Enhanced luminescence of 3,3′-diethyl-2,2′-thiacyanine cations adsorbed on saponite particles

• Spectra of 3,3′-diethyl-2,2′-thiacyanine/saponite colloids were analyzed.
• Dye monomers, H- and J-aggregates were identified as main spectral species.
• Luminescence was strongly enhanced upon the adsorption of dye molecules.
• Exciton coupling significantly influenced spectral properties of hybrid colloids.

Hybrid colloidal dispersions based on cationic dye 3,3′-diethyl-2,2′-thiacyanine iodide (NK88) and saponite (Sap) were prepared and their spectral properties were compared with dye solution. The effect of various NK88/Sap ratios was investigated by absorption and fluorescence spectroscopies. A detailed analysis of absorption spectra based on chemometric methods (principal component analysis and multivariate curve resolution - alternating least squares) revealed a very complex nature of these hybrid systems. Most relevant spectral components were identified as monomeric form, H- and J-aggregates. The rearrangement of initially formed dye species with time led to the increase of the amount of the J-aggregates at the expense of the H-aggregates and the monomers. The larger amounts of the H-aggregates were observed in the specimens with relatively highest dye loadings. NK88 luminescence was significantly enhanced upon the adsorption on Sap particles, but could not be assigned to a single dye form. The participation of different dye forms can explained in terms of strong couplings, such as collective exciton delocalization in dye supramolecular systems formed on Sap surface, and weak coupling between various forms via excitation energy migration and transfer. These interactions led to the emission spectra, whose profiles did not depend on the excitation wavelengths. The colloidal systems based on NK88 and Sap are perspective precursors for hybrid materials with interesting optical and photophysical properties.

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