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Density Functional Theory Studies On Electronic Structure And Optical Properties For Organic ?-conjugated Molecules

Posted on:2020-02-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:B ZhouFull Text:PDF
GTID:1361330596967741Subject:Optics
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With the development of quantum chemistry theory and the improvement of computer hardware level,Density Functional Theory(DFT)is attracting more and more attention from researchers due to its computational efficiency and accuracy.Compared with the traditional density functional,the optimal tuned range-separated density functional theory(RS-DFT)can accurately predict the electronic structure and optical properties of molecules due to its reasonable description of electron localization and delocalization.Organic ?-conjugated molecular materials are widely used in the field of photoelectricity due to their structure modifiability and excellent photoelectric properties.In this thesis,the density functional theory of the ground state and excited state properties of Organic ?-conjugated molecules is studied from the molecular level,so as to summarize the reliable structure-efficiency relationship,further expand the optimization of molecular design,and finally explain its optical properties.The main content and innovation points are as follows:In chapter 1,the background of theoretical and computational chemistry and the necessity of studying organic ?-conjugated molecular systems are reviewed.The development of density functional theory and time-dependent density functional theory are introduced emphatically.On the basis of range-separated density functional theory,the optimal tuning model is introduced especially.At the same time,the caculatation software of quantum chemistry used in this thesis is briefly introduced.The main content and innovation are introduced finally.In chapter 2,the ionization energy,affinity potential and frontier molecular orbital energy of armchair single-walled carbon nanotubes(SWCNTs)were calculated by density functional methods respectively.Compared with the high-level calculation results(IP/EA-EOM-CCSD),it is found that the optimal tuned RS-DFT method has the highest calculation accuracy.In addition,other chemical parameters of SWCNTs are calculated and extended to a longer single-walled carbon nanotube system.In chapter 3,the excited-state properties of oligoacene molecules and their crystals are studied by polarizable continuum model(PCM)-tuned range-separated hybrid functional approach,including of the vertical excitation energy of singlet and triplet states,singlet-triplet energy gap and exciton binding energy.The theoretical results agree well with the experimental results.It is believed that this method will provide an accurate and efficient tool for studying the excited state characteristics of other complex organic solid systems in the future.In chapter 4,the electronic structure and optical properties of a novel organic fluorescence molecule in the second near-infrared window(NIR-?)were investigated based on the optimal tuned RS-DFT and TD-DFT,including of the ground state and excited state electron structure,front molecular orbital,electrostatic potential distribution,absorption and emission wavelength,etc.The effect of the electron donor and the shielding unit on the luminescence properties of the fluorescence molecule,especially the fluorescence quantum yield,was revealed through the combination of theory and experiment.In chapter 5,the optical properties of the organic fluorescent molecules are theoretically designed and calculated by optimal tuned RS-DFT.According to the calculation results,the eligible NIR-? fluorescent molecules are screened out and their luminescence mechanism is explored and analyzed.Finally,by using the principle of symmetry matching in frontier molecular orbital theory,the effect of super valence atoms on the wavelength of fluorescence emission is explained,which will provide a reliable theoretical basis for designing NIR-? fluorescent molecules.
Keywords/Search Tags:Density functional theory, Optimal tuned, Excitation energy, Single-walled carbon nanotube, Oligoacene, NIR-?, Fluorescence probe
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