The Construction Mechanism And Theoretical Research Of The Second Generation Molecular Motor

This article mainly studies the influence of structural modification on the thermodynamic and optical properties of the second-generation molecular motor with quantum chemistry methods.The content contains the following three parts:Firstly,the potential energy surface(PES)scanning is carried out by using density functional theory(DFT)at the level of the combination of M06-2X functional and def-TZVP basis set.Calculated and analyzed the rotation process and conformational reversal of the second-generation molecular motor(motor 1),and then mainly explored the influence of four donor-acceptor substituents(motor 2-5)on the different properties of the molecular motor.Through the analysis of the energy barriers that molecular motors need to cross during the thermal helix inversion process,it is shown that the nature of the substituents will affect the thermal isomerization barriers of the motor.The analysis of frontier molecular orbital(FMO)theory shows that after replacing the methyl group with phenyl,methoxy,fluorine and cyano,the stability of the molecule is reduced..Finally,the study of ultraviolet-visible(UV/Vis)absorption spectra and nuclear magnetic resonance(NMR)spectroscopy confirmed that the configuration of the molecular motor changed from a stable state to an unstable state during the photoisomerization process,the calculation results explain the rotation mechanism of the molecular motor.Secondly,the influence of structural modification on the thermal helix inversion process of molecular motors was studied using density functional theory(DFT)methods for naphthalene-containing molecular motors(L₁)and pyrene-containing molecular motors(L₂)based on 4,5-diazafluorenyl coordination motifs and two complexes(L₁@Zn(CN)₂and L₂@Zn(CN)₂)formed after the motors L₁and L₂coordinate with the metal.The analysis of the rotation energy barrier shows that the expansion of the rotor structure of motor will increase the energy barrier value of the rotation process,but the motors L₁and L₂act as ligands to coordinate with the metal can be an effective method to reduce the rotation energy barrier value.Through frontier molecular orbital(FMO)theory,it is found that the expansion of the?system in the rotor part of the motor can increase the chemical reaction activity of the motor,and then the ultraviolet-visible(UV/Vis)absorption spectra of the motors are calculated,it is found that the expansion of the?system in the upper half of the molecular motor can be a feasible method to move the excitation wavelength to the visible light region.Finally,a hole-electron analysis is carried out,and the study found that the expansion of the?system of the rotor part of the motor and the coordination of the motor as a ligand and metal can improve the hole-electron separation efficiency,which is beneficial to the transfer of electrons.Finally,the theoretical study of the feasibility of a molecular motor—5-(2,4,7-trimethyl-2,3-dihydro-1H-inden-1-ylidene)-5H-cyclopenta[2,1-b:3,4-b']dipyridine(motor L)as a ligand and the changes of some properties after L coordinated with three different metals.The molecular chemical reaction activity of different metals coordinated with the motor are compared by analyzing the thermodynamic properties of molecular motor L coordinated with different metals.Through the geometric optimization analysis of the molecules,it is found that the geometric structure of the molecular motor will be changed to a certain extent after the coordination of the metal.The analysis of the rotational energy barrier,it is shown that the metal coordination of the motor can reduce the energy barrier to be crossed during the thermal helix inversion.Then the rate constants of the molecules are calculated,and the analysis found that the temperature can have a certain effect on the rotation rate of the molecular motor and it is speculated that the molecular motor is difficult to rotate in the reverse direction during the thermal helix reversal step.Through the analysis of frontier molecular orbital(FMO)theory,it is understood that the molecular motor acts as a ligand and coordinates with the metal to increase the chemical reaction activity of the molecule.From the non-covalent interaction and topological analysis,it is known that there is a stronger interaction between Ni(CO)₂and the motor L.