Synthesis, Characterization And Applications Of Novel Water-soluble Conjugated Materials

Water-soluble conjugated materials are more and more widely used in biosensor, vitro/vivo imaging, diagnosis, drug release, therapy, devices and self-assembly application. They have been the research focus in the field of chemistry, biology and optoelectronics. However, they still exhibit some drawbacks such as aggregation-caused quenching, lack of materials with UV-vis absorption and emission in the infrared / near infrared region. In this paper, the following research has been done on the application of water-soluble conjugated materials in bioimaging and supramolecular selfassembly.1. In order to realize the inhibition of aggregation and the red shift of absorption and emission spectra, novel multiple branched water-soluble conjugated materials based on fluorene, tetraphenyl methane, paraxylene dimer and low band gap benzo-2, 1, 3-thiadiazole(BT) were designed, and some compounds have been synthesized.2. Water-soluble conjugated materials have amphiphilic properity because they have hydrophobic backbones and hydrophilic side chains. Different molecule structures and different solvents may show influence on their self-assembly properties and change their conformations. Two meta-linked cationic water-soluble poly(phenyleneethynylene)s, M1’ and M2’, were synthesized and the influence of solvent effect and molecule structure on the conformation of M1’ and M2’ was studied. When the proportion of good solvent(methanol) in the mixed solvent(methanol and water) decreased, the conformations of M1’ and M2’ change from random coil to helical conformation. Alhough BT unit has a larger and more rigid structure than the phenylene unit, the introduction of BT units to the conjugated backbone of M1’ showed very little effect on the conformation, but triggered a shift in emission color of M1’ from blue to yellow, which resulted in efficient fluorescence resonance energy transfer(FRET) between the phenylene ethynylene segments and the low band gap BT units. Besides, the composites of M2’ and MWCNTs were prepared. The composites have a good dispersion in good solvent methanol, and the TEM image showed the distinct helical wrapping superstructure of M2’/MWCNT composite, in which a polymer monolayer wrapped the nanotube surface to form a well-defined helix. The monolayer helical wrapping superstructure of M2’/MWCNT composites can likely be attributed to the backbone flexibility resulting from the presence of meta-phenylene unit and the carbon–carbon triple bond, and the strong π-π interactions between the backbone and the CNT surface, with the cationic side groups acting as solubilizing groups which also separated the individual nanotubes because of charge repulsion.