Synthesis and electropolymerization of a new ion sensitive ethylenedioxy-substituted terthiophene monomer bearing a quinoxaline moiety Buket Bezgin Carbas a , Arif Kivrak a,b , Metin Zora a , Ahmet M. Önal a,⇑ a Department of Chemistry, Middle East Technical University, Ankara 06800, Turkey b Department of Chemistry, Yüzüncü Yıl University, Van 65080, Turkey article info Article history: Received 28 February 2012 Received in revised form 26 April 2012 Accepted 11 May 2012 Available online 22 May 2012 Keywords: Quinoxaline Electrochemical polymerization Fluorescent polymer Electrochromics Ion sensitivity Chemical sensors abstract A new terthienyl based fluorescent polymer bearing pendant quinoxaline moieties directly attached to the 3-positions of the central thiophene ring was synthesized by electrochemical polymerization of 4-(2,5-bis (2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)thiophen-3-yl)pyrrolo[1,2-a]quinoxaline (EE-Q). The corre- sponding polymer, poly(4-(2,5-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)thiophen-3-yl)pyrrolo [1,2-a] quinoxaline) P(EE-Q), was characterized by cyclic voltammetry, FT-IR and UV–vis spectroscopy. The poly- mer exhibits a reversible redox behaviour (E 1=2 p ¼ 0:75 V) accompanied with a reversible electrochromic behavior; brownish red in the neutral state and green in the oxidized state. The band gap value for the polymer was found to be 1.75 eV. Moreover, the sensitivity of both the monomer and its polymer towards metal cations was investigated by monitoring the change in the fluorescence intensity. Among various common ions, both the monomer and its polymer were found to be selective towards Fe 3+ ions by quench- ing the fluorescence efficiency with a Stern–Volmer constant (K sv ) of (1.9  10 3 M 1 ) and (5.0  10 2 M 1 ) for monomer and polymer solutions, respectively. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Fluorescent chemosensors for the detection of metal ions have received great attention for their chemical, biological and environ- mental applications [1–3]. They have distinct advantages such as their inherent simplicity, high sensitivity, selectivity and an easy measurement than other methods [4–7]. Iron is a well known me- tal ion for most organisms, playing a significant role in many bio- chemical processes such as oxygen metabolism and synthesis of DNA and RNA [8,9]. Therefore, detection of trace amounts of Fe 3+ ion is critical and there have been extensive efforts for the develop- ment of selective and sensitive Fe 3+ sensors [10–13]. Quinoxalines are interesting functional materials due to their fluorescence prop- erties with high quantum yields and can be utilized as fluorescence probes in some chemosensors [14]. Some quinoxaline derivatives are able to coordinate to various anionic species [15,16], making them amenable as anion sensors. There are also several reports on their use as metal chelators [17,18]. Recently, we have synthe- sized a series of new fluorescent monomers based on terthienyl systems bearing pendant quinoxaline moieties and found that 4-((2,5-dithiophen-2-yl)thiophen-3-yl)pyrrolo[1,2-a]quinoxaline (TT-Q) monomer and its polymer exhibit high sensitivity towards Fe 3+ ions [19]. Moreover, it was found that the polymer obtained on the basis of donor–acceptor approach exhibits reversible elec- trochromic response with high coloration efficiency. Keeping this in mind, we have synthesized a new monomer, 4-(2,5-bis(2,3- dihydrothieno[3,4-b][1,4]dioxin-5-yl)thiophen-3-yl)pyrrolo[1,2-a] quinoxaline (EE-Q), bearing pendant quinoxaline unit as acceptor group and 3,4-ethylenedioxythiophene (EDOT) as donor groups (Scheme 1). It is expected that the resulting hybrid material with donor–acceptor–donor scaffold would have lower band gap [20–24]. Herein we wish to report our results concerning the syn- thesis and electrochemical polymerization of EE-Q. Electrochromic properties of the new fluorescent polymer were also investigated via in situ spectroelectrochemical techniques. Furthermore, the fluorescence properties of EE-Q and its polymer were investigated in dimethylformamide (DMF). The effect of various metal cations on the fluorescence intensity was also determined. 2. Experimental 2.1. Electropolymerization and characterization All chemicals were purchased from Aldrich Chemical and used as received. Cyclic voltammetry (CV) was performed in a three-elec- trode cell equipped with a platinum (0.02 cm 2 ) working electrode, a platinum wire counter electrode and Ag/AgCl, in 3 M NaCl(aq) solution, as a reference electrode. Polymer film was obtained poten- tiodynamically in dichloromethane (DCM) containing 0.1 M 1572-6657/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jelechem.2012.05.005 ⇑ Corresponding author. Tel.: +90 312 2103188; fax: +90 312 2103200. E-mail address: aonal@metu.edu.tr (A.M. Önal). Journal of Electroanalytical Chemistry 677–680 (2012) 9–14 Contents lists available at SciVerse ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem