Conjugation Enhancement of Intramolecular Exciton Migration\nin Poly(<i>p</i>-phenylene ethynylene)s

Abstract

Efficient energy migration in conjugated polymers is critical to their performance in photovoltaic,\ndisplay, and sensor devices. The ability to precisely control the polymer conformation is a key issue for the\nexperimental investigations and deeper understanding of the nature of this process. We make use of specially\ndesigned iptycene-containing poly(<i>p</i>-phenylene ethynylene)s that display chain-extended conformations\nwhen dissolved in nematic liquid crystalline solvents. In these solutions, the polymers show a substantial\nenhancement in the intrachain exciton migration rate, which is attributed to their increased conjugation\nlength and better alignment. The organizational enhancement of the energy transfer efficiency, as determined\nby site-selective emission from lower energy traps at the polymer termini, is accompanied by a significant\nincrease of the fluorescence quantum yield. The liquid crystalline phase is a necessary requirement for\nthese phenomena to occur, and when the temperature was increased above the nematic−isotropic transition,\nwe observed a dramatic reduction of the energy transfer efficiency and fluorescence quantum yield. The\nability to improve the exciton migration efficiency through precise control of the polymer structure with\nliquid crystalline solutions demonstrates the importance of a polymer's conformation for energy transfer,\nand provides a way to improve the energy transporting performance of conjugated polymers.