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.