Design, Synthesis And Performance Study Of Spirobifluorene-based Two-photon Fluorescent Probes For Amino Acid Recognition

After more than 100 years of development,the research of fluorescent chemical sensors has made unprecedented progress,and its application has been extended to the fields of physiology,pharmacology,biology and environmental science.Our team has been committed to the research of spirofluorene based two-photon fluorescence probes.Using the characteristics of long wave excitation and short wave emission of two-photon probes and their high-efficiency transmission performance,we can effectively avoid the biological damage caused by fluorescence excitation,and apply fluorescent chemical sensors to biological imaging more efficiently.Amino acid is a kind of bioactive macromolecule widely existing in organisms,and it is also one of the most important nutrients in human body.It is the basic unit of protein,which is the first element of human life activities.At the same time,it is of great significance to maintain the total balance of nitrogen in the human body,promote the catalytic metabolism process,participate in the composition of enzymes,hormones and micro biotics,and maintain the normal life activities of organisms.The previous work of the research group was mainly devoted to the recognition of redox substances and the response to metal ions such as zinc and mercury.In this project,we focused on the amino acids that are more closely bound with organisms,and explored other potential properties of spirofluorene probes,hoping to combine spirofluorene two-photon fluorescent probes with physiological and pathological research of organisms Better combination of fluorescent chemical sensing technology will be better applied in the field of life science.Steps of the project development:In the first part,four fluorescence probes,namely SPF-TM1,SPF-TM2,SPF-TM3 and SPF-TM 4,were designed and synthesized for the purpose of recognizing amino acids,and structures of thems were characterized.In order to explore more potential properties of spirodifluorene fluorescent probes,a two-photon fluorescent probe SPF-TM5 based on Schiff base structure was designed and synthesized,and structure was characterized,as well.The second part:the ability of SPF-TM1 and SPF-TM2 to recognize different amino acids was explored.It was found that the probes TM1 and TM2 were fluorescence enhanced two-photon fluorescence probes which could specifically recognize cysteine.Among them,the detection limit of SPF-TM1 for Cys is 36nm,which is one of the lowest among many known amino acid probes.The large steric hindrance of spirofluorene itself creates a unique condition for TM1 to specifically recognize Cys.SPF-TM 2 shows excellent p H stability,which creates stable conditions for amino acid detection and fluorescence imaging in the biological environment with different acidity and alkalinity.In the process of self recognition reaction with Cys,SPF-TM 2 directly eliminates the interference of other amino acids from the mechanism level,and can achieve efficient and specific recognition of cysteine.The third part:other potential properties of SPF-TM5 as a spirofluorene fluorescent probe were explored.It is found that SPF-TM5 has good AIE performance,and it also shows ESIPT effect.We also applied the aggregation induced luminescence effect to the recognition of metal ions and realized the specific recognition of copper ions.On this basis,the performance of SPF-TM5 in continuous detection was further studied.SPF-TM5 is the first spirofluorene based two-photon fluorescence probe to realize continuous detection of Cu²⁺and S^2-.Moreover,the probe has rapid response,and all the detection results can be directly observed through the naked eye,which has the characteristics of high sensitivity and high efficiency.