Investigation of the excited-state dynamics of radical ions in the condensed phase using the picosecond transient grating technique

A study of the dynamics of ground-state recovery of the perylene radical cation (Pe(?(.+))), of perylene radical anion (Pe(.-)), and of anthraquinone radical anion (AQ(.-)) is reported. In boric acid glass, the excited-state lifetime of Pe(.+) is 35 +/- 3 ps, while in concentrated sulfuric acid, it is smaller than 15 ps, the time resolution of the experimental setup. The excited-state lifetime of Pe(.+), Pe(.-), and AQ(.-) generated by photoinduced intermolecular electron-transfer reaction in MeCN is shorter than 15 ps. In the case of Pe(.-), the uncomplete ground-state recovery is ascribed to the occurrence of electron photoejection. The free ion yield in the intermolecular electron-transfer reaction between 9,10-dicyanoanthracene (DCA) and two electron acceptors, was measured in a two-pulse experiment, where the second pulse excited the ensuing DCA(.-). This excitation has no influence on the magnitude of the free ion yield, indicating a short excited-state lifetime of DCA(.-*) relative to the time scale of back electron transfer and ionic dissociation. A red emission, ascribed to the fluorescence of protonated Pe, was detected in boric acid glass and sulfuric acid. No fluorescence that could be clearly ascribed to Pe(.+*) could be observed.