Synthesis and photophysics of new highly luminescent poly(alkylthiophene) derivatives with pyridine in the backbone

Starting from 2,6-bis-(3-octylthiophene-2yl)-pyridine, two new poly(alkylthiophene) derivatives, POTPyOT and POTPy, containing pyridine in the backbone were prepared from nickel(0)-mediated Stille coupling or by palladium-catalyzed Yamamoto coupling. These polymers exhibited good solubility in common organic solvents, thermal stability up to 400 °C, and facile film formation. They were amorphous and give strong luminescence both in CHCl3 solution and solid state film. The polymers emitted blue light in solution with photoluminescence (PL) emission maximum at 420-484 nm and green light with PL emission maximum at 500-514 nm in thin films. These polymers showed a reversible redox reaction at potential from 0 to 1.3 V (vs. SCE). Nevertheless, the reduced form of the polymer was very unstable; it decomposed in the presence of oxygen or water. The emission and UV-vis absorption of the polymer were influenced by the solvent polarity, protonation, and acid-base treatment. These may be the results of the stabilization of the polar excited state by solvation and the change of the conformation in polymer backbone. Electroluminescence (EL) was achieved from a single-layer PLED with the configuration of ITO/POTPyOT/Al. The turn-on voltage of the device is 10 V and the λmax (550 nm) of the EL is voltage independent.