Morphology and environment-dependent fluorescence in blends containing a phenylenevinylene-conjugated polymer

Near-field scanning optical microscopy and single-molecule spectroscopy have been employed to study a large number of blends containing a highly fluorescent and amorphous conjugated polymer, 'superyellow' (a phenylenevinylene copolymer). We find that blend films with a nonfluorescent and semi-crystalline polymer, poly(ethylene oxide) (PEO), with a superyellow content between 9 and 50 mass% exhibit phase separation with no evidence for admixing of the two components, while films with a lower superyellow content of <= 1 mass% content comprise a solid-state solution of superyellow within a crystalline PEO matrix. Interestingly, films with approximately the same amount of superyellow as PEO (similar to those used in, e.g., light-emitting electrochemical cells) exhibit a bi-continuous network morphology. We also report that the superyellow fluorescence spectrum shows a remarkable sensitivity to the physical and chemical environment of superyellow. (C) 2007 Elsevier B.V. All rights reserved.