Study of molecular-colloidal solutions of C₇₀ fullerene: structural features, optical and nonlinear-optical properties

Nonlinear optical rotation of elliptically polarized laser pulses (λ = 532 nm, τ_FWHM ∼ 12 ns) in benzene, toluene, and binary (toluene+acetonitrile) solutions of fullerene C₇₀ - D_5h(6) has been experimentally investigated. Features of (C₇₀)_n clusters' structure have been studied using high-resolution transmission electron microscopy in toluene+acetonitrile mixtures and the fractal mechanism of formation of the large (∼ 280.0 nm) stable clusters in solution, which may contain up to ∼ 16807 molecules of C₇₀ is proposed. It has been demonstrated that the C₇₀ cluster sizes depend on initial concentration of C₇₀, as well as volume fraction of acetonitrile in solvent mixture. Correlations between the processes of nonlinear rotation of polarization ellipse, change of electronic absorption spectra and C₇₀ clusters formation in solutions have been demonstrated. Physical mechanisms of laser induced optical activity in C₇₀ solutions have been discussed. The values of the nonlinear Kerr coefficient (n₂) and nonlinear susceptibility component (χ_xyyx⁽³⁾(ω) ) of C₇₀ solutions in toluene, benzene with various polarization ellipticity θ = 0.2†0.8, and toluene+acetonitrile at different concentrations of C₇₀ for various volume fractions of acetonitrile have been determined. (authors)