Design, synthesis and characterization of conjugated polymers as fluorescent sensors

This dissertation presents extensive studies on a conjugated polymers based fluorescent sensory system. A series of conjugated polymers, poly[ p-(phenyleneethynylene)-alt-(thienylene-ethynylene)] (PPETE) and its derivatives, have been synthesized and characterized by NMR, FTIR, GPC, elemental analysis and UV-Vis. Poly[p-(phenylene-ethynylene)- alt-(thienylene-ethynylene)] (PPETE) was chosen as the basic conjugated polymer due to its high fluorescent quantum yield. Different oligopyridine pendant groups as receptors have been introduced to the conjugated polymers. These polymers are soluble in common organic solvents. The synthesis and characterization of these fluorescent polymers, as well as the photophysics and sensing response in the presence of transition metal ions, are discussed. The results show that the fluorescence of these polymers is highly sensitive to transition metal ions such as Ni2+. The polymers also show some selectivity to different transition metal ions. The effects of different linkages and pendants (including conjugated and non-conjugated) on quenching efficiency suggests that complete conjugation is not a prerequisite for emission quenching, even though the vinylene linked ttp-PPETE was found to have a higher quenching efficiency than the ether linker ttp-O-PPETE.; Molecular design enables us to incorporate different receptors to the conjugated fluorescent polymer backbone for different analytes. The nature of hemi-labile ligand complexes makes them a new class of potential receptors for conjugated polymers. For this reason, the photophysics of the hemi-labile ligand complexes [Ru(bpy)2L]2+(PF₆)₂ [(L = (2-methoxyphenyl)diphenylphosphine (RuPOMe) and (2-ethoxyphenyl) diphenyl-phosphine (RuPOEt)] was explored. These complexes show concentration-dependent absorption and emission behavior in the presence of trace amounts of water due to the formation of aquo-complexes. Temperature dependent lifetime experiments reveal that metal-ligand charge transfer to d-d state transition represents a major decay pathway for the complexes and the energy barrier for this transition is very small.; To develop a sensory device, a solid-state form of polymer is highly preferable. A non-mechanical electrospinning process has been used to fabricate sub-micron fibers from conjugated polymers including poly[2-methoxy-5-(2 ′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly[ p-(phenylene ethynylene)-alt-(thienylene ethynylene)] (PPETE). Poly(ethylene oxide) (PEO) was blended with the fluorescent polymers to obtain the right viscosity for the electrospinning process. The emission maximum of these fibers are red-shifted relative to those of the polymers in solution, but blue-shifted relative to the emission of the spin-cast films. The result implies that there may be a lower degree of polymer aggregation in the electrospinning fibers than in the films.