| Through-space charge transfer has become a thriving strategy of modulating photogenerated charges in organic photo-responsive molecular systems for potential applications in luminescence,optoelectronics and photochemical conversion.However,materials with uniform properties can no longer meet various needs.The development of smart materials that can respond to external stimuli has attracted a lot of interest.For example,the configuration between the electron donor and acceptor is generally fixed in organic molecular systems capable of through-space charge transfer.Although this is conducive to the initial photogenerated electron transfer process,it is not conducive to alleviating charge recombination.The ideal situation is that when the distance between the donor and the acceptor is close,the photo-generated electron transfer occurs,and then the distance between the donor and the acceptor is farther,which reduces the occurrence of the charge recombination process.In this process,light can be used as an external stimulus to adjust it.From the perspective of adjusting the molecular configuration,this paper conducts first-principle simulations,confirms the through-space charge transfer on the constructed molecular model and verifies the response to external light stimuli.This paper is divided into the following chapters:The first chapter mainly introduces three aspects,namely photoelectric conversion,photo-driven CO2 reduction and photo-switch molecules.Energy is very important to the development of society,solar energy is a kind of renewable energy and has the advantages of clean and pollution-free,so it has been favored by many scientists.Both photoelectric conversion and photo-driven CO2 reductions are the ways of people use sunlight.Among them,a key issue that affects the efficiency of using sunlight is the problem of charge recombination.The main work of this paper is to use photo-switch molecule(bridged azobenzene)to dynamically control the through-space charge transfer in organic systems.In chapter 2,we briefly introduce the density functional theory(DFT),time-dependent density functional theory and the quantum chemical calculation software package.Density functional theory uses electron density instead of wave function as the research object,which greatly facilitates the calculation process.The Hohenberg-Kohn theorem is a sign of the birth of modern density functional theory,and the emergence of the KS equation provides people with a method to solve the Schrodinger equation.Since the exchange correlation potential energy in the KS equation is unknown,many approximation methods have been developed later,including local density approximation,generalized gradient approximation,hybrid functional and so on.Time-dependent density functional theory provides a theoretical basis for people to study the information of excited states.In the specific calculation,we select the appropriate calculation software for calculation according to the calculation system and purpose.The third chapter introduces the research on the modulation of through-space charge transfer by bridged azobenzene.We have designed three target molecules with donor-switch-acceptor frameworks.By carrying out first-principles calculations,it can be seen that the Z-isomer of bridged azobenzene in the ground state facilitates π-πstacking of donor-acceptor pair to ensure through-space charge transfer,while the E-isomer of bridged azobenzene destroys this stacking and inhibits charge recombination.The isomerization process from Z configuration to E configuration is self-adaptive upon photoexcitation.In addition,as a CO2 molecule is weakly bound to the anionic acceptor,the former goes bent as a result of charge transfer from the latter,suggesting a path for photo-driven CO2 reduction aided by such a donor-switch-acceptor system.Our research shows the potential of using specific photo-switch to adaptively steer spatial electron transfer within stacked π systems towards photochemical conversion. |
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