Hidden blue emission in [60]fullerene stemming from weak π-π aggregation

Identifier:  imarina:9567965

Handle: https://hdl.handle.net/20.500.11797/imarina9567965

Authors:  Ribeiro-Gonzalez, Antonio; Masip-Sanchez, Albert; Poblet, Josep M; Rodriguez-Fortea, Antonio; Nonell, Santi; Illescas, Beatriz Maria; Martin, Nazario; Garcia-Fresnadillo, David

Abstract:
The unusual UV/blue-green fluorescence of [60]fullerene at micromolar concentrations in ethyl acetate is investigated using steady-state and time-resolved fluorescence techniques. This broad emission exhibits longer lifetimes (approximate to 10 ns) than the well-known weak red fluorescence typically associated with C-60 (approximate to 1 ns). The relative intensity of the blue and red emissions is influenced by several factors, including C-60 concentration, sonication, solvent polarity, the presence of additives (e.g., inert gases or oxygen), and excitation wavelength. Evidence from time-resolved fluorescence anisotropy and computational studies suggests that the unconventional emission originates from the formation of similar to 2 nm-sized fluorophores due to weak intermolecular pi-pi van der Waals interactions, which become ineffective at concentrations below 2 mu M, this concentration being the estimated value for the solubility of C-60 in ethyl acetate. Interestingly, since the intense and long-lived unconventional emission of aggregated C-60 is sensitive to molecular oxygen or solvent polarity, a novel functionality for the singlet excited state of this emblematic molecule in its aggregated state as a luminophore, a fluorescent probe or a photosensitizer has been unveiled.