Exploring the luminescence properties and sensing mechanism of a turn-on TADF probe for sulfite.

Fluorescent probes with a microsecond lifetime have attracted much attention in biological detection. The luminescence properties and responsive mechanisms of a probe [DCF-MPYM-lev-H]- for detecting sulfite and its corresponding product [DCF-MPYM-2H]2- are studied based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations as well as the thermal vibration correlation function method. It is found that the luminescence efficiency of the probe increases obviously after reacting with sulfite, which is induced by increased radiative decay rates and decreased nonradiative rates. In addition, the thermally activated delayed fluorescence (TADF) properties of products are confirmed by analyzing the spin-orbital constants and energy gaps between the singlet excited states and the triplet excited states. The calculation results favor the understanding of the luminescence properties and responsive mechanism of a turn-on TADF probe for sulfite, which may provide a theoretical reference for the development of new TADF probes.