Push-pull heterocyclic dyes based on pyrrole and thiophene: synthesis and evaluation of their optical, redox and photovoltaic properties

Abstract

Three heterocyclic dyes were synthesized having in mind the changes in the photovoltaic, optical and redox properties by functionalization of 5-aryl-thieno[3,2-<i>b</i>]thiophene, 5-arylthiophene and <i>bis</i>-methylpyrrolylthiophene π-bridges with different donor, acceptor/anchoring groups. Knoevenagel condensation of the aldehyde precursors with 2-cyanoacetic acid was used to prepare the donor-acceptor functionalized heterocyclic molecules. These organic metal-free dyes are constituted by thieno[3,2-<i>b</i>]thiophene, arylthiophene, <i>bis</i>-methylpyrrolylthiophene, spacers and one or two cyanoacetic acid acceptor groups and different electron donor groups (alkoxyl, and pyrrole electron-rich heterocycle). The evaluation of the redox, optical and photovoltaic properties of these compounds indicate that 5-aryl-thieno[3,2-<i>b</i>]thiophene-based dye functionalized with an ethoxyl electron donor and a cyanoacetic acid electron acceptor group/anchoring moiety displays as sensitizer for DSSCs the best conversion efficiency (2.21%). It is mainly assigned to the higher molar extinction coefficient, long π-conjugation of the heterocyclic system, higher oxidation potential and strong electron donating capacity of the ethoxyl group compared to the pirrolyl moiety.