Synthesis and solvent dependence of the photophysical properties of [60]fullerene–sugar conjugates

A method for the synthesis of optically pure C60 derivatives containing one or two d-galactose or d-glucose units is described. It involves the synthesis of sugar–malonate derivatives followed by a cyclopropanation reaction with C60. The solvent dependence of the photophysical properties of the methano[60]fullerene–sugar derivatives was studied using nanosecond laser flash photolysis coupled with kinetic UV–vis absorption spectroscopy and time-resolved singlet oxygen luminescence measurements. The triplet properties of these fullerenes, including transient absorption spectra, molar absorption coefficients and quantum yield for the photosensitised production of 1O2 were determined in toluene, benzonitrile and acetonitrile solutions. The transient absorption spectral profiles are solvent independent although small differences are observed in the transient absorption maximum: 720±5 nm for toluene, 710±5 nm for benzonitrile and 700±5 nm for acetonitrile. Triplet state molar absorption coefficients (εT) of C60 derivatives vary from 9456±2090 M−1 cm−1, for compound in toluene, and 15,272±4462 M−1 cm−1, for compound in acetonitrile. Triplet state lifetimes (τT) for methano[60]fullerene–sugar derivatives, under our experimental conditions, are similar in toluene or benzonitrile solutions (47.5±1.1 μs≤τT≤51.4±2.0 μs) but are lower in acetonitrile solutions (31.8±0.6 μs≤τT≤43.0±1.1 μs). Toluene and benzonitrile solutions of C60 derivatives have ΦΔ close to unity.