Photophysics and Light-Activated Biocidal Activity of Visible-Light-Absorbing Conjugated Oligomers

Abstract

The photophysical properties of three cationic π-conjugated oligomers were correlated with their visible light activated biocidal activity vs <i>S. aureus</i>. The oligomers contain three arylene units (terthiophene, <b>4a</b>; thiophene-benzotriazole-thiophene, <b>4b</b>; thiophene-benzothiadiazole-thiophene, <b>4c</b>) capped on each end by cationic −(CH₂)₃NMe₃⁺ groups. The oligomers absorb in the visible region due to their donor–acceptor–donor electronic structure. Oligomers <b>4a</b> and <b>4b</b> have high intersystem crossing and singlet oxygen sensitization efficiency, but <b>4c</b> has a very low intersystem crossing efficiency and it does not sensitize singlet oxygen. The biocidal activity of the oligomers under visible light varies in the order <b>4a</b> > <b>4b</b> ≈ <b>4c</b>