Long diketopyrrolopyrrole-based polymer nanowires prepared by decreasing the aggregate speed of the polymer in solution

Abstract

The preparation of diketopyrrolopyrrole-based polymer nanowires seems very difficult, probably due to the fact that the nanowires length direction is along the main chain not the π-π direction. For the nanowires whose length direction is along the main chain, the probability of the short nanowires to meet the ends of other molecules to grow longer is very small. Herein, we prepared long 3,6-bis-(thiophen-2-yl)-N,N’-bis(2-octyl-1-dodecyl)-1,4-dioxo-pyrrolo [3,4-c]pyrrole and thieno [3,2-b]thiophene (PDBT-TT) nanowires followed a homogeneous nucleation and growth process by slowing the aggregate speed of the PDBT-TT molecules. Slowing the aggregate speed of the molecules was carried out by slow evaporation of the main solvent (the mixed solvent, consisting of a good solvent chloroform (CF) as the main solvent and a marginal solvent 1,2-dichlorobenzene (ODCB) as the co-solvent). CF evaporating at a speed of 30 μL/h allows the solution to be always in the saturated state and the polymer to aggregate slowly. The resulting nanowires are about 75 nm in width and tens of micrometers in length. The density and length of nanowires could be controlled by adjusting the concentration of the pristine solution and the evaporation process, respectively. Higher concentration of the pristine solution results in higher density of nanowires, and the length of nanowires also changed.