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 (m 7 Guo), a cationic nucleoside, on clay minerals under acidic conditions. The fluorescence quantum yield Φ f 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 k nr plays a key role. The value of k nr 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.