Adsorption of 7-Methylguanosine (m7guo) on Clay Minerals and Its Effect on Luminescence Enhancement

We investigated the adsorption behavior and fluorescence properties of 7-methylguanosine (m7Guo), a cationic nucleoside, on clay minerals under acidic conditions. The fluorescence quantum yield Φf was 0.011 in water and 0.126 in a clay dispersion. We observed Surface-fixation-induced emission (S-FIE)—a phenomenon in which fluorescence is enhanced upon adsorption of molecules onto clay mineral surfaces—in this nucleic acid-related molecule. Analysis of the factors contributing to fluorescence enhancement revealed that suppression of the nonradiative decay rate constant knr plays a key role. The value of knr decreased to approximately 1/27 of that in water, indicating that strong immobilization on the clay surface suppresses nonradiative relaxation and stabilizes the excited state.