The efficiency of organic light-emitting diodes crucially depends on triplet harvesters. These accept energy from triplet correlated electron hole pairs and convert it into light. Here, experimental evidence is given that simple aromatic carbonyls, such as thioxanthone, could serve this purpose. In these compounds, the emissive ππ* excitation may rapidly equilibrate with an upper triplet state ( nπ*). This equilibrium may persist for nanoseconds. Population of the nπ* state via energy transfer from an electron hole pair should result in fluorescence emission and thereby triplet harvesting. To demonstrate the effect, solutions of 1,4-dichlorobenzene (triplet sensitizer) and thioxanthone (harvester) were excited at 266 nm with a nanosecond laser. The emission decay reveals a 100 ns decay absent in the thioxanthone only sample. This matches predictions for an energy transfer limited by diffusion and gives clear evidence that thioxanthone can convert triplet excitations into light.

The front cover artwork is provided by the groups of Prof. Peter Gilch (HHU Düsseldorf) and Prof. Andrew Monkman (Durham University). The image shows a chimera illuminated by the fluorescence emission of thioxanthone, the aromatic carbonyl studied here. Due to singlet and triplet excitations in close energetic vicinity, its photophysics exhibits a chimeric behavior. This behavior renders the class of molecules interesting as emitters in OLEDs. Read the full text of the article at 10.1002/cphc.201700683.

The Front Cover picture shows a chimera illuminated by the fluorescence emission of thioxanthone, the aromatic carbonyl studied here. Due to singlet and triplet excitations in close energetic vicinity, its photophysics exhibits a chimeric behavior. More information can be found in the Communication by P. Gilch and co‐workers on page 2314 in Issue 17, 2017 (DOI: 10.1002/cphc.201700683).