Triplet state properties of malonic acid C60 derivatives C60[C(COOR)2]n; R = H, Et; n= 1–6

Laser flash photolysis and pulse radiolysis have been used to determine properties of the lowest triplet state of a series of water-soluble malonic acid derivatives of C60 , C60[C(COOH)2]n with n = 2–6, in water at pH 7.4. Similar studies were carried out on the corresponding ethyl esters, C60[C(COOEt)2]n with n = 1–6, in the non-polar solvents, benzene or toluene. The properties include the T–T absorption spectra, the triplet molar absorption coefficients and the quantum yields of formation, ΦT and ΦΔ of the triplet and of singlet oxygen, respectively. This study shows a general tendency of the λmax of the T–T absorption spectra, and of the ΦΔ values to decrease with increasing number of addends. For regioisomers, the spectroscopic and photophysical parameters are modulated with the pattern of addition. The ΦΔ quantum yields for the acids in aqueous solution are systematically lower than those of the ethyl esters in toluene. The lower ΦΔ values observed for the acids in aqueous solution, and to a lesser extent for the esters in benzonitrile, can be interpreted as due to the presence of solute clusters in polar solvents.