title: Magnetic Field Effects on Triplet-Triplet Annihilation in Solutions: Modulation of Visible/NIR Luminescence.
abstract: Photon upconversion based on sensitized triplet-triplet annihilation (TTA) presents interest for such areas as photovoltaics and imaging. Usually energy upconversion is observed asp-type delayed fluorescence from molecules whose triplet states are populatedviaenergy transfer from a suitable triplet donor, followed by TTA. Magnetic field effects (MFE) on delayed fluorescence in molecular crystals are well known; however, there exist only a few examples of MFE 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 annihilator, we also observed NIR emission from the sensitizer, occurring as a result of triplet-triplet energy transfer back from annihilator, termed "delayed phosphorescence". This emission also exhibits MFE, but opposite in sign to the annihilator fluorescence.
authors.affiliation: Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Tomoyasu
authors.initials: T
authors.lastname: Mani
authors.forename: Sergei A
authors.initials: SA
authors.lastname: Vinogradov
keywords: Delayed Phosphorescence; Magnetic Field Effects; Porphyrin; Spin Dynamics; Tetrabenzoporphyrin; Triplet-Triplet Annihilation; p-type Delayed Fluorescence