Quinoxaline-Based Semiconducting Polymers: Effect of Fluorination on the Photophysical, Thermal, and Charge Transport Properties

Abstract

A novel fluorinated quinoxaline-based acceptor has been synthesized and then copolymerized with an electron-rich benzodithiophene derivative to yield a low band gap polymer (PBDT-QxF). A non-fluorinated analogue of the same polymer (PBDT-Qx) has also been synthesized in order to disclose the effect of fluorination on polymer properties. PBDT-QxF exhibits better thermal and oxidative stability compared to non-fluorinated analogue. Fluorine atoms induce crystalline domains in solid state—possibly as a result of favorable C–F···H interactions—whereas such ordering is absent in PBDT-Qx. Principal component analysis on variable temperature absorption data collected in solution revealed a stabilization energy of ∼0.5 kcal mol–1 per repeat unit upon fluorination. Theoretical calculations predict higher oxidation potential for PBDT-QxF, which is confirmed by experimental data. Theoretical calculations also suggest inductive effect of fluorine atoms on electronic structure. The hole mobility of PBDT-QxF is also higher than that of PBDT-Qx. Overall, the studies show promising photovoltaic properties of this novel monomer if used in low band gap polymers for organic solar cell applications.