Improved energy transfer through the formation of the β phase for polyfluorenes containing phosphorescent iridium(III) complexes

The formation of a β phase and its influence on the energy transfer efficiency were investigated for a series of polyfluorenes containing different contents of phosphorescent iridium(III) complex under various conditions. The effects of iridium(III) complex content, solution concentration, solvent/nonsolvent ratio, as well as temperature on the β-phase formation in the copolymers were studied through UV-vis absorption, photoluminescence, and excitation spectra. First, it was easier to form a β phase for the copolymers with a low content of iridium(III) complex than those with a high content of iridium(III) complex. Second, an aggregation-induced β-phase formation for the copolymers was significantly displayed in the highly concentrated THF solution or THF/H₂O mixtures. In addition, temperature was another factor for β-phase formation. And the β phase could be easily formed at low temperatures for copolymer films. On the basis of the above experimental results, the improved energy transfer from polyfluorene to iridium(III) complex was also observed through the β-phase formation.