Annealing temperature effects on the azodye photoisomerization processes of layer-by-layer self-assembled poly(p-phenylenevinylene)/Congo red thin films

In the present paper the layer-by-layer self-assembly (LbL) technique was used to obtain poly(p-phenylenevinylene) (PPV) films exchanging the counter-ion Cl of the poly(xylylidene tetrahydrothiophenium) (PTHT) precursor polymer by Congo Red (CR) azodye. The objective of the present paper is to study the azodye photoisomerization trans -> cis -> trans process as a function of the PPV thermal annealing procedure. The LbL PTHT/CR films were thermally converted into LbL PPV/CR films at low (110 degrees C) and conventional (230 degrees C) temperatures, and characterized through both absorption and emission techniques. We found that the unexpected emission band above 650 nm, attributed to the azodye, for LbL PPV/CR film thermally converted at lower temperature (110 degrees C) is an evidence of the considerable decrease of CR degradation in the polymeric matrix. Emission anisotropy and selective photoluminescence were carried out to characterize qualitatively the exciton energy transfer. (c) 2012 Elsevier B.V. All rights reserved.