Excited-state dynamics of organic radical ions in liquids and in low-temperature matrices

The excited-state dynamics of the radical cations of perylene (PE.-), tetra cene (TE.-), and thianthrene (TH.+), as well as the radical anions of anthr aquinone (AQ(.-)) and tetracenequinone (TQ(.-)) formed by gamma irradiation in low-temperature matrices (PE.+, TH.+, AQ(.-), and TQ(.-)) or by oxidati on in sulfuric acid (PE.+, TE.+, and TH.+) have been investigated using ult rafast pump-probe spectroscopy. The longest ground-state recovery time meas ured was 100 ps. The excited-state lifetime of PE.+ is substantially longer in low-temperature matrices than in H2SO4, where the effects of perdeutera tion and of temperature on the ground-state recovery dynamics indicate that internal conversion is not the major decay channel of PE.+*:. The data sug gest that both PE.+* and TE.+* decay mainly through an intermolecular quenc hing process, most probably a reversible charge transfer reaction. Contrari ly to AQ(.-*), TQ(.-*) exhibits an emission in the visible which, according to theoretical calculations, occurs from an upper excited state.