Molecular Aggregation and Luminescence Properties of Bulk Poly(2,5-di-n-octyloxy-1,4-phenylenevinylene)

Abstract

Structural development in cast films of poly(2,5-di-n-octyloxy-1,4-phenylenevinylene) (DO-PPV) upon heat treatment was studied by means of polarized light microscopy, X-ray diffraction, ultraviolet−visible spectroscopy, and photoluminescence spectroscopy as well as scanning and transmission electron microscopy. Results indicated the dominance of a lamellar phase of biaxially refringent nematic-like texture upon short-term heat treatments at elevated temperatures (Ta) between 160 and 240 °C. A further increase in Ta results in dissipation of the mesomorphic order near the isotropization temperature Ti = ca. 300 °C. This lamellar phase, 1.8 nm in layer spacing at room temperature, typically consists of beads or grains approximately 10−20 nm in diameter that agglomerate into wormlike features in the absence of external stress. Mechanical shear right after high-temperature annealing results in disintegration of worms formed in the tranquil state; the constituent beads nevertheless reagglomerate into new worml...