Luminescence of Reichardt's dye in polyelectrolyte-modified saponite colloids

Reichardt’s dye (RD) exhibits solvatochromic properties across the entire visible spectrum. This work reports, for the first time, luminescence of RD in colloidal systems of layered silicate saponite (Sap) modified with poly(diallyldimethylammonium) polycations (PDDA), and provides an interpretation of this unique phenomenon. The application of tailored theoretical chemistry methods such as DFT and other approaches supplies a theoretical interpretation of the phenomenon to supplement the results of the experiments. RD luminescence was achieved by preventing the movement of molecules and suppressing non-radiative relaxation processes. This effect only occurred if the negatively-charged phenolate group in the RD molecule interacted with the positively-charged groups of the PDDA cations, while at the same time the positively-charged pyridinium group was also adsorbed onto the negatively-charged Sap siloxane surface. Only at small coverage of the Sap surface by PDDA cations is there sufficient fixation of the RD molecules for them to exhibit luminescent properties. The results suggest that the application of this dye may be extended to luminescent probes, which could be used to characterize the distribution of charge centers on the surfaces of various materials, biopolymers, biological tissues, etc.