Electroluminescence and Photophysical Properties of Polyquinolines

Abstract

The electroluminescence and photophysical properties of a series of 11 polyquinolines were investigated and used to explore the effects of molecular and supramolecular structures on the light-emitting properties of polymers. Thin films of the polyquinolines have photoluminescence quantum yields between 2 and 30% and unusually long excited-state lifetimes of 2.4−5.2 ns. Electroluminescence colors spanning blue, green, yellow, orange, and red were obtained through regulation of the molecular and supramolecular structures of the excimer- and aggregate-forming polyquinolines. ITO/hole transport layer/polyquinoline/Al light-emitting diodes fabricated and evaluated in air had electroluminescence quantum efficiencies between 0.02 and 1% and luminance levels of up to 280 cd/m2 at a current density of 100 mA/cm2. The electroluminescence efficiency approximately scaled linearly with the photoluminescence quantum yield. Favorable reaction at the aluminum/polyquinoline interface is proposed to account for the efficient electron injection and device performance in spite of the large (1.5−1.9 eV) energetic barrier to electron injection. These results provide new insights into the design of efficient light-emitting polymer materials and devices for optoelectronic applications.