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Bioinspired Orientation of β-Substituents on Porphyrin Antenna Ligands Switches Ytterbium(III) NIR Emission with Thermosensitivity.
Title Bioinspired Orientation of β-Substituents on Porphyrin Antenna Ligands Switches Ytterbium(III) NIR Emission with Thermosensitivity.
Authors Ning, Y.; Ke, X.S.; Hu, J.Y.; Liu, Y.W.; Ma, F.; Sun, H.L.; Zhang, J.L.
Journal Inorg Chem
DOI 10.1021/acs.inorgchem.6b02481
Abstract

"Configurational isomerism" is an important approach found in naturally occurring chlorophylls to modulate light harvesting function without significant structural changes; however, this feature has been seldom applied in design of antenna ligands for lanthanide (Ln) sensitization. In this work, we introduced a bioinspired approach by orientation of β-dilactone moieties on porphyrinates, namely cis-/trans-porphodilactones, to modulate the energy transfer process from the lowest triplet excited state of the ligand (T1) to the emitting level of ytterbium(III) ((2)F5/2, Yb*). Interestingly, near-infrared (NIR) emission of Yb(III) could be switched "on" by the cis-porphodilactone ligand, while the trans-isomer renders Yb(III) emission "off" and the ratio of quantum yields is ∼8. Analysis of the structure-photophysical properties relationship suggests that the significant emission difference is correlated to the energy gaps between T1 and Yb* (1152 cm(-1) in the cis- vs -25 cm(-1) in the trans-isomer). More interestingly, due to back energy transfer (BEnT), the Yb(III) complex of cis-porphodilactone exhibits NIR emission with high thermosensitivity (4.0%°C(-1) in solution and 4.9%°C(-1) in solid state), comparable to previously reported terbium (Tb) and europium (Eu) visible emitters, in contrast to the trivial emission changes of the trans-isomer and porphyrin and porpholactone analogues. This work opens up new access to design NIR emissive Ln complexes by bioinspired modification of antenna ligands.