| It is of great significance to study the dynamics of complex systems such as small molecules and two-dimensional materials.First principles and density functional theory have been successfully used to study the properties of condensed matter structures in the ground state.However,there are still many interesting problems to be solved,including the excited state properties of the system and the interesting quantum phenomena and quantum effects contained in the process.The excited state proton transfer process is one of the most basic and important chemical reactions in the field of physics,chemistry,biology,and other sciences.Hydrogen bond as a basic weak interaction exists widely in nature.Based on hydrogen bond interaction,the transfer from proton donor to proton acceptor along the hydrogen bond chain is called the proton transfer process.Due to the stable structure in the ground state,it is difficult to open the proton transfer process.Photoinduced excitation excites electrons from the ground state to the excited state,and the charge transfer and charge redistribution caused by this process will enhance the hydrogen bond interaction,which promotes the occurrence of proton transfer in the excited state.There are many interesting photophysical and photochemical phenomena in this process,including vibrational relaxation,internal transformation,double fluorescence radiation,the formation of tautomeric,and so on.Two-dimensional materials also have attracted wide attention due to their various excellent photoelectric properties and application prospects.Many quantum effects and quantum phenomena can be realized in such systems,like quantum hall effect,valley hall effect,quantum stark effect,quantum decoherence,and quantum beats,which have greatly expanded the applicable space of two-dimensional materials and open new directions for the design of new materials and devices.Therefore,the study of molecular dynamics behavior in the complex system of two-dimensional materials is helpful for us to further understand the properties of materials.The properties of materials in the excited state are more complex,and its physical concepts involve excitation intensity,transition dipole moment,and exciton binding energy.The excited state behaviors of many quasi-particles involve phonon,polaron,and plasmon.In this article,we provide molecular structure analysis,like weak interaction analysis theory,molecular frontier orbital theory,potential energy surface scanning,and infrared vibration frequency analysis for the calculation of complex systems.At the same time,the application of the quantum trajectory surface hopping(QTSH)method also provides a possibility for the analysis of quantum effects in materials.This article uses first-principles and density functional theory combined with non-adiabatic molecular dynamics calculation to carry out theoretical research on the excited state dynamics of small molecules and the excited state electron surface hopping process in a two-dimensional material system.The main research contents of this paper are as follows:In Chapter 3,we exploit the excited state proton transfer process and fluorescence probe mechanisms of 26DB and Bis-26DB molecules.26DB is a molecule with a single hydrogen bond,and its derivative Bis-26DB molecule is a double hydrogen bond system with a symmetrical structure.The complex chemical reaction channels in the double hydrogen bond chain can be understood more deeply through the analysis of the excited state dynamics in this chapter.We clarify the fluoridesensing mechanism by showing that a fluoride anion can spontaneously capture the hydrogen proton with the addition of fluoride anions in the solvent,which facilitates the formation of the anionic forms.These results can be proofed with the UV-VIS spectra experiment.Due to just the hydrogen abstracting process in the S0 state,the excited-state intramolecular proton transfer(ESIPT)process could be inhibited for the 26DB and Bis-26DB systems.Based on Chapter 3,we regulate the excited state proton transfer reaction of BI molecule via solvents successfully in Chapter 4.Due to the five-membered ring hydrogen bond in the BI molecule stretch the length of the hydrogen bond,the hydrogen bond interaction between them is weak.We identify that BI molecules could not directly undergo the ESIPT process in the aprotic solvent like acetonitrile.However,it is found that BI molecules could form multiple hydrogen bond chains with solvent molecules,in the protic solvents like water and ethanol,and the step-by-step proton transfer process along the hydrogen bond chain could be initiated through the photoexcitation process.It is worth mentioning that ethanol solution with weak self-aggregation ability is more helpful to assist BI molecules to open the excited state proton transfer process.After exploring the influence of the solvent effect on proton transfer,we investigate the determinant of ESIPT mechanism by the structure designed for symmetrical and unsymmetrical molecules in Chapter 5.We found that the additional side chain hydroxyl group in M1 effectively increases the proton transfer barrier and has a certain blocking effect.In BSP and its derivatives,the size of the ? stack contributes to the enhancement of molecular rigidity,thus effectively avoiding its torsion phenomenon.At the same time,it can also inhibit the proton transfer process.The study of the above two systems provides a valuable reference for the design of ESIPT molecules.The investigation of applicable 2d materials has made a tremendous effort for the design of new devices and materials.The electron surface hopping process in 2d materials is also important.In Chapter 6,we introduced a very promising ultrathin film photovoltaic material LiAlTe2.Through a series of tests,such as energy band analysis,non-adiabatic molecular dynamics calculation of NAMD,solar spectral absorption,stress,and strain effects.We identify that two-dimensional LiAlTe2 can effectively reduce the internal coulomb interaction force due to the effect of its intrinsic polarization field,which facilitates the disintegration and collection of excitons,and achieves the ultralong carrier life in the excited state.Meanwhile,its adjustable bandgap,wide solar absorption spectrum,and piezoelectric effect in and out of the plane all indicate that it is an excellent ultra-thin film photovoltaic material.In Chapter 7,ab-initio and non-adiabatic molecular dynamics are used to calculate the excited state electron surface hopping process of blue phosphorus.Based on the fewest switches surface hopping(FSSH)method,we use QTSH to calculate the transition of electrons in the system,and at the same time correct the missing spontaneous emission and relaxation terms.We have summarized the three surface jumping modes of electrons in this complex two-dimensional system and found that its behavior can be approximated as a simple three-level V-shaped system.By comparison with the fitting of the V-shaped system,we summarized the quantum beat phenomenon caused by non-adiabatic coupling in this complex two-dimensional system. |
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