Most photochemical reactions obey Kasha's rule, i.e., they take place from the lowest excited state of a given multiplicity. This implies that the excess of energy after light excitation is lost in the course of relaxation to the lowest excited state. Therefore, molecules that are able to use higher excited states for anti-Kasha photochemistry can lead to more efficient light-energy conversions, for instance in the context of photocatalysis. Finding those anti-Kasha molecular systems is usually accomplished in an experimental trial-and-error manner. Instead, computational tools capable to understand and predict these anti-Kasha properties would give the opportunity for the in silico design of more efficient anti-Kasha molecular systems. This work is one step in that direction. Specifically we demonstrate that quantitative predictions of anti-Kasha photoluminescence properties can be derived exclusively from electronic structure calculations, excited state decay rate theories and excited state kinetic modelling. More in detail, the different (non-) radiative rates between all relevant states were evaluated with the thermal vibration correlation function formalism. Our protocol is validated for a series of azulene derivatives, for which we have correctly predicted the exclusive emission from the second excited singlet state. We foresee that the herein developed computational protocol can be used to pre-screen dyes with the desired anomalous photoluminescence properties and eventually design tailored photocatalysts.
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