Fluorescent dimers of rhodamine 6G in concentrated ethylene glycol solution

Aggregation of rhodamine 6G in concentrated ethylene glycol solutions is studied as a function of temperature. The measurements of absorption and fluorescence spectra evidence that the system of interest consists of two fluorescent species: monomers and dimers. Strong overlaps between all absorption and fluorescence hands in this system enable forward and reverse energy transport between monomers and dimers. The quantitative analysis of the effect of nonradiative energy transport (NET) on the fluorescence spectra as well as on the fluorescence quantum yields of monomers and dimers explains the temperature and concentration regularities observed. In particular, it is shown that in the concentrated solution the calculated monomer quantum yield is underrated compared to that measured, if the reverse NET is neglected. The lack of information on the value of the dimer quantum yield does not allow for full analysis of the forward and reverse NET in the system. However, it is shown that if that quantum yield is determined as the best fit parameter, an excellent agreement between the experimental and calculated values is obtained.