Spectroscopic and electrochemical properties of 2-aminophenothiazine

Phenothiazines derivatives are versatile compounds that are used in many fields, depending on the type and position of the substitution on the parent molecule. The photochemical, photophysical and electrochemical properties of several phenothiazine derivatives have been previously reported in detail. However, no reports have been presented for 2-aminophenothiazine (APH), a candidate that provides for the further chemical modification and the introduction of specific substituents. In this work, the photophysical and electrochemical properties of APH were measured in acetonitrile. The APH ground state absorption and fluorescence spectrum (Φf < 0.01) are similar to the corresponding PH parent molecule. A mono-exponential decay fluorescence lifetime of 0.65 ns was determined for APH in acetonitrile. Characterization of the 355 nm nanosecond laser flash photolysis transient species reveals the presence of the triplet–triplet transient intermediate with a high intersystem crossing quantum yield (ΦT = 0.72 ± 0.07), indicating that the APH main excited state deactivation channel is intersystem crossing. The oxidation potential of APH is lower than phenothiazine parent molecule (0.38 V vs. 0.69 V vs. Ag/AgCl(sat)). Altogether, these results show that APH has photochemical and photophysical properties similar to the phenothiazine parent molecule, but with the possibility of providing an amino functionality at 2-position for further chemical modification.