Ultrafast Kinetics Study Of The Electron Transfer Process Between Near-Infrared PbS Quantum Dots And Anthraquinone Molecules

Near-infrared(NIR)PbS quantum dots(QDs)are characterized by high migration rate,multi-exciton effect,and adjustable band gap,etc.PbS QDs not only reserve all advantages of visible light QDs,but their absorption spectrum can extend from ultraviolet visible region into the NIR region,which can cover broader solar spectrum.Therefore,NIR PbS QDs are of extensive application values in photoelectric devices.Electron transfer process plays a crucial part in photoelectric devices,in which QDs serve as the light absorption layer.Thus,effectively regulating the the electron transfer process,especially accelerating it,will be of great significance to improve the photoelectric conversion efficiency.The anthraquinone(AQ)derivative molecules were selected as the electron acceptor,due to strong visible light absorption and high stability.Hence,an in-depth study of the ultrafast kinetic process of electron transfer in PbS-AQ compounds will enable us to better understand the evolutionary mechanism of electron transfer in PbS-organic compounds.It is helpful for us to control this ultrafast kinetics process,and providing a reference for manufacturing better photoelectric conversion devices.The femtosecond transient absorption spectroscopy was used to explore the microscopic regulatory mechanism of environmental effects for the electron transfer process,and a series of results were obtained as follows:(1)The ultrafast transient absorption spectroscopy was used to discuss the effect of temperature(295K to 180K)on the electron transfer process between NIR PbS QDs and AQ molecules.As the temperature declined,the steady-state fluorescence intensity of PbS-AQ compounds was enhanced due to the suppression of the phonon-charge carrier interaction in PbS QDs.The transient spectral results at different temperatures showed that the electron transfer process gradually slowed down at cryogenic temperature,which was ascribed to the thickening of modification chain on the PbS surface and the decrease in the penetrability of the chain at low temperature.In our study,the microscopic influence mechanism of temperature on the electron transfer process between PbS QDs and AQ molecules was revealed.(2)The effect of pressure on electron transfer process between NIR PbS QDs and AQ molecules was studied by combining the ultrafast transient absorption spectroscopy with the high-pressure anvil cell technique.It found that the transient absorption spectrum of PbS-AQ compounds experienced red shift as the pressure elevated,indicating that the increase of pressure could induce the widening of PbS QDs band gap.According to the kinetics global fitting results,the electron transfer process was evidently influenced by the pressure(from atmospheric pressure to 1.50GPa),and the electron transfer rate increased from 9.2 ps to 4.4 ps.It successfully reveals that the promotional electron transfer rate in the NIR was assigned to shortened distance between PbS and AQ under compression.Our results manifested that the pressure could be a new means of controlling the electron transfer rate.(3)The ultrafast electron transfer process between PbS QDs and different chlorine-substituted AQ molecules was studied via the femtosecond transient absorption spectroscopy.The ultrafast kinetics results of PbS-1-CAQ,PbS-1,8-DCAQ,and PbS-1,4,5,8-TTAQ compound showed that the electron transfer process between PbS QDs and different chlorine-substituted AQ molecules was gradually accelerated as the number of chlorine atoms in the acceptor molecules was increased.Through the calculation according to Marcus electron transfer theory,with the increase the number of chlorine atoms substituted in AQ molecules,the driving forces of the complexes were gradually increased,thus speeding up electron transfer process.(4)The electron transfer process from photoinduced PbS QDs to AQ molecular in different solvents(dichloromethane,n-hexane,carbon tetrachloride,and n-dodecane)was explored through the femtosecond transient absorption spectroscopy.The ultrafast kinetics results of PbS-AQ compound system in these four solvents showed that the electron transfer rate of PbS-AQ compound system was the fastest in carbon tetrachloride,while the electron transfer rate in dichloromethane was the slowest.According to Marcus electron transfer theory,the reorganization energy of the system in four solvents was calculated.The calculation results showed that the external reorganization energy of the PbS-AQ compound system varied a lot with the solvent type,and it also affect the ET rates of PbS-AQ compound.