Lanthanide(III) Complexes of Cyclen Triacetates and Triamides Bearing Tertiary Amide-Linked Antennae

The coordination compounds of the trivalent lanthanide ions (Ln(III)) have unique photophysical properties. Ln(III) excitation is usually performed through a light-harvesting antenna. To enable Ln(III)-based emitters to reach their full potential, an understanding of how complex structure affects sensitization and quenching processes is necessary. Here, the role of the linker between the antenna and the metal binding fragment was studied. Four macrocyclic ligands carrying coumarin 2 or 4-methoxymethylcarbostyril sensitizing antennae linked to an octadentate macrocyclic ligand binding site were synthesized. Complexation with Ln(III) (Ln = La, Sm, Eu, Gd, Tb, Yb and Lu) yielded species with overall −1, 0, or +2 and +3-charge. Paramagnetic 1H NMR spectroscopy indicated subtle differences between the coumarin- and carbostyril-carrying Eu(III) and Yb(III) complexes. Cyclic voltammetry showed that the effect of the linker on the Eu(III)/Eu(II) apparent reduction potential was dependent on the electronic properties of the N-substituent. The Eu(III), Tb(III) and Sm(III) complexes were all luminescent. Coumarin-sensitized complexes were poorly emissive; photoinduced electron transfer was not a major quenching pathway in these species. These results show that seemingly similar emitters can undergo very different photophysical processes, and highlight the crucial role the linker can play.

General procedure for CV measurements in water: a solution of LiCl (0.1 M) was prepared and pH was set to ~6.5 by addition of NaOH (0.1 M) or HCl (0.1 M). This solution was added to the electrochemical cell, allowed to stir, and purged with argon for 10 min prior to each measurement. The working electrode was polished with 0.05 µm alumina on a polishing pad, washed with water and ethanol, and dried with air. The three electrodes (GC working electrode, Pt wire auxiliary electrode, and SCE reference electrode) were inserted into the cell setup and a background scan was recorded with a scan rate of 100 mV/s, and four sweeps. A lack of oxygen redox signal verified that oxygen had been removed below detectable levels.
The Eu complex (1 mM) was added in the solution, and the pH of the resulting solution was adjusted to ~6.5 (Table S1)  General procedure for CV measurements in DMF: a sample of TBAPF6 (194 mg) was dissolved in 5 mL of DMF (0.1 M) and purged with argon for 10 minutes. After detecting blank signal without oxygen redox events, the CVs were recorded as it is described in the procedure for aqueous media, with 1 mM concentration of Eu complex. At the end of each experiment a sample of Ferrocene (Fc) was added at the tip of the spatula into the electrochemical cell to adjust potentials according to Fc 0 /Fc + redox events vs SCE which was S5 then shifted according to the difference vs NHE [3]. The cyclic voltammograms of increasing scan rates are displayed in Figures S3541.

UV-Vis absorption and emission spectroscopy. All measurements were performed in
PIPES-buffered HPLC water or D2O at pH 6.5 or pD 6.5.
Quartz cells with 1 cm optical pathlengths were used for the room temperature measurements.
The absorbance spectra were measured by a Varian Cary 100 Bio UV-Visible spectrophotometer (VARIAN AUSTRALIA PTY LTD, Mulgrave, Victoria, Australia).
The emission and excitation spectra, lifetimes, time-resolved spectra and quantum yields were recorded on a Horiba FluoroMax-4P (HORIBA Jobin Yvon, Edison, New Jersey, USA).
All emissions were corrected by the wavelength sensitivity (correction function) of the spectrometer. All measurements were performed at room temperature unless stated otherwise.
Quantum yields were measured at room temperature, using quinine sulfate (QS) in H2SO4 0.05 M (Φref = 0.59) as reference [4] in Equation S1. Quantum yields were calculated according to (3), with Φs the quantum yield of the sample, Φref the quantum yield of the reference, I the integrated corrected emission intensity of the sample (s) and of the reference where the absorptions are identical). The corrected emission spectra of the sample and reference standard were then measured under the same conditions over the 330-800 nm (320-800 nm for carbostyril complexes) spectral range as well as blank samples containing only the solvent (i.e. PIPES-buffered aqueous solutions). The appropriate blanks were subtracted from S6 their respective spectra, and the antenna fluorescence and Ln (III) luminescence were   separated by fitting the section of the antenna emission overlapping the Ln(III) emission with   an exponential decay or with a scaled emission spectrum from the corresponding Gd(III) complexes. The quantum yields were then calculated according to (3 Hydration numbers (q) were obtained by measuring the lifetimes of the same quantity of complex in a PIPES buffered solution in H2O and in D2O and fitting the difference according to the model of Horrocks et al. [7], and Beeby et al [8].
The NIR emission and excitation spectra were recorded on a Horiba Jobin Yvon

Cyclic Voltammetry
In the samples of EuL1-2d Cou Eu 3+ (aq) is also detected in the cyclic voltammograms. Compound

Aqueous solutions
EuL2d Cou -634 -536 -732 196 [a] E1/2 is a half-wave potential, Epa (Epc) is anodic (cathodic) peak potential, ΔE is peaks separation. [b] Values are in mV vs. NHE. Measured in H2O (LiCl 0.1 M, pH 6.57) with a sample concentration of 1 mM at a glassy C electrode using a SCE as a reference electrode and a Pt wire counter electrode with a scan rate of 100 mV/s. Compound    Figure S29. Cyclic voltammograms at various scan rates for EuL1a Car and plot of Ipa and Ipc vs. square root of scan rate.

Equation: y = a*x + b Ipa Ipc
Slope (a) 0.86·10 5 ± 5.16·10 7 1.60·10 5 ± 6.33·10 7 Figure S30. Cyclic voltammograms at various scan rates for EuL2a Car and plot of Ipa and Ipc vs. square root of scan rate.  Figure S31. Cyclic voltammograms at various scan rates for EuL2c Car and plot of Ipa and Ipc vs. square root of scan rate.  Figure S32. Cyclic voltammograms at various scan rates for EuL1d Cou and plot of Ipa and Ipc vs. square root of scan rate.  Figure S33. Cyclic voltammograms at various scan rates for EuL2d Cou and plot of Ipa and Ipc vs. square root of scan rate.  Figure S34. Cyclic voltammograms at various scan rates for EuL2d Cou -OTf and plot of Ipa and Ipc vs. square root of scan rate.   Figure S35. Cyclic voltammograms at various scan rates for Eu(OTf)3 in DMF and plot of Ipa and Ipc vs. square root of scan rate.  Figure S36. Cyclic voltammograms at various scan rates for EuL1a Car in DMF and plot of Ipa and Ipc vs. square root of scan rate.

Equation: y = a*x + b Ipa Ipc
Slope (a) 0.80·10 5 ± 5.23·10 7 1.72·10 5 ± 3.71·10 6 Figure S37. Cyclic voltammograms at various scan rates for EuL1b Car in DMF and plot of Ipa and Ipc vs. square root of scan rate.  Figure S38. Cyclic voltammograms at various scan rates for EuL2a Car in DMF and plot of Ipa and Ipc vs. square root of scan rate.  Figure S39. Cyclic voltammograms at various scan rates for EuL2b Car in DMF and plot of Ipa and Ipc vs. square root of scan rate.  Figure S40. Cyclic voltammograms at various scan rates for EuL1d Cou in DMF and plot of Ipa and Ipc vs. square root of scan rate.  Figure S41. Cyclic voltammograms at various scan rates for EuL2d Cou in DMF and plot of Ipa and Ipc vs. square root of scan rate.           [a] In %, relative to QS (Φ = 0.59) in H2SO4 (0.05 M) [4]. [b] In %, average quantum yield from two independent measurements. [a] In %, relative to quinine sulfate (Φ = 0.59) in H2SO4 (0.05 M) [4]. [b] Fold increase relative to the solution in H2O.  [a] In %, relative to QS (Φ = 0.59) in H2SO4 (0.05 M) [4]. [b] In %, average quantum yield from two or three independent measurements.       where n is the number of nearby N-H oscillators, for Eu [8].    [SmL] = 10 µM in 10 mM aqueous PIPES buffer solutions at pH 6.5.