Design And Synthesis Of Fluorescent Probes Based On Intramolecular Charge Transfer（ICT） Effect And Their Application On The Detection Of Cu²⁺ And Hg²⁺

The environmental pollution problems brought about by the accelerated industrialization process are of widespread concern.Among them,heavy metal pollution poses a serious hazard to the ecological environment and human health.Although copper ions(Cu²⁺)play an important role in the physiological and pathological processes of the human body,they can interfere with cell metabolism and even kill cells if in excess,thus seriously affecting human functions.Mercury（Hg）compounds are a class of dangerous environmental pollutants and strong carcinogens that can enter the food chain and bioaccumulate from contaminated water sources.Therefore,it is particularly important to explore and monitor the levels of Cu²⁺and Hg²⁺in the environment.At present,the traditional methods for detecting Cu²⁺and Hg²⁺have the disadvantages of complicated operation and high cost and time consuming,which make it difficult to achieve real-time and on-site rapid detection of environmental samples.Thus,there is an urgent need to develop methods that can detect Cu²⁺and Hg²⁺in the environment in real time,visually and rapidly.Fluorescent probes are characterized by high sensitivity,high specificity and low cost,and are of wide interest especially for their ability to be applied to biological imaging.Based on the intramolecular charge transfer（ICT）effect,two organic small molecule fluorescent probes were designed and synthesized for the detection of Cu²⁺and Hg²⁺in this study,and the results are as follows.（1）A novel Cu²⁺fluorescent probe（E）-2-（3-（4-（diethylamino）phenyl）acryloyl）phenyl picolinate（DPAP）was synthesized by introducing 2-picolinic acid as a recognition group on the structure of（E）-3-（4-（diethylamino）phenyl）-1-（2-hydroxyphenyl）prop-2-en-1-one.By means of HRMS,NMR and DFT,the reaction mechanism between the probe and Cu²⁺was verified,and it was clarified that Cu²⁺produced the fluorescence quenching phenomenon by blocking the ICT process of the DPAP probe.Spectroscopic analysis of the synthesized probe by UV absorption spectroscopy and fluorescence emission spectroscopy demonstrated that the probe has a large Stokes shift（108 nm）and that the probe can rapidly detect Cu²⁺with a reaction time of only 6 min.In addition,the probe has high response value and high sensitivity,and is not interfered by other analytes such as ions,and the minimum detection limit is 15.2 n M,which can be successfully applied to the detection of Cu²⁺in real water samples.The probe can also be used to visualize the distribution migration patterns of Cu²⁺in cells and zebrafish,showing its potential for applications in environmental and biological sciences.（2）Using（E）-2-（3-（4-aminostyryl）-5,5-dimethylcyclohex-2-en-1-ylidene）malononitrile as a fluorescent group and 4-（diethylamino）-2-hydroxybenzaldehyde as a recognition group,we designed an infrared emission fluorescent probe for the detection of Hg²⁺,2-（3-（（E）-4-（（（E）-4-（diethylamino）-2-hydroxybenzylidene）amino）styryl）-5,5-dimethylcyclo hex-2-en-1-ylidene）malononitrile（DHEY）.The probe DHEY was characterized by HRMS,NMR,and DFT calculations were used to verify the reaction mechanism of the probe with Hg²⁺,and it was clear that Hg²⁺produced fluorescence enhancement by promoting the ICT process of the DHEY probe.The probe exhibits good selective response and anti-interference performance to Hg²⁺,with a detection limit as low as 16 n M and a Stokes shift of 105 nm.In addition,biological experiments have shown that DHEY has good cell permeability and low cytotoxicity,and has been successfully applied to live cells as well as zebrafish by fluorescence imaging.