Synthesis And Luminescence Properties Of Temperature/pH-sensitive Fluorescent Polymer Materials

Fluorescent polymer is a kind of functional polymer with wide research and application. Since the first fluorescent material composed of polymer as a substrate was reported, fluorescent polymers have attracted much attention and recently various new materials have been prepared. However, there are few researches and reports about the multifunctional fluorescent polymers with temperature/pH-sensitive character. Many researches have indicated that there is a higher sensitivity to detect temperature and pH using the fluorometric determination and the geometrical design of fluorescent detector is more flexible. Moreover, it is convenient for the research of fluorescent micrology and the real-time detecting of dynamic distributing and region change in living cell to detect the temperature and pH using the change of different fluorescent parameters of fluorescent molecule, such as fluorescent intensity and fluorescence lifetime. However, the temperature/pH-sensitive fluorescent molecules easily fall out and their consistency property with substrate is not good in applications, which badly affects the stability of instruments. Compared with them, making fluorescent molecules an integral part of polymers with excellent stability and ability to form very homogeneous films through covalent binding is an excellent project to avoid those limitations, which is an important step in the design of fluorescent materials.In this paper, the modified fluorescein and 9-aminoacridine as chromophores were attached successfully on several avirulent, low-cost, biocompatible and water soluble polymers through two different methods, respectively. The synthesized fluorescein and aminoacridine derivatives and fluorescent polymers were characterized by the methods of nuclear magnetic resonance (NMR), mass spectrography (MS), infrared spectra (IR), ultra-violet-visible spectra (UV-Vis), differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and fluorescence spectra, respectively. And the temperature and pH dependences of fluorescence of polymers were investigated in detail.(1) A novel method for attaching fluorescein (via its epoxy derivate) to water soluble polymer and its temperature/pH-sensitive qualities of fluorescence were investigated. 3-Epoxypropoxy fluorescein (EPF) was firstly synthesized through the reaction between fluorescein and epichlorohydrin and poly (vinyl alcohol) (PVA) bearing fluorescein was prepared via ring-opening reaction with EPF. The chemiluminescent and photophysical behaviors of the dye fluorescein derivative and the polymer-containing fluorescein had been studied, and the ability of film forming of PVA-EPF and the effect of different solvents on its fluorescence behavior were also reported. In addition, the pH and temperature dependences of fluorescence of PVA-EPF were investigated in detail. All those observations suggested that the PVA-EPF was an excellent luminescent macromolecular material with a convenient method for the preparation and an excellent water-soluble ability. Moreover, its pH and temperature sensitivities on the fluorescence intensity can be advantageous for it to become a multifunctional material to probe pH and temperature.(2) Two novel water-soluble fluorescent natural polymers bearing fluorescein were synthesized through the reaction between EPF and water-soluble chitosan and starch via ring-opening reaction, respectively. The chemiluminescent and photophysical behaviors of fluorescent natural polymers were studied in detail. The results showed that the fluorescent chitosan and fluorescent starch could still provide temperature and pH sensitivities similar to that of fluorescein, achieving better long-term stability and fast equilibrium response. To our knowledge, there is no report about the temperature and pH sensors from natural polymers via fluorescent techniques. This investigation may provide a new way to prepared low-cost and multifunctional macromolecule biomaterial to probe pH and temperature in biological systems.(3) An allyl monomer bearing xanthene group, allyloxyfluorescein (Al-Flu) was synthesized from fluorescein and allyl bromide in the presence of potassium carbonate in anhydrous N, N-dimethyl formamide (DMF) at room temperature. Copolymer of Al-Flu and acrylamide [poly (Al-Flu-co-AM)] was obtained using AIBN as a thermal initiator in THF. The photophysical behaviors of Al-Flu and poly (Al-Flu-co-AM) were explored by recording the fluorescence spectra in solution, solid and film. In addition, the pH and temperature dependences of fluorescence of water-soluble poly (Al-Flu-co-AM) were investigated in detail. The results showed that poly (Al-Flu-co-AM) had an excellent linear response between relative fluorescence intensity and temperature and had a nonlinear response between relative fluorescence intensity and pH. During the experiment, we could select different olefinic hydrocarbon to copolymerize with Al-Flu according to experimental requirements. Therefore, the design of synthetic method is simple, convenient and practical for the preparation of temperature/pH-sensitive fluorescent polymers.(4) A novel acrylic monomer bearing acridinyl group, acridine-9-N-acrylamide (Ac-9AA) was synthesized. Homopolymer of Ac-9AA and copolymer of Ac-9AA and acrylamide were synthesized with thermal initiator, respectively. The photophysical behaviors of Ac-9AA and its polymers were explored by recording the fluorescence spectra in solution, solid and film. In addition, the pH and temperature dependence on fluorescence of the water-soluble poly (Ac-9AA-co-AM) were investigated in detail. The results showed that the relative fluorescence intensity of poly (Ac-9AA-co-AM) had an excellent linear response between relative fluorescence intensity and temperature and had a nonlinear response between relative fluorescence intensity and pH.In particular, the typical features of temperature/pH-sensitivity of fluorescent polymers prepared in this dissertation would make them very suitable to become a multifunctional polymeric material to probe temperature and pH.