V. P. Kazakov

Luminescence of praseodymium (III) chelates from two excited states (3P0 and 1D2) and its dependence on ligand triplet state energy

The praseodymium (III) b-diketonate and carboxylate chelates emit visible and infrared luminescence in organic solutions at room temperature. Depending on the position of triplet level of the ligand the ff-emission of Pr 3+ was observed either from two excited states ( 3 P0 and 1 D2) at 490, 605, 610, 645, 890 and 1060 nm or from the 1 D2 state only at 605, 890 and 1060 nm. For all chelates studied, the emission has low quantum yield, e.g. 50.2% for 1 D2

Chemiluminescence of praseodymium (III), neodymium (III) and ytterbium (III) β-diketonates in solution excited from 1,2-dioxetane decomposition and singlet–singlet energy transfer from ketone to rare-earth β-diketonates

Abstract This work is concerned with the chemiluminescence (CL) of Nd3+, Yb3+ and Pr3+ β-diketonates in solution. Chemiluminescent reaction of adamantylideneadamantane-1,2-dioxetane (AAD) decomposition generating singlet ( Ad=O S ∗ ) and triplet ( Ad=O T ∗ ) excited adamantanone was used as a source of excited species. AAD chemiluminescence due to emission from Ad=O S ∗ is quenched by Ln3+ β-diketonates: (a) by intermolecular singlet-singlet (S-S) energy transfer from Ad=O S ∗ to β-diketonate ligand levels of Ln(TTA)3·2H2O and Ln(BTFA)3·2H2O; (b) by complex formation between AAD and Pr(FOD)3 or Pr(DPM)3. Corresponding Stern–Volmer quenching constants or stability constants of the complex were measured. Chemiluminescence spectra of Ln3+ β-diketonates were recorded and relative luminescence quantum yields compared. Yb3+ chelates show higher luminescence yields compared to Nd3+, due to a different efficiency of non-radiative energy degradation. Chemiexcitation of Ln3+ ions in the systems studied occurs by: (a) intermolecular singlet–singlet energy transfer: Ad=O S ∗ → L S ∗ → L T ∗ → Ln 3+∗ (where L S ∗ and L T ∗ are the first singlet and triplet excited states of the β-diketonate ligand); (b) intermolecular triplet–triplet energy transfer: Ad=O T ∗ → L T ∗ → Ln 3+∗ ; (c) intracomplex energy transfer from the decomposition of AAD in the complex with Ln3+ β-diketonate. Efficiency of chemiexcitation pathways is different for each Ln3+ β-diketonate and Ln3+ ion.

Mono-thio-β-diketones – a new type of ligands suitable for sensitization of lanthanide luminescence. Infrared luminescence of an intensely colored neodymium and ytterbium mono-thio-β-diketonate chelates

Intensely colored and air/moisture stable mono-thio-β-diketonates of trivalent neodymium and ytterbium show senzitized infrared emission of lanthanide ion when excited with UV and visible light.

Water enhances quantum yield and lifetime of luminescence of europium(III) tris-β-diketonates in concentrated toluene and acetonitrile solutions

Europium tris-b-diketonates (Eu(L)3 � nH2O) show concentration quenching of luminescence in toluene solutions due to the formation of weakly luminescent dimers. Addition of water to the concentrated toluene solutions of Eu(L)3 � nH2O unexpectedly enhances quantum yield ðfÞ and lifetime of Eu 3+ luminescence by causing dissociation of dimers and by reducing quenching of excited Eu 3+ through the ligand-to-metal charge transfer (LMCT). Water also enhances f of Eu(L)3 � nH2O in acetonitrile (although to a lower extent than in toluene) only by reducing LMCT quenching of Eu 3+ . # 2001 Elsevier Science B.V. All rights reserved.

Singlet–singlet energy transfer from ketone to lanthanide ion β-diketonates as studied by chemiluminescence quenching. First observation of infrared chemiluminescence of neodymium (III) and ytterbium (III) in solution

Intermolecular singlet‐singlet energy transfer from excited adamantanone formed at decomposition of adamantylideneadamantane-1,2dioxetane (AAD) to the excited levels of b-diketonate ligand in Ln(TTA)32H2O (TTA — thenoyltrifluoroacetone, Ln D Nd 3C ,Y b 3C ) complexes has been studied by quenching of AAD chemiluminescence (CL) by Ln(TTA)32H2O. Chemiexcitation of Nd 3C and Yb 3C chelates occurs both at intermolecular quenching of AAD CL and at decomposition of AADLn(TTA)3 complex followed by emission of infrared light from Nd 3C or Yb 3C excited ff-levels. The corresponding Nd 3C or Yb 3C CL spectra were recorded and they coincide with their photoluminescence spectra. The Yb(TTA)32H2O has higher photo- and chemiluminescence efficiencies as compared to Nd(TTA) 32H2O due to a larger energy gap between radiative and lower-lying levels in Yb 3C as compared to Nd 3C leading to a lower efficiency of non-radiative relaxation in Yb 3C ion. ©2000 Elsevier Science S.A. All rights reserved.

The influence of excitation of the 4f-orbital of Eu(fod)3 on complex formation with adamantanone and anomalous enhancement of Eu3+ luminescence under the action of H2O and D2O molecules in toluene

The influence of excitation of the 4f-orbital of, β-diketonate Eu(fod)3 (fod is heptafluorodimethyloctanedione) on the formation of the coordination bond with adamantanone (1) was studied by the nonradiative energy transfer technique. The kinetic parameters of fluorescence (FL) and the lifetime (τ) of the Eu3+ ion in toluene solutions were studied. The increase in the stability of the Eu(fod)3·1 complex when f—f-transitions of the Eu3+ ion are excited is related to an increase in the acceptor capability of Eu(fod)3 due to the increasing fraction of the covalent component determined by the participation of 4f-orbitals. An unexpected effect of enhancement of the Eu(fod)3 fluorescence under the action of H2O (D2O) molecules in toluene solutions was observed. The effect is assumed to be caused by an increase in the negative inductive effect when outer-sphere associates with the fluorinated radical of β-diketonate are formed. The mechanisms of the influence of electron-donating inner-sphere ligands and outer-sphere associates on the quantum yield of fluorescence of Eu(fod)3 are discussed.

Photoinduced electron transfer from higher excited singlet states of tryprophan: 1. Effects of the excitation wavelength, pH, and temperature on quenching of Tryptophan fluorescence by europium(III) ions

Effects of the excitation energy, temperature, and pH on the quantum yield and the Stern-Volmer quenching constant for tryptophan fluorescence quenching by europium(III) chloride were studied. Competition between intracomplex reversible photoinduced electron transfer from tryptophan to Eu(III) ions and the processes of internal conversion and vibrational relaxation of higher excited singlet states Sn(n > 1) of tryptophan was revealed.

Fluorescence of the diterpenoid alkaloids lappaconitine andN-deacetyllappaconitine in acetonitrile

The absorption, excitation, and fluorescence spectra of the diterpenoid alkaloids, lappaconitine andN-deacetyllappaconitine, in acetonitrile were studied. On the basis of the coincidence of the spectra with the analogous spectra of model compounds, methyl esters of anthranilic andN-acetylanthranilic acids, the conclusion was drawn that the—OOC(Ph)NRH groups are fluorochromes in the alkaloids studied. The high quantum yield of fluorescence and the bathofluoric shift in the luminescence and absorption spectra ofN-deacetyllappaconitine were explained by an increase in the electron-releasing ability of the —NRH group in the deacetylation of lappaconitine.

Photocatalytic decomposition of dispiro(diadamantane-1,2-dioxetane) initiated by Ce(CIO4)3 in the excited state

Photocatalytic decomposition of dispiro(diadamantane-1,2-dioxetane) (1) to adamantanone (2) initiated by Ce(ClO4)3 in the excited state in the MeCN−CHCl3 (2∶1) mixture was studied. The bimolecular rate constants of quenchingkq were determined from the kinetics of quenching of Ce3+* by dioxetane at different temperatures. The Arrhenius parameters of the quenching were calculated from the temperature dependence ofkq:Ea=3.2±0.3 kcal mol−1 and logA=11.6±6. The quantum yields of photolysis of 1 depending on its concentration and the rate constant of the chemical reaction of Ce3+* with 1 were determined. The latter coincides withkq:kch=(2.6±0.3)·109 L mol−1 s−1 (T=298 K). The fact that the maximum quantum yield of decomposition of dioxetane is equal to 1 indicates the absence of physical quenching of Ce3+* with 1. Nonradiative deactivation of Ce3+* in solutions of MeCN and in MeCN−CHCl3 mixtures was studied. It is caused by the replacement of H2O molecules in the nearest coordination surroundings of Ce3+ by solvent molecules and reversible transfer of an electron to the ligand. The activation parameters of the nonradiative deactivation of Ce+* were determined.

The Influence of 4f Orbital Excitation in Eu(Fod)3 on Complexation with Sulfones in Benzene Solutions

Complexation of sulfones (S) with the β-diketonate Eu(Fod)3 (Fod–heptafluorodimethyloctanedione) in the ground and excited electronic states in benzene solutions was studied. The stability constants and thermodynamic parameters for the formation of complexes Eu(Fod)3 · S in the ground state (K, ΔH0, ΔS0) and Eu(Fod)3* · S in the excited state (K*, ΔH0*, ΔS0*) were determined. The excitation of f–f transitions of Eu(III) was found to enhance the stability of Eu(Fod)3 · S complexes, apparently due to an increase in the acceptor ability of the Eu(III) chelate. This fact confirms the involvement of the 4f orbital in the chemical bond formation. The compensation effect was observed for the thermodynamic parameters: ΔS0 = (2.9 ± 0.3) × 10–3ΔH0 + (35.0 ± 4.0) in the ground and ΔS0* = (3.3 ± 0.3) × 10–3ΔH0* + (49.0 ± 5.0) in the excited states of Eu(Fod)3. It was shown that electronic excitation of the 4f orbital of Eu(Fod)3 influences isotopic effects in complexation with sulfolanes.