Phenothiazines grafted on the electrode surface from diazonium salts as molecular layers for photochemical generation of singlet oxygen

Four amine-derivative phenothiazines were converted to the corresponding diazonium salt forms prior to their electrochemical grafting on the GC electrode with the aim to assess their ability to generate singlet oxygen. It was demonstrated by cyclic voltammetry and XPS spectroscopy that the molecular layers were effectively bound to the GC surface by applying the reductive potential in situ in the reaction diazo-mixture. The chosen procedure without the product separation step, appears to be especially useful due to the high solubility of the resulted phenothiazine diazonium salts. The effectiveness of singlet oxygen generation was measured for all of the grafted surfaces by UVVis spectra monitoring of the adjacent solution phase of 1,3-diphenylisobenzofuran (DPBF), which is well known trapping molecule used in detection of singlet oxygen. The data presented in the work prove that all of the molecular layers are effective singlet oxygen generators that might be used for various areas of applications where a highly oxidative reactant is required.