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Misaiel Dominguez

Calculating rate constant of intersystem crossing from Jablonski diagram

Bilal Sayed  Follow

The lifetime of the excited state is the reciprocal of the sum of rate constants which you are trying to find:

$$\begin{align}\tau(T_1) = \frac{1}{\sum_i k_i(T_1)} &= \pu{6 \times 10^-3 s} \\\sum_i k_i(T_1) &= \frac{1}{\pu{6 \times 10^-3 s}} \\&= \pu{167 s^-1}\end{align}$$

The two lines going from the $T_1 \to S_0$ state represent intersystem crossing (ISC) and phosphorescence. Squiggly lines represent nonradiative transitions, of which ISC is one, so the quantum yield for ISC is 10%. (Straight lines represent radiative transitions, in this case phosphorescence.)

Therefore:

$$\begin{align}k_\text{ISC} &= \Phi_\text{ISC} \cdot \sum_i k_i(T_1) \\&= 0.1 \cdot \pu{167 s^-1} \\&= \pu{16.7 s^-1}\end{align}$$

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