Regioregular Head-to-Tail Poly(4-alkylquinoline)s: Synthesis, Characterization, Self-Organization, Photophysics, and Electroluminescence of New n-Type Conjugated Polymers

Five poly(4-alkylquinoline-2,6-diyl)s (P4AQs), having 100% head-to-tail regioregularity, were synthesized, characterized, and explored as emissive and electron transport materials in polymer light-emitting diodes. The organic solvent (chloroform, tetrahydrofuran, methylene chloride, etc.) soluble poly(4-alkylquinoline)s had reversible electrochemical reduction with an electron affinity (2.6 eV) that was independent of alkyl chain length. X-ray diffraction studies showed that solution-cast films of regioregular P4AQs have self-organized lamellar structures with an interchain π-stacking distance of 3.9−4.1 A and an interlayer d-spacing that varied linearly from 13.4 A for butyl to 22.3 A for tridecyl side chains. The new poly(4-alkylquinoline)s emit blue light at 423−426 nm in dilute chloroform solution and yellow light at 542−557 nm in the solid state. Yellow electroluminescence with a luminance of up to 86 cd/m2 and an external quantum efficiency of up to 0.6% was observed for the P4AQs as emissive materi...