Unexpected photoluminescence of fluorinated naphthalene diimides

Two new amino core-substituted naphthalene diimides (cNDIs) bearing fluorinated side chains have been synthesised. Steady-state and time-resolved fluorescence spectroscopy reveals unprecedented optical properties for the cNDIs with high quantum yields of ~0.8 and fluorescence lifetimes of ~13 ns in a range of solvents. These properties are apparent at the level of single molecules, where the compounds also show exceptional photostability under pulsed-laser excitation. Photon emission is remarkably consistent with very few long timescale (millisecond or longer) interruptions with molecules regularly undergoing >107 cycles of excitation and emission. Intermittencies owing to triplet-state formation occur on a sub-millisecond timescale with a low yield of 1-2%, indicating that the presence of the fluorine atoms does not lead to a significant triplet yield through the heavy-atom effect. These properties make the compounds excellent candidates for single-molecule labelling applications.