Intermolecular Association and Supramolecular Organization in Dilute Solution. 2. Light Scattering and Optical Activity of Poly(p-biphenylylmethyl l-glutamate)

Abstract

Static and dynamic light scattering measurements are reported on dilute solutions of poly(p-biphenylylmethyl l-glutamate), PBPMG, in the helicogenic solvent THF, over a temperature range encompassing an observed reversible transition in the chiral optical properties of these solutions. The results confirm the expected helical conformation for this polypeptide, as well as complete dissolution of the polymer at temperatures above the transition temperature. Association is observed at lower temperatures, with the chains in an ordered parallel array within the aggregates. The association occurs with increasingly poor solvent conditions as the temperature is decreased, with the degree of association in the aggregate increasing concurrently with the change in the optical rotation and circular dichroism (CD) spectrum. It is concluded that the intermolecular association of the chains in the parallel array alters the chiral electronic environment of the biphenyl group, without a conformation change in that chromophore, resulting in the observed transition in the optical rotation and the CD spectrum. Unlike the behavior reported for certain other aggregated systems, the optical transition observed with solutions of PBPMG does not involve the initial formation of a disordered aggregate, which orders itself on reduced solvent quality or temperature, but rather a spontaneous association, such as expected on crossing a phase boundary, with a concurrent optical transition.

The Effect of Thermal Treatment on the Morphology and Charge Carrier Dynamics in a Polythiophene-Fullerene Bulk Heterojunction

“…These thermochromic changes have been observed previously for polythiophene solutions and films and have been ascribed to an improved packing of predominantly planar polymer chains. [7,11,21] In contrast to the changes observed in the absorption spectra of blend films, spin-coating a pure P3HT layer from chloroform directly leads to the optical features associated with the improved packing of the polymer chains. Annealing of such a pure P3HT layer did not significantly change the absorption features (data not shown).…”

“…the polymer chain, is of crucial importance for the conduction of holes. These parameters are largely dependent on the deposition method of the PT layer [6,11] as well as on the PT regioregularity [7] and the annealing process. [3,4,12] Therefore, the hole mobility on PT chains within spin-coated films of PT/fullerene blends is difficult to predict, while the effect of additional treatments on the charge carrier dynamics, such as annealing or a chloroform-vapor treatment, [13] is even more unclear.…”

The formation of crystalline P3HT fibrils upon annealing of a PCBM:P3HT bulk heterojunction

“…These parameters are largely dependent on the deposition method of the PT layer [5,11] as well as on the PT regioregularity [6] and the annealing process [2,3,12]. Therefore, the hole mobility on PT chains within spin-coated films of PT/ fullerene blends is difficult to predict, while the effect of additional treatments on the charge carrier dynamics, such as annealing or a chloroform vapor treatment [13] is even more unclear.…”

Light Scattering, Classical: Size and Size Distribution Characterization

“…In general, two forms may be encountered in the extreme: association involving two or more components at equilibrium at any give concentration; and metastable association, function of temperature is given in reference. (138) In the cited case, the scattering at any given temperature exhibited 'normal' behavior, and could not have been analyzed to reveal association if taken alone. In a different and somewhat unusual, but not unique, example, it has been reported that Kc/R Vv (ϑ,c) is linear in q 2 , albeit giving a molecular weight that is much larger than the true value of M w for the solute.…”