title: Three-dimensional packing structure and electronic properties of biaxially oriented poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) films.
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.
authors.affiliation: School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
authors.forename: Eunkyung
authors.initials: E
authors.lastname: Cho
authors.forename: Chad
authors.initials: C
authors.lastname: Risko
authors.forename: Dongwook
authors.initials: D
authors.lastname: Kim
authors.forename: Roman
authors.initials: R
authors.lastname: Gysel
authors.forename: Nichole
authors.initials: N
authors.lastname: Cates
authors.forename: Dag W
authors.initials: DW
authors.lastname: Breiby
authors.forename: Michael D
authors.initials: MD
authors.lastname: McGehee
authors.forename: Michael F
authors.initials: MF
authors.lastname: Toney
authors.forename: R Joseph
authors.initials: RJ
authors.lastname: Kline
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Bredas