Electropolymerization study of benzothiophenes and characterization of novel poly(dibenzothiophene-S,S-dioxide)

The electrochemical polymerization study of a set of monomers, dibenzothiophene (DBT), benzothiophene-S,S-dioxide (BTO), and dibenzothiophene-S,S-dioxide (DBTO) was reported and novel conducting poly(dibenzothiophene-S,S-dioxide) (PDBTO) was successfully electrosynthesized in boron trifluoride diethyl etherate (BFEE) and in the binary solvent system of BFEE and trifluoroacetic acid (TFA) for the first time. The strong electron-withdrawing sulphonyl group substitution on BTO partly damaged the aromatic system of BT and significantly inhibited electrochemical polymerization. The electronic clouds of DBT and the electron spin density of its radical cation centralized dominantly on the sulfur atom, thus making it impossible to get the corresponding polymer electrochemically. Furthermore, structural characterization, molecular weight, ionization potentials and electron affinities, fluorescence properties, thermal stability, electrical conductivity, and morphology of PDBTO were minutely investigated. From FT-IR spectra and computational results, DBTO was probably polymerized through the coupling at C(3) and C(7) positions, with the same structure to electrosynthesized polyfluorenes. The substitution of sulphonyl group in the fluorene ring increases its electron affinity considerably for improving electron injection/transport. Additionally, as-formed PDBTO was found to be a typical blue-light-emitter with maximum emission at 458nm and concurrently exhibited good electroactivity and thermal stability. The successful electrosynthesis of PDBTO should represent a unique approach to DBTO-based donor–acceptor co-oligomers/polymers, which hold promise for the design of a new generation of optoelectronic materials and are hotly researched in the field of electronic devices currently.