Three-Dimensional Packing Structure and Electronic Properties of Biaxially Oriented Poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2- b ]thiophene) Films

Eunkyung Cho, Chad Risko, Dongwook Kim, Roman Gysel, Nichole Cates Miller, Dag W. Breiby, Michael D. McGehee, Michael F. Toney, R. Joseph Kline, Jean-Luc Bredas

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Abstract

We use a systematic approach that combines experimental X-ray diffraction (XRD) and computational modeling based on molecular mechanics and two-dimensional XRD simulations to develop a detailed model of the molecular-scale packing structure of poly(2,5-bis (3-tetradecylthiophene-2-yl) thieno[3,2-b]thiophene) (PBTTT-C 14) films. Both uniaxially and biaxially aligned films are used in this comparison and lead to an improved understanding of the molecular-scale orientation and crystal structure. We then examine how individual polymer components (i.e., conjugated backbone and alkyl side chains) contribute to the complete diffraction pattern, and how modest changes to a particular component orientation (e.g., backbone or side-chain tilt) influence the diffraction pattern. The effects on the polymer crystal structure of varying the alkyl side-chain length from C 12 to C 14 and C 16 are also studied. The accurate determination of the three-dimensional polymer structure allows us to examine the PBTTT electronic band structure and intermolecular electronic couplings (transfer integrals) as a function of alkyl side-chain length. This combination of theoretical and experimental techniques proves to be an important tool to help establish the relationship between the structural and electronic properties of polymer thin films. © 2012 American Chemical Society.
Original languageEnglish (US)
Pages (from-to)6177-6190
Number of pages14
JournalJournal of the American Chemical Society
Volume134
Issue number14
DOIs
StatePublished - Mar 28 2012
Externally publishedYes

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