Fluorescence of polyaniline films on electrode surfaces. Thickness dependence and surface influence.

P. S ANTONEL; E M ANDRADE; F. V. MOLINA

JOURNAL OF ELECTROANALYTICAL CHEMISTRY

Elsevier

Lugar: Amsterdam; Año: 2009 vol. 632 p. 72 - 79

0022-0728

The dependence of the photoluminescence of polyaniline films, supported onto platinumor fluorine-doped SnO2 (FTO) electrodes, on the film thickness (as measured by thevoltammetric charge) has been studied for different polymer oxidation states. Thefluorescence emission spectra have been corrected for absorption and reflection from theunderlying metal surface. For platinum electrodes, the absolute quantum yield for filmsof different thicknesses, and at several electrode potentials, has been obtained using asreference anthracene in acrilic films. Also, the corrected emission for growing films atdifferent charges was recorded. The potential dependence of the emission intensity isnot affected by the film thickness. The corrected emission intensity on FTO surfacesincreases linearly with thickness due to the increase in the number of fluorophores. Inthe case of Pt, the intensity is null for low thicknesses, quenched by the metallic surface;as the thickness increases beyond a critical value, the emission increases sharply andthen reduces its slope increasing more slowly. The quantum yield on Pt surfaces isaccordingly zero for sufficiently thin films, and then increases in a nearly linear way.The observed behaviour on metal surfaces is found to be due to the interference betweenthe field of the emitting dipole and the surface reflected field, causing vanishingemission for dipoles sufficiently near to the surface, and a complex distance dependenceafterwards. The theoretical model is found to agree with the experiments if a distributionof parallel and perpendicular dipoles is introduced, with dipoles near the surface beingpredominantly parallel.