Effect of Monofluoro Substitution on the Optoelectronic Properties of Benzo[c][1,2,5]thiadiazole Based Organic Semiconductors

The effects of fluorine substitutions on the molecular geometry and optoelectronic properties were investigated based on the conjugated molecular framework consisting of the mono-fluorinated benzo­[c]­[1,2,5]­thiadiazole unit. The two-dimensional nuclear magnetic resonance spectroscopy of model compounds indicated that the fluorine substitution can significantly change the chemical environment of the adjacent hydrogen atoms, which was in consistence with the changed molecular geometry as indicated by single crystal diffractions and theoretical calculations. Based on an AB type of monomer, the regioregular conjugated polymer with specifically oriented fluorine along the vector of the polymer backbone was constructed. The UV–vis absorption, photoluminescent, and electroluminescent spectra demonstrated the slightly hypsochromic shift of the copolymer comprising the fluorine substitution relative to the non-fluorinated counterpart. Of particular interest is that the copolymer based on the fluorinated benzothiadiazole unit exhibited electron-dominant charge transportation, for which the electron mobility is about 1 order of magnitude higher than that of hole mobility.