Mapping the Fluorescence Performance of a Photochromic–Fluorescent System Coupled with Gold Nanoparticles at the Single-Molecule–Single-Particle Level

Single-molecule (SM) fluorescence microscopy was used to investigate the photochromic fluorescent system spiropyran–merocyanine (SP ↔ MC) interacting with gold nanoparticles (AuNPs). We observe a significant increase in the brightness of the emissive MC form, in the duration of its ON time, and in the total number of emitted photons. The spatial distribution of SMs with improved photophysical performance was obtained with 40 nm precision relative to the nearest AuNP. We demonstrate that even photochromic systems with poor photochemical performance for SM can become suitable for long time monitoring and high performance microscopy by interaction with metallic NP.