Elsevier

Polymer

Volume 50, Issue 15, 17 July 2009, Pages 3458-3464
Polymer

Tuning of the neutral state color of the π-conjugated donor–acceptor–donor type polymer from blue to green via changing the donor strength on the polymer

https://doi.org/10.1016/j.polymer.2009.05.042Get rights and content

Abstract

Two donor–acceptor–donor types of π-conjugated monomers were synthesized using Stille coupling reaction. Both monomers were found to produce electroactive polymers upon electrochemical oxidation. The effects of different donor substituents on the polymers' electrochemical and spectroelectrochemical properties were examined. Optical characterization revealed that the band gaps of poly(2-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-(2,3-dihydrobenzo[b][1,4]dioxin-7-yl)-5,8-di(thiophen-2-yl)quinoxaline) (PDBQTh) and poly(2-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-(2,3-dihydrobenzo[b][1,4]dioxin-7-yl)-5-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-8-(2,3-dihydrothieno[3,4-b][1,4]dioxin-7-yl)quinoxaline) (PDBQEd) were 1.5 eV and 1.3 eV, respectively. PDBQEd reveals two distinct absorption bands as expected for this type of donor–acceptor–donor polymer at 423 and 738 nm, while PDBQTh has a single absorption band at 630 nm. The colorimetry analysis revealed that while PDBQTh has a blue color, PDBQEd showed a green color in the neutral state. PDBQEd revealed reversible n-doping.

Introduction

Research in the area of conducting polymers increased dramatically with the doping of polyacetylene which was the simplest organic polymer with high conductivity [1]. Conjugated polymeric organic materials have attracted considerable attention over the past decades for their potential applications in organic electronic devices, due to their tunable band gaps, redox properties, processability, flexibility and low cost [2], [3], [4].

Electron-rich heterocycle based polymers such as polythiophene and its derivatives are the most promising and best studied conducting polymers because of their flexibility towards synthetic modifications. The most useful fundamental property that can be controlled by the structural modification is the polymer band gap, Eg, whose magnitude defines the color of conducting polymer [5]. The different colors observed with these compounds while switching between their different redox states is one of the most important advantages of organic electrochromic materials. Applications that use this property include architectural smart windows, rear-view mirrors for cars, sensors and electrochromic displays [6]. In the history of electrochromic materials, the discovery of third additive primary color green was probably one of the most important steps for the commercialization of full-color electrochromic displays [7]. Recently, conjugated polymers that are green at neutral state were the derivatives of quinoxaline [8], [9]. The latest contributions have come from alternation of electron-rich (donor) and electron-poor (acceptor) units in the polyconjugated backbone. A regular alternation of conjugated donor and acceptor moieties in a conjugated polymer that increases double bond character leads to broadening of valence and conduction bands and induces small band gaps [10], [11], [12], [13]. Reports on alternating quinoxaline/oligothiophene copolymers show interesting absorption properties revealing independence of the absorption maxima on the length of the oligothiophene [14], [15].

In this study, the contributions of donor heterocycles of varying strength on the electrochromic properties of new donor–acceptor–donor polymers were examined. Thiophene and EDOT have been used as the donor moieties. To complete alternation on the monomers, acceptor unit with benzo-1,4-dioxane was inserted in the molecule.

Section snippets

Materials

All chemicals were purchased from Aldrich except anhydrous tetrahydrofuran (THF) and n-butyl lithium which were purchased from Acros. They were used as received without purification. 4,7-Dibromo-2,1,3-benzothiadiazole (2) [16], 3,6-dibromo-1,2-phenylene-diamine (3) [17], 5,8-dibromo-2-(2,3-dihydrobenzo[b][1,4]dioxin-5-yl)-3-(2,3-dihydrobenzo[b][1,4]dioxin-8-yl)quinoxaline (6) [18], tributyl(thiophen-2-yl)stannane (8) [19] and tributyl(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)stannane (10) [20]

Synthesis

Bromination of benzothiadiazole was performed in a mixture of HBr/Br2 to give the dibrominated compound in very high yields [16]. Subsequent reduction of the compound was achieved using excess amount of NaBH4 [17]. A simple condensation reaction was performed with the dibromo diamino and 1,2-dione to give the corresponding dibromoquinoxaline [18]. Stannylation of EDOT and thiophene was achieved by addition of equimolar strong base, n-BuLi followed by addition of Bu3SnCl [19], [20]. Lastly a

Conclusion

Target monomers based on 2-(2,3-dihydrobenzo[b][1,4]dioxin-5-yl)-3-(2,3-dihydrobenzo[b][1,4]dioxin-8-yl)quinoxaline as the common acceptor unit were synthesized to understand the effects of donor strength on the optoelectronic and redox properties of the resulting electropolymerized materials. The electrochemical cyclic voltammograms of the polymers showed a distinct reversible redox peaks. The band gap of the resulting polymers was found from the investigation of optical absorption properties

Acknowledgments

Authors gratefully thank TUBITAK-Department of Science Fellowships and Grant Programmes.

References (20)

  • K. Aydemir et al.

    Polymer

    (2008)
  • A. Pennisi et al.

    Electrochim Acta

    (1999)
  • T. Michinobu et al.

    Polymer

    (2008)
  • H. Shirakawa et al.

    J Chem Soc Chem Commun

    (1977)
  • A.J. Heeger

    Angew Chem Int Ed

    (2001)
  • D.M. Welsh et al.

    Macromolecules

    (2002)
  • T. Johansson et al.

    Mater Chem

    (2003)
  • I. Schwendeman et al.

    Chem Mater

    (2002)
  • G. Sonmez et al.

    Macromolecules

    (2005)
  • A. Durmus et al.

    Chem Mater

    (2007)
There are more references available in the full text version of this article.

Cited by (40)

  • An electrochemically and optically stable electrochromic polymer film based on EDOT and 1,2,3,4-tetrahydrophenazine

    2019, Organic Electronics
    Citation Excerpt :

    Table 1 demonstrates those polymer films and summaries their basic optical properties. Rather than electrochromics with bis-substituted quinoxalines [14–18] or other aimed quinoxaline and EDOT based polymers [36–40], electron withdrawing quinoxaline based heterocyles (characterized as electrochromics) were especially compared [19–22]. Structures of these polymers were shown in Fig. 8.

  • Diversity of electron acceptor groups in donor–acceptor type electrochromic conjugated polymers

    2019, Solar Energy Materials and Solar Cells
    Citation Excerpt :

    As such, a trend between type of thiophene donors and optical and EC properties can be seen from the comparison of these polymers with 2,3-di (p-tert-butylphenyl)-QX acceptors in D-A-D configuration. Similarly, polymer P139, with thiophene donors and QX acceptors substituted with benzo-1,4-dioxane had a larger Eg and blue-shifted absorption λmax compared to its EDOT counterpart P129, and was only p-dopable switching from blue to transmissive on oxidation [143]. Polymers P140a and P140b with furan-disubstituted QX had thiophene and 4-methoxythiophene donors in repeating units of D-A-D configurations, respectively [146].

View all citing articles on Scopus
View full text