Synthesis and characterization of novel fluorene–based green copolymers and their potential application in organic light-emitting diodes

Abstract

Fluorene-benzothiadiazole (PFBT), commercially known as F8BT, and fluorene-thiophene (PFT) copolymers were synthesized by the Suzuki-Miyaura coupling polycondensation technique in the presence of a phase transfer catalyst (Aliquat 336). These novel copolymers showed higher molar masses, lower dispersivity, and thermal stability above 400 °C when synthesized under the modified (M) action of Aliquat 336 (F8BT-M). Polymer Light-emitting diodes (PLEDs) were assembled with the novel synthesized copolymers as the emitter layer. For F8BT-M, a maximum luminance of 327 cd/m2 was achieved, while a diode containing just the commercial F8BT resulted in only 210 cd/m2. As for the PFT copolymers, it was observed that for the Aliquat 336 sample synthesized in a 60h extended (E) (PFT-ME), the luminance of the PLED was much higher than that where the reaction time was 48 h (PFT-M), with a luminance of 168 cd/m2 and 54 cd/m2, respectively. Without Aliquat 336, the PFT copolymer did not show an electroluminescent signal. The improved electroluminescence in the copolymers with Aliquat 336 was attributed to the improved synthesis conditions, i.e., reaction time and catalytic system employed. The results suggest that copolymers with luminescent and morphological properties, more suitable for light-emitting devices, might be obtained with simple modifications during synthetic polycondensation reactions.

Keywords

• Synthesis of copolymers
• F8BT
• PFT
• Green emitting copolymers
• PLEDs