| The fluorescence properties and aggregation behavior of poly(2,6-[4-phenylquinoline]), PPQ, poly(2,6-[p-phenylene]-4-phenylquinoline), PPPQ, and poly(2,5-pyridine), PPY, were investigated. The polymers were incorporated into different host materials and emissions at different wavelengths were obtained. The different emitting color was attributed to each unique aggregation state: In the sol-gel system, at high polymer concentrations, red light was emitted, indicating the formation of aggregates of multiple chains in each silica channel. At low concentrations, the glass emitted blue light reflecting a monomer-like state, suggesting chain isolation. At intermediate concentrations, the emitted light was green, yellow and orange, depending on a different degree of polymer chain interactions.; In porous silica, light was emitted at different wavelengths by varying the pore size from 81 to 972 Å. Poly(ethylene glycol)-b-poly( p-phenylene ethynylene)-b-poly(ethylene glycol), Triblock, was used for comparison with PPQ. PPQ and Triblock emitted blue light in the monomer-like states at small pore sizes, and the emissions red-shifted with increasing pore size to 300 Å. As the pore size continued to increase, there was sufficient space for PPQ to orient in different directions, reducing the polymer chain interaction and causing the emission to blue shift. The bulky Triblock, however, obliged the chains to align in a relatively planar geometry and to retain the strong polymer chain interaction and emission at longer wavelengths.; When PPQ or PPY was blended with poly(vinyl alcohol), the emission peak shifted only from 450 to 550 nm. When blended with poly(acrylic acid) or poly(methacrylic acid), the emission peak progressed from 460 to 565 and 605 nm with an increase in poly(acrylic acid) or poly(methacrylic acid) concentration. This was due to the protonation of the quinoline residues and steric hindrance that resulted in a better mixing at the molecular level.; Dynamic light scattering and atomic force microscopy were used to investigate the aggregation behavior of PPQ in formic acid solutions. It was found that the aggregation state depended on the PPQ concentration and that the aggregates grew and gradually approached equilibrium. The chains formed a tortuous fibrillar network and aggregates in the shapes of calderas and spheres. An increase in the aggregate size with increasing PPQ concentration was evident. |
