Light absorption promotes molecules to excited states. This happens whenever a plant utilizes solar energy in photosynthesis, when the retinas of eyes detect light, and also when sun light burns our skin. Such excited states also have tremendous technological relevance. To name only a few fields: Photovoltaics, light emitting diodes, photo-aging of dyes and polymers, and modern microscopy. Excited states come in at least two flavors related with the electron spin: singlet and triplet. These two flavors have grossly different properties. Excited singlet states emit light, a phenomena know as fluorescence and they are usually short-lived. Excited triplet states are “dark” and long-lived. Upon excitation the organic molecule thioxanthone in certain solvents features properties of both flavors. In a joint theoretical and experimental study by the groups of Christel Marian and Peter Gilch this chimeric behavior was deciphered. In this molecule singlet and triplet states exhibit the same energy allowing for their co-existence. The computations by Marian et al. reproduce the findings like excitation energies, rate constants, and spectral patterns with high accuracy. In the future this will allow designing molecules with such properties which are of interest - for instance - as molecular sensors.

Read more http://pubs.acs.org/doi/abs/10.1021/jp5099415 and http://pubs.acs.org/doi/abs/10.1021/jp5099393.