Synthesis and optical properties of a novel polyfluorene derivative

We report the synthesis and optical properties of a novel polyfluorene derivative: poly(3,5-dimethylphenyl ester of 4-(9-methyl-9H-fluorene-9-yl)-butane-l-sulfonic acid) (PFS). Optical spectroscopies such as absorption, photoluminescence, cw and transient photoinduced absorption (PA) techniques were used to study the optical properties. The absorption spectrum shows a weaker band at 3.5 eV and also contains strong bands peaked at 3.95, 4.1 and 4.3 eV. The PL spectrum shows a structureless band centered at 2.8 eV. The PA spectrum at 80 K shows a broad high energy (HE) band peaked at 2.1 eV and three low energy (LE) bands located at 0.5, 0.71 and 1.05 eV. The recombination dynamics of the photoexcitations at 2.1 eV was studied by measuring the intensity and frequency dependence of the PA signal and by fitting the results using a bimolecular recombination (BR) process. We have also studied the temperature dependence of the transient decay of the HE PA band from 80 to 290 K. The BR coefficient was approximately constant from 80 to 220 K and showed an Arrhenius temperature dependence with an activation energy of 0.24 eV for T > 240 K. (C) 2003 Elsevier Science B.V. All rights reserved.