¹H NMR spectroscopic study of the solution structure of a conjugated polymer

The structure of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4- phenylenevinylene] (MEH-PPV) solutions with a number of common deuterated organic solvents was studied by means of ¹H NMR spectroscopy. The resonance bands of the polymer backbone protons appear at much lower frequencies in CDCl₃ compared to their positions in aromatic solvents. This has been attributed to the π-π self-stacking interaction of the polymer segments in the aliphatic solvent, which is replaced by a polymer-solvent π-π interaction in the aromatic solvents. In mixed solvent systems with an aliphatic solvent component and an aromatic one, the intensities of the polymer resonances pass through a maximum at intermediate solvent compositions. This has been attributed to the minimum aggregation tendency of the polymer at these solvent compositions. The results suggest that a mixed solvent system constituting an aliphatic component and an aromatic component might be a choice for casting films of hairy-rod type conjugated polymers if minimization of aggregate domains in the films is desired.