SternVolmer

The Stern–Volmer relation describes the quenching of fluorescence (or phosphorescence) by a quencher in solution. It relates the intensity or lifetime of emitted light in the absence of quencher (F0, τ0) to that observed at a quencher concentration [Q] (F, τ). The simplest form for steady-state fluorescence is F0/F = 1 + KSV [Q], where KSV is the Stern–Volmer quenching constant.

Dynamic (collisional) quenching contributes to KSV via KSV = Kq τ0, with Kq the bimolecular quenching rate constant. In this case, F0/F = τ0/τ = 1 + Kq τ0 [Q], and the excited-state lifetime τ decreases as [Q] increases. Static quenching involves formation of a nonfluorescent ground-state complex, yielding F0/F = 1 + Ka [Q], where Ka is the association constant; here the emissive-state lifetime can remain unchanged.

When both static and dynamic processes occur, the overall relation is F0/F = 1 + (Kq τ0 + Ka) [Q], and this total constant is often denoted KSV. A plot of F0/F versus [Q] (the Stern–Volmer plot) is linear for a single quenching mechanism; deviations from linearity can indicate a combination of mechanisms, sphere-of-action effects, or complex formation.

Applications of the Stern–Volmer equation include studying quenching mechanisms, determining quencher efficiency, and facilitating sensor and assay design in chemistry, biochemistry, and materials science. Temperature, viscosity, and solvent effects influence KSV and Kq, reflecting changes in diffusion and interaction dynamics of the system.