Spectroelectrochemical Properties of 1,10-Phenanthroline Substituted by Phenothiazine and Carbazole Redox-active Units

Complexes of 1,10-phenanthrolines with cations of transition metals have broad range of applications. This work aims at designing and investigating phenothiazine and carbazole substituted 1,10-phenanthrolines as ligands for future complexes with transient metal cations. The combined electrochemical, spectroelectrochemical and DFT studies were employed to demonstrate the effect of broken symmetry in substituted 4,7-di(phenothiazine)-1,10-phenanthrolines on their spectroelectrochemical properties. A reversible color change (new absorption band around 500 nm) due to phenothiazine radical cation was observed in the first oxidation step. Results further indicate that phenothiazine substituents behave as two equivalent but almost electronically isolated redox centres. The work additionally presents a comprehensive reaction mechanistic study of oxidation and reduction processes complemented by HPLC-MS/MS identification.