Characteristics of the reduced radicals of a series of 7-aminocoumarin dyes (C) have been investigated in different solvents using pulse radiolysis (PR) technique. Since these coumarin dyes are almost insoluble in water, a mixed solvent (MS) system containing 5.0 mol dm(-3) of 2-propanol (2PNL) and 1.0 mol dm(-3) of acetone (ACT) in water has been used in the present work to substitute the aqueous solvent. In MS, for a wide pH range of similar to1-9, the reduced coumarin radicals are formed in the neutral form, CH.. These radicals show two absorption bands, one in the 300-400 nm region and the other in the 500-600 nm region. As the coumarin dyes undergo hydrolysis in strongly alkaline solutions, PR studies in MS could not be extended beyond pH similar to9. In 2PNL, the reduced coumarin radicals are also formed in the CH. form, even in the presence of similar to1 mol dm(-3) of a strong proton acceptor like triethylamine (TEA). Since the pK(b) value of TEA is 3.19, it is indicated that the acid dissociation constant of the CH. radicals (pK(a)(R)) must be > 11. The PR results in MS and 2PNL clearly indicate that the anionic form of the reduced coumarin radicals (C.-) formed by initial one-electron reduction of the dyes undergo very fast protonation to give the CH. form in the solution. To avoid protonation of C.-, PR experiments were carried out in acetonitrile (ACN) solutions in the presence of similar to1 mol dM(-3) of aniline (AN). With this high concentration, AN efficiently scavenges the cation radicals from the solvent ion pairs (ACN(+...)e(-)) formed following the electron pulse, and thus the equivalent amount of electrons become available to reduce C to C.-. It is seen that the C.-radicals of all the coumarin dyes studied have unusually weak absorption bands in the 500-800 nm region. Since the coumarin dyes are good electron acceptors, present results on CH. and C.- radicals will be useful in elucidating the ET mechanism using coumarin dyes as the electron acceptors.