Pyridine-EDOT Heteroarylene-Vinylene Donor-Acceptor Polymers

Two heteroarylene-vinylene donor-acceptor polymers, P(2,6-Py-V-EDOT) and P(2,5-Py-V-EDOT), containing vinylene-spaced simple donor (EDOT) and acceptor (pyridine) moieties, are presented. The central pyridine ring of the repeating unit is either 2,6- or 2,5-substituted, leading to different structural and electronic properties of the monomers. Polymers were obtained by either oxidative electropolymerization or Yamamoto coupling and fully characterized by NMR, UV-vis absorption, GPC, TGA, DSC, electrochemistry, and spectroelectrochemistry. Detailed ab initio computations have been performed for the monomers and model oligomers for analyzing their optical and electronic properties. GPC showed that isolated polymers obtained via Yamamoto poly coupling have low molecular weights, likely due to solubility issues. The electrochemical polymerizations led to p- and n-dopable polymers, with 2,5-Py-V-EDOT yielding more reversible n-doped process. The energetic positions revealed HOMO (-5.1 and -5.0 eV), LUMO (-3.4 eV), and narrow bandgap (1.6 and 1.7 eV) energies closely matching materials-design rules for optimized organic photovoltaic devices. Preliminary investigation in photovoltaic devices in combination with C71-PCBM afforded relatively modest power conversion efficiencies of 0.5% (AM 1.5G, 100 mW/cm2), which were attributed to the low molecular-weight of the polymers accessible via the chemical route.