Fluorescent Molecular Probes Based On Novel PET Machanism For Cations Detection

Fluorescent probes exhibiting high selectivity toward a specific target analyte is in great demand dueto its low cost, high throughput capability, and point-of-care monitoring. The photoinduced electrontransfer （PET） process has been widely exploited. Generally, PET sensors based on nitrogen donors arehighly sensitive to environmental pH stimuli, because the degree of nitrogen protonation is strongly pHdependent. This pH sensitivity is unfavorable to obtaining reproduciable and reliable signals for most PETsensors used in a wide pH span. The molecular recognition of the reported PET probes only relies on Ndonors is unfavorable to detect target analyte for their pH sensitivity. To overcome this problem, pHinsensitive atoms, such as S, Se had been introduced in the probes as novel PET donors. The resulted novelfluorescent probes with dual PET processes are desirable pH inert by simultaneously introducing nitrogenand heteroatom （S, Se） donor to ensure the PET processes are always“ON”in both acidic and basic media.This design enables the fluorescence signal of the free chemosensor to be always“OFF”, leading toremarkable signal turn-on ratios over a wide pH span before and after binding of a guest species.In this paper, a series of fluorescent probes （HC1-HC3, HF1-HF2, HA1-HA3） base on the dyes ofcoumarin, fluorescein and 1,2-dihydroxy anthraquinone as report groups have been synthesized. Theirstructures were characterized by1H NMR,13C NMR, ESI-HRMS, and elemental analysis, the resesrchresult list as follows:The fluorescent probes HC1-HC3 exhibit high sensitivity and selectivity for Ag⁺due to inhibiting anintramolecular PET quenching pathway. The fluorescent probes demonstrate unique ability to discriminatebetween Ag+and chemically close ions. Due to inhibiting a PET quenching pathway, fluorescentenhancement factors over 4-fold are observed for these probes under the binding of the Ag+cation to thechemosensors, and with detection limit down to the 5.2×10^-8M, 5.2×10-8M, 2.45×10-7M range,respectively, are obtained. The highly selective and sensitive Ag+-chemosensors may have wideapplications for quantitative measurement of silver ion.Two novel fluorescent derivatives HF1 and HF2 based on acyclic N, S-donor ligands are synthesizedby using a“one-step”Mannich reaction synthetic procedure. These sensors exhibited excellent selectivitiestoward Ag+by forming the 1 : 2 stoichiometry of L-Ag⁺（HF1, HF2） complexes. Further investigationsshowed that they have disassociation constant of 1.3618×10^-11M²and 1.4551×10^-11M²with silver ionsderived by the nonlinear least-squares function.Fluorescet probes HA1-HA3 based on PET mechanisms possessing dual PET processes bysimultaneously introducing both nitrogen and heteroatom （S, Se） donors were achieved. The fluorescencesignal of the free chemosensors is in a normal-off state due to the heteroatom （S, Se） donor beinginsensitive to pH stimuli. As a result, the devices can be used over a wide pH span of 3-11. Upon bindingAl3+, significant fluorescence enhancements with turn-on ratio over 50-fold were triggered by the inhibitionof PET processes from both the heteroatom （S, Se） and the nitrogen donors to the fluorophore.