2.4. Quenching Behavior Modeling

Quenching has a variety of mechanisms, usually including dynamic quenching and static quenching. When a collision between the fluorescent substances and quencher occurs, dynamic quenching would occur. Different from the dynamic quenching, the fluorophore forms a ground-state non-fluorescent complex with the quencher, resulting in static quenching. The two types of quenching could be well discriminated by their varying dependence on viscosity and temperature. The Stern–Volmer equation (Equation (1)) was usually utilized to judge the type of quenching by the modeling function in Origin 2019 [35].

where F₀ and F are the fluorescence intensity of the original fluorescent substance with a quencher (phenolic acids et al.) free and with a quencher, respectively; K_q represents the quenching rate constant of the phenolic acid; τ₀ represents the lifespan of the fluorophore without quencher and the average value is about 10⁻⁸ s; K_sv represents the dynamic quenching constant; Q represents the concentration of quencher.

The Stern–Volmer equation with modification (Equation (2)) was utilized to determine the binding site number and binding affinity by the modeling function in Origin 2019.

where F₀ is the fluorescence intensity of the original fluorescent substance without a quencher, F represents the fluorescence intensity with the quencher; Q represents the concentration of quencher; K_A represents the binding affinity; n represents the number of the binding site.