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

Abstract

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 Å and an interlayer d -spacing that varied linearly from 13.4 Å for butyl to 22.3 Å 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/m 2 and an external quantum efficiency of up to 0.6% was observed for the P4AQs as emissive materials. A large improvement in performance of poly(2-methoxy-5-(2‘-ethyl-hexyloxy)- p -phenylenevinylene)-based light-emitting diodes (a luminance of up to 700 cd/m 2 and an external quantum efficiency of up to 3.0%) was observed when the P4AQs were used as the electron transport materials. The new regioregular poly(4-alkylquinoline)s are promising n-type conjugated polymer semiconductors for electronic and optoelectronic devices.