Dynamic vertical triplet energies: Understanding and predicting triplet energy transfer

A computational approach for modeling and predicting triplet energy sensitization of organic molecules is described, which involves sampling the instantaneous, vertical energy gaps over molecular vibrational motions. This approach provides new theoretical support for the hot-band mechanism of energy transfer, in which the energy difference between donor and acceptor can be lessened by geometric distortions. We demonstrate excellent predictive performance against experimental triplet energies, with R² = 0.97 and a mean absolute error (MAE) of 1.7 kcal/mol, for a collection of 24 small organic molecules, whereas a static, adiabatic description performs significantly worse (R² = 0.51, MAE = 9.5 kcal/mol). Using this approach, it is possible to quantitatively predict the correct E/Z-isomerism of alkenes under energy transfer, for which adiabatic calculations predict the wrong outcome.