Design, Synthesis Of Water-soluble Two-Photon Absorption Materials And Their Potential Applications In Biological Field

Two-photon absorption (2PA) is one of the third-order nonlinear optical properties involving the simultaneous absorption of two photons from ground state to excited state. Comparing with one-photon absorption (1PA) employing one photon of higher energy for the excitation,2PA uses two photons of lower energy as the excitation source and is becoming more popular due to the advantages it provides. They include deeper penetration depth, up-converted fluorescence, intrinsically localized excitation and so on. There is a strong demand for efficient2PA materials with good integrated performance. Maximizing the2PA cross-section is not the only consideration when using a two-photon dye in biological system, bio-compatibility and fluorescence quantum yield are also critical factors. The research on this scope is only in the beginning stage because it is a cross field involving chemistry, biology, medicine and physics. In this thesis, to pursue these researches, three kinds of water-soluble two-photon materials were designed and synthesized, their photophysical properties as fluorescence probes, fluorescence dyes or photosensitizers for photodynamic therapy were studied, and their potential applications of some materials were also explored.The main contents of this thesis are described as follows:Chapter1is the introduction of the whole thesis. At first, the concept, some basic information and measurement of2PA were presented. Then the key structure-property relationships of linear organic2PA materials were briefly summarized, and recent progress and development of2PA materials in the field of two-photon probe and photodynamic therapy were also given. Based on the problems and deficiencies of the research on TPA materials, an outline of the research projects in this thesis are designed and listed at last.In chapter2, a new water-soluble two-photon probe CuL2for pyrophosphate anion (PPi) is designed and synthesized, and shows turn-on fluorescence with high sensitivity and selectivity. To the best of our knowledge, this is the first water-soluble two-photon fluorescent turn-on probe for PPi. The structure and purity of L was characterized by nuclear magnetic resonance (NMR), and high resolution mass spectra (HRMS). Their photophysical and PPi recognition properties were studied by UV-Vis absorption spectra, fluorescence spectra and two-photon excited fluorescence method. The probe CuL2can selectively detect small amount of PPi particularly in the presence of a large excess of PO43(?) and ATP, and its detection limit to PPi is3.2×108M. By two-photon titration experiments, the association constant of CuL2and PPi is determined to be about105.2. The sensing mechanism of CuL2to PPi was preliminarily discussed by theoretical calculations and mass spectra, two possible sensing mechanisms was proposed. Moreover, in chapter2, three compounds, with similar structures to L (L-A, L-B and L-C), were designed and synthesized, the structures and purities of them were characterized by NMR, mass spectra (MS) and elemental analysis (EA). By the method of two-photon excited fluorescence, the relationship between the molecular structures and the two-photon absorption properties of them (L, L-A, L-B and L-C) was studied.In chapter3, by the introduction of (3-diketone group as an efficient acceptor in a D-?-A-?-D structure, which shows diketone-enol tautomerism, we present a design approach that solves the common confusion how to obtain a large two-photon cross-sections dye with good biological compatibility at the same time, while shows high fluorescence sensitivity to the polarity of the environment. Four two-photon fluorescent dyes were synthesized, and the structures and purities of them were characterized by NMR, MS or EA. Their one-photon and two-photon photophysical properties, bio-compatibilities and polarity-sensitivities were studied by UV-Vis absorption spectra, fluorescence spectra and two-photon excited fluorescence method. Their one-photon excited fluorescence cell images were also reported. The results indicate that Dk-B has very good comprehensive performance:the water-solubility of DK-B is as high as12?M, its molecular weight is only482g/mol, its two-photon action cross-sections is as high as411GM in DMF, its two-photon excited fluorescence is red (maximum emission wavelength is longer than600nm in DMF). Moreover, it was found that the dyeing speed of Dk-B is very fast and its fluorescence polarity-sensitivity is very good when employing it as a red fluorescence dye in cell image.In chapter4, a water-soluble cyclodextrin derivative with a two-photon absorption chromophore (TPACD) and a water soluble porphyrin derivative (TOPyP) were designed and synthesized separately at first, and then a novel water-soluble2PA-PDT (two-photon absorption photodynamic therapy) photosensitizer (4TPACD+TOPyP) was prepared through supermolecular self-assembly process. The structures and purities of TPACD and TOPyP were characterized by NMR, MS or EA seperately. By the methods of UV-Vis absorption spectra, fluorescence spectra and two-photon excited fluorescence, their one-photon and two-photon photophysical properties were tested. The ability of the self-assembled photosensitizer to generate singlet oxygen was also studied. Efficient energy transfer, as high as89%, from the TPACD to TOPyP was observed in aqueous solutions. The two-photon absorption cross-sections of the self-assembled photosensitizer was enhanced to2537GM while the value of TOPyP was only57GM. Meanwhile, the efficient energy transfer contributes to effective singlet oxygen generation, by a factor of2.1at820nm two-photon excitation, from the porphyrin guest molecule. To the best of our knowledge, this is the first2PA-PDT photosensitizer through cyclodextrin-porphyrin self-assembly process, and provides a new route for the design of the2PA-PDT photosensitizer.