Theoretical Investigations on the Detecting Mechanism of a Typical 2,4,6-Trinitrophenol Fluorescence Sensor and Its Design Strategy.

Fluorescence sensors based on small organic molecules are drawing increasing attention. In this contribution, the underlying detection mechanism of a typical fluorescence sensor for 2,4,6-trinitrophenol (TNP) based on fluorescence quenching is comprehensively investigated. The TNP molecule is proved to plant an intermolecular electron transfer state (dark state) below the bright state. Strong π-π interaction is observed between the sensor and TNP, which provides considerable orbital overlaps between the sensor and analyte. Electron transfer from the sensor to analyte is facilitated by such a strong interaction, which quenches the sensor's fluorescence. The design strategy for such TNP sensors is proposed based on the detection mechanism, and a series of new sensors is designed, which is likely to have better sensitivity than the original sensor.