LB film structure of poly(2-methoxy,5-(8-methoxy-3,6-dioxa-1-undecoxy)-p-phenylene vinylene) studied by spectroscopy

A PPV derivative, poly(2-methoxy,5-(8-methoxy-3,6-dioxa-1-undecoxy)-p-phenylene vinylene), has been synthesized by the Gilch route to study the influence of a long alkyl side chain and a di(ethylene oxide) methyl ether group on the multilayer structure obtained by Langmuir-Blodgett (LB) technique. UV-visible, PL, and FTIR spectra are applied to study the conformation and orientation of the MMDU-PPV molecules in multilayer organization. MMDU-PPV is apt to form a transferable monolayer film, in which the plane of its pi system is perpendicular to the air-water interface. The adjacent conjugated main chains of MMDU-PPV in LB films are aligned in parallel fashion and packed with the plane of its pi system approximately perpendicular to the layer plane and not organized to compact pi-stacking structure for introducing di(ethylene oxide) methyl ether (DEOM) side chains to conjugated main chains. The long alkyl side chains are characterized by all trans-zigzag conformation and average tilt angle of 36+/-1.5 degrees. The layer-by-layer multilayer of MMDU-PPV obtained by Langmuir-Blodgett technique exhibits some in-plane anisotropy and more pure photoluminescence than that of the dilute MMDU-PPV solution.