Chem. Mater. 2010, 22, 2333–2340 2333 DOI:10.1021/cm903455w
Polyaniline Exhibiting Stable and Reversible Switching in the Visible Extending into the Near-IR in Aqueous Media Jacob Tarver,† Joung Eun Yoo,†,‡ and Yueh-Lin Loo*,† †
Department of Chemical Engineering and Department of Chemistry, Princeton University, Princeton, New Jersey 08544, and ‡Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712 Received November 12, 2009. Revised Manuscript Received January 22, 2010
Spun-cast films comprising polyaniline (PANI) that is template synthesized with poly(2-acrylamido-2-methyl-1-propanesulfonic acid), PAAMPSA, can be reversibly switched between emeraldine salt, leucoemeraldine base, and for the first time, pernigraniline base states in aqueous media at near-neutral pHs. Transitions between the green, transparent and violet states occur within 1-10 s, comparable to the electrochromic switching times reported for thin films deposited via layer-bylayer approaches. Solvent annealing in dichloroacetic acid induces structural rearrangement within PANI-PAAMPSA, resulting in significantly improved stability and reversibility upon repeated cycling, and moreover, imparting tunable polyelectrochromism that extends into the near-infrared (1100 nm). Introduction Electrochromic materials comprise redox-active species that exhibit significant, lasting, and reversible changes in color upon the injection or withdrawal of electrons. Electrochemical manipulation of the redox processes in thin layers of these materials thus allows the modulation of the spectral characteristics of light that is transmitted. Upon oxidation, for instance, an electrochromic material can switch from a clear form to a colored form, or vice versa. Electrochromic materials are thus promising candidates in display applications. Devices utilizing electrochromic materials are lauded for their low power consumption because of the passive transmissive mechanism of their operation, as opposed to the active emissive mechanism associated with light emitting diodes (LEDs).1 Specifically, electrochromic materials require only an initial current pulse at a sufficiently strong potential to induce the desired electrochemical reaction and accompanying chromic change; in the absence of oxidizing or reducing contaminants, this change is permanent and the device only demands backlighting. LEDs, on the other hand, require a constant power supply for continuous photoemission. Additionally, electrochromic devices are easy to fabricate, as the electrochromic materials can be coated directly onto transparent electrodes without the need for the complex patterning that is required for LEDs.2 *To whom correspondence should be addressed. E-mail:
[email protected].
(1) Lampert, C. M. Sol. Energy Mater. 1984, 11, 1–27. (2) DeLongchamp, D. M.; Kastantin, M.; Hammond, P. T. Chem. Mater. 2003, 15, 1575–1586. (3) Platt, J. R. J. Chem. Phys. 1961, 34, 862–863. (4) Green, M.; Smith, W. C.; Weiner, J. A. Thin Solid Films 1976, 38, 89–100. r 2010 American Chemical Society
Electrochromism has been reported in redox-active inorganics, such as tungsten oxide;3,4 small-molecule organics, such as viologen;5 as well as conducting polymers, such as copolymers and derivatives of polypyrrole and polythiophene.6,7 Although tungsten oxide was the first electrochromic material of commercial interest, inorganic electrochromic materials typically exhibit slow switching speeds 10-100 s and have proven costly to process because of the need for high-vacuum sputtering deposition.8 Small-molecule organics, though easy to process, have shown poor stability as they easily diffuse away from the electrode and into the electrolyte. Electrochromic polymers, alternatively, hold the promise of robust film integrity, facile film formability, and fast switching times (
