Manifestation of fluorophore segmental motion in carbon dots in steady-state fluorescence experiments

The steady state fluorescence anisotropy of carbon dot solutions of different viscosities η and its variation with temperature T has been investigated. The dependence of the anisotropy on T/η is shown to be described by the Perrin equation, which implies that Brownian rotational motion of carbon dots in solution is a basic mechanism of fluorescence depolarization. Peculiarities of the Perrin plot testify that the luminous entity ("fluorophore") responsible for carbon dot fluorescence displays noticeable segmental motions, which are independent of the overall rotational diffusion of the dots. The Perrin model fit to the experimental data yields the effective volumes of the fluorophore VF = 0.35 ± 0.15 nm3 and of the carbon dot as a whole VC = 10.5 ± 1.8 nm3. The rotational motions of the fluorophores are shown to be limited and spectrally dependent. A feasible nature of the fluorophores in question is discussed.