Conjugated Polymers With Phosphorescent Iridium(Ⅲ) Complexes:Design,Synthesis And Their Applications

Conjugated polymers (CPs) are π-conjugated macromolecules with delocalized π-electronic "molecular wires", allowing for more rapid and efficient intra-chain and inter-chain exciton migrations and amplified signal outputs. Phosphorescent transition-metal complexes (PTMCs) have gained increased attention in sensing and imaging applications during the recent years. They exhibit several unique photophysical properties compared with pure organic luminophores, such as high quantum efficiency, long emission lifetime, tunable emission wavelength, large Stokes shift, as well as excitation in visible range. In this thesis, phosphorescent Ir(Ⅲ) complex (as energy acceptor) was introduced into the CPs main chains (as energy donor) to yield a new series of phosphorescent probes for chemo/bio-sensing and bioimaging applications. The details are summarized as follows:1. A series of conjugated polyfluorenes containing different contents of Ir(Ⅲ) complexes has been designed and synthesized. The β phase was observed for these polymers in various conditions. The effects of iridium(Ⅲ) complex content, solution concentration, solvent/non-solvent ratio, as well as temperature on the β-phase formation and energy transfer in the copolymers were investigated through UV-vis absorption, photoluminescence and excitation spectra. For the copolymers with low content of iridium(Ⅲ) complex, it was easier to form β phase than those with high content of iridium(Ⅲ) complex. An aggregation-induced β-phase formation for the copolymers was significantly displayed in the highly concentrated THF solution or THF/H2O mixtures. Temperature was another factor for β-phase formation. The β phase could be easily formed in the low temperatures for copolymer films and an annealing treatment also influenced its formation. The formation of β-phase was found to make the energy transfer from fluorene to iridium(Ⅲ) complex more efficient.2. A novel series of phosphorescent conjugated polymers with on-chain heavy metal Iridium(Ⅲ) complex were designed and prepared successfully, which were characterized by1H NMR,13C NMR as well as GPC. Their photophysical properties were investigated in both solution and film. The effect of the Ir(Ⅲ)-complex content, solution concentration and temperature on energy transfer from flourene unit to Ir(Ⅲ)-complex guest were studied. It suggested that energy transfer became more efficient in films than that in solution. Increased concentrations and decreased temperatures could make more efficient energy transfer process. 3. For the development of excellent optical probes for Hg2+, a series of simple conjugated polymers containing phosphorescent Ir(Ⅲ) complexes in their backbones, which were capable of ratiometric optical sensing for Hg+with high sensitivity and selectivity, have been designed and synthesized. They can work as excellent polymer chemodosimeters for Hg2+utilizing the Hg2+-induced decomposition of Ir(Ⅲ) complex, exhibiting a pronounced optical signal change with the switchable phosphorescence and fluorescence even when the concentration of Hg2+was as low as0.5ppb in THF solution. With the addition of Hg2+, the phosphorescent emission intensity of Ir(Ⅲ) complexes at618nm quenched completely. While the emission from polymer backbones increased and the emission wavelength was red-shifted simultaneously, realizing the ratiometric detection. Excellent selectivity for Hg2+over other potentially interfering cations was also realized. In addition, an obvious emission color change of polymer solution from red to yellow-green was observed, realizing "naked-eye" detection. Importantly, the solid films of these polymer chemodosimeters also exhibited high sensitivity and rapid response to Hg2+, demonstrating the possibility for the fabrication of sensing devices with fast and convenient detection for Hg2+.4. A hybrid complex composed of an anionic conjugated polyelectrolyte (PFB-SO3Na) and a cationic phosphorescent Ir(Ⅲ) oligomer was formed through electrostatic interaction by simply physical mixing in aqueous media. Due to their opposite charge properties and effective spectral overlap, fluorescence resonance energy transfer occurs from blue-emissive PFB-SO3Na to red-emissive phosphorescent Ir(Ⅲ) complex, which allows ratiometric and colorimetric Hg2+sensing in aqueous solution with good selectivity, sensitivity, as well as visible detection. Moreover, time-resolved photoluminescent technique was applied for Hg2+detection, which can effectively eliminate the background interference and improve the sensing sensitivity and signal-to-noise ratio in complicated media.5. The application of a time-resolved photoluminescence technique and fluorescence lifetime imaging microscopy for biosensing and bioimaging based on phosphorescent conjugated polyelectrolytes (PCPEs) containing Ir(Ⅲ) complexes and polyfluorene units has been investigated. The specially designed PCPEs form50nm nanoparticles with blue fluorescence in aqueous solutions. Electrostatic interaction between the nanoparticles and heparin improves the energy transfer between the polyfluorene units to Ir(Ⅲ) complex, which lights up the red signal for naked-eye sensing. Good selectivity has been demonstrated for heparin sensing in aqueous solution and serum with quantification ranges of0～70μM and0～5μM, respectively. The signal-to-noise ratio can be further improved through time-resolved emission spectra especially when the detection is conducted in complicated environment, e.g. in the presence of fluorescence dyes. In addition to heparin sensing, the PCPEs have also been used for specific labeling of live KB cell membrane with high contrast using both confocal fluorescent cellular imaging and fluorescence lifetime imaging microscopies. This study provides a new perspective for designing promising CPEs for biosensing and bioimaging applications.