Spectral properties of TMPyP intercalated in thin films of layered silicates

The objective of this study was to investigate the spectral characteristics of tetracationic porphyrin dye (TMPyP), intercalated into films of three smectites. The smectites represented the specimens of high (Fluorohectorite; FHT), medium (Kunipia F montmorillonite; KF), and low layer charge (Laponite; LAP). Intercalation of TMPyP molecules was proven by XRD measurements. The molecular orientations of the dye cations were studied by means of linearly polarized ultraviolet-visible (UV-vis) and infrared (IR) spectroscopies. Both the UV-vis and the IR spectroscopy proved the anisotropic character of the films. The spectral analysis of the polarized UV-vis spectra and consequent calculations of tilting angles of the transition moments in the region of Soret band transitions were in the range of 25-35 degrees . The determined angles indicated that the molecular orientation of the dye cations was almost parallel to the surface of the silicates. Slightly higher values, determined for a FHT film, indicated either a slightly more tilted orientation of the dye cations or the change of molecular conformation after the intercalation of the dye. Quenching of TMPyP fluorescence was observed, resulting from the formation of bimolecular layer arrangements with sandwich-type assemblies of the dye molecules.