The photo-physical characteristics of semiconductor polymer are systematically stud- ied through comparing poly （9,9-dioctylfluorene） （PFO） and poly （9,9-dioctylfluorene-co- benzothiadiazole） （F8BT）. The quant...The photo-physical characteristics of semiconductor polymer are systematically stud- ied through comparing poly （9,9-dioctylfluorene） （PFO） and poly （9,9-dioctylfluorene-co- benzothiadiazole） （F8BT）. The quantum chemical calculation shows that the introduction of benzothiadiazole unit facilitates the intrachain charge transfer （ICT） and modulates the electronic transition mechanism of polymer. The transient absorption measurement exhibits that intrachain exciton relaxation is dominant in the decay of excited PFO in a monodis- perse system and intrachain exciton interaction could appear at high excitation intensity. In F8BT solution, the ICT state exists and participates in the relaxation of excited state. The relaxation processes of PFO and F8BT in the condensed phase both accelerate and show obvious exciton-exciton annihilation behavior at high excitation intensity. At the same excitation intensity, the mean lifetime of F8BT is longer than that of PFO, which may be assigned to the excellent delocalization of charge.展开更多
Two new diarylamine-substituted 1, 8-naphthalimide derivatives are synthesized by Cu I/18-crown-6/K2CO3 catalyst system and characterized by Fourier transform infrared （FT- IR）, ^1H-NMR and elemental analyses. The U...Two new diarylamine-substituted 1, 8-naphthalimide derivatives are synthesized by Cu I/18-crown-6/K2CO3 catalyst system and characterized by Fourier transform infrared （FT- IR）, ^1H-NMR and elemental analyses. The UV-vis absorption and photoluminescent （PL）spectra of the systems in n-hexane, tetrahydrofuran（THF）, and CH2Cl2 are investigated. These naphthalimide molecules have an absorption band centered at about 450 nm, which is assigned to an intramolecular chargetransfer （ICT）transition, and they emit light at 492, 501 nm in a nonpolar solvent such as n-hexane, and at 600, 620 nm in a polar solvent such as CH2Cl2. From the Lippert-Mataga equation, the difference of the dipole moment between the excited state and the ground state is estimated to be 9.2 and 9.8 D for 4- （ diphenylamine ）-N-（ 2-methoxyphenyl ）-1, 8-naphthalimide （ DMN-1 ） and 4-（ 2-naphthylphenylamine ）-N-（ 2- methoxyphenyl）-1, 8-naphthalimide （DMN-2）, respectively. This large change in the dipole moment upon excitation is typical for photoinduced ICT processes.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
The excited state photophysics of low bandgap polymer APFO3 has been investigated in detail. The chemical calculations confirm that the intrachain charge transfer （ICT） may occur after photo-excitation and is mainly...The excited state photophysics of low bandgap polymer APFO3 has been investigated in detail. The chemical calculations confirm that the intrachain charge transfer （ICT） may occur after photo-excitation and is mainly responsible for the first absorption band. The transient absorption results confirm that ICT indeed exists and competes with the vibra-tional relaxation at the same time, when APFO3 is in a monodisperse system. This ICT process would disappear due to the influence of interchain interaction when APFO3 is in the condensed phase, where the exciton decay would be dominant in the relaxation process after photoexcitation. The photoexcitation dynamics of APFO3 film blending with PC61BM are presented, which shows that the exciton may be dissociated completely as the percentage of PC61BM reaches ～50%. Meanwhile, the photovoltaic performance based on blend het-erojunction shows that the increase of photocurrent is little if the percentage of PC61BM exceeds ～50%. Overall, the present study has covered several fundamental processes taking place in the APFO3 polymer.展开更多
The excited-state symmetry-breaking charge transfer (SBCT) dynamics in quadrupolar or octupolar molecules without clear infrared markers is usually hard to be tracked directly. In this work, on the basis of the evolut...The excited-state symmetry-breaking charge transfer (SBCT) dynamics in quadrupolar or octupolar molecules without clear infrared markers is usually hard to be tracked directly. In this work, on the basis of the evolution of instantaneous emission dipole moment obtained by femtosecond transient fluorescence spectroscopy, we presented a real-time characterization of the solvent-induced SBCT dynamics in an octupolar triphenylamine derivative. While the emission dipole moment of the octupolar trimer in weakly polar toluene changes little during the excited-state relaxation, it exhibits a fast reduction in a few picoseconds in strongly polar tetrahydrofuran. In comparison with the uorescence dynamics of dipolar monomer, we deduced that the emitting state of the octupolar trimer in strongly polar solvent, which undergoes solvent-induced structural uctuation, changes from exciton-coupled octupolar to excitation localized dipolar symmetry. In weakly polar solvent, the octupolar symmetry of the trimer is largely preserved during the solvation stabilization.展开更多
UV-Vis absorption spectra of the molecular complex formed by imidazole （Ira） and chloranil （CA） were measured in chloroform. The stoichiometry of the imidazole-chloranil （hn-CA） complex was determined as 1：1 by...UV-Vis absorption spectra of the molecular complex formed by imidazole （Ira） and chloranil （CA） were measured in chloroform. The stoichiometry of the imidazole-chloranil （hn-CA） complex was determined as 1：1 by applying Benesi-Hildebrand＇s equation and Job＇s continuous variation method. Density function theory （DFT） and MP2 calculations were performed to study the structures and the binding energies of the Im-CA complex. The calculations located four conformations （denoted as S1-S4） for the Ira-CA complex, two edge（Im）-to-face（CA） linked and two edge（Im）-to-edge（CA） linked. It was found that the edge-to-face conformers are more stable than the edge-to-edge ones. The bonding characteristics of these conformers were investigated with natural population analysis （NPA）, topological analysis of electron density, and natural bond orbital （NBO） analysis. It was revealed that the edge-to-face conformers are charge-transfer （CT） complexes whereas the edge-to-edge conformers are the hydrogen bond complexes. For the most stable conformation of the Ira-CA complex （S1）, the charge transfer interaction of the imidazole n（N15） lone pair orbital with the chloranil π＊ （C1=O7） orbital plays a crucial role in the Ira-CA binding, and the binding is further strengthened by the O7… H2O hydrogen bond. The electronic excitation energies of the complex （S1） were calculated with time-dependent DFT （TDDFT）, and the observed UV-Visible spectrum of the complex was analyzed based on the computed results.展开更多
The symmetric and quadrupolar donor-acceptordonor(D-A-D)molecules usually exhibit excitedstate charge redistribution process from delocalized intramolecular charge transfer(ICT)state to localized ICT state.Direct obse...The symmetric and quadrupolar donor-acceptordonor(D-A-D)molecules usually exhibit excitedstate charge redistribution process from delocalized intramolecular charge transfer(ICT)state to localized ICT state.Direct observation of such charge redistribution process in real-time has been intensively studied via various ultrafast time-resolved spectroscopies.Femtosecond stimulated Raman spectroscopy(FSRS)is one of the powerful methods which can be used to determine the excited state dynamics by tracking vibrational mode evolution of the specific chemical bonds within molecules.Herein,a molecule,4,4′-(buta-1,3-diyne-1,4-diyl)bis(N,N-bis(4-methoxyphenyl)aniline),that consists of two central adjacent alkyne(-C≡C-)groups as electron-acceptors and two separated,symmetric N,N-bis(4-methoxyphenyl)aniline at both branches as electron-donors,is chosen to investigate the excited-state photophysical properties.It is shown that the solvation induced excited-state charge redistribution in polar solvents can be probed by using femtosecond stimulated Raman spectroscopy.The results provide a fundamental understanding of photoexcitation induced charge delocalization/localization properties of the symmetric quadrupolar molecules with adjacent vibrational markers located at central position.展开更多
Blue light-emitting polyfluorenes containing dibenzothiophene-S,S-dioxide(SO) unit in alkyl side chain(PF-FSOs and PF-CzSOs) were synthesized. All the polymers show high thermal stability with the decomposition temper...Blue light-emitting polyfluorenes containing dibenzothiophene-S,S-dioxide(SO) unit in alkyl side chain(PF-FSOs and PF-CzSOs) were synthesized. All the polymers show high thermal stability with the decomposition temperatures over400 °C. The highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) energy levels of the copolymer slightly decrease with the increase of SO content in side chain. PL spectra of the polymers show slightly red shift and broadening with the increase of solvent polarities, indicating unremarkable intramolecular charge transfer(ICT) effect in the polymers containing SO unit in alkyl side chain. EL spectra of the polymers are almost unchanged in the current densities from 100 to 400 mA cm.2, indicating the superb EL stability of the resulted polymers. The EL spectra of the copolymers exhibit obvious blue-shift and narrowing with the CIE of(0.18, 0.11) for PF-FSO10 and(0.17, 0.11) for PF-CzSO10, respectively,compared with PF-SO10 containing SO unit in main chain with the CIE of(0.16, 0.17) and PFO with the CIE of(0.18, 0.18).The superior device performances were obtained with the luminous efficiency(LEmax) of 1.17 and 0.68 cd A.1 for PF-FSO15 and PF-CzSO20, respectively, compared with the LEmax of 0.37 cd A.1 for PFO. The results indicate that linking SO unit to alkyl side chain of the polyfluorene is a promising strategy for efficient blue light-emitting polymers.展开更多
文摘The photo-physical characteristics of semiconductor polymer are systematically stud- ied through comparing poly （9,9-dioctylfluorene） （PFO） and poly （9,9-dioctylfluorene-co- benzothiadiazole） （F8BT）. The quantum chemical calculation shows that the introduction of benzothiadiazole unit facilitates the intrachain charge transfer （ICT） and modulates the electronic transition mechanism of polymer. The transient absorption measurement exhibits that intrachain exciton relaxation is dominant in the decay of excited PFO in a monodis- perse system and intrachain exciton interaction could appear at high excitation intensity. In F8BT solution, the ICT state exists and participates in the relaxation of excited state. The relaxation processes of PFO and F8BT in the condensed phase both accelerate and show obvious exciton-exciton annihilation behavior at high excitation intensity. At the same excitation intensity, the mean lifetime of F8BT is longer than that of PFO, which may be assigned to the excellent delocalization of charge.
基金The Ph.D.Programs Foundation of Ministry of Educa-tion of China(No.20030286012)the High Technology Research and De-velopment Program of Jiangsu Province(No.BG2005034)
文摘Two new diarylamine-substituted 1, 8-naphthalimide derivatives are synthesized by Cu I/18-crown-6/K2CO3 catalyst system and characterized by Fourier transform infrared （FT- IR）, ^1H-NMR and elemental analyses. The UV-vis absorption and photoluminescent （PL）spectra of the systems in n-hexane, tetrahydrofuran（THF）, and CH2Cl2 are investigated. These naphthalimide molecules have an absorption band centered at about 450 nm, which is assigned to an intramolecular chargetransfer （ICT）transition, and they emit light at 492, 501 nm in a nonpolar solvent such as n-hexane, and at 600, 620 nm in a polar solvent such as CH2Cl2. From the Lippert-Mataga equation, the difference of the dipole moment between the excited state and the ground state is estimated to be 9.2 and 9.8 D for 4- （ diphenylamine ）-N-（ 2-methoxyphenyl ）-1, 8-naphthalimide （ DMN-1 ） and 4-（ 2-naphthylphenylamine ）-N-（ 2- methoxyphenyl）-1, 8-naphthalimide （DMN-2）, respectively. This large change in the dipole moment upon excitation is typical for photoinduced ICT processes.
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.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.21103161 and No.11274142） and the China Postdoctoral Science Foundation （No.2011M500927）.
文摘The excited state photophysics of low bandgap polymer APFO3 has been investigated in detail. The chemical calculations confirm that the intrachain charge transfer （ICT） may occur after photo-excitation and is mainly responsible for the first absorption band. The transient absorption results confirm that ICT indeed exists and competes with the vibra-tional relaxation at the same time, when APFO3 is in a monodisperse system. This ICT process would disappear due to the influence of interchain interaction when APFO3 is in the condensed phase, where the exciton decay would be dominant in the relaxation process after photoexcitation. The photoexcitation dynamics of APFO3 film blending with PC61BM are presented, which shows that the exciton may be dissociated completely as the percentage of PC61BM reaches ～50%. Meanwhile, the photovoltaic performance based on blend het-erojunction shows that the increase of photocurrent is little if the percentage of PC61BM exceeds ～50%. Overall, the present study has covered several fundamental processes taking place in the APFO3 polymer.
基金supported by the National Natural Science Foundation of China (No.21673252, No.21333012, No.21672211, and No.21773252, No.21827803)the Strategic Priority Research Program of the Chinese Academy of Sciences (No.XDB12020200)
文摘The excited-state symmetry-breaking charge transfer (SBCT) dynamics in quadrupolar or octupolar molecules without clear infrared markers is usually hard to be tracked directly. In this work, on the basis of the evolution of instantaneous emission dipole moment obtained by femtosecond transient fluorescence spectroscopy, we presented a real-time characterization of the solvent-induced SBCT dynamics in an octupolar triphenylamine derivative. While the emission dipole moment of the octupolar trimer in weakly polar toluene changes little during the excited-state relaxation, it exhibits a fast reduction in a few picoseconds in strongly polar tetrahydrofuran. In comparison with the uorescence dynamics of dipolar monomer, we deduced that the emitting state of the octupolar trimer in strongly polar solvent, which undergoes solvent-induced structural uctuation, changes from exciton-coupled octupolar to excitation localized dipolar symmetry. In weakly polar solvent, the octupolar symmetry of the trimer is largely preserved during the solvation stabilization.
基金ACKNOWLEDGMENT This work was supported Science Foundation of China by the National Natural （No.20473078）.
文摘UV-Vis absorption spectra of the molecular complex formed by imidazole （Ira） and chloranil （CA） were measured in chloroform. The stoichiometry of the imidazole-chloranil （hn-CA） complex was determined as 1：1 by applying Benesi-Hildebrand＇s equation and Job＇s continuous variation method. Density function theory （DFT） and MP2 calculations were performed to study the structures and the binding energies of the Im-CA complex. The calculations located four conformations （denoted as S1-S4） for the Ira-CA complex, two edge（Im）-to-face（CA） linked and two edge（Im）-to-edge（CA） linked. It was found that the edge-to-face conformers are more stable than the edge-to-edge ones. The bonding characteristics of these conformers were investigated with natural population analysis （NPA）, topological analysis of electron density, and natural bond orbital （NBO） analysis. It was revealed that the edge-to-face conformers are charge-transfer （CT） complexes whereas the edge-to-edge conformers are the hydrogen bond complexes. For the most stable conformation of the Ira-CA complex （S1）, the charge transfer interaction of the imidazole n（N15） lone pair orbital with the chloranil π＊ （C1=O7） orbital plays a crucial role in the Ira-CA binding, and the binding is further strengthened by the O7… H2O hydrogen bond. The electronic excitation energies of the complex （S1） were calculated with time-dependent DFT （TDDFT）, and the observed UV-Visible spectrum of the complex was analyzed based on the computed results.
基金supported by the National Natural Science Foundation of China(No.22133001,No.11774233,No.21773252,No.21773257,No.21827803)the Project for high-grade,precision and advance in Beijing(BUPT)。
文摘The symmetric and quadrupolar donor-acceptordonor(D-A-D)molecules usually exhibit excitedstate charge redistribution process from delocalized intramolecular charge transfer(ICT)state to localized ICT state.Direct observation of such charge redistribution process in real-time has been intensively studied via various ultrafast time-resolved spectroscopies.Femtosecond stimulated Raman spectroscopy(FSRS)is one of the powerful methods which can be used to determine the excited state dynamics by tracking vibrational mode evolution of the specific chemical bonds within molecules.Herein,a molecule,4,4′-(buta-1,3-diyne-1,4-diyl)bis(N,N-bis(4-methoxyphenyl)aniline),that consists of two central adjacent alkyne(-C≡C-)groups as electron-acceptors and two separated,symmetric N,N-bis(4-methoxyphenyl)aniline at both branches as electron-donors,is chosen to investigate the excited-state photophysical properties.It is shown that the solvation induced excited-state charge redistribution in polar solvents can be probed by using femtosecond stimulated Raman spectroscopy.The results provide a fundamental understanding of photoexcitation induced charge delocalization/localization properties of the symmetric quadrupolar molecules with adjacent vibrational markers located at central position.
基金supported by the National Key Basic Research and Development Program of China (2015CB655004)the National Natural Science Foundation of China (51473054, 91333206)the Fundamental Research Funds for the Central Universities, South China of Technology (2017MS020)
文摘Blue light-emitting polyfluorenes containing dibenzothiophene-S,S-dioxide(SO) unit in alkyl side chain(PF-FSOs and PF-CzSOs) were synthesized. All the polymers show high thermal stability with the decomposition temperatures over400 °C. The highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) energy levels of the copolymer slightly decrease with the increase of SO content in side chain. PL spectra of the polymers show slightly red shift and broadening with the increase of solvent polarities, indicating unremarkable intramolecular charge transfer(ICT) effect in the polymers containing SO unit in alkyl side chain. EL spectra of the polymers are almost unchanged in the current densities from 100 to 400 mA cm.2, indicating the superb EL stability of the resulted polymers. The EL spectra of the copolymers exhibit obvious blue-shift and narrowing with the CIE of(0.18, 0.11) for PF-FSO10 and(0.17, 0.11) for PF-CzSO10, respectively,compared with PF-SO10 containing SO unit in main chain with the CIE of(0.16, 0.17) and PFO with the CIE of(0.18, 0.18).The superior device performances were obtained with the luminous efficiency(LEmax) of 1.17 and 0.68 cd A.1 for PF-FSO15 and PF-CzSO20, respectively, compared with the LEmax of 0.37 cd A.1 for PFO. The results indicate that linking SO unit to alkyl side chain of the polyfluorene is a promising strategy for efficient blue light-emitting polymers.
