Transfer of photoenergy in π-Conjugated polymers. Two types of photoluminescence that involve energy transfer along a polymer chain

Two types of energy transfer in π-conjugated polymers have been investigated using time-resolved photoluminescence (PL) techniques: type i, perpendicular-type energy transfer from the 2,3-di(p-tolyl)-quinoxaline unit to the π-conjugated main chain of poly[2,3-di(p-tolyl)quinoxaline-5,8-diyl], and type ii, parallel-type energy transfer from the oligo(pyridine-2,5-diyl) (O-Py) unit to the oligo(selenophene-2,5-diyl) (O-Se) unit in a block-type copolymer of O-Py and O-Se. Both types of energy transfer were very fast with a time constant shorter than approximately 0.1 ns; in particular, the type ii energy transfer took place with a time constant of approximately 5 ps. Both π-conjugated polymers were considered to contain segments with various effective π-conjugation lengths, and the energy transfer to the segment with a larger effective π-conjugation length and a smaller π-π* transition energy required a longer transition time. A polarizing film was obtained by utilizing the perpendicular-type energy transfer.