Theoretical Study On Detection Of Small Molecule Fluorescence Probes Based On ESIPT Mechanism

Since the discovery of fluorescent probe technology,the study of its photophysical and photochemical properties has received a lot of attention from researchers and has been applied in various fields such as industrial,biological,and environmental monitoring.There are more and more fluorescent probes named according to various different luminescence mechanisms with the technical process of probes.Among them,fluorescent probes based on excited state intramolecular proton transfer(ESIPT)have been widely studied due to its special luminescent properties.ESIPT-type molecules are widely used in materials,medicine,chemistry,and many other fields because of their excellent photophysical properties such as large Stokes shifts,double fluorescence emission,and avoidance of self-absorption due to the occurrence of excited state proton transfer processes.Wherein,the use of molecules with ESIPT properties as fluorescent probes to detect various substances such as organic small molecules,protein activities,metal ions and anions in the environment and in living organisms is even more remarkable.Although many probe molecules with excellent properties have been experimentally studied by observing luminescence phenomena and researchers have tried to explain the experimental phenomena with theory,the explanation of microscopic phenomena such as isomerization and charge transfer is still inadequate.Therefore,theoretical work is also essential for the development of probe technology.In this paper,we have attempted to investigate the detection mechanism of different proton transfer types of probes from theoretical analysis: taking the chalcone derivative probe Pr1 as an example,the detection mechanism of single proton transfer type probes was studied,and the reasons for the fluorescence quenching phenomenon in experiments caused by photoinduced electron transfer and twisted intramolecular charge transfer processes were explained;taking the salicylaldehyde zine derivative AE-Phos,we have studied the detection mechanism of double proton transfer probes and explained the ESIPT behavior by theoretical analysis.The specific source of experimental fluorescence was determined by theoretical simulations to exclude the fluorescence interference from other substances;in addition,the luminescence properties of the probe molecule were also modulated by introducing different substituent groups at the ortho and meta positions of the hydrazine probe HP1 of benzoxazole derivatives,and the calculation results showed that the probe molecule product has a larger Stokes shift and better luminescent properties,indicating better application potential.