The Introduction Of External Electric Field And The Replacement Of Molecular Framework Units Are Used To Study The Mechanism Of Chemical Process Regulation

The dissertation aims to reveal the regulation mechanism based on external electric field(EEF)and molecular skeleton unit replacement in chemical reaction,so as to provide a theoretical reference for the effective tuning of chemical reaction.In the first part,based on external fields applied in different directions and with different intensities,the mechanisms of EEF regulated Diels-Alder reactions were explored at density function theory(DFT)level and an EEF contribution decomposition(ECD)was proposed,which provides an intuitive and quantitative insight on electric-fields tuning of chemical reactions.Moreover,ECD model was applied to the hetero-DA reaction between the dienone and the benzofuran derivative,furthing comfirming the generalization of the model.In the second part,the DFT,time-dependent DFT(TD-DFT),multireference complete active space self-consistent field(CASSCF)and restricted active space self-consistent field(RASSCF)were applied to explore the effect of isoelectronic substitution of the BN unit on the photochemical process of a diphenyl benzophenene(DPDBF).At the same time,the influence of the substituent effect on the charge transfer in the electron excitation process is also investigated,which is an important factor affecting the lumininescent efficiency of the molecule.Those results provide a basic theoretical foundation for the photochemical regulation strategy based on isoelectronic BN/CC unit substitution.The main contents include:1.The mechanisms of electric fields tuning on three intermolecular Diels-Alder reactions involving butadiene with ethylene,cyclopentadiene with maleic anhydride,and 1,4-dihydroxy-1,3-butadiene with acetaldehyde in dichloromethane solution under EEFs(Fx,Fy,and Fz from-0.0075?0.0075 au)were studied at M06-2X-D3/6-311+G(d,p)level,along with a new energy-decomposition-like scheme for EEF contribution decomposition(ECD)being proposed.The results show that reaction systems introducing hetero-atoms are more sensitive than those have pure carbon atoms,and EEFs oriented along the forming bonds efficiently tune the reaction reactivity while those perpendicular to the forming bonds play a potential role for endo/exo product selectivity.Furthermore,the EEFs contribution decomposition model provides a resolution for separating the structural and electronic effects caused by EEFs as geometry re-equilibrium and static-induction term and it can be applied for decomposition analysis of any physical quantities including TSs' energetics,activation barriers as well as the charge distribution and dipole moments of TS.The ECD model was further applied to the hetero-DA reaction between the dienone and benzofuran derivative.The mechanism of electric fields tuning on the reaction was studied at M06-2X/6-311+G(d,p)level,which comfirms the generalization of the model in the reaction system with larger molecular skeleton and flexibility.The combination of ECD model with other analysis models,such as distortion-interaction analysis,can give a clear physical picture of EEF-tuning reactions.In a word,the EEF-contribution decomposition analyses will shed light on the effective tuning of chemical reactions by the electric field.2.The potential applications of isoelectronicity of BN/CC units in the field of organic electronics and optoelectronic materials have obtained increasing attention in recent years.Taking DPDBF and its isomeric BN counterpart(BN-DPDBF)as objects of research,we carried out(TD)CAM-B3LYP,CASPT2//(TD)CAM-B3LYP,RASPT2//(TD)CAM-B3LY and CASPT2//CASSCF methods to investigate isoelectronic substitution effect of the BN unit on their photochemical process.We also evaluated the substituent effects on charge transfer during electron excitation,which has a close connection with the fluorescence quantum yield.The results present that the C=C double bond is significantly weakened by the replacement of a BN unit,which makes the rotation process easier to occur and the charge transfer more evident during the electron excitation process.In addition,molecular skeleton unit replacement with BN unit could contribute to an obviously large energy gap between So and S1,which,along with the relatively large structural and energy differences between the S1/S0-CI and the excited state intermediate,suppress the internal conversion via non-adiabatic decay and thus increase the fluorescent quantum yields.Furthermore,when the electron-withdrawing substituent is introduced on the fragment 1(=BPh2)of BN-DPDBF,the inter-fragment charge transfer become more evident during the electron excitation process,and the result is reversed for electron-donating substituent.The extent of inter-fragment charge transfer often affects the luminescent properties of molecules,the more obvious charge transfer during the electronic excitation process,the lower fluorescence quantum yield can be expected,and vice versa.Further study on the molecular photochemical reaction mechanism of DPDBF and BN-DPDBF can provide a theoretical reference for the effective regulation of molecular luminescence properties based on the BN/CC unit isoelectronic replacement.