Molecular Recognition And Logic Function Based On The Salicylidene Schiff Base

Supramolecular chemistry is one new developing research area. Molecular recognition, once described as "lock and key" for the unique combination of molecules, which is one of the process related closely to supramolecular chemistry, has developed more and more function in synthesis chemistry, life sciences, material sciences and information sciences. Compared with electric and magnetic signal, optical signal has some advantages such as convenience, high sensitivity and selectivity. Moreover, the "naked eye" detection, watching the color change with no instruments, has become the focus in molecular recognition. Furthermore, molecular logic function has been another focus in many crossed studies, based on which, molecular brake and molecular keypad lock has become one foreland of this research area.Firstly, we choose one binaphyl bridged salicylidene Schiff base with chlorine atoms in the phenyl of the salicylidene (BCHB), which was once applied as one ligand for molecular structure and asymmetric catalysis, as receptor to study its ability in cation and anion recognition. It can be concluded that, when the solution of BCHB was titrated with fluoride anion, the absorption would be affected dramaticly because of the deprotonation function. The color of the solution was then from colorless to yellow. In the same condition, other anions such as chloride, bromide, iodide, phosphate had no obvious change for this. Andthen, many kinds of metal cations were introduced to the fluoride acted solution. As can be seen from the result of absorbance and fluorescence that only the addition of Zn²⁺ and Cu²⁺ can cause a obvious change, indicating the presence of of unique coordination complex with deprotonated BCHB respectively. The naked eye observation also shows that only Zn²⁺ and Cu²⁺ can result in a yellow to light green color change, while the others remain the original state and the disturbance for color change can be neglected.On the other hand, BCHB presents a tunable system integrated with one OR logic gate as well as one INHIBIT logic gate with Zn²⁺ and Cu²⁺ as chemical inputs by monitoring fluorescence and absorbance as output signals. Also, one IMPLICATION gate operating in fluorescence mode with Cu²⁺ and EDTA as chemical inputs, based on their different binding capability, is present in the system. This research has been rarely reported.Furthermore, we choose the same structure as BCHB but with no chlorine atoms in the phenyl of the salicylidene (BHB) as another receptor for molecular recognition. Exhibiting absorption and fluorescence changes in the presence of Zn²⁺ in chloroform and ethanol mixed solution, BHB could be used as a fluorescent chemosensor for the detection of Zn²⁺. Furthermore, by monitoring the fluorescence and absorbance as output signals, BHB can function as a combinatorial logic circuit for a molecular half-subtractor with Zn²⁺ and UV irradiation as input variables. Most of the reported molecular half-subtractors mainly focused on acid, base, and other chemical input variables, with UV light irradiation as an independent input, to the best of our knowledge, has not been reported yet.Lastly, we choose one simple salicylidene Schiff base SPEA as another receptor to study its ability for anions recognition. With THF as organic solvent, F- and CN- could be detected through both absorbance and fluorescence change. Noting that, F- can be detected in rather low concentration (10-8) for its high sensitivity with the receptor. When using ethanol as organic solvent, the spectrum of SPEA could only be affected by the additon of CN-. In conclusion, SPEA can be developed as a sensor for F- and CN- in different solution.In additon, we also studied the stimulating spectral results of F- acted SPEA with Zn²⁺ and EDTA as inputs in THF solution. It could be found that with different input sequence, the result of fluorescence would be totally different. Then, SPEA can be also applied as a new receptor for developing one simple keypad lock for information secuirity in molecular level.In summary, we choose three kinds of salicylidene Schiff base as receptors to study their molecular recognition and molecular logic function. It can be concluded that, BCHB exhibits"naked eye"colour change and significant fluorescence change in preference to other anions. And then, its deprotonated derivative behaves as a chromogenic detector for Cu²⁺ and a dual ratiometric fluorogenic and chromogenic chemosensor for Zn²⁺ over other metal ions. Moreover, we can describe two sets of integrated logic gates through the emission and absorbance mode respectively; BHB can be developed as a new selective fluorescence probe for Zn²⁺ among other metal cations. Furthermore, under the individual actions of Zn²⁺ ion and UV light as well as the combination of the two actions, we successfully obtained a monomolecular half-subtractor circuit, which responds to one optical and one chemical input producing two optical outputs; SPEA can be a effective sensor for F- and CN- in THF solution and can only detect CN- in ethanol solution. In addition, a keypad lock can be developed with Zn²⁺ and EDTA as two inputs with different results for different sequences. It can offer a new information secuirity platform in molecular level.