Molecular Recognition And Its Logic Function Of Schiff Base Receptors

Supramolecular chemistry is"the chemistry beyond the molecule", as opposed to molecular chemistry based on covalent bonds between atoms, supramolecular chemistry is based on weak intermolecular interaction. There is a need for more intermolecular binding sites and interaction to form strong intermolecular forces. Molecular recognition is one of the cores for molecular recognition, it includes cation recognition, anion recognition and neutral molecular recogniton. Molecular recognition is applied to molecuar logic function recently, there are excellent application prospects for microelectronics and information technology in the future. There are C = N bond and hydroxyl group on the benzene ring for the structure of salicylidene Schiff bases, which makes salicylidene Schiff bases can chelate with a variety of cations, while salicylaldehyde Schiff bases react with a lot of anions through nucleophilic addition reactions and intermolecular hydrogen bonding, so it is possible for salicylaldehyde Schiff bases to recognize the ions selectively and be used in molecular logic circuits. Therefore, the design and synthesis for new salicylaldehyde Schiff bases with ion recognition are great significance. We designed a series of salicylidene Schiff bases in order to research the selective recognition for ions and use them in molecular logic circuit.The work in this thesis mainly includes five parts as follow:First, we used six salicylaldehyde molecules with donating electron groups, withdrawing electron groups and different conjugated level's goups to react with p- phenylenediamine and 2-phenyl-3-(p-aminophenyl)acrylonitrile by condensation reaction between aldehyde group and amine group, and the molecules' purity were verified by NMR spectra.Second, we used three molecules with slightly different structures, namely, B1, B2 and C, to study the anion recognition ability by UV and fluorescence spectroscopy and found that only salicylidene Schiff base with chlorine atoms (B2) can selectively recognize CN^- better. Among the seven anions (10 equiv.) tested in THF solution, the UV-vis and fluorescence spectral changes for B2 upon addition of CN^-, AcO^ï¿£and H₂PO₄^- were same, while there were no changes for spectroscopy adding Clï¿£, Brï¿£and Iï¿£into solution of B2. Unlike spectral changes of the six aions above, UV-vis and fluorescence spectra had a large change upon addition of CN^-, so B2 can recognize CN^- through spectral changes, and the naked eye observation also showed that only CN^- can result in colorless, orange to violet color changes. Andthen the corresponding color changes under a UV lamp were brown, red and blue. Moreover the absorbance spectra change of B2 with the addition of cyanide in THF-H2O (4:1, v/v) solution was large, and the color of the solution could also changed from colorless to yellow in the meantime. However, the addition of other anions including F^-, AcO^- and H₂PO₄^- didn't promote any change of the absorbance spectra. Therefore cyanide could be detected by both the absorbance change and the naked-eye color change even in aqueous media.Third, we used salicylidene Schiff base with amino group (B5) in THF to study the cation recognition ability through adding eihgteen kinds of cations (3 equiv.) by UV-vis and fluorescence spectra and found that molecule B5 can selectively recognize Cu²⁺ and Zn²⁺ better. Then upon addition of Zn²⁺, the fluorescence emission intensity of B5 increased largely, while the fluorescence emission intensity quenched by adding CU2+ into the solution of B5, at the same time, the addition of other cations promoted no change of the fluorescence spectra or slightly decrease of the fluorescence intensity. So B5 can recognize Cu²⁺ and Zn²⁺ through fluorescence spectral changes, andthen the emission profiles of the B5/ Cu²⁺ complexes were unperturbed in the presence of other metal ions. In addition, B5 can only recognize Cu²⁺ through absorption spectral changes, and the absorption band centered at 423 nm gradually decreased with a light blue shift of the absorption band, moreover, the naked eye observation also showed that Cu²⁺ can bring about yellow to light yellow color changes.Fourth, we used salicylidene Schiff base with amino group (B5) in THF to study the anion recognition ability through adding seven anions (10 equiv.) by UV-vis and fluorescence spectra and found that molecule B5 can selectively recognize F^- and CN^- better. And upon addition of CN^-, the band centered at 543 nm gradually decreased with a new peak emerged at 470 nm, while the fluorescence emission intensity increased largely by adding F^- into the solution of B5, what is more, the addition of other ations didn?t promote any change of the fluorescence spectra. So B5 can recognize CN^- and F^- through fluorescence spectral changes. Andthen, B5 can recognize CN^- and F^- through absorption spectral changes, also ,the naked eye observation indicated that F^- and CN^- can bring about yellow to sepia and claybank changes respectively.Fifth, based on properties that B5 reacted with ions and changes of the fluorescence emission intensity by adding ions into B5 with different order, we successfully constructed two NOR gates, one XNOR gate and two INHIBIT gates by setting logic threshold reasonably. In addition, the chemical inputs of CN^- (10equiv.) and Cu²⁺ (3equiv.) in a sequential manner generated an output which mimicked the functions of a security keypad lock.