As time progresses, the solute molecules appear in the absorption spectrum, at different rates depending on their size (in the figure: red first, blue later). The time dependence of the absorption amplitudes is given by a simple mathematical function (obtained by solving the diffusion equation), and a straightforward mathematical procedure transforms the time-dependence axis of the two-dimensional data set into a diffusion-constant (or equivalently, size-) axis (Fig. ). In the following, we will demonstrate how UV/Vis-DOSY can be used to simultaneously obtain molecular sizes and electronic absorption spectra in three types of mixed solutions.