Preparation and Luminescence Properties of Polymeric 2,5-Bis[2´-(8´´-alkoxyquinolin-2´´-yl)ethenyl]hydroquinone Derivatives

Abstract

A PPV-type polymer (1) incorporating 5,5´-diquinolinyl moieties is prepared by a Yamamoto homo-coupling reaction from the dibromide (2). Since all the hydroxyl groups were alkylated, this polymer showed high solubility in most organic solvents. It can be spin-coated readily to form a thin layer in the fabrication of light emitting diode (LED) devices. The adjacent quinoline rings are twisted to form a dihedral angle due to steric hindrance, so that π-conjugation is confined within each monomer unit. The emission spectra of (1) and (2) are nearly identical. The reduction potential of (1) was estimated to be –1.10 V (onset), with a band gap of 2.53 eV (490 nm). A single hetero-junction LED device fabricated by combining the films of poly(vinylkarbazol) (PVK) and (1) yielded promising results. The device ITO/PVK/(1)/Ca/Al exhibited a turn-on voltage at 6 V and reached a maximal brightness of 250 cd/m² at 15 V. An alternate potential usage of (1) as an electron-injecting material was also explored on a green-light device using coumarin-6 as an emitter.