Design And Synthesis Of Near-Infrared Fluorescent Molecular Probes Based On Si-Substituted Xanthenes For Molecular Recognition

With the development of chemiluminescence,the synthesis of luminescence molecular materials and preparation of relevant devices gradually caused more and more concern of researchers.Due to the high sensitivity,real-time detection,remote testing and other advantages,fluorescence detection have obtained vigorous development in the application of molecular recognition and sensing.Design and synthesis of high sensitive and selective fluorescent moelcular probes has attracted much attention in recent years.Compared the fluorescent probes whose excitation and emission wavelengths are in the short-wavelength region,near-infrared(NIR)fluorescent probes have many advantages such as the low phototoxicity,low light scattering,deep tissue penetration,minimum interference from the background autofluorescence of organisms and favorable for fluorescence staining.While the kinds of NIR fluorescent probes are various,there also exist a lot of problems on water solubility,light stability,biological adaptability and difficulties of modification.Based on this,the development of new NIR fluorescence probes on recognition and detection of small molecule has important research and application value.Fluorescent probes based on silicon-substituted xanthenes,a novel fluorescent dye in which the 10,O atom in xanthene is replaced by Si atom,have attracted considerable interest on account of their excellent NIR photophysical properties as well as biocompatible characteristics.In this paper,we have designed and synthesized three NIR fluorescent probes based on silicon-substituted xanthene(SiR)which detect F-,phosgene and sulfur mustard(SM)respectively.The optical characteristics and detecting applications of the three fluorescent probes were investigated,verifying the practical value of the three NIR fluorescent molecular probes based on Si-substituted xanthenes.Firstly,a novel NIR fluorescent molecular probe(SiROPS)based on SiR towards F-was designed and synthesized.SiROPS has high selectivity and sencitivty on the detection of F-.The cleavage of F-to the ortho positions of dimethylphosphinotlhionyl group in the meso aryl involves the suppression of internal rotation upon phosphorylation of a reactive phenolate and the activating rotation of o-OH,which resulting in a large fluorescence "turn-off' response.The Job's plot suggests that the stoichiometry ratio is 1:1 between SiROPS and F-.The detection limit of the probe to F" was 48 nM in the dynamic range of 0.5-20?M.In addition,the proposed probe has been used to detect F-in water samples and toothpaste samples with satisfying results,which demonstrate the high selectivity of SiROPS towards F-.Secondly,a new NIR fluorescent molecular probe(SiR-amide)based on SiR for the detection of phosgene was designed and synthesized.The fast and sensitive phosgene detection was achieved by the conversion reaction of amide to nitrile,which resulted in a large fluorescence turn-on response.The response time of SiR-amide to phosgene was 4 min with a detection limit of 8.9 nM in solution.This probe was found to be sensitive to the presence of phosgene and highly selective toward phosgene over triphosgene,nerve agent mimics and acyl chlorides.Furthermore,a test paper,with SiR-amide was fabricated for the selective detection of phosgene gas at a low concentration level(0.1 mg/L).The fluorescence changes in the color from colorless to amaranth was easily observed by naked eye either from both solutions and the test paper.All of this work provided a very promising NIR fluorescent probe for rapid,selective and sensitive detection of phosgene both in solution and in the gas phase.At last,we have developed two SiR-based NIR fluorescent molecular probes,SiRXT-1 and SiRXT-2 detecting sulfur mustard(SM).Such a nearly nonfluorescent SiRXT probe readily reacts with SM via a nucleophilic reaction process and therefore yielded a highly fluorescent sulfide alkylation SiR derivative,whose excitation and emission wavelengths are in the NIR region.Compared the optical characteristics of the two probes,we found that SiRXT-2 which has the allyl group,had the longer recognition emission wavelength and higher fluorescence quantum yield.The proposed sensing mechanism was supported by UV-vis and fluorescence spectroscopy,]H NMR,MS spectrum.The response time of SiRXT-2 to SM was less than 1 imin with a detection limit of 3.2?M in solution.This probe was found to be sensitive to the presence of SM and highly selective toward phosgene over other analytes.A TLC plate with SiRXT-2 was fabricated for the selective and rapid detection of SM gas at a low concentration level.The response time of SiRXT-2 to SM was less than 1 min with a detection limit of 0.5 ppm in gas phase.All of the research results verified that SiRXT-2 is a NIR fluorescent molecular probe for rapid,selective and sensitive detection of SM both in solution and in the gas phase.