Synthesis of Small Band Gap Poly[Bis-EDOT-Isoindigo] via Direct Arylation and Oxidative Electropolymerization, and Its Optoelectronic Properties

Abstract

We have demonstrated a chloride-promoted direct arylation of 6,6′-dibromo-N,N′-(2-ethylhexyl)isoindigo, ID, with 4.0 equivalent of 3,4-ethylenedioxythiophene, EDOT, giving a small band gap donor-acceptor oligomer, 6,6′-bisEDOT-N,N′-(2-ethylhexyl)isoindigo, BEDOTID in 97% yield. The polymerization of BEDOTID was performed by following two approaches; (1) electro-oxidative (homo-coupling) reaction in dichloromethane and (2) Pd-catalyzed oxidative (homo-coupling) reaction in chloroform. These approaches afforded insoluble poly[bis-EDOT-isoindigo], PBDOTID. Characterization of PBEDOTID was performed with the film prepared by electro-oxidative polymerization, which showed low optical and electrochemical band gap properties (1.33 and 1.28 eV, respectively) based on the electron-donating EDOT and electron-accepting isoindigo units. The measurement of the current density on scan rate justified that the obtained PBEDOTID film was uniform.