For single molecule spectroscopy (SMS), molecules under study are usually immobilized in a polymer matrix e. g. poly(methyl methacrylate). We show a very significant improvement of the conjugated polymer MEH-PPV photo-stability and decrease of the luminescence impurities concentration when the matrix is purified. We identify benzoyl peroxide (a common radical initiator) as a possible oxidizing agent which residuals in the polymer matrix destroy MEH-PPV. These results show that purification and selection of a matrix obtained by radical-free synthetic technique are of great importance for SMS as well as other technologies using polymer matrices as hosts for light-emitting materials. (C) 2014 Elsevier B. V. All rights reserved.