Circularly polarized luminescence from racemic lanthanide(III) complexes with achiral ligands in aqueous solution using circularly polarized excitation

Abstract

Inorg. Chem. 1986, support the electron-transfer scheme shown in Figure 5. In the presence of 0.1 M C1-, the first reduction involves (P)InCl and [(P)InCl]-while the second reduction involves both [(P)InCl]-and (P)In(py)z, which is formed after C1-dissociation. This is illustrated by the voltammogram at 0.1 V/s. At 15 V/s, dissociation of CI-does not occur during the time scale of the measurement and only the top set of electrode reactions in Figure 5 take place. At all other scan rates, intermediate behavior is observed, and between two and four oxidation peaks are obtained depending upon scan rate.In conclusion, the electrochemical studies are consistent with the ligand-addition reactions reported earlier for the (P)InX system.l0 The formation of a mono-and bis(N-methylimidazole) adduct is observed by electrochemistry for all of the neutral compounds but the formation of bis(pyridine) adducts is observed only for the S03R-derivatives. The electrochemistry also provides information on nitrogenous base addition to the species formed 25, 26 17-2622 2617 after reduction by one or two electrons. In the presence of pyridine or N-MeIm the formation of [(P)InX(L)]-or (P)In(L)z is observed after reduction by one electron. The exact species formed is dependent upon both the nature of the axial ligand and the ligand concentration. However, after the addition of a second electron to [(P)InX(L)]-or (P)In(L)z, a pentacoordinated indium porphyrin dianion is always formed. Acknowledgment. The support of the National Science Foundation (Grant CHE-82 15507) is gratefully acknowledged. Registry No. N-MeIm, 616-47-7; (TPP)InS03Ph, 70619-92-0; (TP-P)InS03CH3, 70619-88-4; (TPP)InCI, 63128-70-1; (TPP)InOAc, 96150-61-7; (OEP)InSO,Ph, 70619-98-6; (OEP)InS03CH3, 70619-94-2;(OEP)InCI, 32125-07-8; (OEP)InOAC, 961 50-60-6; (TPP)InS03Ph(NThe circularly polarized luminescence (CPL) and total luminescence (TL) spectra are reported for aqueous solutions of tris complexes of Tb(III), Eu(III), Sm(III), and Dy(II1) with 2,6-pyridinedicarboxylic acid in basic media. The optical activity is generated from these racemic solutions by using as the excitation source circularly polarized Ar ion laser lines. No CPL was observed from similarly prepared solutions of Tb(III), Eu(III), and Sm(1II) with oxydiacetic acid. CPL was measured for the aqueous complex of Dy(II1) with oxydiacetic acid. These results are interpreted in terms of the kinetic stability of the complexes formed, and comparisons are made with other optical and with NMR measurements.

On the determination of empirical absolute chiral structure: Chiroptical spectrum correlations for D3 lanthanide (III) complexes

“…For this purpose, solutions of Eu(ODA) 3 3À are not suitable, since the complex has been shown to racemize on the lifetime of the Eu(III) excited staten which is approximately 1 msec. 15 On the other hand, complexes of Eu(DPA) 3 3À seem to be an excellent candidate for this particular application, since they do not racemize appreciably at room temperature, 23 and the racemic equilibrium is affected by adding various chiral agents. 6 However, as indicated above, this complex crystallizes as a racemic mixture and, therefore, no assignments of the sign of the CPL or CD to enantiomeric structures from resolved crystals are possible.…”

“…[12][13][14] In aqueous solutions the complexes are stable on the emission lifetime of the luminescent Eu(III) and Tb(III) ions and, therefore, although they exist as racemic mixtures, one can prepare chiral excited state distributions through circularly polarized laser excitation and as a result detect circularly polarized luminescence (CPL) from a solution that is racemic in the ground state. 15,16 These complexes are also of interest in studies aimed at exploiting the chiral discriminatory interactions between added chiral adducts to the aqueous solutions containing the racemic complex as a method of determining absolute configuration. A rational approach to this possible application requires knowledge of which enantiomer is preferred when the chiral substance is added so that the particular chiral discriminatory interactions (coulombic, hydrogen bonding, steric, etc.)…”

Absolute Chiral Structures of Inorganic Compounds

“…CPL from these systems may be observed if the equilibrium between the enantiomers is perturbed either by the addition of a Pfeiffer agent as described above, or in some instances, by photo-preparing a nonracemic excited-state distribution of complexes by circularly polarized excitation. 155 In Figure 5.33, we show the CPL spectrum of Tb(III) with the tetraphosphinate complex shown following circularly polarized laser excitation. 155 This experiment is successful because the racemization process is slow relative to the emission lifetime of Tb(III) ($2 ms).…”

“…155 In Figure 5.33, we show the CPL spectrum of Tb(III) with the tetraphosphinate complex shown following circularly polarized laser excitation. 155 This experiment is successful because the racemization process is slow relative to the emission lifetime of Tb(III) ($2 ms).…”

Emission detected circular dichroism from long‐lived excited states: Application to chiral Eu(III) systems

“…11 This complex is known to form chiral racemic D 3 complexes in aqueous solution which can be made nonracemic through the addition of chiral noncoordinating environment compounds. [12][13][14][15] The perturbed racemic mixture used for the new measurements reported here has been chosen only because it is well characterized, and CPL and conventional CD results have previously been published. We also report the EDCD spectrum of the chiral tris complex of Eu(III) with (R,R)-N,N 0 -bis(1-phenylethyl)-2,6-pyridinedicarboxamide.…”