Solutions of polyaniline (PANI) doped with camphor sulfonic acid (CSA) in m-cresol are studied with dynamic light scattering. Dynamic light scattering measurements performed on dilute solutions (c ⩽ c∗) show that, while some aggregation is present, PANI-CSA exists as single chains in solution at low concentrations (about 10−4–10−6) in m-cresol. The conformation of the polymer chains was studied as a function of polymer and added salt concentration. We find that the polymers extend as the polymer concentration is lowered and that the increase in the hydrodynamic radius can be expressed by a power law of the electrostatic screening length. This behavior is typical of polyelectrolytes in dilute solution, providing a basis for understanding the conformation changes of this metallic polymer in solution.

The poly(3-alkylthiophenes) are a class of electrically conducting polymers which are of particular scientific and commercial interest due to their solubility and meltabillty. A series of poly(3-octylthiophene) (P3OT) fractions having molecular weights in the range M(w) = 30,000 to 400,000 were generated by preparative gel permeation chromatography (GPC). Although the polymer remained weakly aggregated when dissolved in pure THF, the addition of an organic salt (1 wt.% tetrabutylammonium p-toluenesulfonate) resulted in complete molecular dissolution. We were thus able to completely and consistently describe the polymer's single-chain properties using three dilute solution characterization methods: viscometry, GPC, and integrated light scattering. The molecular weight dependence of the intrinsic viscosity and the radius-of-gyration were established, and were characteristic of solutions near the theta condition, indicating poor solvent quality. Calculation of the persistence length from our data revealed that the polymer backbone is only 2 to 3 times more rigid than common flexible polymers, despite its conjugated ring structure.

We report the results of light scattering, absorption, excitation, and emission spectroscopy of three polyphenylene vinylene (PPV) derivatives; poly[2-methoxy, 5-(2′-ethyl-hexyloxy-p-phenylene- vinylene] (MEH-PPV), poly[2-butoxy, 5-(2′-ethyl-hexyloxy-p-phenylene-vinylene] (BEH-PPV), and poly[2-dicholestanoxy-p-phenylene-vinylene] (BCHA-PPV) in solution with p-xylene. We find that increasing the size of the solubilizing side chains increases the intrinsic persistence length of the polyphenylene vinylene backbone and that this change in stiffness has dramatic effects on the photoluminescence of polyphenylene vinylene. We have determined the luminescence quantum efficiencies of the polyphenylene vinylene derivatives relative to a known standard, Rhodamine 6G, and find that the photoluminescence can be greatly enhanced by increasing the intrinsic stiffness of the polymer backbone. The stiffest polymer, poly[2-dicholestanoxy-p-phenylene-vinylene] (BCHA-PPV), has a quantum efficiency of 0.66±0.05. The quantum efficiency decreases to 0.22±0.05 for poly[2-butoxy, 5-(2′-ethyl-hexyloxy-p-phenylene-vinylene] (BEH-PPV) and 0.20±0.05 for poly[2-methoxy, 5-(2′-ethyl-hexyloxy-p-phenylene-vinylene] (MEH-PPV), the most coiled derivative. Excitation profiles of the three derivatives also show an increase in nonradiative decay at high energies when the polymer assumes a more coiled comformation. Thus, the quantum yields are dependent on pump energy.

Light scattering and optical spectroscopy experiments were performed on [2-methoxy, 5-(2'-ethyl-hexyloxy-p-phenylene-vinylene] (MEH-PPV), poly[2-butoxy, 5-(2'-ethyl-hexyloxy-p-phenylene-vinylene] (BEH-PPV), and poly[2-dicholestanoxy-p-phenylene-vinylene] (BCHA-PPV) in solution with p-xylene to determine the effects of side chain size on the structure and optical properties of PPV. We find that increasing the size of the solubilizing side chains increases the intrinsic persistence length of the PPV backbone and this change in rigidity has dramatic effects on the photoluminescence of PPV. Quantum yield determination relative to Rhodamine 6G shows the luminescence efficiency of the rigid BCHA-PPV is 0.66 +/- 0.05 and that the yield decreases to 0.20 +/- 0.05 for MEH-PPV, the most coiled derivative. Excitation profiles show an increase in non-radiative decay at high energies when the backbone is more flexible.

Recent theories have related the molecular-weight dependence of the conductivity of a conjugated polymer to the relative importance of interchain and intrachain charge transport processes. This prompted an experimental search for this effect using a series of fractionated poly(3-octylthiophenes). No significant molecular-weight dependence was found over the range 30 000⩽Mw⩽400 000, indicating that interchain transport does not limit the macroscopic conductivity of these samples. However, even small differences in the degree of crystallinity among the polymer samples were determined to have a profound effect on the conductivity.