Study On Inner Filter Effect And Rhodol Based Schiff Base Fluorescent Probe

Fluorescent probes have the advantage of strong universality,high sensitivity,simple operation,qucik response and low cost.They are widely used in the detection of various substances,especially the non-invasive detection method,which is very suitable for the on-line detection of living organisms.In recent years,more and more fluorescence mechanisms have been applied to the design and development of fluorescent probes.The sensing method based on inner filter effect（IFE）reduces the difficulty of organic synthesis because it does not need any covalent or noncovalent connection between the absorber and the fluorophore,and shows obvious simplicity,adjustability,time-saving and economic advantages.Unfortunately,this type of fluorescent probe is generally of low sensitivity and relatively poor selectivity,because any compound with absorption at the excitation wavelength will filter the fluorescence of the fluorophore and interfere with the detection,which greatly limits the application of this kind of probe.In the first part of the article,based on IFE,an Extinction Coefficient Difference Inner Filter Method（εDIFM）is found,which can selectively identify analytes from substances with absorption at the excitation wavelength of fluorophores.In order to verify this method,a selective detection method for 2,4,6-trinitrophenol（TNP）was developed usingεDIFM.In this method,Rh B,a commercial rhodamine dye,was used as the fluorophore.The UV lamp wavelength（365 nm）used to observe TLC was used as the excitation wavelength.Its selectivity,anti-interference ability,linear range and detection limit were studied by UV-Vis absorption spectra and fluorescence spectra.The results showed that the linear detection range of TNP was 0-260μM,the linear correlation coefficient（R²）was 0.99674,and the detection limit（DL）was 0.088μM.Even in substances with absorption at 365 nm like TNP,such as 2,4-dinitroaniline（2,4-DTA）,4-nitroaniline（4-TA）and 2,4-dinitrophenylhydrazine（2,4-DTH）,the use ofεDIFM can also selectively recognize TNP.It is worth noting thatεDIFM is the most selective method among all the IFE based TNP detection methods reported in the literature.This method can be used to detect TNP in water samples.In addition,TNP test paper was developed and combined with smart phone color recognizer App to establish a low-cost,real-time,on-site quantitative analysis method for TNP.Rhodol is a fusion of rhodamine and fluorescein.It inherits the excellent photophysical properties of fluorescein and rhodamine,such as high extinction coefficient,quantum yield and photostability.At the same time,it has chemical properties such as easy modification and good solubility in various solvents.In recent years,fluorescent probes based on rhodol structure have become a hot research topic.In the second part of this paper,rhodol-schiff-based probes RHO-C=N-1 and RHO-C=N-2 were designed and synthesized using formyl rhodol（RHO-CHO）as matrix.Their structures were determined by mass spectrometry,¹H NMR and ¹³C NMR spectra.The nucleophilic reaction of-C=N-in probe RHO-C=N-1 with H₂O makes the fluorescence emission blue shift,so as to realize the detection of water content in ethanol.UV-Vis absorption spectra and fluorescence spectra experiments show that the probe can realize the sensitive detection of water content in ethanol,the linear range is0-18%（v/v）,and the detection limit is as little as 0.032%（v/v）.Similarly,with-C=N-as the recognition site,probe RHO-C=N-1 and probe RHO-C=N-2 can selectively recognize diamine.The results of UV-Vis absorption spectra,fluorescence emission spectra,¹H NMR and ¹³C NMR spectrum show that both probe RHO-C=N-1 and probe RHO-C=N-2 have good selective recognition ability and anti-interference ability for1,4-butanediamine,and the linear range is 0-45μM.The detection limits were 0.47μM and 0.79μM respectively.In addition,four solid-state indicators（filter paper and TLC plate containing probe RHO-C=N-1 and probe RHO-C=N-2）have been developed,which can realize the rapid on-site inspection of the freshness of fish and prawns.