Twisted intramolecular charge transfer: A time-dependent density functional theory study on the sensing mechanism of a Schiff base sensor for fluoride

•The sensing mechanism of a Schiff-base sensor has been theoretically confirmed.•Calculated excitation energies are in good agreements with reported spectra.•The TICT process could explain the weak fluorescence of the sensor.•S0 and S1 geometrical change are analyzed for the sensor and its anion.