INTERMOLECULAR ASSOCIATION AND SUPRAMOLECULAR ORGANIZATION IN DILUTE-SOLUTION .1. REGIOREGULAR POLY(3-DODECYLTHIOPHENE)

Static and dynamic polarized and depolarized light scattering characte rization of dilute solutions of regioregular poly(3-dodecylthiophene) is described to study intermolecular association as a function of the thermal history of the solutions. It is shown that metastable aggregat ion obtains under all of the conditions studied, including temperature s as high as 65 degrees C. Under some conditions, the aggregated moiet y appears to have a disklike shape at room temperature, with appreciab le depolarized scattering, attributed to an extended chain structure, consistent with the formation of the lamellar suprastructure character istic of the bulk, with the polythiophene chains adopting an extended conformation and forming a nematic phase in a polythiophene lamella fa ced by lamellae rich in alkyl chains. Under other conditions, especial ly at low temperature, elongated supramolecular structures are formed, with the polythiophene chains in an extended conformation. The revers ible thermochromic effect is associated with enhanced order of the alk yl side chains with decreasing temperature, facilitating coplanar conf ormers in the polythiophene backbones, with the attendant enhancement in the pi-pi transitions of the thiophene ring electronic absorption spectra. This behavior is analogous to the events in the thermochromic event in the bulk. Such supramolecular structures could intervene in normal film casting solution processing, with effects on the electroni c or optical properties of the cast film. This interpretation of the l ight scattering data suggests strategies to enhance or suppress lamell a formation in solvent-cast films.