Organoboron copolymers containing thienothiophene and selenophenothiophene analogues: optical, electrochemical and fluoride sensing properties

Abstract

Conjugated donor–acceptor (D–A) copolymers possessing alternating fused bicyclic aromatic rings thieno[3,2-b]thiophene, selenopheno[3,2-b]thiophene, thieno[2,3-b]thiophene and selenopheno[2,3-b]thiophene as donors, thiophene as a π-conjugated bridge and mesitylboron as an acceptor were synthesized and characterized by spectroscopic methods. Large Stokes shifts of 96–166 nm were recorded and the solution quantum yields of the polymers were in the range of 5–18%. Their ionization potentials and electron affinities were investigated by cyclic voltammetry. Optical band gaps varied between 2.26 and 2.78 eV. (TD)-DFT studies were performed to unveil their electronic structures, Kohn–Sham orbitals and electronic transitions. Absorption and emission measurements revealed that these polymers have high sensitivity to fluoride anions, among which the polymer possessing cross-conjugated thienothiophene units had the best sensing properties supported by orbital composition analysis with Mulliken partition. Thus, copolymers P1–P4 could be used as colorimetric and fluorescent sensors for small fluoride anions.