Zero-dimensional environmentally friendly carbon quantum dots(CQDs)combined with two-di-mensional materials have a wide range of applications in optoelec-tronic devices.We combined steady-state and transient absorp-ti...Zero-dimensional environmentally friendly carbon quantum dots(CQDs)combined with two-di-mensional materials have a wide range of applications in optoelec-tronic devices.We combined steady-state and transient absorp-tion spectroscopies to study the energy transfer dynamics between CQDs and molybdenum disulfide(MoS_(2)).Transient absorption plots showed photoinduced absorption and stimulated emission features,which involved the intrinsic and defect states of CQDs.Adding MoS_(2)to CQDs solution,the lowest unoccupied molecular orbital of CQDs transferred energy to MoS_(2),which quenched the intrinsic emission at 390 nm.With addition of MoS_(2),CQD-MoS_(2)composites quenched defect emission at 490 nm and upward absorption,which originated from another energy transfer from the defect state.Two energy transfer paths between CQDs and MoS_(2)were efficiently manipulated by changing the concentration of MoS_(2),which laid a foundation for improving device performance.展开更多
The mixture of graphene oxide （GO） and dye molecules may provide some new applications due to unique electronic, optical, and structural properties. Methylene blue （MB）, a typ- ical anionic dye, can attach on GO v...The mixture of graphene oxide （GO） and dye molecules may provide some new applications due to unique electronic, optical, and structural properties. Methylene blue （MB）, a typ- ical anionic dye, can attach on GO via π-π stacking and electrostatic interaction, and the molecule removal process on GO has been observed. However, it remains unclear about the ultrafast carrier dynamics and the internal energy transfer pathways of the system which is composed of GO and MB. We have employed ultrafast optical pump-probe spectroscopy to investigate the excited dynamics of the GO-MB system dispersed in water by exciting the samples at 400 nm pump pulse. The pristine MB and GO dynamics are also analyzed in tandem for a direct comparison. Utilizing the global analysis to fit the measured signal via a sequential model, five lifetimes are acquired：（0.61±0.01） ps, （3.52±0.04） ps, （14.1±0.3） ps, （84±2） ps, and （3.66±0.08） ns. The ultrafast dynamics corresponding to these lifetimes was analyzed and the new relaxation processes were found in the GO-MB system, compared with the pristine MB. The results reveal that the functionalization of GO can alter the known decay pathways of MB via the energy transfer from GO to MB in system, the increased intermediate state, and the promoted energy transfer from triplet state MB to ground state oxygen molecules dissolved in aqueous sample.展开更多
We detect a relaxation process of excited SQ02 dye in the chlorobenzene solution and an- chor SQ02 on Al2O3 and TiO2 film, so as to investigate the photophysical properties of pristine SQ02 in the monodisperse system,...We detect a relaxation process of excited SQ02 dye in the chlorobenzene solution and an- chor SQ02 on Al2O3 and TiO2 film, so as to investigate the photophysical properties of pristine SQ02 in the monodisperse system, aggregation state, and the corresponding inter- facial electron transfer process. The experimental data show that the lifetime of SQ02 in the monondisperse system is ～2.0 ns, but that of SQ02 anchored on the Al2O3 film could obviously decrease to ～21 ps. The time of electron transfer from excited SQ02 to TiO2 film is estimated to be ～2.6 ps and the yield of electron injection is estimated to be ～89.1%, which matches the incident photon to current efficiency of dye-sensitized solar cell based on SQ02. In addition, some dyes are found to pack on the other dyes anchored on the nanocrystal film, and their relaxation time could reach ～60 ps. They couldn＇t participate in the interfacial electron transfer, since they are far away from the TiO2 interface.展开更多
Using the fully propagated time-dependent Hartree–Fock method, we identify that both the dynamic core polarization and multiorbital contributions are important in the attosecond transient absorption of CO molecules.T...Using the fully propagated time-dependent Hartree–Fock method, we identify that both the dynamic core polarization and multiorbital contributions are important in the attosecond transient absorption of CO molecules.The dynamics of core electrons effectively modifies the behaviors of electrons in the highest occupied molecular orbital, resulting in the modulation of intensity and position of the absorption peaks. Depending on the alignment angles, different inner orbitals are identified to contribute, and even dominate the total absorption spectra. As a result, multi-electron fingerprints are encoded in the absorption spectra, which shed light on future applications of attosecond transient absorption in complex systems.展开更多
The ultrafast photoisomerization and excited-state dynamics of trans-4-methoxyazobenzene (trans-4-MAB) in solutions were investigated by femtosecond transient absorption spectroscopy and quantum chemistry calculations...The ultrafast photoisomerization and excited-state dynamics of trans-4-methoxyazobenzene (trans-4-MAB) in solutions were investigated by femtosecond transient absorption spectroscopy and quantum chemistry calculations. After being excited to the S2 state, the two-dimensional transient absorptions spectra show that cis-4-MAB is produced and witnessed by the permanent positive absorption in 400-480 nm. Three decay components are determined to be 0.11, 1.4 and 2.9 ps in ethanol, and 0.16, 1.5 and 7.5 ps in ethylene glycol, respectively. The fast component is assigned to the internal conversion from the S2 to S1 state. The other relaxation pathways are correlated with the decay of the S1 state via internal conversion and isomerization, and the vibrational cooling of the hot S0 state of the cis-isomer. Comparing of the dynamics in different solvents, it is demonstrated that the photoisomerization pathway undergoes the inversion mechanism rather than the rotation mechanism.展开更多
Photoinduced electron transfer processes between fullerenes (C60 / C70) and N, N, N, N tetra - ( p-methylphenyl ) - 4, 4 diamino - 1, 1- diphenyl ether ( TPDAE ) have been studied by nanosecond laser flash photolysis....Photoinduced electron transfer processes between fullerenes (C60 / C70) and N, N, N, N tetra - ( p-methylphenyl ) - 4, 4 diamino - 1, 1- diphenyl ether ( TPDAE ) have been studied by nanosecond laser flash photolysis. Quantum yields and rate constants of electron transfer from TPDAE to excited triplet state of fullerenes (C60 / C70 ) in benzonitrile have been evaluated by observing the transient absorption bands in the near-IR region where the excited triplet state, radical anion of fullerenes ( C60 / C70 ) and radical cations of TPDAE appear.展开更多
The ultrafast excited state dynamics of trans-4-aminoazobenzene （trans-4-AAB） in ethanol was investigated by femtosecond transient absorption spectroscopy. After being excited to the S2 state by 400 nm, trans-4-AAB ...The ultrafast excited state dynamics of trans-4-aminoazobenzene （trans-4-AAB） in ethanol was investigated by femtosecond transient absorption spectroscopy. After being excited to the S2 state by 400 nm, trans-4-AAB decays from the S2 state to the hot S1 state by internal conversion with time constant of -70 fs. The photoisomerization through inversion mechanism on the S1 potential energy surface and the internal conversion from the S1 state to the hot So state are observed, respectively. The average timescale of these two decay pathways is -0.7 ps. And the vibrational cooling of the hot So state of cis- and trans-4- AAB occur with time constants of -4 and N13 ps, respectively. Furthermore, the ultrafast intersystem crossing process are also observed. The timescale of intersystem crossing from the S2 state to the T4 state is about 480 ps while from the S1 state to the T2 state is -180 ps.展开更多
The excited state of Chlorophyll a is investiga.ted by ferntosecond transient absorption. The transient absorption spectra of Q band and By band of Chlorophyll a in ethanol have been observed. The fast kinetics of Chl...The excited state of Chlorophyll a is investiga.ted by ferntosecond transient absorption. The transient absorption spectra of Q band and By band of Chlorophyll a in ethanol have been observed. The fast kinetics of Chlorophyll a which exhibit two ultrafast components were also ineasured. The one is assigned to transient absorption of the inhomogencously broadened ground state absorption spectrum, while the other is the response of the solvent to the change of the electron configuration in the excited state due to solvation dynamics of the polar solvent molecules. To understand the anisotropy of Chlorophyll a in ethanol, the anisotropy profile was also performed by 405 nm excitation and found that the anisotropy profile is 0.143. The possible combination of θda, θdb and η at at excitation of By band has been simulated.展开更多
Ultrafast extreme ultraviolet (XUV) transient absorption spectroscopy measures the time- and frequencydependent light losses after light–matter interactions. In the linear region, the matter response to an XUV light ...Ultrafast extreme ultraviolet (XUV) transient absorption spectroscopy measures the time- and frequencydependent light losses after light–matter interactions. In the linear region, the matter response to an XUV light field is usually determined by the complex refractive index ̃n. The absorption signal is directly related to the imaginary part of ̃n, namely, the absorption index. The real part of ̃n refers to the real refractive index, which describes the chromatic dispersion of an optical material. However, the real refractive index information is usually not available in conventional absorption experiments. Here, we investigate the refractive index line shape in ultrafast XUV transient absorption spectroscopy by using a scheme that the XUV pulse traverses the target gas jet off-center. The jet has a density gradient in the direction perpendicular to the gas injection direction, which induces deflection on the XUV radiation. Our experimental and theoretical results show that the shape of the frequency-dependent XUV deflection spectra reproduces the refractive index line profile. A typical dispersive refractive index line shape is measured for a single-peak absorption;an additional shoulder structure appears for a doublet absorption.Moreover, the refractive index line shape is controlled by introducing a later-arrived near-infrared pulse to modify the phase of the XUV free induction decay, resulting in different XUV deflection spectra. The results promote our understanding of matter-induced absorption and deflection in ultrafast XUV spectroscopy.展开更多
Attosecond transient absorption(ATA)has been developed as an all-optical technique for probing electron dynamics in matter.Here we present a scheme that can modify the laserinduced state and the corresponding ATA spec...Attosecond transient absorption(ATA)has been developed as an all-optical technique for probing electron dynamics in matter.Here we present a scheme that can modify the laserinduced state and the corresponding ATA spectrum via excitation by a pair of XUV attosecond pulses and by a time-delayed mid-infrared(MIR)laser probe.Different from the scheme of the electronic excitation by a single XUV attosecond pulse,the application of a pair of XUV pulses provides extra degrees of freedom,such as the time delay and the intensity ratio between two XUV pulses,which make it possible to adjust the pump process,resulting in the modification of the ATA spectrum.We show that by varying the time delay between the two XUV pulses,the population of the dark state and the ATA spectrum of the laser-induced state have periodic modulations.We also demonstrate that the peak of the ATA spectrum of the laser-induced state appears at a fixed time delay between the XUV pair and the MIR laser when the intensity ratio is large,and it changes with the time delay when the intensity ratio is small,which can be related to either one of two peaks in the population of the dark state.展开更多
Small-molecule organic solar cell is a category of clean energy potential device since charge transfers between donor and acceptor.The morphologies,co-assembly behavior,interaction sites,and charge transfer of BTID-nF...Small-molecule organic solar cell is a category of clean energy potential device since charge transfers between donor and acceptor.The morphologies,co-assembly behavior,interaction sites,and charge transfer of BTID-nF(n=1,2)/PC71BM donor-acceptor system in the active layer of organic solar cell have been studied employing scanning tunneling microscopy(STM),scanning tunneling spectroscopy(STS),density functional theory(DFT)calculations,and transient absorption(TA)spectroscopy.The results show that BTID-1F and BTID-2F form bright strip structures,whereas BTID-nF(n=1,2)/PC71BM form ridge-like structures with each complex composed of one BTID-nF(n=1,2)molecule and four PC71BM molecules which adsorbed around the BTID-nF(n=1,2)molecule by S···πinteraction.With the assistance of S···πinteraction between BTID-nF(n=1,2)and PC71BM,BTID-nF(n=1,2)/PC71BM co-assembled ridge-like structures are more stable than the BTID-nF(n=1,2)ridge structures.To investigate the charge transfer of BTID-nF(n=1,2)/PC71BM system,STS measurements,DFT calculation,and TA spectroscopy are further performed.The results show that charge transfer occurs in BTID-nF(n=1,2)/PC71BM system with the electron transferring from BTID-nF(n=1,2)molecules to PC71BM.展开更多
A bulk heterojunction in organic solar cells is where charge separation and recombination occur.Molecular orientation at the interface is one of the key factors that dictate solar cell efficiency.Although X-ray scatte...A bulk heterojunction in organic solar cells is where charge separation and recombination occur.Molecular orientation at the interface is one of the key factors that dictate solar cell efficiency.Although X-ray scattering-based methods can determine donor/acceptor domain orientations between an anisotropic phase and an isotropic fullerene-based phase,the rise of nonfullerene solar cells presents a new challenge in delineating local molecular directions at the interface between two anisotropic donor/acceptor domains.Here,we determine interfacial molecular orientations of three high-efficiency small molecule solar cells(ZR1:Y6,B1:BO-4 Cl,and BTR:BO-4 Cl)using polarization-selective transient absorption spectroscopy.The polarization anisotropy of charge separation dynamics indicates an angle of~90°between ZR1 and Y6 molecules at the interface,an angle close to 0°between B1 and BO-4 Cl,and random orientations between BTR and BO-4 Cl.These observations provide complementary information to X-ray scattering measurements and highlight polarization-selective transient absorption spectroscopy as a tool to probe interfacial structure and dynamics of key photophysical steps in energy conversion.展开更多
Over the past decade the integration of ultrafast spectroscopy with nanoscience has greatly propelled the development of nanoscience, as the key information gleaned from the mechanistic studies with the assistance of ...Over the past decade the integration of ultrafast spectroscopy with nanoscience has greatly propelled the development of nanoscience, as the key information gleaned from the mechanistic studies with the assistance of ultrafast spectroscopy enables a deeper understanding of the structure–function interplay and various interactions involved in the nanosystems.This mini-review presents an overview of the recent advances achieved in our ultrafast spectroscopy laboratory that address the ultrafast dynamics and related mechanisms in several representative nanomaterial complex systems by means of femtosecond time-resolved transient absorption spectroscopy. We attempt to convey instructive, consistent information regarding the important processes, pathways, dynamics, and interactions involved in the nanomaterial complex systems,most of which exhibit excellent performance in photocatalysis.展开更多
Nanoparticles with non-spherical shapes are now being widely used for various photonic applications.We observe experimentally that the magnitude as well as the time dependence of the transient absorption of a colloid ...Nanoparticles with non-spherical shapes are now being widely used for various photonic applications.We observe experimentally that the magnitude as well as the time dependence of the transient absorption of a colloid of silver nanoplatelets depends on the relative polarization of the pump and probe pulses.There have been a few reports about the dependence of the transient signal magnitude on polarization,but little information is available on its temporal dependence.Using a theoretical model,we show that this observed behavior arises from the fact that the energy absorption by a non-spherical nanoparticle depends on,among other factors,the nanoparticle orientation with respect to the pump and probe polarization directions.It is essential to consider this when estimating nanoparticle characteristics such as carrier thermalization time,carrier–phonon scattering time,and complex polarizability from transient absorption measurements.展开更多
In DMSO/water(4:1),photolysis of the dihydroxy-Sn(IV)-rnesoporphyrin dimethyl ester (SnP)/methyl viologen(MV^(2+))/ethylene diamine tetraacetic acid(EDTA)ternary system produces methyl viologen cation radical with a q...In DMSO/water(4:1),photolysis of the dihydroxy-Sn(IV)-rnesoporphyrin dimethyl ester (SnP)/methyl viologen(MV^(2+))/ethylene diamine tetraacetic acid(EDTA)ternary system produces methyl viologen cation radical with a quantum yield of 0.67,much higher than that of systems with other metal complexes of rnesoporphyrin dimethyl ester.Neither EDTA nor MV^(2+) quenches the stationary fluorescence of SnP,implying that the reaction does not take place at the singlet state.With flash photolysis we obtain the T-T absorption spectrum of SnP(λ_(max)-440 nm).By following the decay of this absorption,the triplet life time of SnP is estimated to be 41 μs.The life time is related to the concentration of either MV^(2+) or EDTA.Good linear relationships are obtained by plotting τ_0/τ vs.the concentration of MV^(2+) or EDTA(Stern-Volmer plot),from which we determine the quenching constants:k_q(MV^(2+))=5.5×10~7 mol^(-7) s^(-1);kq(EDTA)=2.7×10~7 mol^(-1),s^(-1).The data suggests that upon photolysis of the above ternary system,both oxidative quenching and reductive quenching of the triplet state of the sensitizer are occurring.From the measured phosphorescence spectrum(λ_(max) 704nm)and the ground state redox potentials (E_(1/2)^(red)～-0.84V,E_(1/2)^(ox)～ Ag/AgCl,KCl(sat.)),we obtain the redox potential of triplet SnP to be E (P^+/P)～-0.33 V, E(P/P-)～+0.92 V.Matching this data with the redox potential of MV^(2+) and EDTA,we establish the fact that during the photolysis of the SnP/MV^(2+)/EDTA ternary system,both oxidative and reductive quenching are thermodynamically favorable processes.This is also the reason why the SnP sensitized reaction is much more efficient relative to other mesoporphyrin derivatives.展开更多
In this study,diodo boron dipyrromethene(BODIPY)is employed a8 the energy donor and 3,4,9,10-perylene tetracarboxylic dianhydride(PDA)as the energy acceptor,enabling the synthesis of two new compounds:a BODIPY-perylen...In this study,diodo boron dipyrromethene(BODIPY)is employed a8 the energy donor and 3,4,9,10-perylene tetracarboxylic dianhydride(PDA)as the energy acceptor,enabling the synthesis of two new compounds:a BODIPY-perylene dyad named P1,and a triad named P2.To investigate the impact of the energy donor on the photophysical processes of the system,P1 comprises one diodo-BODIPY unit and one PDA unit,whereas P2 contains two diodo-BODIPY moieties and one PDA unit.Due to the good spectral complementarity between diiodo-BODIPY and PDA,these two compounds exhibit excellent light-harvesting capabilities in the 400-620 nm range.Steady-state fluorescence spectra demonstrate that when preferentially exciting the diodo-BODIPY moiety,it can effectively transfer energy to PDA;when selectively exciting the PDA moiety,quenching of PDA fluorescence is observed in both P1 and P2.Nanosecond transient absorption results show that both compounds can efficiently generate triplet excited states,which are located on the PDA part.The lifetimes of the triplet states for these two compounds are 103 and 89μs,respectively,significantly longer than that of diiodo-BODIPY.The results from the photooxidation experiments reveal that both P1 and P2 demonstrate good photostability and photooxidation capabilities,with P2 showing superior photooxidative efficiency.The photooxidation rate constant for P2 is 1.3 times that of P1,and its singlet oxygen quantum yield is 1.6 times that of P1.The results obtained here offer valuable insights for designing new photosensitizers.展开更多
The bimetallic nanostructures that mix a plasmonic metal with a transition metal in the form of the core-shell nanoparticles are promising to promote catalytic performance.But it is still unclear how the heat(hot elec...The bimetallic nanostructures that mix a plasmonic metal with a transition metal in the form of the core-shell nanoparticles are promising to promote catalytic performance.But it is still unclear how the heat(hot electrons and phonons)transfers on the interface between two metals.We have designed and synthesized Au@Cu bimetallic nanoparticles with Au as core and Cu as shell.By using transient absorption spectroscopy,we find that there are two plasmon induced heat funneling processes from Au core to Cu shell.One is the electron temperature equilibrium(electron heat transfer)with equilibration time of~560 fs.The other is the lattice temperature equilibrium(lattice heat transfer)with equilibration time of~13 ps.This plasmon induced heat funneling may be universal in similar bimetallic nanostructures,so our finding could contribute to further understanding the catalytic mechanism of bimetallic plasmonic photothermal catalysis.展开更多
Photo-induced proton coupled electron transfer(PCET)is essential in the biological,photosynthesis,catalysis and solar energy conversion processes.Recently,p-nitrophenylphenol(HO-Bp-NO2)has been used as a model compoun...Photo-induced proton coupled electron transfer(PCET)is essential in the biological,photosynthesis,catalysis and solar energy conversion processes.Recently,p-nitrophenylphenol(HO-Bp-NO2)has been used as a model compound to study the photo-induced PCET mechanism by using ultrafast spectroscopy.In transient absorption spectra both singlet and triplet states were observed to exhibit PCET behavior upon laser excitation of HO-Bp-NO2.When we focused on the PCET in the triplet state,a new sharp band attracted us.This band was recorded upon excitation of HO-Bp-NO2 in aprotic polar solvents,and has not been observed for p-nitrobiphenyl which is without hydroxyl substitution.In order to find out what the new band represents,acidic solutions were used as an additional proton donor considering the acidity of HO-Bp-NO2.With the help of results in strong(~10^-1 mol/L)and weak(~10^-4 mol/L)acidic solutions,the new band is identified as open shell singlet O-Bp-NO2H,which is generated through protonation of nitro O in 3HO-Bp-NO2 followed by deprotonation of hydroxyl.Kinetics analysis indicates that the formation of radical·OBp-NO2 competes with O-Bp-NO2H in the way of concerted electron-proton transfer and/or proton followed electron transfers and is responsible for the low yield of O-Bp-NO2H.The results in the present work will make it clear how the3HO-Bp-NO2 deactivates in aprotic polar solvents and provide a solid benchmark for the deeply studying the PCET mechanism in triplets of analogous aromatic nitro compounds.展开更多
Two dimethylamino-carbaldehyde derivatives with differentπ-bridge lengths were prepared,and their transient optical properties and photophysical mechanisms were investigated by transient absorption spectroscopy and Z...Two dimethylamino-carbaldehyde derivatives with differentπ-bridge lengths were prepared,and their transient optical properties and photophysical mechanisms were investigated by transient absorption spectroscopy and Z-scan measurements.Owing to the difference in molecular structures,the two compounds exhibit different populations of locally excited states and,therefore,they also produce different transient absorption spectra.After photoexcitation,both molecular materials exhibit a wide excited state absorption band from 450 nm to 1000 nm.Meanwhile,the excited state lifetimes are dramatically different,2 ns and 100 ps,for the two molecules.A figure of merit greater than 2 at the wavelength of1000 nm is obtained.The results show that modulating the population of the locally excited states in this type of molecule can be a promising approach for obtaining optical switching and solar cell materials.展开更多
Antimony trisulfide(Sb_(2)S_(3)) solar cells suffer from large open circuit voltage deficits due to their intrinsic defects which limit the power conversion efficiency.Thus,it is important to elucidate these defects’...Antimony trisulfide(Sb_(2)S_(3)) solar cells suffer from large open circuit voltage deficits due to their intrinsic defects which limit the power conversion efficiency.Thus,it is important to elucidate these defects’ origin and defects at the interface.Here,we discover that sulfide radical defects have a significant impact on the performance of Sb_(2)S_(3)solar cells.Moreover,it has been illustrated that these defects at the CdS/Sb_(2)S_(3)interface can be reduced by optimizing the deposition process.A trap distribution model is used to quantify the defect density at the CdS/Sb_(2)S_(3)interface.It shows that the interface defects can be reduced by24% by improving the deposition process.This work reveals the importance of interface defects and guides the future optimization of Sb_(2)S_(3)solar cells.展开更多
基金supported by the National Natural Science Foundation of China(No.61805134 and No.11974229)Applied Basic Research Program in Shanxi Province,China(No.201801D221016 and No.202103021223254)+2 种基金Scientific and Technological Innovation Pro-grams of Higher Education Institutions in Shanxi(No.2020L0235 and No.2021L257)Linfen Key Re-search and Development Program(No.2028)Graduate Innovation Project in Shanxi Province(No.2022Y498).
文摘Zero-dimensional environmentally friendly carbon quantum dots(CQDs)combined with two-di-mensional materials have a wide range of applications in optoelec-tronic devices.We combined steady-state and transient absorp-tion spectroscopies to study the energy transfer dynamics between CQDs and molybdenum disulfide(MoS_(2)).Transient absorption plots showed photoinduced absorption and stimulated emission features,which involved the intrinsic and defect states of CQDs.Adding MoS_(2)to CQDs solution,the lowest unoccupied molecular orbital of CQDs transferred energy to MoS_(2),which quenched the intrinsic emission at 390 nm.With addition of MoS_(2),CQD-MoS_(2)composites quenched defect emission at 490 nm and upward absorption,which originated from another energy transfer from the defect state.Two energy transfer paths between CQDs and MoS_(2)were efficiently manipulated by changing the concentration of MoS_(2),which laid a foundation for improving device performance.
基金This work was supported by the National Natural Basic Research Program of China （No.2013CB922200）,the National Natural Science Foundation of China （No.11674128, No.11474129, and No.11504129）, Jilin Province Scientific and Technological Development Program, China （No.20170101063JC）, the Thirteenth Five- Year Scientific and Technological Research Project of the Education Department of Jilin Province, China （No.n00）.
文摘The mixture of graphene oxide （GO） and dye molecules may provide some new applications due to unique electronic, optical, and structural properties. Methylene blue （MB）, a typ- ical anionic dye, can attach on GO via π-π stacking and electrostatic interaction, and the molecule removal process on GO has been observed. However, it remains unclear about the ultrafast carrier dynamics and the internal energy transfer pathways of the system which is composed of GO and MB. We have employed ultrafast optical pump-probe spectroscopy to investigate the excited dynamics of the GO-MB system dispersed in water by exciting the samples at 400 nm pump pulse. The pristine MB and GO dynamics are also analyzed in tandem for a direct comparison. Utilizing the global analysis to fit the measured signal via a sequential model, five lifetimes are acquired：（0.61±0.01） ps, （3.52±0.04） ps, （14.1±0.3） ps, （84±2） ps, and （3.66±0.08） ns. The ultrafast dynamics corresponding to these lifetimes was analyzed and the new relaxation processes were found in the GO-MB system, compared with the pristine MB. The results reveal that the functionalization of GO can alter the known decay pathways of MB via the energy transfer from GO to MB in system, the increased intermediate state, and the promoted energy transfer from triplet state MB to ground state oxygen molecules dissolved in aqueous sample.
文摘We detect a relaxation process of excited SQ02 dye in the chlorobenzene solution and an- chor SQ02 on Al2O3 and TiO2 film, so as to investigate the photophysical properties of pristine SQ02 in the monodisperse system, aggregation state, and the corresponding inter- facial electron transfer process. The experimental data show that the lifetime of SQ02 in the monondisperse system is ～2.0 ns, but that of SQ02 anchored on the Al2O3 film could obviously decrease to ～21 ps. The time of electron transfer from excited SQ02 to TiO2 film is estimated to be ～2.6 ps and the yield of electron injection is estimated to be ～89.1%, which matches the incident photon to current efficiency of dye-sensitized solar cell based on SQ02. In addition, some dyes are found to pack on the other dyes anchored on the nanocrystal film, and their relaxation time could reach ～60 ps. They couldn＇t participate in the interfacial electron transfer, since they are far away from the TiO2 interface.
基金Supported by the National Basic Research Program of China under Grant No 2013CB922203the National Natural Science Foundation of China under Grant No 11374366+1 种基金the Innovation Foundation of National University of Defense Technology under Grant No B110204the Hunan Provincial Innovation Foundation for Postgraduate under Grant No CX2011B010
文摘Using the fully propagated time-dependent Hartree–Fock method, we identify that both the dynamic core polarization and multiorbital contributions are important in the attosecond transient absorption of CO molecules.The dynamics of core electrons effectively modifies the behaviors of electrons in the highest occupied molecular orbital, resulting in the modulation of intensity and position of the absorption peaks. Depending on the alignment angles, different inner orbitals are identified to contribute, and even dominate the total absorption spectra. As a result, multi-electron fingerprints are encoded in the absorption spectra, which shed light on future applications of attosecond transient absorption in complex systems.
基金supported by the National Natural Science Foundation of China(No.21603049,No.11674355,No.11705043,No.21327804,No.11364043)the Fundamental Research Funds for the Central Universities(No.JZ2015HGBZ0532)+1 种基金the Industry-UniversityResearch Fund of Hefei University of Technology Xuancheng Campus(No.XC2016JZBZ11)the Natural Science Foundation of Xinjiang Uygur Autonomous Region(No.2016D01A058)
文摘The ultrafast photoisomerization and excited-state dynamics of trans-4-methoxyazobenzene (trans-4-MAB) in solutions were investigated by femtosecond transient absorption spectroscopy and quantum chemistry calculations. After being excited to the S2 state, the two-dimensional transient absorptions spectra show that cis-4-MAB is produced and witnessed by the permanent positive absorption in 400-480 nm. Three decay components are determined to be 0.11, 1.4 and 2.9 ps in ethanol, and 0.16, 1.5 and 7.5 ps in ethylene glycol, respectively. The fast component is assigned to the internal conversion from the S2 to S1 state. The other relaxation pathways are correlated with the decay of the S1 state via internal conversion and isomerization, and the vibrational cooling of the hot S0 state of the cis-isomer. Comparing of the dynamics in different solvents, it is demonstrated that the photoisomerization pathway undergoes the inversion mechanism rather than the rotation mechanism.
文摘Photoinduced electron transfer processes between fullerenes (C60 / C70) and N, N, N, N tetra - ( p-methylphenyl ) - 4, 4 diamino - 1, 1- diphenyl ether ( TPDAE ) have been studied by nanosecond laser flash photolysis. Quantum yields and rate constants of electron transfer from TPDAE to excited triplet state of fullerenes (C60 / C70 ) in benzonitrile have been evaluated by observing the transient absorption bands in the near-IR region where the excited triplet state, radical anion of fullerenes ( C60 / C70 ) and radical cations of TPDAE appear.
文摘The ultrafast excited state dynamics of trans-4-aminoazobenzene （trans-4-AAB） in ethanol was investigated by femtosecond transient absorption spectroscopy. After being excited to the S2 state by 400 nm, trans-4-AAB decays from the S2 state to the hot S1 state by internal conversion with time constant of -70 fs. The photoisomerization through inversion mechanism on the S1 potential energy surface and the internal conversion from the S1 state to the hot So state are observed, respectively. The average timescale of these two decay pathways is -0.7 ps. And the vibrational cooling of the hot So state of cis- and trans-4- AAB occur with time constants of -4 and N13 ps, respectively. Furthermore, the ultrafast intersystem crossing process are also observed. The timescale of intersystem crossing from the S2 state to the T4 state is about 480 ps while from the S1 state to the T2 state is -180 ps.
基金This work was supported by tile National Natural Science Foundation of China （NSFCNo.29825107,No.29853001）,the Knowledge Innovation Program of the Chinese Academy of Sciences（Grant：DICP K200/E3）and NKBRSF,Support is also provided from the National Science Council of Taiwan and Academia Sinica.
文摘The excited state of Chlorophyll a is investiga.ted by ferntosecond transient absorption. The transient absorption spectra of Q band and By band of Chlorophyll a in ethanol have been observed. The fast kinetics of Chlorophyll a which exhibit two ultrafast components were also ineasured. The one is assigned to transient absorption of the inhomogencously broadened ground state absorption spectrum, while the other is the response of the solvent to the change of the electron configuration in the excited state due to solvation dynamics of the polar solvent molecules. To understand the anisotropy of Chlorophyll a in ethanol, the anisotropy profile was also performed by 405 nm excitation and found that the anisotropy profile is 0.143. The possible combination of θda, θdb and η at at excitation of By band has been simulated.
基金support of the Joint Centre for Extreme Photonics.Funding:This work is supported by the start-up grant of ShanghaiTech University,Double First-Class Initiative Fund of ShanghaiTech University,Shanghai Rising-Star Program(22QA1406200)National Natural Science Foundation of China(12274297,92250303)+7 种基金Shanghai Science and Technology Program(21511105000)NSERC Discovery Grant program(RGPIN-327147-2012)by the U.S.Army Research Office through Award W911NF-14-1-0383Part of this research used Beamline 03U of the Shanghai Synchrotron Radiation Facilitysupported by the ME2 project under contract no.11227902the National Natural Science Foundation of China.Y.F.and C.J.are supported by the National Natural Science Foundation of China(12274230,91950102,and 11834004)Funding of NJUST(TSXK2022D005)H.X.is supported by the National Natural Science Foundation of China(12074063 and 12264003)。
文摘Ultrafast extreme ultraviolet (XUV) transient absorption spectroscopy measures the time- and frequencydependent light losses after light–matter interactions. In the linear region, the matter response to an XUV light field is usually determined by the complex refractive index ̃n. The absorption signal is directly related to the imaginary part of ̃n, namely, the absorption index. The real part of ̃n refers to the real refractive index, which describes the chromatic dispersion of an optical material. However, the real refractive index information is usually not available in conventional absorption experiments. Here, we investigate the refractive index line shape in ultrafast XUV transient absorption spectroscopy by using a scheme that the XUV pulse traverses the target gas jet off-center. The jet has a density gradient in the direction perpendicular to the gas injection direction, which induces deflection on the XUV radiation. Our experimental and theoretical results show that the shape of the frequency-dependent XUV deflection spectra reproduces the refractive index line profile. A typical dispersive refractive index line shape is measured for a single-peak absorption;an additional shoulder structure appears for a doublet absorption.Moreover, the refractive index line shape is controlled by introducing a later-arrived near-infrared pulse to modify the phase of the XUV free induction decay, resulting in different XUV deflection spectra. The results promote our understanding of matter-induced absorption and deflection in ultrafast XUV spectroscopy.
基金supported by the National Natural Science Foundation of China(Grant Nos.91950102 and 11834004)the Natural Science Foundation of Jiangsu Province(Grant No.BK20220925)the Funding of Nanjing University of Science and Technology(NJUST)(Grant No.TSXK2022D005)
文摘Attosecond transient absorption(ATA)has been developed as an all-optical technique for probing electron dynamics in matter.Here we present a scheme that can modify the laserinduced state and the corresponding ATA spectrum via excitation by a pair of XUV attosecond pulses and by a time-delayed mid-infrared(MIR)laser probe.Different from the scheme of the electronic excitation by a single XUV attosecond pulse,the application of a pair of XUV pulses provides extra degrees of freedom,such as the time delay and the intensity ratio between two XUV pulses,which make it possible to adjust the pump process,resulting in the modification of the ATA spectrum.We show that by varying the time delay between the two XUV pulses,the population of the dark state and the ATA spectrum of the laser-induced state have periodic modulations.We also demonstrate that the peak of the ATA spectrum of the laser-induced state appears at a fixed time delay between the XUV pair and the MIR laser when the intensity ratio is large,and it changes with the time delay when the intensity ratio is small,which can be related to either one of two peaks in the population of the dark state.
基金the National Basic Research Program of China(Nos.2017YFA0205000 and 2016YFA0200700)the National Natural Science Foundation of China(Nos.21773041,21972031,21301092,and 20962002)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB36000000).
文摘Small-molecule organic solar cell is a category of clean energy potential device since charge transfers between donor and acceptor.The morphologies,co-assembly behavior,interaction sites,and charge transfer of BTID-nF(n=1,2)/PC71BM donor-acceptor system in the active layer of organic solar cell have been studied employing scanning tunneling microscopy(STM),scanning tunneling spectroscopy(STS),density functional theory(DFT)calculations,and transient absorption(TA)spectroscopy.The results show that BTID-1F and BTID-2F form bright strip structures,whereas BTID-nF(n=1,2)/PC71BM form ridge-like structures with each complex composed of one BTID-nF(n=1,2)molecule and four PC71BM molecules which adsorbed around the BTID-nF(n=1,2)molecule by S···πinteraction.With the assistance of S···πinteraction between BTID-nF(n=1,2)and PC71BM,BTID-nF(n=1,2)/PC71BM co-assembled ridge-like structures are more stable than the BTID-nF(n=1,2)ridge structures.To investigate the charge transfer of BTID-nF(n=1,2)/PC71BM system,STS measurements,DFT calculation,and TA spectroscopy are further performed.The results show that charge transfer occurs in BTID-nF(n=1,2)/PC71BM system with the electron transferring from BTID-nF(n=1,2)molecules to PC71BM.
基金financially supported from National Key R&D Program of China(2016YFA0200700)the National Natural Science Foundation of China(22071207,21721001,21805230,51873217,21734008,51773047,52073068)。
文摘A bulk heterojunction in organic solar cells is where charge separation and recombination occur.Molecular orientation at the interface is one of the key factors that dictate solar cell efficiency.Although X-ray scattering-based methods can determine donor/acceptor domain orientations between an anisotropic phase and an isotropic fullerene-based phase,the rise of nonfullerene solar cells presents a new challenge in delineating local molecular directions at the interface between two anisotropic donor/acceptor domains.Here,we determine interfacial molecular orientations of three high-efficiency small molecule solar cells(ZR1:Y6,B1:BO-4 Cl,and BTR:BO-4 Cl)using polarization-selective transient absorption spectroscopy.The polarization anisotropy of charge separation dynamics indicates an angle of~90°between ZR1 and Y6 molecules at the interface,an angle close to 0°between B1 and BO-4 Cl,and random orientations between BTR and BO-4 Cl.These observations provide complementary information to X-ray scattering measurements and highlight polarization-selective transient absorption spectroscopy as a tool to probe interfacial structure and dynamics of key photophysical steps in energy conversion.
基金support from the National Natural Science Foundation of China (21573211 and 21421063)the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB01020200)the Fundamental Research Funds for the Central Universities of China (WK2340000063)
文摘Over the past decade the integration of ultrafast spectroscopy with nanoscience has greatly propelled the development of nanoscience, as the key information gleaned from the mechanistic studies with the assistance of ultrafast spectroscopy enables a deeper understanding of the structure–function interplay and various interactions involved in the nanosystems.This mini-review presents an overview of the recent advances achieved in our ultrafast spectroscopy laboratory that address the ultrafast dynamics and related mechanisms in several representative nanomaterial complex systems by means of femtosecond time-resolved transient absorption spectroscopy. We attempt to convey instructive, consistent information regarding the important processes, pathways, dynamics, and interactions involved in the nanomaterial complex systems,most of which exhibit excellent performance in photocatalysis.
文摘Nanoparticles with non-spherical shapes are now being widely used for various photonic applications.We observe experimentally that the magnitude as well as the time dependence of the transient absorption of a colloid of silver nanoplatelets depends on the relative polarization of the pump and probe pulses.There have been a few reports about the dependence of the transient signal magnitude on polarization,but little information is available on its temporal dependence.Using a theoretical model,we show that this observed behavior arises from the fact that the energy absorption by a non-spherical nanoparticle depends on,among other factors,the nanoparticle orientation with respect to the pump and probe polarization directions.It is essential to consider this when estimating nanoparticle characteristics such as carrier thermalization time,carrier–phonon scattering time,and complex polarizability from transient absorption measurements.
文摘In DMSO/water(4:1),photolysis of the dihydroxy-Sn(IV)-rnesoporphyrin dimethyl ester (SnP)/methyl viologen(MV^(2+))/ethylene diamine tetraacetic acid(EDTA)ternary system produces methyl viologen cation radical with a quantum yield of 0.67,much higher than that of systems with other metal complexes of rnesoporphyrin dimethyl ester.Neither EDTA nor MV^(2+) quenches the stationary fluorescence of SnP,implying that the reaction does not take place at the singlet state.With flash photolysis we obtain the T-T absorption spectrum of SnP(λ_(max)-440 nm).By following the decay of this absorption,the triplet life time of SnP is estimated to be 41 μs.The life time is related to the concentration of either MV^(2+) or EDTA.Good linear relationships are obtained by plotting τ_0/τ vs.the concentration of MV^(2+) or EDTA(Stern-Volmer plot),from which we determine the quenching constants:k_q(MV^(2+))=5.5×10~7 mol^(-7) s^(-1);kq(EDTA)=2.7×10~7 mol^(-1),s^(-1).The data suggests that upon photolysis of the above ternary system,both oxidative quenching and reductive quenching of the triplet state of the sensitizer are occurring.From the measured phosphorescence spectrum(λ_(max) 704nm)and the ground state redox potentials (E_(1/2)^(red)～-0.84V,E_(1/2)^(ox)～ Ag/AgCl,KCl(sat.)),we obtain the redox potential of triplet SnP to be E (P^+/P)～-0.33 V, E(P/P-)～+0.92 V.Matching this data with the redox potential of MV^(2+) and EDTA,we establish the fact that during the photolysis of the SnP/MV^(2+)/EDTA ternary system,both oxidative and reductive quenching are thermodynamically favorable processes.This is also the reason why the SnP sensitized reaction is much more efficient relative to other mesoporphyrin derivatives.
基金supported by the Research Project for Outstanding Young People in Universities of Anhui Province(No.2023AH030099)the China Postdoctoral Science Foundation(No.2023M733378)+3 种基金the National Natural Science Foundation of China(No.21702042,No.22305059,No.22103010)the National University Students'Innovation and Entrepreneurship Training Program(No.202311059024)the Anhui Provincial Natural Science Foundation(No.2308085QB59)the Anhui Provincial Excellent Scientific Research and Innovation Team(No.2022AH010096).
文摘In this study,diodo boron dipyrromethene(BODIPY)is employed a8 the energy donor and 3,4,9,10-perylene tetracarboxylic dianhydride(PDA)as the energy acceptor,enabling the synthesis of two new compounds:a BODIPY-perylene dyad named P1,and a triad named P2.To investigate the impact of the energy donor on the photophysical processes of the system,P1 comprises one diodo-BODIPY unit and one PDA unit,whereas P2 contains two diodo-BODIPY moieties and one PDA unit.Due to the good spectral complementarity between diiodo-BODIPY and PDA,these two compounds exhibit excellent light-harvesting capabilities in the 400-620 nm range.Steady-state fluorescence spectra demonstrate that when preferentially exciting the diodo-BODIPY moiety,it can effectively transfer energy to PDA;when selectively exciting the PDA moiety,quenching of PDA fluorescence is observed in both P1 and P2.Nanosecond transient absorption results show that both compounds can efficiently generate triplet excited states,which are located on the PDA part.The lifetimes of the triplet states for these two compounds are 103 and 89μs,respectively,significantly longer than that of diiodo-BODIPY.The results from the photooxidation experiments reveal that both P1 and P2 demonstrate good photostability and photooxidation capabilities,with P2 showing superior photooxidative efficiency.The photooxidation rate constant for P2 is 1.3 times that of P1,and its singlet oxygen quantum yield is 1.6 times that of P1.The results obtained here offer valuable insights for designing new photosensitizers.
基金supported by the National Naural Science Foudation of China(No.21873013 and No.22273006).
文摘The bimetallic nanostructures that mix a plasmonic metal with a transition metal in the form of the core-shell nanoparticles are promising to promote catalytic performance.But it is still unclear how the heat(hot electrons and phonons)transfers on the interface between two metals.We have designed and synthesized Au@Cu bimetallic nanoparticles with Au as core and Cu as shell.By using transient absorption spectroscopy,we find that there are two plasmon induced heat funneling processes from Au core to Cu shell.One is the electron temperature equilibrium(electron heat transfer)with equilibration time of~560 fs.The other is the lattice temperature equilibrium(lattice heat transfer)with equilibration time of~13 ps.This plasmon induced heat funneling may be universal in similar bimetallic nanostructures,so our finding could contribute to further understanding the catalytic mechanism of bimetallic plasmonic photothermal catalysis.
基金supported by the National Natural Science Foundation of China(No.21973082)。
文摘Photo-induced proton coupled electron transfer(PCET)is essential in the biological,photosynthesis,catalysis and solar energy conversion processes.Recently,p-nitrophenylphenol(HO-Bp-NO2)has been used as a model compound to study the photo-induced PCET mechanism by using ultrafast spectroscopy.In transient absorption spectra both singlet and triplet states were observed to exhibit PCET behavior upon laser excitation of HO-Bp-NO2.When we focused on the PCET in the triplet state,a new sharp band attracted us.This band was recorded upon excitation of HO-Bp-NO2 in aprotic polar solvents,and has not been observed for p-nitrobiphenyl which is without hydroxyl substitution.In order to find out what the new band represents,acidic solutions were used as an additional proton donor considering the acidity of HO-Bp-NO2.With the help of results in strong(~10^-1 mol/L)and weak(~10^-4 mol/L)acidic solutions,the new band is identified as open shell singlet O-Bp-NO2H,which is generated through protonation of nitro O in 3HO-Bp-NO2 followed by deprotonation of hydroxyl.Kinetics analysis indicates that the formation of radical·OBp-NO2 competes with O-Bp-NO2H in the way of concerted electron-proton transfer and/or proton followed electron transfers and is responsible for the low yield of O-Bp-NO2H.The results in the present work will make it clear how the3HO-Bp-NO2 deactivates in aprotic polar solvents and provide a solid benchmark for the deeply studying the PCET mechanism in triplets of analogous aromatic nitro compounds.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.U1630103 and 11704273)Natural Science Foundation of Jiangsu Province,China(Grant No.BK20170375)Natural Science Foundation of the Higher Education Institutions of Jiangsu Province,China(Grant No.17KJB140021)
文摘Two dimethylamino-carbaldehyde derivatives with differentπ-bridge lengths were prepared,and their transient optical properties and photophysical mechanisms were investigated by transient absorption spectroscopy and Z-scan measurements.Owing to the difference in molecular structures,the two compounds exhibit different populations of locally excited states and,therefore,they also produce different transient absorption spectra.After photoexcitation,both molecular materials exhibit a wide excited state absorption band from 450 nm to 1000 nm.Meanwhile,the excited state lifetimes are dramatically different,2 ns and 100 ps,for the two molecules.A figure of merit greater than 2 at the wavelength of1000 nm is obtained.The results show that modulating the population of the locally excited states in this type of molecule can be a promising approach for obtaining optical switching and solar cell materials.
基金support from the National Key R&D Program of China(2019YFE0120300)the National Natural Science Foundation of China(NSFC,11904266,62204174 and 91850207)the Fundamental Research Funds for the Central Universities(2042021kf0202 and 2042021kf0069)。
文摘Antimony trisulfide(Sb_(2)S_(3)) solar cells suffer from large open circuit voltage deficits due to their intrinsic defects which limit the power conversion efficiency.Thus,it is important to elucidate these defects’ origin and defects at the interface.Here,we discover that sulfide radical defects have a significant impact on the performance of Sb_(2)S_(3)solar cells.Moreover,it has been illustrated that these defects at the CdS/Sb_(2)S_(3)interface can be reduced by optimizing the deposition process.A trap distribution model is used to quantify the defect density at the CdS/Sb_(2)S_(3)interface.It shows that the interface defects can be reduced by24% by improving the deposition process.This work reveals the importance of interface defects and guides the future optimization of Sb_(2)S_(3)solar cells.
