Photoresponse and anisotropy of rhodamine dye intercalated in ordered clay layered films

In order to elaborate organized two-dimensional arrangements of fluorescent dyes in host solid layered materials, rhodamine 6G (R6G) is encapsulated in supported thin films of laponite (Lap) clay. Clay films are elaborated by the spin-coating technique and their surface morphology is analyzed by scanning electron (SEM) and atomic force (AFM) microscopies. The internal order of the stacked clay layers is checked by X-ray diffraction technique (DRX). The thermostability of R6G in the Lap films is discussed on the basis of several thermogravimetric and calorimetric techniques (TG, DTA and DSC). The R6G adsorbed species in Lap films are characterized by absorption and fluorescence (steady-state and time-resolved) spectroscopies. Monomers, dimers and higher-order aggregates are identified for very low (<0.1%), moderate (1–25%) and high (>40% of the total cation exchange capacity, CEC, of the clay) dye content, respectively. Both non-fluorescence H-type and fluorescent J-type aggregates of R6G in Lap films are characterized.Absorption and fluorescence techniques with linearly polarized light are applied to evaluate the anisotropic photoresponse of R6G in Lap films, from which the preferential orientation of dye molecules with respect to the clay layers can be evaluated. The validity of the newly established fluorescence polarization is contrasted with the well-established absorption polarization method, and the emission spectroscopy with linearly polarized light can be applied to establish the preferential orientation of fluorophore molecular probes incorporated in any rigid and ordered 2D host materials, including monolayers and biological membranes.