Terbium(III) Luminescent Complexes as Millisecond-Scale Viscosity Probes for Lifetime Imaging

Abstract

Fluorescent probes that are able to directly measure viscosity are attractive candidates for the study of intracellular environments. We report a new class of luminescent rotors, based on the sensitized emission of a terbium(III) complex. A 4-fold increase in both quantum yield and luminescence lifetime was observed in viscous media for the studied complexes, with a lifetime ranging from 0.23 to 0.89 ms over a broad range of viscosities (0.6-1200 cP). The presented approach, relying on the millisecond-scale luminescence lifetime of the lanthanide ions, was applied to fixed T24 cancer cells using temporal sampling lifetime imaging microscopy.

Fluorescent Molecular Rotors for Viscosity Sensors

“…To this end, ratiometric molecular rotors have been developed that exhibit dual emission of viscosity sensitive( probe) and insensitive (reference) FL signals. [7,18,67,68] Ratiometric analysiso ft he viscosity-dependent probe signal with respect to the internal reference provides normalized data accounting for probe concentration.…”

“…Recently,F MRs based on the sensitized emission of at erbium(III) complex (Figure20b)w as reported. [67] Lanthanide ions with f-f transitions exhibit sharp,n arrow bands of luminescence which has very weak intensity but extremelyl ong lifetimes in the millisecond range. These emissionb ands can be distinguishedf rom all spectrally broad and short-lived emissions in the intracellular environment such as endogenousa utofluorescence and other molecular fluorescencef rom most exogenous dyes.…”

Triplet‐State Position and Crystal‐Field Tuning in Opto‐Magnetic Lanthanide Complexes: Two Sides of the Same Coin

“…Amongst the lanthanide ions, terbium (in its trivalent form,T b 3 + )i se specially appealing because of the possibility to harness its properties both from a magnetic and opticals tandpoint. Countlesse xamples of Tb 3 + -based single-molecule magnets (SMMs) [20][21][22][23][24] as well as luminescent complexes of the same ion [12,15,25,26] have been reported. These luminescent species have been appliede xtensively as probesi na ssays [25,27,28] and for lighting purposes.…”

“…Countlesse xamples of Tb 3 + -based single-molecule magnets (SMMs) [20][21][22][23][24] as well as luminescent complexes of the same ion [12,15,25,26] have been reported. These luminescent species have been appliede xtensively as probesi na ssays [25,27,28] and for lighting purposes. [29][30][31] More recently,t heir application as luminescent thermometers is being widely explored [32][33][34] with outstanding results in terms of thermalr eadout performance.…”

Solvent polarity and oxygen sensitivity, rather than viscosity, determine lifetimes of biaryl-sensitised terbium luminescence

“…Such properties are not unusual per se, 5,6 but in this case they help to rationalise the properties of related systems that have been promulgated very recently as millisecond viscosity probes. 7,8 Indeed, it is suggested that such probes are best considered as being sensitive primarily to dissolved oxygen in the medium, and are therefore not viscosity probes at all. The solvatochromism of the biaryl complexes of Eu 3+ and Tb 3+ has been examined in six solvents of varying viscosity, under both aerated and degassed conditions.…”