Synthetic Metals 159 (2009) 1409–1413 Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet Conformational analysis of the conducting copolymer poly(3,4-ethylenedioxythiophene-co-pyrrole) Stephen A. Fossey a,∗ , Ferdinando F. Bruno a , Jayant Kumar b , Lynne A. Samuelson a a U.S. Army Natick Soldier Research, Development & Engineering Center, 15 Kansas Street, Natick, MA 01760, United States b Center for Advanced Materials, University of Massachusetts Lowell, Lowell, MA 01854, United States article info Article history: Received 30 June 2008 Received in revised form 9 March 2009 Accepted 15 March 2009 Available online 23 April 2009 Keywords: PEDOT Polypyrrole Conducting copolymer DFT Flexible electronics Polymer actuators abstract Electronic structure methods have been used to investigate conducting copolymers of 3,4- ethylenedioxythiophene (EDOT) and pyrrole (Py). The calculations show the planar anti conformation and the syn conformers have extended conjugation. In the anti conformation the EDOT–Py dimer is calculated to have a lower reorganization energy (0.390 eV) than either homodimer (0.423 eV EDOT; 0.455 eV Py) and consequently is expected to have higher charge carrier mobility. The HOMO–LUMO gap of the copoly- mers is intermediate between the two homopolymers and for regular sequences varies monotonically as a function of the monomer content. Published by Elsevier B.V. 1. Introduction Optoelectronic devices utilizing -conjugated polymers are now being commercialized [1]. Electronic structure methods have been used to investigate the band gap [2] and charge carrier mobili- ties of conducting oligomers and polymers. The use of computation allows the rapid investigation of various chemical structures as well as detailed investigation of conformational effects. Among other advantages, conducting polymers are well suited to low cost fab- rication techniques such as layer-by-layer deposition [3] and can be coated onto flexible substrates such as textiles to enable new flexible applications [4–6]. Among the more successful conducting polymers are poly(3,4- ethylenedioxythiophene), PEDOT, and polypyrrole, Ppy. We have recently described the synthesis of a novel conducting copolymer of 3,4-ethylenedioxythiophene (EDOT) and pyrrole (Py) using a syn- thetic enzyme (“synzyme”) catalyst in a template polymerization [7]. Here we present the results of a conformational analysis of copolymers of 3,4-ethylenedioxythiophene and pyrrole. ∗ Corresponding author. Tel.: +1 508 233 5360; fax: +1 508 233 5521. E-mail address: stephen.fossey@us.army.mil (S.A. Fossey). 2. Methods Calculations were carried out using the Gaussian 03 [8] pro- gram on an IBM P3, IBM P4, or SGI Origin 3800 system at the Army Research Laboratory – Major Shared Resource Center or an SGI Altix at the Aeronautical Systems Center Major shared Resource Center. Visualization was with the GaussView 03W program on a personal computer. Several different electronic structure calculations were used depending on the method required and the size of the calculation. Since we expect the interaction of atoms with lone pair elec- trons and amide hydrogens maybe important, diffuse functions, indicated by “+”, and polarization functions for heavy atoms and hydrogens, indicated by “d” and “p” respectively, were included in the basis set [9] when computationally reasonable. Fig. 1 shows the general structure for the copolymers. The computational details are presented when discussing the results of the calculations. 3. Results and discussion 3.1. Torsional potentials of dimers The torsional potentials of the dimers were calculated using density functional theory (DFT) and Møller–Plesset (MP) perturba- tion theory. Fig. 2 shows the torsional potential around the bond 0379-6779/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.synthmet.2009.03.018