Ion-mediated single-molecular optical switching and sensing based on the fluorophore-tethered calix[4]pyrrole.

The design and synthesis of the first asymmetrically "two-walled"meso-substituted calix[4]pyrrole tethered by a fluorophore and its subsequent implication as an archetype sequential 'on-off-on-off' fluorescent single-molecular switch are reported. The current system permits us to extend the sensitivity up to sub-nanomolar levels with the detection limit as low as 0.4 nM.