Molecular Basis of Mesophase Ordering in a Thiophene-Based Copolymer

• Published in: Macromolecules Vol. 41; no. 15; pp. 5709 - 5715
• Main Authors: DeLongchamp, Dean M, Kline, R. Joseph, Jung, Youngsuk, Lin, Eric K, Fischer, Daniel A, Gundlach, David J, Cotts, Sarah K, Moad, Andrew J, Richter, Lee J, Toney, Michael F, Heeney, Martin, McCulloch, Iain
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 12.08.2008
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Thermal and thermodynamic properties; Electrical properties; Thermotropic state; Charge carrier mobility; Temperature effect; Mesomorphic state structure; Experimental study; Phase transitions; Conducting polymers; Side chain; Liquid crystal polymers; Aromatic copolymer; Thiophene derivative copolymer; Conformation
• DOI: 10.1021/ma800440f
• ISSN: 0024-9297

The carrier mobility of poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) semiconductors can be substantially enhanced after heating through a thermotropic mesophase transition, which causes a significant improvement in thin film structural order. By directly measuring film structure throughout a heating and cooling cycle, we identify the molecular origin of this mesophase transition as the melting of interdigitated linear alkane side chains, in this case quaterdecyl. The morphology and phase behavior throughout the thermal cycle are controlled by the changing conformation of the side chains. Surprisingly, the melting of the side chains allows increases in the backbone order, π−π stacking, and carrier mobility. Upon cooling, the side chains recrystallize to preserve the excellent mesophase order and enhanced electrical performance.