Magnetic Field Effects on Triplet-Triplet Annihilation in Solutions: Modulation of Visible/NIR Luminescence

Photon upconversion based sensitized triplet-triplet annihilation (TTA) presents interest for such areas as photovoltaics and imaging. Usually, energy upconversion is observed as p-type delayed fluorescence from molecules whose triplet states are populated via energy transfer from a suitable triplet donor, followed by TTA. Magnetic field effects (MFEs) on delayed fluorescence in molecular crystals are well-known; however, there exist only a few examples of MFEs on TTA in solutions, and all of them are limited to UV-emitting materials. Here, we present MFE on TTA-mediated visible and near-infrared (NIR) emission, sensitized by far-red-absorbing metalloporphyrins in solutions at room temperature. In addition to visible delayed fluorescence from the annihilator, we also observed NIR emission from the sensitizer, occurring as a result of triplet-triplet energy transfer back from the annihilator, termed delayed phosphorescence. This emission also exhibits MFEs, but opposite in sign to the annihilator fluorescence.