Synthesis and characterization of new polyquinolines containing 9,9′-spirobifluorene units

Polyquinolines, which contain 9,9'-spirobifluorene units in the main chain, were synthesized via the acid-catalyzed Friedlander condensation reactions of bis(o-aminoketone) with bisacetyl monomers. In the spiro-fused bifluorene moiety, the two mutually perpendicular fluorene rings were connected via a common tetracoordinated carbon atom. This structural feature leads to polymers that possess high thermal stability and good solubility in common organic solvents. The polyquinolines have similar lowest energy transitions that can be attributed to a pi-pi* transition with lambda(max) values in the 363-385 nm range and exhibit blue emission. A model compound was synthesized to demonstrate that the tetrahedral bonding carbon at the center of the spiro moiety could serve as a conjugation interrupt to effectively control the conjugation length of the polymers. The electrochemical behaviors of these polymers were investigated by cyclic voltammetry. The reversible reduction and low-lying LUMO energy level suggest that some of the polyquinolines might have potential for use as materials for electron injection and transport in polymer LEDs.