 23△1g state, has been interpreted with a preliminary simulation.
基金ACKN0WLEDGMENT This work was supported by the National Nature Science Foundation of China （No.10374040）.
文摘Metal-free indoline dyes for dye-sensitized solar cells were studied by employing quantum chemistry methods. Comparative study of the properties of both ground and excited states of metal-free indoline dyes for dye-sensitized solar cells revealed： （i） as the number of rhodanine rings increases, the energy difference between HOMO and LUMO decreases and there is a red shift in the absorption spectrum with the binding energy increased, and the transition dipole moment decreased; （ii） Based on an analysis of charge differential density, we observed that the charge and energy are transfered from the phenylethenyl to the indoline and rhodanine rings; （iii） The electron-hole coherences are mainly on the indoline and rhodanine rings, and the exciton sizes are 30 and 40 atoms for indoline dyes with one and two rhodanline rings, respectively. These results serve as a good example of computer-aided design in metal-free indoline dyes for dye-sensitized solar cells.
基金supported by the National Key Research and Development Program on Nano Science and Technology of MOST(No.2016YFA0200602 and No.2018YFA0208702)the National Natural Science Foundation of China(No.21573211 and No.21633007)the Anhui Initiative in Quantum Information Technologies(AHY090200)
文摘In this work, we investigated the energy transfer (EnT) and electron transfer (ET) processes as well as their relationship in the carbon quantum dots/rhodamine B (CQDs/RhB) including o-CQDs/Rh B and m-CQDs/RhB systems by using photoluminescence spectroscopy in combination with steady-state and transient absorption spectroscopy. We found that the ET process is negligible in the o-CQDs/RhB system with an EnT efficiency as high as 73.2%,while it becomes pronounced in the m-CQDs/RhB system whose EnT efficiency is lower than 33.5%. Such an interplay of En T and ET processes revealed in the prototypical composite system consisting of carbon quantum dots and dye molecules would provide helpful insights for applications of relevance to exciton quenching.
基金Excellent Youth Foundation of Hunan Province(03JJY1008) Science Foundation for Post-doctorate of China(2004035083) Science Foundation of Central South University(0601059)
文摘Based on the charge injection and recombination processes and the triplet-triplet annihilation process, a model to calculate the electroluminescent(EL) efficiency is presented. The influences of the applied electric field on the injection efficiency, recombination efficiency and electroluminescent efficiency are discussed. It is found that: (1) The injection efficiency is increasing while the recombination efficiency is decreasing with the applied electric field increasing. (2) The EL efficiency is enhanced at low electric field slowly but is decreasing at high electric field with the increase of applied voltage. (3) The EL efficiency is decreasing with the increase of the host-guest molecular distance (R). So, it is concluded that the EL efficiency in single-layer organic electrophosphorescent devices is dominated by injection efficiency at lower electric field and recombination efficiency at higher electric field.
基金supported by Ministry of Science and Technology of China(No.2017YFA0204702)the National Natural Science Foundation of China(No.21627805,No.21673004,No.21804004,and No.21821004)。
文摘Molecular packing patterns are crucial factors determining electron/energy transfer processes that are critical for the optoelectronic properties of organic thin film devices.Herein,the polarization-selective ultraviolet/infrared(UV/IR)mixed frequency ultrafast spectroscopy is applied to investigate the relative molecular orientations in two organic thin films of 7-(diethylamino)coumarin-3-carboxylic acid(DEAC)and perylene.The signal anisotropy changes caused by intermolecular energy/electron transfers are utilized to calculate the cross angles between the electronic transition dipole moment of the donor and the vibrational transition dipole moments of the acceptor,yielding the relative orientation between two adjacent molecules.Using this method,the relative orientation angle in DEAC film is determined to be 53.4°,close to 60°of its single crystalline structure,and that of the perylene film is determined to be 6.2°,also close to-0.2°of its single crystalline structure.Besides experimental uncertainties,the small difference between the angles determined by this method and those of single crystals also results from the fact that the thin film samples are polycrystalline where some of the molecules are amorphous.
文摘Iron-based single-atom catalysts with nitrogen-doped carbon as support(Fe-SA/NPC)are considered effective alternatives to replace Pt-group metals for scalable application in fuel cells.However,synthesizing high-loading Fe-SA catalysts by a simple procedure remains challenging.Herein,we report a high-loading(7.5 wt%)Fe-SA/NPC catalyst prepared by carbon-assisted pyrolysis of metal complexes.Both the nitrogen-doped porous carbon(NPC)support with high specific surface area and ο-phenylenediamine(o-PD)play key roles role in the preparation of high-loading Fe-SA/NPC catalysts.The results of X-ray photoelectron spectroscopy,high-angle annular dark-field scanning transmission electron microscopy,and X-ray absorption fine structure spectroscopy experiments show that the Fe atoms are anchored on the carbon carriers in a single-atom site configuration and coordinated with four of the doped nitrogen atoms of the carbon substrates(Fe-N_(4)).The activities of the Fe-SA/NPC catalysts in the oxygen reduction reaction increased with increasing iron loading.The optimized 250Fe-SA/NPC-800 catalyst exhibited an onset potential 0.97 V of and a half-wave potential of 0.85 V.Our study provides a simple approach for the large-scale synthesis of high-loading single-atom catalysts.
基金Project(50803008) supported by the National Natural Science Foundation of ChinaProject(2002CB613403) supported by the Ministry of Science and Technology (MOST) of China+1 种基金Project(09JJ6085) supported by the Natural Science Foundation of Hunan Province,ChinaProject(08hjyh02) supported by the Open Project Program of Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education,China
文摘A new functionalized heteroleptic iridium complex coordinated with 1-phenylisoquinoline （1-piq） and a functionalized fl-diketone （G1）, Ir（1-piq）2G1, was synthesized and characterized by 1H-NMR, mass spectrometry and elemental analysis. The larger conjugation of the replacement of acetylacetone （acac） by a functionalizedβ-diketonate ligand led to a significant decrease in the HOMO level toward vacuum level, while Ir（1-piq）2G1 and Ir（1-piq）2（acac） showed red phosphorescent emissions of about 620 nm in dichloromethane solution. The phosphorescent polymer light-emitting devices were achieved, with the complexes incorporated with polyfluorene （PFO） as a host polymer doped with 30% of 5-（4-biphenylyl）-2-（4-tert-butylphenyl）-1,3,4-oxadiazole （PBD） as electron transport material. The energy transfer mechanism of the devices was also discussed. The lower EL performance of Ir（1-piq）2G1 is ascribed to the inter-ligand energy transfer, indicating that it is important to control the energy level of the cyclometalated and ancillary ligands.
基金support from the Natural Science Foundation of Shanghai(19ZR1479400)the State Key Laboratory for Modication of Chemical Fibers and Polymer Materials,Donghua University(KF1818)the State Key Laboratory of Advanced Technology for Materials Synthesis and Processing(Wuhan University of Technology)。
文摘Platinum(Pt)is an efficient catalyst for hydrogen evolution reaction(HER)and oxygen reduction reaction(ORR),but the debate of the relevance between the Pt particle size and its electrocatalytic activity still exist.The strong metal–support interaction(SMSI)between the metal and carrier causes the charge transfer and mass transport from the support to the metal.Herein,Pt species(0.5 wt.%)with various particle sizes supported on carbon nanotubes(CNTs)have been synthesized by a photo-reduction method.The^1.5 nm-sized Pt catalyst shows much higher HER performance than the counterparts in all pH solutions,and the mass activity of it is even 23–36 times that of Pt/C.While for ORR,the^3 nm-sized Pt catalyst exhibits the optimal performance,and the mass activity is 3 times and even 16 times that of Pt/C in acidic and alkaline media,respectively.The high HER and ORR performances of the^1.5 nm-and^3 nm-sized Pt catalysts benefit from the SMSI between Pt and the CNTs matrix and the higher ratio of face sites to edge sites,which is meaningful for the design of efficient electrocatalysts for renewable energy application.
基金supported by the National Natural Science Foundation of China (Grant No.50976002)
文摘A comprehensive performance evaluation of a solar assisted transcritical CO2-based Rankine cycle system is made with exergy analysis method. The actual thermal data taken from the all-day experiment of the system are utilized to determine energy transfer and the exergy destructions in each component of the system. In addition, a hypothetical carbon dioxide expansion turbine is introduced, then two thermodynamic models for solar transcritical carbon dioxide Rankine cycles with a throttling valve (experiment) and with an expansion turbine have been established with exergy analysis method. The obtained results clearly show that solar collector contributes the largest share to system irreversibility and entropy generation in the all-day working state, and the exergy improvement potential of solar collector is the maximum in the working state. So this component should be the optimization design focus to improve system exergy effectiveness. For the cycle with the turbine, the energy efficiency and the entropy generation are not much higher than the cycle with throttling valve, but the exergy efficiency of the cycle with turbine is twice of the cycle with throttling valve. It provides more guidance when the transcritical CO2-based Rankine system is in a large-scale solar application.
