Single-center LnIII ratiometric luminescent temperature probes based on singlet → singlet and singlet → triplet sensitizations

Abstract

Luminescence thermometry based on Ln^III systems has become a hotspot in nanotechnology, biotechnology, and integrated optics, whereas the self-calibrated two-band intensity ratiometric method excels in this. Herein, propyldiphenylphosphine oxide (pdppo)-functionalized polydimethylsiloxane (PDMS) was reacted with [Ln(X-bza)₃(H₂O)₂] complexes (Ln = Eu, Tb, or Yb, X-bza = 3,5-dichlorobenzoate or 3,5-dibromo benzoate) leading to chemically bound [Ln(X-bza)₃(pdppo)₂]-PDMS membranes. The systems were used as luminescent temperature probes by exploiting a new strategy based on two different thermally dependent excitation channels arising from spin-allowed singlet → singlet or spin forbidden singlet → triplet transitions. To define the thermometric parameter, the intensity ratio of the Ln^III emission spectra measured upon singlet → singlet or singlet → triplet excitation was considered, which enables achieving ratiometric single-centered Eu^III or Tb^III or Yb^III-based luminescent temperature probes within 50–320 K. The maximum thermal sensitivity lies within 0.5–1.6% K⁻¹ whereas the largest value was accomplished for [Yb(3,5-bbza)₃(pdppo)₂]-PDMS (1.6% K⁻¹ at 120 K), which is among the best value reported for NIR-emitting single-center Ln^III luminescent temperature probes.