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

Abstract

A method for the synthesis of optically pure C 60 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 C 60. 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 1O 2 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 ( ε T) of C 60 derivatives vary from 9456±2090 M −1 cm −1, for compound 10 in toluene, and 15,272±4462 M −1 cm −1, for compound 6 in acetonitrile. Triplet state lifetimes ( τ T) for methano[60]fullerene–sugar derivatives, under our experimental conditions, are similar in toluene or benzonitrile solutions (47.5±1.1 μs≤ τ T≤51.4±2.0 μs) but are lower in acetonitrile solutions (31.8±0.6 μs≤ τ T≤43.0±1.1 μs). Toluene and benzonitrile solutions of C 60 derivatives have Φ Δ close to unity.