Knowledge Bank

“It is known that the phosphorescence lifetime of the halonaphthalenes decreases as the atomic number of the halogen atom $increases1$. This was $attributed1$ to an increase in the spin orbit perturbation (which gives rise to the observed emission). The purpose of this work is to examine the exact mechanism by which the halogen enhances the spin orbit perturbation in these molecules. A comparison of the polarization results of the phosphorescence of naphthalene $\alpha$-halonaphthalenes and $\beta$-halonaphthalenes clearly shows that the halogen does not merely enhance the perturbation which is already present in the parent hydrocarbon, but rather introduces new strong perturbing states of its own. Possible spin-orbit vibronic schemes which explain the observed results will be discussed together with results on other related systems.”