Design And Synthesis Of Two-photon Water-Soluble Conjugated Polymers For Fluorescence Imaging

In recent years,water-soluble conjugated polymers(WSCPs)have been rapidly developed due to their successful application in the interdiscipline of chemistry,materials and biological sciences.In the red/near-infrared light region(600–1000 nm),biological tissue has less absortption and scattering of light,stronger light penetration ability,and weaker biological autofluorescence,which is advantageous for deep detection in vivo imaging.Two-photon organic conjugated materials can be excited in this band,and have good optical properties,low biotoxicity,easily tailored structure and other characteristics.It has an extremely attractive application prospect in the field of molecular imaging and other biomedical research field.However,most of these materials currently have poor water solubility.Their fluorescence emission is not in the red/near infrared light region,fluorescence quantum efficiency and two-photon absorption cross-section are low,or many materials lack active targeting.Therefore,we have designed and developed a series of novel phosphonium fluorene-based water-soluble conjugated polymers.The fluorene group with high fluorescence quantum efficiency was the electron donor,the narrow band gap group was the electron acceptor,and vinyl bond was the conjugated bridge,and the long alkoxy side chain was introduced to improve water-solubility and two-photon fluorescence active absorption cross section.The main research work done in this paper are as follows:(1)A cationic water-soluble conjugated polymer(PFVDBT)with D-?-A-?-D structure was synthesized by the alternating copolymerization of narrow bandgap 4,7-bis(2-bromo-5-thienyl)-2 1,3-benzothiadiazole(A)and fluorine group with long alkoxy side chain(D)through Heck reaction.PFVDBT realized two-photon excitation and near-infrared emission.PFVDBT-HA NPs were synthesized by combining PFVDBT with hyaluronic acid(HA),which reduced fluorescence quenching in water,achieved active tumor targeting and improved the problem of adsorption by cell membrane Singlet oxygen quantum yield of PFVDBT was 43%,and PFVDBT-HA NPs can generate singlet oxygen in cells under two-photon excitation,which is expected to be used for two-photon tumor-targeting fluorescence imaging and photodynamic therapy(PDT).(2)With narrow bandgap 4,7-bis(vinyl phenyl)-2,1,3-benzothiadiazole as receptor,the D-?-A type conjugated polymers P1,P2,P3 and their cationic products P2',P3' with different receptor doping ratios were synthesized through Heck reaction.Then,the structure-activity relationships between doping ratio and material solubility and photophysical properties were studied.With many hydrophilic side chains,P2,P3 and ionized P2',P3' show good solubility and singlet oxygen quantum yield in water.Particularly,P2 and P3,which exhibit both high fluorescence quantum efficiency(0.65,0.58)and singlet oxygen quantum yield(86%,90%)in water,are expected to become excellent photosensitizers in PDT.The non-charged P2 entered cells fast and showed stable one-photon and two-photon imaging capabilities.The presence of tertiary amine groups in the side chains caused P2 to mainly enter lysosome of cell.In the future,it can be developed as a water-soluble lysosometargeting probe for two-photon imaging.