Role of the Weak Interactions during the 2,4,6-Trinitrophenol Detecting Process of a Fluorescein-Based Sensor

Achieving fast and precise fluorescence sensing of 2,4,6-trinitrophenol (TNP) is of fundamental importance for homeland security and environment protection. Weak interactions between the sensor and an analyte always play a critical role, which is capable of affecting the photophysics of the sensor. This study performs a thorough investigation on the effects of the weak interaction between TNP and a typical fluorescein-based sensor. The photophysics of the sensor before and after interacting with TNP is fully discussed by analyzing the potential energy surface (PES) of the sensor and rate constants of the excited-state dynamic processes. TNP is found to affect the PES greatly, which plants an intermolecular electron transfer state (dark state) below the bright state. The π-π interaction is proved to induce considerable orbital overlaps between the analyte and the sensor, which facilitates the electron transfer process and generates the dark state.