Combined Techniques for the Characterization of Polyfluorene Copolymers and Correlation with their Optical Properties.

Abstract

New red- and green-emitting copolymers, hereafter core-copolymers, bearing a 4,7-bis(thiophen-2-yl)benzothiadiazole and a benzothiadiazole residue respectively as bridging core between two identical polymeric arms were synthesized by Suzuki coupling reaction of the dibromine derivative of such chromophores and essentially borolane-ended alternating copolymers [namely P(TPAF)] of triphenylammine disubstituted fluorene and dialkylsubstituted fluorene. All polymer samples were characterized by 1H NMR and in particular by MALDI–TOF MS. MALDI mass spectra allow the identification of many end groups of the initial blue-emitting macromers and therefore of the side reactions occurring during Suzuki polycondensation. The average molar masses were determined by two different SEC apparatus, one calibrated with conventional polystyrene narrow standards and the other with an absolute calibration curve built up by SEC/MALDI–TOF MS analysis of selected SEC fractions of polydisperse red and green core-copolymers. MALDI mass spectra of these fractions give reliable information on their composition, which combined with their integrated area calculated from the corresponding normalized SEC curves, enable the estimation, for the first time, of the percentage of macromolecules containing the dyes composing the neat core-copolymers. Optical characterization, performed by UV–visible absorption and photoluminescence measurements, of the same SEC fractions gives results in agreement with the different compositions determined by their MALDI mass spectra.