Hexyl‐Derivatized Poly(3,4‐ethylenedioxyselenophene): Novel Highly Stable Organic Electrochromic Material with High Contrast Ratio, High Coloration Efficiency, and Low‐Switching Voltage

Abstract

Currently, there is significant interest in the design of new electrochromic (EC) materials exhibiting a high contrast ratio (a large change in percent transmittance between the colored and bleached states), high coloration efficiency (efficient color changes in response to applied charge) and long-term stability. EC materials could be employed in the fabrication of efficient displays and ECwindows if they could bemade to exhibit a large change in transmittance upon application of a small charge. While considerable research was performed on inorganic EC materials, better performance has been reported recently using conducting polymers, mostly based on poly(3,4ethylenedioxythiophene) (PEDOT) and its derivatives. Conducting polymers offer better processability and better color tunability than their inorganic andmolecular counterparts. PEDOT film can be quite rapidly switched between the absorptive (neutral) and transmissive (doped) states at low switching potentials. The neutral PEDOT film shows a band gap of around 1.6 eV and a light sky blue appearance as a doped film. The coloration efficiency (CE) of PEDOT is 137 cm C 1 at full switch, 183 cm C 1 at 95% of full switch, 206 cm C 1 at 85% of full switch, and the dibutyl derivative of poly(3,4-propylenedioxythiophene) (PProDOT(Bu)2) [13] obtained by Reynolds’ group achieves a CE of 1365 cm C , which is currently the highest CE value reported for an electropolymerized EC film measured in liquid electrolyte. The stability of the electrochromic materials is another crucially important feature for practical application. Reynolds’ group studied PEDOT, PEDOT-C8, and PEDOT-C14 films and found that the films retained 65%, 50%, and 62% of their electroactivity after 6000, 9000, and 16000 switching cycles, respectively. However, the contrast ratios were less than 65%. Kumar’s group obtained a dibenzyl poly(3,4-propylenedioxythiophene) (PProDOT-Bz2) that has the highest known contrast ratio (89%), a CE of 575 cm C 1 and high stability after 5000 switching cycles. The poly(1,4-bis(2-(30,40-ethylenedioxy)thienyl)-2-methoxy-5-200ethylhexyloxybenzene) (P(BEDOT-MEHB)) reported by Wudl’s group has a CE of 680 cm C 1 and also exhibits high stability after 5000 switching cycles, though it has a contrast ratio of only 57%. Catellani et al. reported that poly(3-butylthiophene) can