Construction And Theoretical Study Of Fluorescent Molecular Sensors For Three Classes Of Crown Ether Derivatives

In this paper,quantum chemistry,density functional theory（DFT）and time dependent density functional theory（TD-DFT）are used to design a double functional crown ether derivative sensor.The sensing mechanism and molecular switching functions of molecular devices were calculated.Three crown ether derivative fluorescence sensors in this paper are mainly discussed:（1）Theoretical study of a fluorescent molecular devices based on anthracene schiff aza 18-Crown-6.（2）Theoretical design of a fluorescent sensor with configuration transformed metal ion recognition of aza18-crown-6.（3）Theoretical design of double functional molecular devices with benzo18-crown-6Firstly,a fluorescent molecular devices based on anthracene schiff-aza18-Crown-6（L1）was designed through the theoretical calculations.L1 interacted with the metal ion Cu²⁺,which is to form the complex L₁/Cu²⁺（L₂）,.The free ligand（L₁,L₂）and its complex L/Mⁿ⁺are fully geometrically optimized at the M06-2X/6-311（d,p）/SDD level,and frequency calculations are performed at the same level.The results of natural bond theory（NBO）analysis indicate that the free ligands L₁ and L₂ have a strong interaction with the metal ion Ca²⁺.The frontier molecular orbital（FMO）analysis showed the electron cloud distribution of the free ligands（L1,L2）before and after the reaction,as well as the generation and inhibition of PET（Photoinduced Electron Transfer）effect.The time-dependent density functional theory and CAM-B3LYP method were used to calculate and discuss the absorption spectrum and excited state of the free ligand（L1,L2）and its complex L/Mⁿ⁺.We designed a fluorescent sensor with"ON-OFF-ON".At the same time,Ca²⁺can be selectively coordinated.Secondly,a novel configuration-transformed fluorescent molecular sensor was designed.DFT was applied to study the free ligand L（L1,L2）and its metal ion complex L/Mⁿ⁺geometrically optimized structure.The interaction of the free ligand L with a series of metal ions(Na⁺,K⁺,Mg²⁺,Ca²⁺,Sr²⁺)has been calculated by NBO and the Mayer bond order.The results of NBO calculation showed that K⁺and Sr²⁺interacted strongly with free ligand L.The results of Mayer bond order indicated that Sr²⁺is more strongly bonded to free ligand L than K⁺.The absorption spectra,excited states and fluorescent emission spectra of free ligands L₁,L₂ and complex L/Mⁿ⁺were calculated by TD-DFT.The absorption spectra results showed that the absorption peak of L₂/Sr²⁺is different from that of L2,accompanied by blue shift.It indicates that the free ligand L2can specifically recognize the metal ion Sr²⁺.In addition,the absorption intensity of L₂/Sr²⁺is significantly enhanced compared with other molecules,so we believe that L₂/Sr²⁺is an excellent fluorescent molecular sensor.Thirdly,A bifunctional fluorescent chemical sensor with allosteric switch and metal ion recognition Cis-L（Cis-stilbene-embedded（E）-N-（anthracene/pyrene 9-ylidene）benzo18-crown-6）was designed.The binding energy,the combined free energy and Gibbs free energy results showed that the complex L/M²⁺could exist stably.It is concluded by the theory of natural orbital that the interaction between Sr²⁺ions and free ligands L₁,L₂ is stronger than that of other metal ions with free ligands L1,L2.The B3LYP method and6-311（d）/LANL2DZ level was used to calculate the excited state,absorption spectrum,excitation energy,frontier molecular orbital value and orbital energy gap value for L1,L2and its complex L/M²⁺.The orbital energy gap value shows the difficulty of electronic transition.And the distribution of the frontier molecular orbital map explains the fluorescent luminescence mechanism of L₁ and L₂.