Revisiting the Synthesis of Tetramethoxyindolo[3,2-b]indole Derivatives and the Study of Their Photoinduced Radical Formation in Halogenated Solvents

We previously reported that the attempt to synthesize tetramethoxyindolo[3,2-b]indole led to an undefined product. Now, it is confirmed that its instability is derived from the one-electron transfer from the tetramethoxyindolo[3,2-b]indole derivatives to halogenated solvents under ultraviolet-visible (UV-vis) light irradiation, forming a stable indolo[3,2-b]indole radical cation while causing the carbon-halogen (C-X, X = Cl, Br, I) bond scission.