Influence of Dissolution Status in Eutectic Mixtures on Crystallization Routes of Semiconductive Polyalkylthiophenes

Upon the dissolution of comb-like polyalkylthiophenes in the melt of a crystalline hexamethylbenzene compound, eutectic molten mixtures were prepared, which were found to involve disparate mixing statuses of polyalkylthiophenes. When more than 2 wt % of polyalkylthiophenes is mixed in molten solutions, metastable face-on lamellae of polyalkylthiophenes widely spread upon efficient eutectic solidification, instead of stable edge-on crystalline lamellae. Beyond a critical concentration of polyalkylthiophene, the association of board-like thiophene backbones into stripe-like micelles in molten solutions was proposed as a preceding background. When the association tendency in molten mixture declines with the decrease of concentration or molecular weight, only edge-on lamellae are precipitated. Furthermore, as indicated by the structural analysis via electron diffraction patterns, the stacking of metastable face-on nanostructures is able to transform to stable edge-on crystals via collaborative rotation and lateral association of thiophene backbones. Nevertheless, with the attachment of a longer side chain, this structural evolution is hindered by enhanced kinetic barriers, and thus regular stacking of face-on nanostructures is able to persist and progress as an alternative organization route. For face-on nanostructures serving as a preordering state prior to the growth of edge-on crystals, annealing temperatures capable of initiating an overall structural transition within thin film have been explored and manifested as an indication of the metastability.