Synthesis and Characterization of Fluorene-Based Conjugated Polymers Containing Thiophene Derivatives in Main Chain

Abstract

Three novel alternating copolymers containing 9,9-dioctylfluorene and thiophene derivatives, poly[(9,9-dioctylfluorene-2,7-diyl)-alt-(4,4′-bis(3″-hexyl-2″thienyl)-biphenyl-5”,5″-diyl)] (P1), poly[(9,9-dioctylfluorene-2,7-diyl)-alt-(5,5′-bis(3″-hexyl-2”thienyl)-2,2′-bithiophenyl-5”,5″-diyl)] (P2), and poly[(9,9-dioctylfluorene-2,7-diyl)-alt-(5,5′-bis(3″-hexyl-2″thienyl)-2,2′-biselenophenyl-5”,5″-diyl)] (P3) were synthesized by a palladium-catalyzed Suzuki polymerization. The synthesis, thermal stability, as well as the optical and electrochemical properties of these polymers are systematically investigated. The polymers were thermally stable up to 400°C, and readily soluble in common organic solvent. The absorption and emission maxima of the copolymers varied according to the type of incorporated aromatic group (thiophene, selenophene, or phenylene).

Keywords:

• Electroluminescence
• polyfluorene
• thiophene

Acknowledgments

This work was supported by BK21 of the Ministry of Education and Human Resources Development, by a grant (M2009010025) from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy (MKE) and by a grant from the cooperative R&D Program funded by the Korea Research Council Industrial Science and Technology, Republic of Korea.

Notes

^a M _n, M _w, and PDI of the polymers were determined by gel permeation chromatography using polystyrene standards.

^b Glass transition temperature determined by differential scanning calorimetry (DSC).

^a The film fluorescence quantum yields measured on quartz plates relative to P1 assuming 1.00 for comparison.

^b Calculated from E_1/2 (energy level of ferrocene of 4.8 eV under vacuum).

^c Calculated from the HOMO level and optical band gap.

^d The optical band gap was determined from the UV-vis. absorption onset in the solid state.

^a Maximum of the EL spectrum at a voltage of 10 V.

^b Determined from EL spectrum (Figure 5).

^c Voltage needed for brightness of 1 cd/m².