Optical properties of molecular aggregates of oxazine dyes in dispersions of clay minerals

The molecular aggregation of oxazine 1 (Ox1) and oxazine 4 (Ox4) in reduced charge montmorillonite (RCM) colloids was investigated by absorption and fluorescence spectroscopies. The aggregation was significantly influenced by the structure of dye cations. Presence of four hydrophobic ethyl groups attached to the ammonium substituents in Ox1 cation prevented formation of closely packed sandwich-type assemblies (H-aggregates). Significant effect of the layer charge was observed for Ox4/RCMs dispersions. Large amounts of the Ox4 H-aggregates were formed in the systems with RCMs of the highest layer charge and reflected in quenched fluorescence. The presence of J-aggregates was proven by absorption spectra for the systems with Ox4 and low-charge RCMs. The flocculation of the lowest charge RCM colloids led to an extensive reduction of the luminescence. The trends and effects of the dye molecular structure and RCM properties are compared with the results previously published for other types of dyes.