We have used pulsed radiolysis to elucidate the neutral triplet and charged excited states in soluble conjugated polymers, including poly(2-methoxy-5-(2'-ethyl-hexoxy)-p- phenylenevinylene), (MEH-PPV), poly(2,5-pyridinediyl) (PPY) and poly(4-hexyl-2,5-pyridinediyl) (HPPY) in various solvents. Using a range of triplet sensitizers we have determined the S0 - T1 energy separation in these polymers to be 1.27 plus or minus 0.07 eV, 2.4 plus or minus 0.1 eV and 2.5 plus or minus 0.1 eV respectively. Our experimental results confirm that photoinduced absorption features observed in the range 1 to 2 eV in these polymers, are due to triplet-triplet absorption. Triplet state lifetimes and molar absorption coefficients in solution have also been determined. This work not only demonstrates the versatility of the pulse radiolysis technique but also gives, for the first time, important and unambiguous assignment and detail on the various excited state species in conjugated polymers.
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