Lutetium(III) porphyrinoids as effective triplet photosensitizers for photon upconversion based on triplet-triplet annihilation (TTA)

We described the first application of lanthanide complexes of porphyrinoids, exemplified by lutetium (Lu), as efficient photosensitizers in photon upconversion (UC) based on triplet–triplet annihilation (TTA). Compared to the widely used d block metals, Lu(III) porphyrinoids exhibit a better sensitization ability in photon UC based on TTA (TTA-UC), which is ascribed to the extra-long triplet lifetime compared with the d block metal counterparts, using 9,10-bis(2-phenylethynyl)anthracene (BPEA) or rubrene as an acceptor. Notably, the Lu(III) complex of the porphyrin (Lu-1)/BPEA pair showed a high upconversion efficiency of 12.4% in degassed toluene. Importantly, to demonstrate the potential application of Lu porphyrinates in TTA-UC based bioimaging, we prepared nanomicelles and mesoporous silica nanoparticles with Lu-1/BPEA or Lu(III) porpholactone (Lu-2)/BPEA pairs. In living cell imaging, the capability of Lu-1 or Lu-2 as a TTA-UC sensitizer has been observed, displaying their potential application in biological studies. This work enriches the repertoire of metal sensitizers in TTA-UC with the capability of living cell imaging and, more importantly, also extends the scope of lanthanide coordination chemistry to lanthanide chemical biology related to biological optical materials and medicine.