Design,Synthesis And Properties Of Novel Fluorescence Sensor Based On Porphyrins

Porphyrins have unique photophysical and photochemical properties,and have always been a research hotspot in terms of photoelectric properties,which are widely used in many frontier scientific and technological fields,such as biological imaging or photodynamic therapy.Traditional porphyrin probes still have certain limitations due to the simple synthetic routes,which limits their application in fluorescence sensors and biological imaging.First,the absorption spectra of traditional porphyrin probes is mainly located in the visible region and cannot penetrate deep tissues.This is the main disadvantage of traditional single-photon excitation.Second,the fluorescence quantum yield of traditional porphyrin probes is small(0.3-0.13),which is particularly inadequate for an excellent fluorescent probe;third,the targeting of organelles is not clear.In view of the above problems,the exploration of structural design and performance optimization of new porphyrin-based fluorescent dyes is of significance both in the application of fluorescence sensing,biological imaging,and disease detection.Fluorescence bioimaging provides a unique method for cell morphology,which can visualize the details of tissues with subcellular resolution,and has become a powerful tool for processing and studying the microenvironment in living cells and tissues.An ideal fluorescence sensing system can provide reliable fluorescence response to the target analytes under the analysis conditions.These analytes can be chemical,environmental or biological analytes.Two-photon fluorescence uses infrared or near-infrared light as the excitation light source.This long-wave excitation has strong penetrability,which can perform fluorescence imaging in deep tissues and effectively eliminate the interference of background fluorescence and scattered light in biological samples.The modification of fluorescent probes with electron donors or extended ?-systems enables the emission of the fluorescent probes to the near infrared region,which can improve the brightness and resolution of bioimaging.With the different working principles,such as fluorescence resonance energy transfer and intramolecular charge transfer,different types of ratiometric fluorescent probes can be constructed,which helps to improve the detection accuracy of analytes.Targeting strategies(including organelles targeting)are expected to significantly improve the accuracy of the detection and further study of cell biology while reducing adverse side effects.In this thesis,a series of one/two-photon organic small molecule systems based on porphyrin compounds were designed and synthesized,and their application potentials in fluorescence sensing and biological imaging were further explored.The main research contents are as follows:(1)A Porphyrin-pyranine dyad based on FRET for pH ratiometric fluorescence sensing and microscopy imagingThe use of fluorescence imaging to detect intracellular pH is of great significance for cell biology and medical research.Though a large number of new pH probe systems have been reported,such as supramolecules and quantum dots,the design of small-molecule pH fluorescent probes still play an important role because of their simple preparation and easy modification.In Chapter 2,we designed and synthesized the porphyrin-pyranine dayd Por-Py 1 based on fluorescence resonance energy transfer(FRET),and applied to pH detection in living cells.We chose pyranine as the energy donor and porphyrin as the pH-responsive group and energy receptor.When Por-Py 1 is excited by light,the excited energy of Py donor is transferred to the Por receptor,producing two fluorescence bands at 435 and 650 nm.When the pH value gradually changes from 8.58 to 3.92,the pyridyl group at the meso position of the Por moiety and the central pyrrole gradually undergo reversible protonation,leading to the simultaneous change of absorption and emission of the porphyrin.In addition,Por-Py 1 shows good cell permeability and lysosomal targeting ability,thus can be applied in the pH detection of A549 cells.(2)Multipolar porphyrin-Triazatruxene arrays for two-photon fluorescence cell imagingDue to the advantages of deep tissue penetration and high resolution,two-photon fluorescent materials are in great demand in biological imaging applications.In the third chapter of this thesis,we designed and synthesized a series of two-photon fluorescent materials TAT-(ZnP)n(n=1-3).The three dyes show excellent two-photon absorption properties and high fluorescence quantum yields(?em=0.40-0.47),which represents a great breakthrough for porphyrin-based two-photon fluorescent materials.With the help of density functional theory calculations,these results can be explained by the extension of D-?-A-D conjugated system and the formation of quadrupole/octapole molecules.In addition,the three dyes show good biocompatibility and preferential targeting ability to cell membranes,thus they can be successfully applied to TPEF imaging in living cells.(3)A two-photon viscosity fluorescence rotor for mitochondria viscosity sensing and fluorescence imaging applicationChanges in the microenvironment of cells are of great significance for the study of cell biology and physiological conditions of living individuals.In the fourth chapter of this thesis,based on the octopolar molecules in Chapter 3,we designed and synthesized a fluorescent rotor TAT-(ZnP-TPP)3 for the detection of mitochondrial viscosity and two-photon fluorescence imaging.Due to its large?-conjugated system and octupolar structure,the fluorescent probe exhibits high two-photon absorption performance(3435 GM at 870 nm)and high fluorescence quantum yield(0.35).In addition,based on the intramolecular charge transfer(ICT)mechanism,the fluorescent probes exhibit different predominant conformations in solvents with different viscosities.Upon the excitation of light,the probe show two unsynchronized changes of the emission in different viscosity solvents,thereby affording a sensitive fluorescence ratio change to viscosity.The probe showed low toxicity to A549 cells and strong fluorescence in two-photon imaging,and also strong mitochondrial targeting ability.Combined with spectroscopic experiments,TAT-(ZnP-TPP)3 can be successfully used for real-time monitoring of mitochondrial viscosity.