The fates of sulfur-centered radical zwitterions were determined following triplet-sensitized electron transfer from thioether-containing aromatic carboxylic acids. 4-Carboxybenzophenone was used as the triplet sensitizer and four carboxylic acids, (phenylthio)acetic acid (1), S-benzylthioglycolic acid (2), 4-(methylthio)phenylacetic acid (3), and 4-(methylthio)benzoic acid (4), were the electron-donating quenchers. Following laser-induced electron transfer, the time development of the ensuing free-radical reactions was monitored by optical spectroscopy. The reference spectra of the photoinduced transients were selectively generated by a complementary pulse radiolytic method in order to determine extinction coefficients and spectral shapes. By use of these reference spectra, the observed transient spectra from laser flash photolysis were resolved into their components. From this information, concentration profiles and initial quantum yields of the radicals were determined along with triplet quenching rate constants. The chemistry of the free radicals was discussed with the aid of computations from density functional theory (DFT). DFT also was used to supplement the spectral assignments as well as for computation of the thermochemistry of the free radicals. The sulfur-centered radical zwitterions from 1 and 2 decayed rapidly. Those from 1 decayed into (CH2)-C-.-S-C6H5 and CO2. A majority of those from 2 also decayed via decarboxylation but, in addition, through fragmentation. The CH3-S-.+-C6H4-CH2-CO2- radicals from 3 could be observed directly for microseconds and decayed with roughly equal probability through decarboxylation and deprotonation. The CH3-S*+-C6H4-CO2 radicals from 4 were also observed directly but failed to decarboxylate because of the high energy of activation needed to form the substituted phenyl radical.