A Jablonski diagram, named after the Polish physicist Aleksander Jab?o?ski, is a diagram that illustrates the electronic states of a molecule and the transitions between them. The states are arranged vertically by energy and grouped horizontally by spin multiplicity. Radiative transitions are indicated by straight arrows and nonradiative transitions by squiggly arrows. The vibrational ground states of each electronic state are indicated with thick lines, the higher vibrational states with thinner lines.
Radiative transitions involve the absorption, if the transition occurs to a higher energy level, or the emission, in the reverse case, of a photon. Nonradiative transitions arise through several different mechanisms, all differently labelled in the diagram. Relaxation of the excited state to its lowest vibrational level is labelled vr in the diagram. This process involves the dissipation of energy from the molecule to its surroundings, and thus it cannot occur for isolated molecules. A second type of nonradiative transition is internal conversion (ic), which occurs when a vibrational state of an electronically excited state can couple to a vibrational state of a lower electronic state. A third type is intersystem crossing (isc); this is a transition to a state with a different spin multiplicity. In molecules with large spin-orbit coupling, intersystem crossing is much more important than in molecules that exhibit only small spin-orbit coupling. This type of nonradiative transition can give rise to phosphorescence.
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