Photoinduced H-aggregation of cationic dyes on metal-oxide surfaces via light activated molecular migration

Molecular transport by use of light energy is a new photofunction for light powered molecular carriers and light induced nano-structure formation on a substrate. However, this research field has not been cultivated yet. In order to understand the basic mechanism and potentialities, experimental observations of photoactivated molecular migration and its functions in various systems are required. Here, we report visible light induced H-aggregation of cationic dyes (methylene blue and toluidine blue) on metal-oxide surfaces (TiO₂ and ZnO) via photoactivated surface migration of these dyes. Our research widely expands the scope of photoinduced surface molecular migration to the conventional dyes and metal-oxide surfaces, and also demonstrates that the photoinduced molecular assembly provides a photochromic function. It is noteworthy that high aggregates, which are difficult to form in the dark, can be formed by the photoinduced surface migration of excited dyes.