Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

12.2 Fluorescence quenching (Stern-Volmer equation) 242
12.2 Fluorescence quenching (Stern-Volmer equation)
I
Kinetic model:
A + → A ∗ 1
A ∗ → A +
A ∗ +Q → A + Q
(12.2)
If any other radiationless processes can be neglected, we find
[A ∗ ]
= 1 [A]
+ [Q]
(12.3)
I Fluorescence intensity I 0 in the absence of the quencher Q:
0 ∝ [A ∗ ]
= 1 [A] (12.4)
I Fluorescence intensity I in the presence of the quencher Q:
∝ [A ∗ ]
=
1 [A]
+ [Q]
(12.5)
I
Stern-Volmer equation:
y
0
= 1 [A]
1 [A]
+ [Q]
= + [Q]
=1+ [Q] (12.6)
0
=1+ 0 [Q] (12.7)
0 =( ) −1 is the radiative lifetime.
I Conclusion: Aplotof 0 vs. [Q] should give a straight line with intercept 1 and
slope 0 [Q].