Bioinspired Orientation of β-Substituents on Porphyrin Antenna Ligands Switches Ytterbium(III) NIR Emission with Thermosensitivity

Inorg Chem. 2017 Feb 20;56(4):1897-1905. doi: 10.1021/acs.inorgchem.6b02481. Epub 2017 Feb 1.

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) (2F5/2, 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.

MeSH terms

  • Coordination Complexes / chemical synthesis
  • Coordination Complexes / chemistry*
  • Infrared Rays
  • Ligands
  • Molecular Structure
  • Porphyrins / chemistry*
  • Temperature*
  • Ytterbium / chemistry*

Substances

  • Coordination Complexes
  • Ligands
  • Porphyrins
  • Ytterbium