Time-resolved fluorescence and steady-state absorption measurements of FMN aqueous solutions were carried out over very broad dye concentration range. Efficient formation of FMN dimers with simultaneous absence of higher order aggregates even at highest concentrations was found from absorption spectra measurements. It was found that fluorescence intensity decays are strongly accelerated in the presence of dimers due to excitation energy trapping and become nonexponential. Mean localization time of excitation energy and mean number of its jumps between FMN molecules were calculated as a function of concentration. (C) 2007 Elsevier B.V. All rights reserved.