IR reflection–absorption spectroscopic study of Langmuir–Blodgett films of selected porphyrins and their dyads to fullerene on gold substrates

The paper deals with IR absorption and reflection–absorption examinations of Langmuir–Blodgett layers of zinc porphyrins covalently linked to fullerene C60. The spectra were recorded with unpolarized and polarized light (p-polarization and s-polarization) at various incident angles to receive data on interactions of the systems with the solid substrates and on orientation of the systems with respect to the solid substrate. A comparison of the calculated and experimental IR absorption data were discussed in terms of the normal modes assigned for the porphyrins. All alternations in the shape or localization of the absorption bands represented normal modes after porphyrin oligomer or porphyrin–fullerene dyad formation reflect the changes of the charge density distribution and configuration of the bonded molecular moieties. We have shown that the polarized reflection–absorption spectra of thin films are strongly dependent on the light polarization. However, the reflection–absorption spectra of LB films of the porphyrin, porphyrin oligomer and their dyads with fullerene recorded with unpolarized light approximate the absorption spectra of adequate compounds dispersed in KBr matrix. A similarity between the p-polarized and unpolarized spectra suggests that both porphyrins and dyads are nearly perpendicularly oriented to the surface of the gold substrate.