Development Of New Photochromic System And Fluorescent Porbes For Metal Ions Based On Schiff Base Derivatives

Schiff base derivatives are well known organic molecules which have beenwidely studied. They can be facilely prepared and derivatized, and usually low cost.Schiff base derivatives are likely to form complexes with metal ions, which makethem very useful in coordination chemistry, analytical chemistry and materialchemistry. In this work, a new photochromic system and a series of fluorescentprobes for metal ions based on Schiff base derivatives were developed.First, a new photochromic system based on rhodamine B salicylaldehydehydrazone metal complex was developed. These complexes were facilely preparedand derivatized, and could be used in both solutions and solid matrix with goodphotochromic properties. The photochromic mechanism was suggested as the resultof UV light-promoted isomerization of the salicylaldehyde moiety from the enol-formto the keto-form, which changed the chelation with metal ion, induced the ringopening of rhodamine B spirolactam, and thus resulted in distinct color andfluorescence change. More importantly, this system showed fast photoresponse andgood fatigue resistance, the thermal bleaching rate was effectively tunable by usingdifferent temperatures, metal ions, solvents and substituent groups in salicylaldehydepart. This system has been used for photoprinting, anti-fake coating and UV strengthmeasurement in solid matrix. The work provides new insights into the developmentof new photochromic materials based on metal complex.Second, a series of salicylaldehyde-2-pyridinehydrazone derivatives weredesigned and synthesized as“turn-on”fluorescent chemosensors for the detection ofZn(II). These chemosensors showed good selectivity to Zn(II), even Cd(II) showednegligible fluorescence enhancement, which usually induced a similar fluorescenceresponse to that of Zn(II). In the presence of Zn(II), as high as40-fold fluorescenceenhancement was obtained in water at neutral pH. Under the optimal condition, thedetection limit for Zn(II) was as low as25nmol/L and the linear range was as wide as0-10.00μmol/L. These chemosensors were successfully used for the detection of Zn(II) in real water samples and for monitoring Zn(II) within live cells.Salicylaldehyde-2-pyridinehydrazone moiety in the chemosensor acts as bothfluorophore and receptor, providing new insights into the development of fluorescentchemosensors for the detection of Zn(II) in water at neutral pH.Finally, a coumarin derivative of7-N, N-diethylaminocoumarin-3-aldehyde-benzoylhydrazone was designed and synthesized as a ratiometric fluorescentchemodosimeter for the detection of Cu(II). The chemodosimeter showed stronggreen fluorescence in water at pH7.0. When it formed a complex with Cu(II),Cu(II)-promoted hydrolysis of coumarin lactone moiety of the chemodosimeteroccurred. After that, a product with blue fluorescence was obtained which could bedetected even by naked-eye. Under the optimal condition, the chemodosimetershowed an excellent selectivity to Cu(II) cause only Cu(II) could promote thehydrolysis of coumarin lactone moiety. Limit of detection for Cu(II) with this methodwas15nmol/L.