Nanowire shish-kebab structures and molecular orientation control of all-conjugated diblock copolymers

Herein we propose a facile strategy to prepare nanowires and nanowire "shish-kebab" (NWSK) structures by controlling the crystallization behavior of all-conjugated rod-rod diblock copolymers poly[(p-phenylene)-block-(3-hexylthiophene)]s (PPP-b-P3HT (BmTn)) with varying main chain lengths. Depending on the block length and ratio (i.e., PPP/P3HT, abbreviated as B/T), nanowires with low B/T ratios (copolymers with long P3HT blocks; B8T32 and B14T34) and NWSKs with high B/T ratios (copolymers with long PPP blocks; B29T9 and B39T18) were formed for PPP-b-P3HT all-conjugated diblock copolymers. The formation of nanowires is governed by a strong interchain π-π stacking similar to the P3HT homopolymer, with an edge-on orientation of the P3HT moiety, whereas NWSKs are formed as a result of the particular face-on molecular orientation of PPP moiety. As the length of the P3HT moiety was increased (the block ratio of PPP/P3HT reduced), the NWSKs were transformed into nanowires gradually because of the decreasing density of "kebabs". For diblock copolymers with high PPP/P3HT ratios, the transition of the molecular orientation from face-on to edge-on was obtained by thermal annealing.