Yb to Tb Cooperative Upconversion in Supramolecularly Assembled Complexes in a Solution

Abstract

The podand-type ligand L, based on a tertiary amine substituted by three pyridyl-6-phosphonic acid functions, forms hydrated complexes with Ln3+ cations. The luminescence properties of the YbL complex were studied in D2O as a function of the pD and temperature. In basic conditions, increases in the luminescence quantum yield and the excited state lifetime of the Yb centered emission associated with the 2F5/2 → 2F7/2 transition were observed and attributed to a change in the hydration number from two water molecules in the first coordination sphere of Yb at acidic pH to a single one in basic conditions. Upon the addition of TbCl3 salts to a solution containing the YbL complex in D2O, heteropolynuclear Yb/Tb species formed, and excitation of the Yb at 980 nm resulted in the observation of the typical visible emission of Tb as a result of a cooperative upconversion (UC) photosensitization process. The UC was further evidenced by the quadratic dependence of the UC emission as a function of the laser power density.

Upconverting photons at the molecular scale with lanthanide complexes

“…0.2% for YbL D ). These results are encouraging for future iterations 73 but clearly one prospective challenge is enabling high stability of all metal ions – not just the sensitizers. We envisage supramolecular multitopic ligands to satisfy this criterion.…”

“…Fig.9CP with d-f systems: (a) solid-state crystals of Cr III /Yb III 73. (b) supramolecularly assembled metastable RuYb 3 76.…”

Upconversion in a d–f [RuYb3] Supramolecular Assembly

“…Efficiently piling up photons in molecular or supramolecular assemblies to generate upconversion (UC) − in solution, particularly in water, is still a challenge of modern chemistry. Since the pioneering work of Piguet and co-workers in 2011, only few examples have been reported, − but this burgeoning field sees each new iteration as a step forward toward better molecular UC devices. Except for the rare case of molecular UC based on triplet–triplet annihilation (TTA) with organic dyes, all examples rely on successive ascendances of the energy ladder using long-lived d–d or f–f electronic transitions, sometimes using indirect excitation by an organic near-infrared (NIR) absorbing dye. , This is typically the case for the Cr to Er energy transfer in hetero-trinuclear [Cr 2 ErL 3 ] helicates, for solution-state Yb to Tb , and Yb to Er − UC within hetero-polynuclear assemblies, or for Yb to Cr in solid mixtures .…”

Solution‐State Cooperative Luminescence Upconversion in Molecular Ytterbium Dimers

“…[8,9] In the subsequent years this has been expanded to encompass a range of discrete upconverting systems, operating by excited state absorption (ESA), [10][11][12] energy transfer UC, or cooperative sensitizaton (CS). [15][16][17][18] At the molecular scale, much attention must be paid to minimize quenching due to the increased prevalence of nonradiative de-excitation processes from molecules in solution, primarily through OH, NH, and CH oscillators in the first or second coordination sphere. [20][21][22] This is achieved by using sterically encumbering ligand systems, [23] deuteration of the ligand scaffold, [16] or using perdeuterated solvents.…”