Reversible aggregation, precipitation and re-dissolution of rhodamine 6G in aqueous sodium dodecyl sulfateElectronic supplementary information (ESI) available: (1) R6G dimerization in aqueous solution: (a) determination of the equilibrium constant, (b) reconstruction of the monomer and dimer spectra, (c) determination of the free monomer content of any solution. (2) Poisson distribution. (3) Ion-pair crystal analysis: (a) optical microscopy, (b) X-ray diffraction analysis. See http://www.rsc.org/suppdata/cp/b3/b310946a/