Spray Coatable Electrochromic Dioxythiophene Polymers with High Coloration Efficiencies Benjamin D. Reeves, † Christophe R. G. Grenier, † Avni A. Argun, † Ali Cirpan, † Tracy D. McCarley, ‡ and John R. Reynolds* ,† Department of Chemistry, Center for Macromolecular Science and Engineering: University of Florida, Gainesville, Florida 32611-7200, and Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803-1804 Received April 21, 2004; Revised Manuscript Received July 14, 2004 ABSTRACT: Four new disubstituted propylenedioxythiophene polymers have been synthesized by Grignard metathesis on the 1-5 g scale. All polymers were found to be soluble in chloroform, methylene chloride, toluene, and tetrahydrofuran and were fully structurally characterized having GPC determined number-average molecular weights ranging from 33000 to 47000 g mol -1 . Dilute polymer solutions in toluene exhibited strong red fluorescence with moderate quantum efficiencies from 0.38 to 0.50. Homogeneous thin films were formed by electropolymerization and spray casting polymer solutions onto ITO coated glass slides at thicknesses of ca. 150 nm. The films were electroactive, switching from a dark blue-purple to a transmissive sky blue upon p-doping, often with subsecond switching times, and high electrochromic contrast luminance changes (% ΔY) of 40-70%. These studies revealed that the branched derivatives, [poly(3,3-bis(2-ethylhexyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)] and [poly(6,8-dibromo- 3,3-bis(2-ethylhexyloxymethyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)], gave an electrochemical re- sponse and associated color change over a much smaller voltage range in comparison to the linear chain substituted derivatives, [poly(3,3-dihexyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)] and [poly(3,3-bis- (octadecyloxymethyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)]. Composite coloration efficiency values were found up to 1365 cm 2 /C; this was considerably larger than values obtained from previously studied alkylenedioxythiophene based polymers (∼375 cm 2 /C). Introduction Great effort has been made over the last 2 decades to study and utilize the electronic properties of thiophene- based conducting polymers while optimizing their processability. 1-3 This has led to the use of polythio- phenes in various applications including light emitting devices, 4 chemical sensors, 5 rechargeable batteries, 6 organic thin film transistors, 7 and electrochromic de- vices. 8 Processability of polythiophenes has undergone vast improvements by derivatizing the 3-position of the ring with flexible substituents. 9-11 The regioregularity of these poly(3-alkyl thiophenes) (p3AT’s) plays an important role in property control. 12 Models of regio- random, regioregular, and regiosymmetric polymers are illustrated in Scheme 1. If the unsymmetrical monomer only couples in a head-to-tail fashion, the alkyl substit- uents do not interfere with the conjugation of the thiophene rings via steric interactions, and the resulting polymer is regioregular. While numerous methods 12,13 have been employed for synthesizing regioregular p3AT’s, the latest method developed by McCullough and co-workers, Grignard metathesis polymerization, does not require long reac- tion times, cryogenic temperatures, or nontrivial prepa- ration of reagents often seen with other methods. 14,15 Poly(thiophenes) show excellent potential for use in electrochromic devices due to the drastic change in the electromagnetic spectrum upon charge injection (doping) with the parent polymer switching from red to blue upon oxidation. 16 Derivitizing the 3- and 4-positions of the thiophene ring with an alkylenedioxy brigde lowers the band gap and the oxidation potential due to the two electron donating oxygen atoms. 17,18 Poly(3,4-ethylene- dioxythiophene) (PEDOT) is cathodically coloring, switch- ing between a dark blue in the neutral state and a transmissive sky blue in the oxidized state. By taking advantage of the synthetic flexibility of the PEDOT monomer structure, we have been successful in synthesizing and studying the electrochromic proper- ties of many derivatives of PEDOT. 19-22 We have developed synthetic methodologies to vary the alkylene- * Corresponding author. E-mail: reynolds@chem.ufl.edu. † University of Florida. ‡ Louisiana State University. Scheme 1 7559 Macromolecules 2004, 37, 7559-7569 10.1021/ma049222y CCC: $27.50 © 2004 American Chemical Society Published on Web 09/04/2004