Photogeneration of singlet oxygen by thionine molecular layer grafted on electrode surface from its diazonium salt

• The thionine immobilized on a surface preserves its ability to form an effective exited state after absorption of Vis light
• This effective exited state is able to transfer its energy into oxygen molecule converting triplet oxygen into singlet oxygen
• Immobilization of thionine may occur in the electrochemical reduction step directly from its diazo-reaction mixture
• Thionine monolayer on carbon substrate produces singlet oxygen under visible light radiation with approximately constant rate

Thionine (Th) was electrochemically grafted to the glassy carbon (GC) surface from its corresponding diazonium salt to investigate it as a singlet oxygen source under light excitation. As confirmed by cyclic voltammetry data the Th molecules may form a monolayer structure in the reduction process carried out directly from the diazotization reaction mixture without a time-consuming separation step. It was found that illuminated grafted Th at a level of monolayer coverage on GC surface is able to generate singlet oxygen at a constant rate. To determine efficiency of the photogeneration process a singlet oxygen selective trap, 1,3-diphenylisobenzofuran (DPBF), was employed, which was monitored using UVVis spectroscopy. The progress of the trap decay was determined in terms of its half-life.