The effect of pendant conjugated vinylborane moieties on the electronic structure of oligothiophenes and their anion binding behaviour was investigated. The vinylborane groups were introduced by hydroboration of alkynyl- functionalized 2,5-dibromothiophene with dimesitylborane (Mes2BH). The reaction yielded a 1:1 mixture of the α- and β-borylated isomers, which were separated and individually isolated by reverse-phase column chromatography. Grignard metathesis polymerization (GRIM) of the dibromothiophenes yielded oligomeric materials (Mn = 1.5 to 1.7 kDa) capable of anion binding. DFT analyses on borane-functionalized terthiophene model compounds indicated that efficient extension of conjugation from the thiophene main chain to the vinylborane pendant group in the sterically less encumbered β-isomer greatly impacts on the photophysical properties. Anion titration experiments revealed the strong binding of F- and CN -, which is accompanied by a fluorescence enhancement that is especially pronounced for the β-isomer.
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