Synthesis Of Novel Fluorescent COF Nanomaterials And Their Sensing And Imaging Applications

Covalent organic frameworks（COFs）have been widely used in gas storage and separation,electrochemical energy storage,heavy metal ion adsorption,photocatalysis,electronic devices and biomedicine.Due to its excellent optical properties and unique structure,fluorescent COF has shown great advantages in biosensing and bioimaging.In our paper,TFBPA-TAPA@PF-127 and TFBPA-TABPA@PF-127 quantum dots（QDs）were prepared by solvent-assisted exfoliation and in-situ chemical modification with PF-127.After that,high-performance fluorescence sensing of Fe³⁺and high-quality two-photon fluorescence bioimaging were realized based on TFBPA-TAPA@PF-127 and TFBPA-TABPA@PF-127 QDs,respectively.The detailed research contents are as follows:PartⅠ:TFBPA-TAPA two-dimensional fluorescent COF was firstly prepared by solvothermal method and then TFBPA-TAPA@PF-127 QDs were further prepared by solvent-assisted ultrasonic exfoliation and synchronous chemical modification with PF-127.The specific surface area,pore diameter,thermal stability and optical properties of TFBPA-TAPA two-dimensional fluorescent COF were investigated.The results show that TFBPA-TAPA COF has good crystallinity.Its pore size and specific surface area are about 1.9 nm and 564 m² g^-1,respectively.TFBPA-TAPA COF shows excellent thermal stability below 500°C.The morphology,structure and fluorescence properties of TFBPA-TAPA@PF-127 QDs were characterized,and the fluorescent sensing properties of TFBPA-TAPA@PF-127 QDs towards Fe³⁺were investigated.Experimental results show that the TFBPA-TAPA@PF-127 QDs are about 4 nm in size and have good optical absorption under visible light.The fluorescent quantum yield and two-photon absorption cross-section of TFBPA-TAPA@PF-127 QDs are estimated to be 8.9%and 14 GM,respectively.The TFBPA-TAPA@PF-127 QDs have good fluorescent stability,and can realize fast and highly sensitive fluorescence sensing of Fe³⁺with a detection limit of 50μM and a linear detection range of 200-800μM.Part II:TFBPA-TABPA two-dimensional fluorescent COF was firstly prepared by solvothermal method and then TFBPA-TABPA@PF-127 QDs were further prepared by solvent-assisted ultrasonic exfoliation and synchronous chemical modification with PF-127.The surface area,pore size,thermal stability and optical properties of TFBPA-TABPA two-dimensional fluorescent COF were investigated.The experimental results show that TFBPA-TABPA COF has good crystallinity.Its pore size and specific surface area is about 1.8 nm and 250 m² g^-1,respectively.It shows excellent thermal stability under 540°C.The morphology,structure and fluorescent properties of TFBPA-TABPA@PF-127 QDs were characterized and the two-photon fluorescent imaging properties of TFBPA-TABPA@PF-127 QDs were also studied.Experimentalresults show that TFBPA-TABPA@PF-127 QDs are about 4.2 nm in size,and have good optical absorption under visible light and two-photon fluorescent characteristics with a two-photon absorption cross section of 21 GM.TFBPA-TABPA@PF-127 QDs can interact with histone and DNA,which makes them achieve two-photon fluorescent imaging of cell nucleus.Furthermore,TFBPA-TABPA@PF-127QDs can realize the maximum imaging depth of 300μm towards tumor tissues.In summary,we have fabricated two novel two-photon fluorescent COF QDs.Their unique fluorescent properties make them be prospective for applications in the fields of biosensors and bioimaging.