Transitions of fluorescent Rhodamine 6G dye molecules into metastable dark states with lifetimes of several seconds were observed by single-molecule detection (SMD) using far-field confocal microscopy. The samples were protected with different organic thin films and were characterized using atomic force microscopy. The data are compared to published models: The best fit is found with a model suggesting that oxygen migration or polarity changes are responsible for the transitions. For further studies with molecules close to each other, we studied the capability of cantilever-SNOM sensors for SMD. Using an alpha-SNOM we were able to demonstrate 40 nm optical resolution of these new near-field tips for single-molecule fluorescence imaging in direct comparison with confocal microscopy on samples of Rhodamine 6G molecules protected by PMMA.