A New Strategy To Improve The Quantum Yields Of Rhodamine Dyes And Its Application In Fluorescent Probes

Rhodamines have been widely utilized as fluorescent probes,fluorescent labeling and laser dyes on account of their large extinction coefficients,relatively high fluorescence quantum yields(up to 0.8 in organic solvents)and good photostability.However,due to the presence of twisted intramolecular charge transfer(TICT),the quantum yield of traditional rhodamines(such as tetramethyl rhodamine,tetraethyl rhodamine)in aqueous solution are greatly reduced,below than 0.5.In order to improve the fluorescence quantum yields of rhodamines,and make them better suitable for biochemical related researches,developing a new strategy to improve the quantum yields of fluorescent dyes by inhibiting the TICT process is one of the current hot spots in scientific researches.In the first chapter,the author summarized rhodamine dyes,including the relationship between structure and properties of rhodamine dyes,their application in biological researches,their limitations and improvement methods in practical applications.In the second chapter,in order to further improve the fluorescence quantum yields of rhodamines and their NIR derivatives in aqueous solution,we developed a new strategy based on inhibiting twisted intramolecular charge transfer to improve the quantum yields of the dyes.Five kinds of rhodamine dyes that including piperidinyl,diethylamino,azetidinyl,4-methyl-1,4-azaphosphinane 4-oxide and thiomorpholine 1,1-dioxide auxochrome,were synthesized,respectively.The structure and photophysical properties of these rhodamine dyes were characterized by analytical characterization techniques such as NMR spectra,high resolution mass spectra,UV-Vis absorption spectra and fluorescence spectra.The results showed that the negative inductive effect exerted by electron-withdrawing groups can obviously improve the ionization potential(IP)of amino auxochromes,thereby effectively inhibiting twisted intramolecular charge transfer and markedly improving the quantum yields of rhodamine dyes in aqueous solution.Among them,the quantum yield of the rhodamine dye containing 1,1-dioxide morpholine chromophore can reach 0.99.At ths same time,its photostability and fluorescence lifetime are also significantly improved.This strategy is also applicable to other fluorescent dyes.We extended the thiomorpholine 1,1-dioxide auxochrome to several other fluorescent dyes including carbon-rodamine,silicon-rodamine,phosphorus-rodamine,oxazine,coumarin and 1,8-naphthalimide.The results showed that the quantum yields of these dyes can also be greatly improved.In the third chapter,based on the research ideas of chapter two,we developed a new “turn-on” type fluorescent probe for real-time detection of HCl O/Cl O-based on the mechanism of inhibiting TICT.The structure of the probe was characterized by NMR spectra and high-resolution mass spectra.The recognition and sensing behavior of the probe for HCl O /Cl O-was further studied by combining UV-Vis absorption spectra and fluorescence spectra.It was found that the probe showed high selectivity,high sensitivity and ultrafast response characteristics to HCl O /Cl O-,and it was not affected by environmental p H values.Further research showed that the probe can be used to quantitatively detect hypochlorous acid in tap water.