CommunicationsHighly Conductive, RegioregularAlkoxy-Functionalized Polythiophenes: A NewClass of Stable, Low Band Gap MaterialsElena E. Sheina, Sonya M. Khersonsky,Edward G. Jones, and Richard D. McCullough*Department of Chemistry, Carnegie Mellon UniVersity,Pittsburgh, PennsylVania 15213ReceiVed January 13, 2005ReVised Manuscript ReceiVed May 9, 2005Electrically conductive polymers are entering a new eraas devices and applications are beginning to enter themarketplace. Decades of revolutionary research has not onlycreated exciting new science but also led to new plasticelectronics.1Due to very high electrical conductivities,regioregular polythiophenes (rr-PTs) are being used in plasticphotovoltaics, as the hole transport layer in OLEDs, in fieldeffect transistors, and as conductive components in newcoatings and bulk plastics.2,3Alkoxy-substituted analoguesof PTs exhibit even more desirable properties, such asreduced band gaps, low oxidation potentials, and a highlystable conducting state.4-6However, these materials possessrather low conductivities (1 S/cm) and are not very stable.A major breakthrough in the development of the com-mercially viable conductive polymers was the synthesis ofpoly(3,4-ethylenedioxythiophene) (PEDOT), which exhibitedhigh stabilities in the oxidized state and conductivities up to600 S/cm.7-9Unfortunately, this material is generally onlyprocessible as a colloidal suspension in water and producesfairly low conductivities (10-50 S/cm), thereby limiting itsusefulness in many commercial applications. Nevertheless,since the discovery of PEDOT in 1989, dioxythiophenechemistry has developed exponentially and has rapidly* To whom correspondence should be addressed. E-mail:[email protected].(1) (a) Chiang, C. K.; Fincher, C. R., Jr.; Park, Y. W.; Heeger, A. J.;Shirakawa, H.; Louis, E. J.; Gau, S. C.; MacDiarmid, A. G. Phys.ReV. Lett. 1977, 39, 1098. (b) Burroughes, J. H.; Bradley, D. D. C.;Brown, A. R.; Marks, R. N.; Mackay, K.; Friend, R. H.; Burns, P. L.;Holmes, A. B. Nature (London) 1990, 347, 539. (c) Gelinck, G. H.;Geuns, T. C. T.; de Leeuw, D. M. Appl. Phys. Lett. 2000, 77, 1487.(d) Kline, R. J.; McGehee, M. D.; Kadnikova, E. N.; Liu, J.; Frechet,J. M. J. AdV. Mater. 2003, 15, 1519. (e) Sirringhaus, H.; Tessler, N.;Friend, R. H. Science (Washington, D.C.) 1998, 280, 1741. (f) Drury,C. J.; Mutsaers, C. M. J.; Hart, C. M.; Matters, M.; de Leeuw, D. M.Appl. Phys. Lett. 1998, 73, 108. (g) Dodabalapur, A.; Bao, Z.; Makhija,A.; Laquindanum, J. G.; Raju, V. R.; Feng, Y.; Katz, H. E.; Rogers,J. Appl. Phys. Lett. 1998, 73, 142.(2) (a) McCullough, R. D. AdV. Mater. 1998, 10, 93. (b) Skotheim, T.A.; El senbaumer, R. L.; Reynolds, J. R. Handbo ok of ConductingPolymers, 2nd ed.; Marcel Dekker: New York, 1998; p 225.(3) (a) McCullough, R. D.; Lowe, R. D. J. Chem. Soc., Chem. Commun.1992, 70. (b) McCullough, R. D.; Lowe, R. D.; Jayaraman, M.;Anderson, D. L. J. Org. Chem. 1993, 58, 904. (c) McCullough, R.D.; Tristram-Nagle, S.; Williams, S. P.; Lowe, R. D.; Jayaraman, M.J. Am. Chem. Soc. 1993, 115, 4910. (d) Chen, T. A.; Wu, X.; Rieke,R. D. J. Am. Chem. Soc. 1995, 117, 233.(4) (a) Jen, K. Y.; Eckardt, H.; Jow, T. R.; Shacklette, L. W.; Elsenbaumer,R. L. J. Chem. Soc., Chem. Commun. 1988, 215. (b) Eckardt, H.;Shacklette, L. W.; Jen, K. Y.; Elsenbaumer, R. L. J. Chem. Phys.1989, 91, 1303. (c) Van Dort, P. C.; Pickett, J. E.; Blohm, M. L. Synth.Met. 1991, 41, 2305.(5) (a) Leclerc, M.; Daoust, G. J. Chem. Soc., Chem. Commun. 1990,273. (b) Daoust, G. J.; Leclerc, M. Macromolecules 1991, 24, 455.(c) Faı¨d, K.; Cloutier, R.; Leclerc, M. Macromolecules 1993, 26, 2501.(6) Chen, S. An.; Tsai, C. C. Macromolecules 1993, 26, 2234.(7) (a) Bayer AG, Eur. Patent 339 340, 1988. (b) Jonas, F.; Schrader, L.Synth. Met. 1991, 41, 831. (c) Heywang, G.; Jonas, F. AdV. Mater.1992, 4, 116. (d) Dietrich, M.; Heinze, J.; Heywang, G.; Jonas, J. J.Electroanal. Chem. 1994, 369, 87. (e) Winter, I.; Reece, C.; Hormes,J.; Heywang, G.; Jonas, F. Chem. Phys. 1995, 194, 207.(8) (a) Skotheim, T. A. Handbook of Conducting Polymers; MarcelDekker: New York, 1986. (b) Heuer, H. W.; Wehrmann, R.;Kirchmeyer, S. AdV. Funct. Mater. 2002, 12, 89. (c) De Paoli, M. A.;Nogueira, A. F.; Machado, D. A.; Longo, C. Electrochim. Acta 2001,46, 4243. (d) Groenendaal, L. B.; Zotti, G.; Aubert, P. H.; Waybright,S. M.; Reynolds, J. R. AdV. Mater. 2003, 15, 855. (e) Scrosati, B.Applications of ElectroactiVe Polymers; Chapman & Hall: London,1994.VOLUME 17, NUMBER 13 JUNE 28, 2005© Copyright 2005 by the American Chemical Society10.1021/cm050083o CCC: $30.25 © 2005 American Chemical SocietyPublished on Web 06/04/2005become the frontier of PT-based inherently conductivepolymers (ICPs). The pioneering work of Reynolds has ledto regiosymmetric PXDOTs including the first soluble, verystable dialkylated poly(3,4-propylene dioxythiophenes) (Pro-DOT-R2) that exhibit moderate conductivities (e.g., 7 S/cm,for chemically prepared samples) and possess excellent redoxand electrochromic properties.10Despite these discoveries,generating materials that possess high carrier mobilities andlong-term stabilities in the oxidized state and are easilyprocessible remains a great challenge. Here we present thesynthesis and unique physical properties for a new class ofregioregular 3-alkoxy functionalized polythiophenes thatexhibit high electrical conductivities and very good stabilitieswhen doped with iodine vapor followed by exposure toambient conditions. In addition, we present air doping ofthe polymers by atmospheric oxygen.For the first time, a series of soluble structurally regio-regular alkoxy-substituted PTs (>98% head-to-tail (HT)couplings) of high molecular weights was synthesizedthrough the Grignard Metathesis (GRIM) method,11whichutilizes a chain-growth nickel complex-initiated cross-coupling reaction.12Previously, 3-hexyloxythiophene (HOT,2a) and 3-[2-(2-methoxyethoxy)ethoxy]thiophene (MEET,2b) monomers were polymerized via an oxidative chemicalpolymerization with ferric chloride (FeCl3).6However, theresulting materials were regioirregular oligomers of lowmolecular weight (1387 and 860 for 2a and 2b, respectively).Furthermore, higher molecular weight fractions of thesepolymers were infusible and insoluble solids due to cross-linking via R,β′ couplings between thiophene rings.In this work, dibromoalkoxythiophenes monomers(1a-d) were synthesized in 80-90% yields first by copper(I) mediated substitution of 3-bromothiophene,13followedby a