Excited-state Dynamics of Fullerene Nanoparticles Dispersed in Pure Water

Abstract

Femtosecond transient absorption dynamics of C 60 nanoparticles in pure water revealed a strong quenching of the singlet excited state, independent of the excitation light intensity on a 10-ps time scale, and an extremely low yield of the triplet state of C 60 nanoparticles upon photoexcitation.Fullerene (C 60 ) has received a considerable amount of attention due to its unique physical and chemical properties, and it is now recognized to have great potential in various research fields such as electronics, medicine, and biology. Although a pure molecular solution of C 60 in pure water cannot be prepared, C 60 forms stable colloidal assemblies in water under certain conditions. 15 The relatively high solubility of C 60 nanoparticles, herein termed as nC 60 , in water has raised concerns regarding their potential impact on human and ecological systems, because there are reports of significant cytotoxicity effects. 611 Furthermore, the photophysical properties of nC 60 , particularly the generation of reactive oxygen species, have been of interest for potential explorations for the photodynamic therapy. Some studies have been on the photophysical properties of nC 60 dispersed in water have been carried out. 4,1214 Colloidal suspensions of nC 60 in water with a particle size less than 100 nm are formed by several methods, including reprecipitation, 1 solvent replacement, 2 and ultrasonication. 3 In these preparation methods, C 60 is first dissolved in organic solvents such as toluene and THF, which are highly toxic to living cells and tissues, and nC 60 is then solubilized with the aid of a surfactant or a polymer in some cases. For biological studies and medical applications, an aqueous colloid of nC 60 without any chemical additives is of interest and can be prepared by the laser ablation method.5 By exposing a suspension of C 60 powder in pure water to an intense pulse laser, nC 60 with a mean size of 50 nm are formed and the prepared colloidal solution is very stable over one month without any surfactants. 4 This letter reports on the excited-state dynamics of aqueous colloids of nC 60 prepared by laser ablation. We present, for the first time, the transient absorption spectra and kinetic lifetimes of the photoexcited state of nC 60 dispersed in pure water with femtosecond temporal resolution. Moreover, we demonstrate a very rapid decay of the singlet excited state that is independent of the excitation light intensity and results in a very low yield of the triplet excited state concerning aqueous nC 60 suspensions.Aqueous colloids of nC 60 with a mean diameter of ca. 50 nm were prepared by laser ablation; 4 in this method, C 60 microcrystal powder (>99.9% pure, Sigma-Aldrich) suspended in pure water (1 © 10 ¹2 wt %) was irradiated with the second harmonic (532 nm) of nanosecond YAG laser pluses (FWHM: 7 ns; repetition rate: 10 Hz) for 1 h. Samples were measured using a femtosecond transient absorption measurement system. 15 The wavelength of the excitation pulse was set to 350 nm, and its pulse duration was c...

Singlet oxygen generation from Li+@C60nano-aggregates dispersed by laser irradiation in aqueous solution

“…Absorption spectra in dichloromethane solutions are shown as grey lines. 28 The decay rate constant of the slower part was determined to be 6.6 Â 10 8 s À1 , which is virtually the same as that of the formation of the triplet excited state of Li + @C 60 (7.0 Â 10 8 s À1 ) (see Fig. The transient absorption band at 960 nm taken at 10 ps after the femtosecond laser pulse excitation at 393 nm is assigned to the singlet excited state of Li + @C 60 [ 1 (Li + @C 60 )*] in nano-aggregates (Fig.…”

“…S2 in the ESI †). 28 The p stacking in (Li + @C 60 ) n is much weaker than those of (C 60 ) n and (C 60 ) n because (Li + @C 60 ) n contains equivalent number of PF 6 À counter anions in the nano-aggregates to avoid p-p interaction between the fullerene cages. 28 The decay rate constant of the slower part was determined to be 6.6 Â 10 8 s À1 , which is virtually the same as that of the formation of the triplet excited state of Li + @C 60 (7.0 Â 10 8 s À1 ) (see Fig.…”

Introduction of Fullerenes into Hydrogels via Formation of Fullerene Nanoparticles

“…Furthermore, there is an additional broad absorption peak at 400–550 nm. These observations are characteristic of crystalline C 60 nanoparticles . A TEM image of the C 60 nanoparticle dispersion is shown in Figure c.…”

“…Furthermore, there is an additional broad absorption peak at 400–550 nm. These features are characteristic of crystalline C 60 and arise from the close electronic interactions between adjacent C 60 molecules . The crystallinity strongly affects the function of fullerene nanoparticles.…”

Preparation and photo-induced activities of water-soluble amyloid β-C60 complexes

“…Chemical modications such as the addition of hydroxyl groups have been performed to solubilize fullerenes in water. [9][10][11][12][13] Other methods such as the inclusion of organic macromolecules, [14][15][16] laser ablation, 7,17 and solvent substitution methods 18 have also been proposed. A variety of water-soluble fullerene derivatives have now been chemically synthesized; however, a sufficient amount of fullerene derivative seems not to be readily prepared in many cases.…”