Resonance energy transfer between cyanine dyes in hybrid films of layered silicate prepared by layer-by-layer method

Layer-by-layer (LbL) assemblies exhibiting efficient resonance energy transfer (RET) were prepared by alternating deposition on a quartz slide substrate. Each of the prepared films contained alternating layers of poly electrolyte: poly(diallyldimethylammonium chloride) (PDDA) and saponite nanolayers (SapNL), which were prepared from layered synthetic saponite (Sap), which adsorbs cyanine dye cations, 3,3'-diethyl-oxocyanine iodide (OxCy) or 3,3'-diethyl-2,2'-thiacyanine iodide (ThCy). These dyes had been also selected due to their high photoactivity in Sap systems, and because they form a suitable pair for RET. Films with both the dyes were prepared to obtain alternating layers containing these dyes. Simpler films containing one type of dye were prepared for comparison. Absorption spectroscopy was used to monitor any changes occurring during the deposition of the films. The dyes did not alter their spectral properties, and the formation of dye aggregates was negligible. The deposition of each new PDDA layer led to the release of the dye cations from the outer surface of the film. This phenomenon was interpreted as competitive adsorption between the dye and PDDA cations. Fluorescence spectroscopy was applied to characterize the luminescence of the films and the efficiency of energy transfer. Typical values of RET efficiency were in the range of 0.8-0.9, and slightly increased with the number of deposited layers. This could be interpreted as a consequence of increasing film thickness as the number of layers that were actively involved in this photophysical process gradually increased. LbL assemblies are very interesting materials that can be prepared in a simple way but exhibit very interesting properties.