Synthesis, photophysical, and electroluminescent properties of arylenevinylenes-co-pyrrolenevinylenes derived from divinylaryl bridged bispyrroles

Abstract

Synthesis, characterization, and photophysical properties of four different pi-conjugated oligomers containing alternate arylenevinylene and pyrrolenevinylene repeat units are reported. The optoelectronic properties are traced from the molecules to oligomers and to thin films and single layer electroluminescent (EL) devices. These oligomers exhibited strong absorption and emission corresponding to pi-pi* transitions which vary with electronic nature of the aryl moieties. The band gaps of these oligomers are in the range 1.84-2.04 eV and they emit in the orange to red region. The photoluminescence (PL) spectra of the oligomers P1-P4 in solution and film state are significantly different from each other. The time-resolved fluorescence decay in dichloromethane solution showed a fast decay profile for the anthracene-bridged oligomer and a relatively slow decay for benzene-bridged oligomer. Polymer light emitting diodes (PLEDs) with single active layer of oligomers with the configuration ITO/PEDOT:PSS/oligomer/Ca/Al exhibited low turn on voltages and yellow to deep red emission. Though the anthracene-bridged oligomer did not show any detectable PL in the film state, a weak electroluminescence (EL) emission around 730 nm was observed