Photon Upconversion from Near-Infrared to Blue Light with TIPS-Anthracene as an Efficient Triplet–Triplet Annihilator

Photon upconversion (PUC) via triplet–triplet annihilation (TTA) from near-infrared (NIR) to blue photons could have important applications especially to bioimaging and drug delivery accompanied by photochemical reaction. The fundamental challenges in achieving this has been the large anti-Stokes shift combined with the need to efficiently sensitize within the biological transparency window (700–900 nm). This calls for materials combinations with minimal energy losses during sensitization and minimal energy requirements to drive efficient TTA. Here, we demonstrate efficient PUC converting from NIR energy to blue photons using the commercially available material 9,10-bis[((triisopropyl)silyl)ethynyl]anthracene (TIPS-Ac) as the annihilator. With a conventional triplet sensitizing system, TIPS-Ac performed TTA with an efficiency of 77 ± 3% despite a relatively small driving force, compared to conventional TTA material converting from NIR to blue, for the TTA of less than 0.32 eV. Combined with Pt(II) meso-tetraphenyltetrabenzoporphine (PtTPBP), which is a heavy atom triplet sensitizer that directly generates triplets upon NIR photon excitation, the resulting system allowed for an anti-Stokes shift of 1.03 eV. Our results highlight the use of direct triplet generation via NIR excitation as a useful path to achieving large anti-Stokes shift and also show that high TTA efficiencies can be achieved even in the absence of large driving energies for the TTA process.The authors thank the Winton Programme for the Physics of Sustainability and the Engineering and Physical Sciences Research Council for funding. V.G. acknowledges funding from the Swedish Research Council, Vetenskapsrådet 2018-00238. A.P. acknowledges the financial support from the Marie Curie Fellowship (MILORD project, No. 748042). D.B. is an FNRS Research Director