The Application Of Imines In Molecular Optical Sensors And Dynamic Combinatorial Chemistry

Imines contain C=N double bond in their structure,and they are widely used in the field of recognition and dynamic combinatorial chemistry,because imines can be synthesized simply and exchange reactions among them are easy to happen.Imines can be used as optical sensors for many ions and molecules,because of their high selectivity,sensitivity and low detection limit,etc.Besides,they can further be used in the area of cell imaging and logical switches.At the same time,the conditions for exchange of imine bonds are mild and controllable.Imines,as one of the common dynamic bonds used in dynamic chemistry,are widely used in self-sorting systems,molecular switches and machines,dynamic networks and self-healing materials,etc.Our work is focused on the recognation and dynamic exchange of the imines.Firstly,we designed and synthesized the imine sensor L,which contained an "O-N-O" coordination site and could be used for detection of Al3+ and PPi ions continuously.The highly selective fluorescence ?turn-on? detection of Al3+ in aqueous media could be realized and the solution shew green fluorescence obviously.Because Al3+ and L could form 1:1 L-Al3+ complex,which produced chelation-enhanced fluorescence(CHEF)effect.Furthermore,the L-Al3+ complex was used as a fluorescence "turn-off" sensor for PPi subsequently in aqueous solution due to strong attraction between Al3+ and PPi.Then the L-Al3+ complex destroyed and the green fluorescence disappeared.In addition,L can be applied to map Al3+ in living cells.Secondly,based on different mechanism,the molecule L mentioned above could be further developed as a sensor for F? and CN? recognation in dual channel,realizing the discriminating detection of multiple analytes by a single sensor.The colorimetric response to fluoride was based on a deprotonation process,and the fluorescent recognition of CN? was realized though an oxidative cyclization reaction happened when CN? existed as a catalyst,generating hydroxyphenylbenzoxazole(HBO)H.The cyclization product H displays bright green fluorescence in solid state due to ESIPT(excited-state intramolecular proton transfer)as well as AIEE(aggregation-induced emission enhancement)effect.It is interesting that the selective detection of CN? could be realized in water with surfactant assisted.Because micellar can improve the solubility of water-insoluble L in water,and offer a microenvironment for the oxidation reaction happened between the sensors and ions in water as well as the aggregation of the reaction product H.In addition,considering the interaction between Al3+ and F?,the conversion of optical signals could be realized in dual channel.At the same time,text papers absorbed sensor L were prepared and provided a reliable and convenient method for detection of CN? in practical application.Thirdly,we synthesized an imine TPE-2Ben containing tetraphenylethylene(TPE)structure,and found that it could realize fluorescence ?turn-on? detection of primary amine vapors selectively.The TPE-2Ben sensor loaded on the test paper had no fluorescence originally.In the presence of primary amine vapors,the amino groups would react with the C=N bonds in the sensors to generate a new kind of imine and tetraphenylenediamine(TPE-2NH2).We found that TPE-2NH2 had AIE effect,so as a result,fluorescence appeared.TPE-2Ben had no fluorescence in solid,it seemed like "protecting groups" were introduced in the structure.Then,the imine exchange process was able to get rid of the "protecting groups",showing bring fluorescence in solid.This method could be used to prepare easy-to-take test paper for detecting primary amine vapors.Besides,it could also be applied as the invisible ink,the invisible words written by TPE-2Ben would appear under the ultraviolet lamp after treaed by amine vapors.Then,from p-phenylenediamine(B)and 3-pyridinecarboxaldehyde(A),gelator ABA could form though the formation of C=N bonds,then metal-organic gel generated in appropriate solvents via the coordination between nickel ions and N atom on pyridine ring of the gelators(Ni2+-N).This ?one-pot? preparation of gels could be done in situ at room temperature,without the traditional preparation process of heating and cooling.The obtained metal-organic gel had multiple physical stimulus responsiveness,including heat and mechanical force.In addition,the resulting metal-organic gel could respond to chemical stimuli.When diamines were added to the gel,the gel would break into sol,because the exchange reaction between amino and imine bond happened,generating the new imine that could not form gel.This ?one-pot? preparation method was based on the formation of imine bonds,and the gel destruction process was based on the exchange reaction.It can provide some ideas for the designing of other stimuli-responsive materials.Finally,we designed and demonstrated a new approach to generating organogels through dynamic covalent exchange of C=C/C=N bond recombination.Several influence factors for the thermodynamic equilibrium of the C=C/C=N exchange reactions were studied,including solvents,chain length,and temperature.After mixing two components that could not form the gel(such as K and I-16)in the appropriate solvents,gel could form gradually.It was caused by the formation of the gelator generated from the exchange reaction.At the same time,along with the formation of gel,the gelator will be amplified as the optimal component.The selective up-regulation of the gelator constituent indicated that self-organization acted as driving force towards higher organization.In a word,we studied the application of imines in molecular optical sensors and dynamic combinatorial chemistry in our work.We used the imine sensors to realize the detection of ions in aqueous solution and amine vapors in solid state,which is very prominent in the aspects of selectivity,sensitivity and application.It is meaningful for the development of molecular optical sensors in the future.At the same time,we studied the formation and destruction of gel based on the dynamic exchange properties of imine bond.We also used the exchange reaction to generate and enlarge the gelator,which expanded the application of imine bond in dynamic combinatorial chemistry.