Effect of ring size on benzimidazole unit on electro-optical properties of donor

By Al-Ogaidi, Saad; Karabay, Baris; Karabay, Lutfiye Canan; Cihaner, Atilla
Published in Journal of Electroanalytical Chemistry NULL 2016

Abstract

Abstract A new series of fluorescent donor-acceptor-donor (D-A-D) type monomers based on benzimidazole acceptor unit bearing various cycloalkane appendages, called 4,7-di-2,3-dihydrothieno[3,4-b] [1,4]dioxin-5-ylspiro[benzimidazole-2,1?-cyclopentane] (E5E), 4,7-di-2,3-dihydrothieno[3,4-b] [1,4]dioxin-5-ylspiro[benzimidazole-2,1?-cyclohexane] (E6E) and 4,7-di-2-thienylspiro[benzimidazole-2,1?-cyclohexane] (T6T), were synthesized and polymerized via potentiostatic and potentiodynamic methods. The effect of ring size on benzimidazole unit and the kind of donor moiety in D-A-D system on the electrochemical and optical properties have been studied systematically. The optical studies showed that the ring size of the benzimidazole unit has no effect on the absorbance and fluorescence properties, whereas the oxidation potential of the E5E, {E6E} and {T6T} monomers varied with respect to both the ring size and the kind of donor unit: 0.89 V, 0.83 V and 1.22 V vs Ag/AgCl, respectively. All polymers have ambipolar (p- and n-type doping) and electrochromic properties. While the polymer films {PE5E} and {PE6E} are green at neutral state and transparent at oxidized state, the polymer {PT6T} has no appreciable color change between its neutral and oxidized states. The polymers {PE5E} and {PE6E} bearing 3,4-ethylenedioxythiophene unit as donor units exhibited lower band gap values (1.21 eV and 1.18 eV, respectively) than the polymer {PT6T} (1.53 eV). When compared to PT6T, {PE5E} and {PE6E} polymers are more stable under ambient condition. While {PE5E} retained 76% of its electroactivity after 4000 cycles, {PE6E} has 65% of its electroactivity after 2000 cycles.

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