Interfacial and solution-phase self-assembly of π-conjugated polymers

Unlike inorganic semiconductors, the molecular packing and nanoscale morphology of conjugated polymers directly impact their optical and electrical properties and, ultimately, their device performance. Control of their structure at multiple length scales is necessary to truly exploit the potential of these functional materials in organic electronics. This thesis will then demonstrate control of the molecular and nanoscale structure of conjugated polymers. Structural control by controlled oxidation of conjugated polymers led to the oxidation-induced photoluminescence of poly(3-alkoxythiophenes). The phenomenon is unusual as oxidation typically quenches the photoluminescence of typical conjugated polymers. The oxidation process introduced defects to the π-conjugated backbone that disrupted the planarity of the pristine polymer, at the same time, reducing the conjugation length. The increased band gap reduced the probability of nonradiative decay, hence the PL increase with oxidation. We developed a new approach called Pack-and-Align Lithography (PAL) to fabricate nanoarrays of conjugated polymers based on the interfacial self-assembly of conjugated rod-coil copolymers. Self-assembly of poly(3-hexylthiophene)-block-poly(ethylene glycol) at the air-water interface led to large-area, free-standing films of ordered nanowires, which can be transferred to arbitrary solid substrates. The charge carrier mobility of the PAL film was found to be orders of magnitude higher than that of spin-cast films, demonstrating that PAL is an effective thin film fabrication tool for functional polymers. The interfacial self-assembly was found to be hierarchical where single chains pack into nanowires that align into nanowire arrays. The rigidity of the conjugated rod block was important in the formation of the nanowire while the rigidity of the nanowire was necessary for the ordering into the two-dimensional nanoarray. Introducing curvature at the air-water interface led to the large-area alignment of nanowires up to ∼60 microns in length. Finally, we demonstrate the solution-phase self-assembly of conjugated block copolymers into highly crystalline sheets. The high degree of molecular and nanoscale organization demonstrates that the solution-phase self- assembly of conjugated block copolymers is a powerful approach in controlling the morphology of conjugated polymers