A. I. Voloshin

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.

Synthesis, structure and luminescence properties of new rare earth metal complexes with 1-phenyl-3-methyl-4-acylpyrazol-5-ones

The isolation and characterization of new lanthanide complexes of formula [Ln(QL)3(EtOH)(H2O)], (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb; HQL = 1-phenyl-3-methyl-4-phenylacetylpyrazol-5-one) [Ln(QL)3(H2O)2] (L = La or Lu), [Ln(QS)3(EtOH)(H2O)] (Ln = Tb or Eu; HQS = 1-phenyl-3-methyl-4-thienoylpyrazol-5-one, [Tb(QO)3(EtOH)(H2O)] (HQO = 1-phenyl-3-methyl-4-furanoylpyrazol-5-one) [Tb(QF)3(H2O)2] (HQF = 1-phenyl-3-methyl-4-trifluoroacetylpyrazol-5-one) and [NBu4][Ln(Q)4] (Ln = Eu or Tb, Q = QF or QL) is reported. The crystal structure of the tris(β-diketonate) complexes [Nd(QL)3(EtOH)(H2O)], [Dy(QL)3(EtOH)(H2O)](EtOH), and [Eu(QS)3(H2O)(EtOH)] containing eight-coordinate lanthanide ions in a square antiprismatic environment has been determined. The coordination environment in the tetrakis complex [NBu4][Eu(QF)4] is also close to the square antiprismatic one. Photoluminescence (PL) and phosphorescence studies of selected derivatives are reported.

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.

Mechanically induced chemiluminescence in the dispiro(adamantane-1,2-dioxetane)—Eu(fod)3 system

Luminescence accompanying an impact mechanical treatment of solid particles of the complex of Eu(fod)3 (fod is 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione) with dispiro(adamantane-1,2-dioxetane) (1) was discovered and studied. The luminescence has a complex structure, and its spectrum belongs to the excited EuIII ions. The emission of light is observed only in a mechanical mixture of the Eu(fod)3 with dioxetane1 and in their cocrystallized form, but not in the case of the components taken separately. The mechanism by which the impacts cause the luminescence is considered. It was shown that the luminescence is not triboluminescence, but is chemiluminescence induced by the decomposition of compound1.

Chemiluminescence in the thermal decomposition of di(tert-butyl) trioxide

Intense chemiluminescence (CL) in the visible and IR regions arising during the thermal decomposition of di(tert-butyl) trioxide has been observed. The decomposition rate constants have been determined. The emitter of CL in the IR region is singlet oxygen, that of CL in the visible region is triplet excited acetone. Kinetic and spectral data and thermochemical and MNDO calculations point to a homolytic mechanism of decomposition. The formation of the CL emitters occurs in the reactions of radicals that arise upon the decay of di(tert-butyl) trioxide.

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.