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

Abstract

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, Φ_T and Φ_Δ of the triplet and of singlet oxygen, respectively. This study shows a general tendency of the λ_max of the T–T absorption spectra, and of the Φ_Δ values to decrease with increasing number of addends. For regioisomers, the spectroscopic and photophysical parameters are modulated with the pattern of addition. The Φ_Δ quantum yields for the acids in aqueous solution are systematically lower than those of the ethyl esters in toluene. The lower Φ_Δ 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.