Regulation Of The Character Of Spiropyran Based On Chemical Reaction And Its Application On Sensing

Spiropyrans, as an important class of photochromic compounds which canundergo reversible changes of structure and colour, have been widely used. But theprevious methods of regulating the ring opening of spiropyrans based on chemicalsubstance are confined to the supramolecular interaction, and this means that theinteraction between guest molecules and spiropyrans is very weak, which influencesthe regulation effect. Secondly, the modes of regulating the conversion of spiropyransfrom ring opening to closure are restricted to light or heat, while few attention hasbeen paied attention to study the new ways. On the other hand, while the opticalcharacters of spiropyrans are used widely, only a handful of study on theelectrochemical characters of spiropyrans has been reported. Covelent interactionwith strong force and can not be interfered easily by other factors. In view of theabove limitations, we constructed three new systems to regulate the optical andelectrochemical characters of spiropyrans based on chemical reaction (covelentinteraction) in this research paper, and the details are described as follows:(1) A new method to regulate the optical character of spiropyran based on theunique nucleophilic reaction between fluoride and silicon ether was developed. Wedesigned and synthesized a spiropyran SPS which is colorless in buffer solution(CH3CN/Tris-HCl,4:6), and the absorption spectrum displays an absorptionmaximum at ultraviolet region. No significant absorption is observed in the visibleregion, which suggests SPS is existed in the form of ring closure. In the presence of F-,F-cleaves the Si-O bond incorporated in SPS, which makes the spiropyran converts toits form of ring opening, and the absorption at495nm is observed accompanying withthe colour chage from colorless to orange-red. So we constracted a platform forrecognizing and sensing F-, and developed a new meachanism to regulate the opticalcharacter of spiropyran.(2) A new meachanism to regulate the optical character of spiropyran based onthiol-induced aromatic nucleophilic substitution reaction was proposed. We designeda series of the ring opening forms of spiropyrans-merocyanine derivatives MC-DNS-R,the substituents R of which are different at6-position. The merocyanine derivativeswere stabilized by2,4-dinitrobenzenesulfonyl unit which is the reaction site withthiols. We choose MC-DNS-Br as the probe by optimization. In the presence of Cys,negative oxygen ion was released and the colour changed to purple-red, because thiol induceded the occurrence of nucleophilic substitution reaction. But the the ringopening form is not stable and converts to its ring closure form, the absorption ofwhich is at360nm. The changes of absorption spectrum suggest the regulation ofspiropyran from ring opening to closure can be realized through this reaction. So weconstruct a new regulation mechanism which can selectively recognize and sense Cys.(3) A method to regulate the electrochemical character of spiropyran based onhadrolysis reaction was constructed. We designed a6-β-galactose-functionedspiropyran SP-β-gal. When SP-β-gal was exposed to ultraviolet light or acid whichmakes the heterolytic cleavage of the C-O bond in SP-β-gal, no electrochemical signalwas observed. In the presence of β-galactosidase, because of the occurrence ofβ-galactosidase-induced hydrolysis reaction, the glycoside was hydrolyzed and thenthe probe contained two phenolic oxygen ions or phenolic hydroxys, the structure ofwhich exhibted obvious electrochemical signal. So we not only extend the applicationof spiropyran in the recognizing and sensing biological macromolecules, but alsoconstruct a platform to regulate the electrochemical character of spiropyran.