Chapter 11, Problem 11.11P

Interpretation Introduction

Interpretation:

The value of quenching rate constant $k_Q$ has to be determined.

Concept introduction:

Quenching: The reduction in fluorescence intensity due to a number of processes.

These processes can occur during the excited state life time (example: collsional quenching, energy transfer, charge transfer reactions) or they may occur due to formation of complexes in the ground state.

Using Stern-Volmer relation the quenching rate constant $k_Q$ can be calculated.

$\frac{F_0}{F}=1+k_q\tau \boxed{\begin{array}{l}\text{where,}\\ {\text{F}}_{\text{0}}\text{:}\text{Fluorescence}\text{intencity}\text{in}\text{absence}\text{of}\text{quenches}\\ \text{F}\text{:Fluorescence}\text{intencity}\text{in}\text{presence}\text{of}\text{quenches}\\ {\text{k}}_{\text{q}}\text{:}\text{Quenching}\text{rate}\text{constant}\\ \text{τ}\text{:}\text{Fluorescene}\text{time}\text{in}\text{absence}\text{of}\text{quenches}\end{array}}$

In fluorescence, the radiation that is emitted spontaneously ceases as soon as the (within nanoseconds) the exciting radiation gets extinguished.

In phosphorescence, an intersystem crossing to a triplet state takes place and hence the radiation that is emitted spontaneously will persist for more time.