Efficient synthesis of benzobisazole terpolymers containing thiophene and fluorene

Abstract

We report the synthesis and lumuminescence properties of three novel polymers composed of 9,9-dioctylfluorene and a donor–acceptor-donor (D–A-D) triad of a benzobisazole moiety sandwiched between two octylthiophenes. The requiste monomers, 2,6-bis(5-bromo-3-octylthiophen-2-yl)-benzobisazoles were obtained efficiently via the Lewis acid catalyzed cyclization of 2-bromo-3-octyl-5-(triethoxymethyl)thiophene and the corresponding diamino diols or dithiols. The polymers were synthesized in excellent yield by the Suzuki coupling reaction between the D–A-D benzobisazole monomers and 9,9-dioctylfluorene bisboronic acid. Alkyl side chains provided the polymers with solubility in common organic solvents, enabling characterization using gel permeation chromatography, ¹H NMR, UV-Vis and fluorescence spectroscopy. The polymers have optical bandgaps of 2.43–2.63 eV and HOMO levels at −5.54 to −5.65 eV relative to vacuum as determined by UV visible and photoelectron spectroscopy respectively. Light-emitting diodes using blends of the copolymers in a poly(N-vinyl carbazole) matrix yielded blue-green emission with luminous efficiencies of 0.86 Cd/A at ∼505 nm. This efficient and high-yielding route is a promising approach for the synthesis of polymers containing benzobisazole moieties.