Theoretical Study On Molecular Gear And Molecular Recognition Of Triptycene

Based on quantum computational chemistry methods,the applications of triptycene and their derivatives in molecular recognition and molecular gears are studied by using density functional theory（DFT）.The main contents include the following three parts:Firstly,the molecular recognition system of a novel host molecule of triptycene-derived oxacalixarenes（Tp）and a paraquat derivative guest molecule was theoretically studied.There are cis-Tp A and trans-Tp B isomers in the macrocyclic host molecule derived from triptycene.In this study,two kinds of functionals,theωB97X-D and B3LYP-D3,were used to optimize their geometric structure in the gas phase.The macrocyclic body of oxacalixarenes and the methyl viologen cation guest form the inclusion complexes MV²⁺@Tp A and MV²⁺@Tp B.And the noncovalent interactions in the inclusion complex make the molecular conformation more stable.¹HNMR spectrum and vibration frequency analysis show that the structure of the host molecule changes during the formation of inclusion complex.Thermodynamic data indicate that the formation of host-guest inclusion complex is spontaneous and thermodynamically favorable.The frontier molecular orbital and orbital energy gap of inclusion complexes are analyzed theoretically.The noncovalent interactions between the host and the guest are studied using molecular electrostatic potential,natural bond orbital,reduced density gradient and topological analysis theory.Secondly,a molecular bevel gear with triptycene as rotor and naphtho[2,1,8-def]isoquinoline as stator was constructed and designed.The rotational process and conformation conversion of the gear were carried out using density functional theory.The molecular structure was geometrically fully optimized by combining M06-2X functional with def-TZVP basis set.The gear rotates around the C?N single bond,and the potential energy curve of rotational potential energy and dihedral Angleθ(H₇₁?N₆₇?C₁?C₅)is obtained by flexible scanning.Further analysis of the conformational structure of stationary points on the potential energy surface reveals that the gear rotates in two modes:gear rotation and gear slippage.The data of single point energy and thermodynamic correction indicate that the rotational energy barrier is smaller than the sliding energy barrier.The conformational analysis of the gear shows that its ground state structure adopts the C₂configuration,while the transition state structures adopt the C_sconfiguration（gear rotation）and C_2vconfiguration（gear slippage）,respectively.The noncovalent interactions and topological analysis theory conformed that the stable molecular C₂conformation is mainly achieved through the strong intramolecular attraction and van der Waals interactions.Thirdly,the molecular gear system with Pt（Ⅱ）as the center and azaphospha-triptycene as the rotor was theoretically studied.The electronic structure and geometry of the cis-[Pt Cl₂（Tp）₂]and trans-[Pt Cl₂（Tp）₂]isomers of gear were investigated at the M06-2X/def2-SVP level using density functional theory.The gear rotates around the P-Pt single bond,and the angle change curves of the dihedral anglesθandφare obtained through flexible scanning.Further analysis of the motion correlation between the two rotors of cis and trans gear isomers during rotation and their corresponding rotation energy barrier.The thermodynamic properties of cis-trans isomers at different temperatures were calculated,and their stability was compared.The transition state（TS）of the cis-trans isomerization reaction of gears was found,and the energy barriers for the isomerization reaction of cis→TS and TS→trans were calculated and analyzed,and then the difficulty of isomerization conversion was evaluated.The time-dependent density functional theory（TD-DFT）calculated the ultraviolet UV-vis absorption spectrum of the molecule.The data showed that the ultraviolet absorption wavelength of the gear is blue shifted from the trans isomerization to the cis.In addition,the charge transfer of the trans gear structure and chemical reaction activity is slightly higher than that of the cis structure.