In summary, we present a simple and inexpensive method to simultaneously measure the size and characterize the electronic structure of molecules and particles in solution, by providing their UV/Vis absorption spectrum together with their diffusion coefficient. The method can also be used to investigate mixed solutions, giving two-dimensional spectra in which the UV/Vis spectra of species with different sizes appear at different positions on the diffusion-coefficient axis, similar to the two-dimensional spectra obtained from NMR-DOSY, but with optical wavelength rather than chemical shift on the horizontal axis. As the size separation relies on the diffusion coefficient, we believe that a size resolution similar to that of NMR-DOSY should be achievable, and we hope to