Synthesis of a viologen-tetratitanate intercalation compound and its photochemical behaviour

Methyl viologen has been intercalated into the interlayer space of layered tetratitanic acid by a method involving the displacement of guest molecules using an n-propylammonium tetratitanate intercalation compound. The viologen tetratitanate intercalation compound changed colour to blue when irradiated by a mercury lamp under vacuum conditions or a nitrogen atmosphere. The formation of radical cations was confirmed by visible and e.s.r. spectroscopy. The electron donor for the photoreduction is thought to originate from the tetratitanate layers. The colour was stable as long as the vacuum conditions were maintained, and fading did not occur rapidly even after the introduction of air, requiring > 1 h for the colour to fade completely. These results indicate remarkable stability of the viologen radical cations in this intercalation compound.