Potential and film thickness dependence of the photoluminescence of Aryl Amine Polymers

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

San Pedro, San Pablo (Brasil)

Congreso; 54th ISE (International Society of Electrochemistry) Annual Meeting; 2003

International Society of Electrochemistry

Aryl amine conducting polymers, such as polyaniline (PANI) have been found to show photoluminiscence in their reduced state, which is quenched when the polymer is oxidized [1, 2]. However, quantitative studies are lacking. The fluorescence of PANI films has been studied here as a function of potential and film thickness. Absorption spectra were also recorded in order to obtain the fluorescence quantum yields. The fluorescence measurements were conducted on PANI films of different thicknesses on platinum electrodes, obtained by electrochemical polymerization using cyclic voltammetry, and the emission spectra were recorded at an incidence angle of ~ 20º. Absorption spectra were obtained for PANI films electropolymerized in the same way onto semitransparent Au thin films. The fluorescence emission intensity, in the reduced (leucoemeraldine) state as a function of polymer film thickness (measured through the voltammetric charge) shows a complex behavior. For low thicknesses none or minimum emission is observed; this is attributted to the metallic quenching of the fluorescence. Beyond a critical thickness, the emission increases sharply, then reaches a maximum and finally decays slightly towards a limiting value. The decay is interpreted as due to the atenuation of the waves reflected on the metal surface: both the excitation wave absorbed after being reflected, and the emited one reaching the detector after reflection are exponentially attenuated as the film thickness increases. Thus, the limiting emited intensity corresponds to a thick film with no reflection at the back. The fluorescence emission of poly(2-methoxyaniline), a polymer which depending on the synthesis conditions shows either a conducting or a redox behavior, was also studied. The conducting form has a fluorescence response similar to that of PANI, whereas the redox form shows low emission. [1] Y. Son, H. H. Patterson, C. M. Carlin, Chem. Phys. Lett. 192 (1989) 461.[2] M. K. Ram, G. Mascetti, S. Paddeu, E. Maccioni, C: Nicolini, Synth. Metals 89 (1997) 63.