Photochromic Properties Of Naphthopyran In Nanostructures And Their Application In Fluorescence Regulation And Light Controlled Release

In this thesis, novel photochromic nanoparticles were prepared via miniemulsion copolymerization that is a simple and rapid method to regulate the properties of photochromism of naphthopyran in a wide range. This may widen the potential applications in other filed..In addition, we use the reversible addition fragmentation chain transfer polymerization method to fabricate light responsive polymers based on naphthopyran derivatives. Fluorescence microscopy, dynamic light scattering and fluorescence spectra were used to study the abilities in photoswitching and light controlled release. The main contents of this treatiseare as follows:1. Novel naphthopyran derivative based photochromic polymer nanoparticles are prepared via miniemulsion copolymerization with methyl methacrylate(MMA) and n-butyl methacrylate(BMA) monomers. The systematic modulation of the photochromic rate can be achievedvia tuning the ratio of MMA and BMA monomers to lead the naphthopyrans to swing between rigid and soft surroundings. Transmission electron micrographs(TEM) and dynamic light scattering(DLS) images prove that the nanoparticles are discrete and smooth. The typical spectral characteristics of naphthopyran in the polymer nanoparticles indicate that the photochrome is incorporated into the nanoparticles successfully. In addition, the polymer nanoparticles exhibit good photochromic reversibility and stability upon UV irradiation and thermal back reaction.2. A fluorescence resonance energy transfer process was built with photochromic naphthopyran derivatives as light response groups and acceptor groups, naphthalimide fluorescent dye as donor groups. The polymerization method of reversible addition-fragmentation chain transfer polymerization(RAFT) was used to prepare two amphiphilic block copolymers, P(St-co-NP)-b-PNIPAM and P(St-co-MANI)-b-PNIPAM, and the mixed polymers self-assembly into micelles in aqueous solution with the mixed PSt block as the core and the hydrophilic PNIPAM block as the shell.Transmission electron microscopy(TEM) was used to characterize the particle morphology. The fluorescence resonance energy transfer process can occur between photochromic naphthopyran derivatives and MANI dyes, resulting the reversibility of the fluorescence modulation(“on” and “off”) of the micelles upon UV and thermal back reaction. Dynamic light scattering(DLS) was used to measure the diameter change of the polymer assemblies upon UV irradiation and keeping in dark, becausethe photoisomerization of naphthopyrans could reversibly cleavage or reform the nano-polymer assembly. Moreover, Nile Red was used as the hydrophobic probe guess, the poymer micelles could release and re-encapsulate guest NR upon UV irradiation and thermal back reaction for three times. These results indicate that the multi-functional nano-polymeric micelles have the potential applications in biological imaging, drug delivery.3. A dual-responsive amphiphilic diblock copolymer,poly(styrene-co-1-(2-methacryloxyethoxy)-2-(2-pyridyl)benzimidazole)-block-Poly(N-isopropylacrylamide-co-8-methacryloxy-[3-biphenyl-3-phenyl]-3H-naphtho[2,1-b]pyran-co-4-methamino-9-ally l-1,8-naphthalimide), also denoted as P(St-co-PBI)-b- P(NIPAM-co-NP-co-MANI),also denoted as P(St-co-PBI)-b-P(NIPAM-co-NP-co-MANI), was synthesized by reversible addition fragmentation chain transfer(RAFT) polymerization followed by assembling into micelles with hydrophobic P(St-co-PBI) block as core and thermoresponsive P(NIPAM-co-NP-co-MANI) block as the shell in aqueous solution.Dynamic light scattering(DLS), transmission electron microscopy(TEM) and optical transmittance were used to characterize the particle morphology and thermosensitivity of the micelles solution. In addition, the fluorescence emission of the micelles could be reversibly modulated “on” and “off” by the photochromic naphthopyran upon UV and thermal back reaction, which promoted naphthopyran transformation between merocyanine forms and original closed form. Moreover, the spatial distance between the two fluorescence dyes could be regulated by temperature, resulting from the collapse or extension of PNIPAM in aqueous solution. This property enabled the polymeric assemblies to serve as sensitive ratiometric fluorescent thermometers.