Photophysics and Electrochemistry of some Thione Far-Red/Near-IR Triplet Emitters

The photophysics and cyclic voltammetry of two novel phosphorescent thiones, 2,2-dimethyl-indan-1-one-3-thione (DMIKT) and 2,2-dimethyl-indan-1,3-dithione (DMIDT), and three known phosphorescent thiones, 4H-pyran-4-thione (PT), 4H-1-benzopyran-4-thione (BPT) and 2,2-dimethylindan-1-thione (DMIT), have been characterised and compared. The phosphorescence emission of DMIT, DMIKT and DMIDT extends from the red into the near-IR spectral region. The additional carbonyl or thione group of DMIKT and DMIDT causes a significant shift in the emission maxima to 680 nm compared to that of DMIT, at 637 nm, in perfluorinated hydrocarbons. In acetonitrile the emission maxima of DMIKT and DMIDT are at 696 and 706 nm, respectively, and the spectra show vibronic bands which extend out beyond 850 nm. There is a significant reduction in triplet lifetime along this series (from 44 (±2) μs (DMIT) to 10 ((±0.8) μs (DMIKT) in perfluorinated solvents, and 8.6 (±0.5) (DMIT), 1.3 (±0.5) (DMIKT) and 0.35 (±0.07) μs (DMIDT) in acetonitrile), as well as a reduction in the rate constant for ground-state quenching of the triplet, (from 9.8 ((±0.9) to 3.5 ((±0.6) and 1.3 ((±0.2) × 10⁹ mol⁻¹ dm³ s⁻¹ for the same compounds). The addition of the C=O or C=S groups also causes a decrease in phosphorescence quantum yield with the highest emission quantum yield obtained for DMIT (Φ _P = 0.149 (±0.015)). Electrochemical studies show that while PT and BPT exhibit irreversible redox behaviour, DMIT, DMIKT and DMIDT all show at least one reversible reduction wave attributed to a one-electron process centred on the C=S moiety. The suitability of these lumophores for use in OLEDs is discussed.     

Finestructure, hyperfine structure and isotope shift of 4f 6s7s in Er I

The isotope shift (IS) and hyperfine structure (hfs) of nine levels (31720 to 38921 cm^-1) assigned to the configuration 4 f ¹² 6 s 7 s in neutral erbium have been determined experimentally using Doppler-reduced saturation absorption spectroscopy in a gas discharge. We performed a fine structure analysis in the SL-coupling scheme of the single configuration 4 f ¹² 6 s 7 s, confirming and extending the classification of even parity Er I levels. We discriminated the different hfs contributions of the 4f¹² core and the (6 s +7 s) outer electrons of the shell in a non-relativistic JJ-coupling approach and in the relativistic effective tensor operator formalism in SL-coupling. The relativistic one-electron parameters of the hfs for ¹⁶⁷Er were fitted to the experimental data by a least squares fit procedure: [0pt] a ⁰¹ _4f =-147(3) MHz, [0pt] a ¹⁰ _6s + a ¹⁰ _7s =-1840(30) MHz, [0pt] b ⁰² _4f =6560(80) MHz. The level dependencies of the isotope shift were evaluated based on crossed second order (CSO) effects. We obtained the following results for the CSO parameters for the isotope pairs ^170-168Er: d _6s7s =-740(30) MHz, z _4f = 0(5) MHz, ( g _3,6s ( f , 6 s )+ g _{3, 7s} ( f , 7 s ))= -24(15) MHz and for ^170-166Er: d _6s7s =-1500(50) MHz, z _4f =0(10) MHz, ( g _3,6s ( f ,6 s )+ g _3,7s ( f +7 s ))=-50(29) MHz. The resulting parameters for the hfs are compared with those known for other configurations of the Er atom and ion. Received 16 May 1999 and Received in final form 31 January 2000     

The spin-crossover complex [Fe(tpa)(NCS) 2 ]

The temperature-induced spin crossover of iron(II) in the [ Fe ( tpa )( NCS ) ₂ ] complex has been investigated by nuclear forward scattering (NFS), nuclear inelastic scattering (NIS), extended X-ray absorption fine structure (EXAFS) spectroscopy, conventional M?ssbauer spectroscopy (MS) and by measurements of the magnetic susceptibility (SQUID). The various measurements consistently show that the transition is complete and abrupt and exhibits a hysteresis between 102 and 110 K. The dependence of the hyperfine parameters of the high-spin (HS) and of the low-spin (LS) phase on temperature is gradual while the effective thickness (determined by the Lamb-M?ssbauer factor f _LM ) shows a step at the transition temperature. This step could be identified clearly because the effective thickness is measured directly by NFS. The Lamb-M?ssbauer factor, the Debye temperature and the mean-square displacement of iron(II) could be determined for the HS and for the LS phase. When comparing the NIS data with the results from density functional theory (DFT), the Fe-N stretching vibrations of both LS and HS phases could be unambiguously identified and the f _LM could be factorized for both phases into a lattice and a molecular part. The structural information from EXAFS and DFT geometry optimization are in reasonable agreement. Received 19 June 2001     

Electron-pair densities of group 2 atoms in their and terms

Electron-pair intracule (relative motion) and extracule (center-of-mass motion) densities are studied in both position and momentum spaces for the ¹ P and ³ P terms of the group 2 atoms Be (atomic number Z =4), Mg (Z =12), Ca (Z =20), Sr (Z =38), Ba (Z =56), and Ra (Z =88). In position space, the ¹ P - ³ P difference in the intracule densities shows that the probability of a small interelectronic distance is larger in the triplet for all the six atoms, as reported for the lightest Be atom in the literature. The position-space extracule density clarifies that the triplet electrons are more likely to be at opposite positions with respect to the nucleus than the singlet electrons for all the atoms. In momentum space, the singlet generally has a larger probability of a small relative momentum between two electrons as a na?ve manifestation of the Fermi hole in the triplet. The extracule density in momentum space shows that the ¹ P term has a distribution larger in a large center-of-mass momentum region than the ³ P term. Received: 26 August 1998 / Received in final form: 1 February 1999     

Energy loss of 18 keV electrons in gaseous T and quench condensed D films

Measurements of the energy loss of fast electrons at an energy of 18 keV have been performed on molecules of hydrogen isotopes, gaseous T ₂ and frozen D ₂ . Whereas in the case of gaseous T ₂ the values of total inelastic cross-section ( cm² for E = 18.6 keV), average energy loss ( eV) and peak position of the energy loss spectra ( eV) agree well with the expectations, the corresponding values for quench condensed D ₂ differ significantly from the ones for gaseous T ₂ . We observe a significant lower total inelastic cross-section ( cm², for E = 18.6 keV) larger average energy loss ( eV) and higher peak position ( eV). These differences may be interpreted in terms of changes of the final state spectrum. A CI calculation for a D ₂ cluster shows indeed a clear shift of the excited states in agreement with the observation. Received 24 August 1999     

Elastic anomalies and orientational glass transition in Na(CN) Cl mixed crystals. A Brillouin spectroscopic study

High performance Brillouin spectroscopy (BS) has been used to study the elastic properties (static and dynamic) of the orientational glassy state of Na(CN)_xCl_1-x samples ). The temperature behaviour of the elastic properties reveals a more complex scenario for the orientational glass transition than generally believed. The shear elastic constant shows the well-known c ₄₄ ( T ) anomaly, indicated by a minimum, found in other cyanide mixed crystals. The results obtained for the hypersonic attenuation are in clear contradiction with the dynamic character of the c ₄₄ ( T )-minimum. The temperature behaviour of the longitudinal elastic constant c₁₁ of very dilute Na(CN)_xCl_1-x samples shows two striking features: i) Similar to the anomalous temperature behaviour of c ₄₄ ( T ), lowering the temperature c ₁₁ ( T ) first decreases, goes through a minimum and then rises again. The minimum takes place at a temperature above the temperature, , where c ₄₄ ( T ) reaches its minimum value. ii) A kink-like anomaly of c ₁₁ ( T ) is observed at lower temperatures. This second anomaly is similar to the classical one observed in canonical glasses at their glass transition temperature . Received 8 April 1999 and Received in final form 3 June 1999     

Enlarged surface meshes and normalization conditions for columns and rows of matrices in the COSMO method

Earlier, normalization conditions for the columns of the PCM (Polarized Continuum Model) were determined and a method of enlarged surface meshes was developed. We developed similar methods for the COSMO (COnductor-like Screening MOdel). These methods make it possible to introduce larger surface meshes without loss of accuracy and perform fast calculations of the solvation energy and the Born radii in the SGB (Surface Generalized Born) method. In addition, the corrections proposed in this work provide a significant enhancement in the accuracy of numerical calculations.     

Numerical solutions of matrix Riccati equations for radiative transfer in a plane-parallel geometry

Abstract

In this paper, we conduct numerical experiments with matrix Riccati equations (MREs) which describe the reflection (R) and transmission (T) matrices of the specific intensities in a layer containing randomly distributed scattering particles. The theoretical formulation of MREs is discussed in our previous paper where we show that R and T for a thick layer can be efficiently computed by successively doubling R and T matrices for a thin layer (with small optical thickness τ_Δ). We can compute R(τ_Δ) and T(τ_Δ) very accurately using either a fourth-order Runge–Kutta scheme or the fourth-order iterative solution. The differences between these results and those computed by the eigenmode expansion technique (EMET) are very small (<0.1%). Although the MRE formulation cannot be extended to handle the inhomogeneous term (source term) in the differential equation, we show that the force term can be reformulated as an equivalent boundary condition which is consistent with MRE methods. MRE methods offer an alternative way of solving plane-parallel radiative transport problems. For large problems that do not fit into computer memory, the MRE method provides a significant reduction in computer memory and computational time.     

Potential use of small basis set on the calculations of electronic properties of some four-membered heterocycles: a conformational study

The potential use of small basis sets upon a low level of theory was studied on the calculations of electronic properties (dipole moment, static polarisability and static hyperpolarisabilities) of a series of 16 four-membered heterocycles with an exocyclic double bond at the position 3 (1–16). First, the calculations were performed within the Hartree–Fock (HF) approximation using 6-31G, 6-31G(d,p) and 6-31+G(d,p) as basis sets for the different conformational states of each molecule, and the results obtained were compared with the MP2/6-31+G(d,p) results reported. In the second place, in order to know the real potential of HF calculations, these were compared with those calculated using larger approaches such as MP2/6-311+G(d,p), MP2/aug-cc-pVDZ, CCS/6-311+G(d,p), CCS/aug-cc-pVDZ, CCS/aug-cc-pVTZ, CCSD/6-31+G(d) and CCSD/cc-pVDZ, taken into account only the planar and equilibrium geometries of each molecules. The HF approaches permit us to obtain a good qualitative representation of the dipole moment as a function of puckering angle in comparison with MP2, CCS and CCSD levels for all tested molecules. However, only HF/6-31+G(d,p) provides quantitative values of dipole moment for the heterocycles 1, 5 and 13 in comparison with MP2, CCS and CCSD levels. On the other hand, the polarisability and hyperpolarisabilities were quite sensitive to the quality of level of theory and basis sets. In particular, HF/6-31+G(d,p) predicted a representative approximation of alpha for the molecule 16 in comparison with larger methods as MP2/aug-cc-pVDZ, CCS/aug-cc-pVDZ and CCS/aug-cc-pVTZ, while a detailed analysis showed that HF can be used in the calculation of alpha for the molecules 3, 7, 11 and 15, but it requires the use of extended basis sets. Also, HF/6-31+G(d,p) predicted values of beta very similar to those calculated at the MP2 and CCSD levels used, for the planar and equilibrium geometry of the molecules 10 and 14. Furthermore, HF/6-31+G(d,p) described a representative dependence of this property with the puckering angle for the heterocycles 9, 10 and 14, compared with the MP2 curves.     

Conformational Analysis of Baclofen Analogues by 1H and 13C NMR: Phaclofen,Saclofen, and Hydroxy-Saclofen. Influence of the Anionic Moiety

The conformations of three analogues of baclofen 1: phaclofen, saclofen, and hydroxy-saclofen 2–4, potent GABA_B antagonists, in solution (D₂O) are estimated from high-resolution (300 MHz) H NMR coupling data. Conformations and populations of conformers are calculated by means of a modified Karplus-like relationship for the vicinal coupling constants. H NMR spectral analysis evidences how 1–3 keep in solution the preferred a conformation around C3-C4 bond. A partial rotation is set up around C2–C3 bond (the conformations about C2–C3 are all highly populated in solution) particularly for 2 and 3 while 1 shows a relative preferred a conformation. This evidences the influence of the anionic moiety.     

A novel electron scattering apparatus combining a laser photoelectron source and a triply differentially pumped supersonic beam target: characterization and results for the resonance

A novel electron scattering apparatus for high resolution studies of angle-differential elastic and inelastic electron scattering from atoms and molecules in the gas phase is described and its performance characterized. It combines a laser photoelectron source, a triply differentially pumped collimated supersonic beam target (half angle 0.015 rad, background to beam density ratio < 0.01), and several electron multipliers for simultaneous detection of elastically scattered electrons and metastable atoms (or molecules) due to inelastic scattering. In detailed test measurements of the yield for the production of metastable He^*(2³S₁) atoms around its threshold, the dependence of the overall energy width on various experimental parameters has been investigated. So far a resolution down to 7 meV (FWHM) has been obtained. Under such conditions we have investigated the profile of the He^- (1 s 2 s ^{2 2} S _1/2 ) resonance at the scattering angles 22 ^° , 45 ^° , and 90 ^° . From a consistent fit of the measured profiles by resonant scattering theory we determine a new value for the resonance energy ( E _r = 19.365(1) eV) and an accurate resonance width ( Γ = 11.2(5) meV). These results are consistent with the previously recommended values. Received 23 July 2002 Published online 29 October 2002 RID="a" ID="a"e-mail: hotop@physik.uni-kl.de RID="b" ID="b"Permanent address: Department of Physics and Astronomy, Drake University, Des Moines, IA 50311, USA.     

Factory-roof-shaped phase front at the paraelectric-ferroelectric transition in KD PO : an incoherent interface

The phase front during the 218 K transition in KD₂PO₄ crystals under a thermal gradient perpendicular to the c ferroelectric axis is observed to have a factory-roof shape. This shape is studied versus the magnitude of G_e in samples cut with faces in (100), (010), (001) planes or in ( 0), (110), (001) ones. A geometric approach as well as the calculation of the elastic-strain energy caused by lattice misfits along the phase front demonstrate the incoherent interface nature of the phase front. Furthemore, the results and their interpretation allow to predict the sign of the lattice deformation u _xx ( > 0). Received 25 April 2002 Published online 29 November 2002     

Theoretical study on structures and stability of SiC3S isomers

Various levels of calculations are carried out to explore the potential energy surfaces (PES) of singlet and triplet SiC₃S, a molecule of potential interest in interstellar chemistry. At the DFT/B3LYP/6-311G(d) level, a total of 57 minimum isomers and 92 interconversion transition states are located. The structures of the most relevant isomers and transition states are further optimized at the QCISD/6-311G(d) level followed by CCSD(T)/6-311?+?G(2df) single-point energy calculations. At the QCISD level, the lowest-lying isomer is the chain-like SiCCCS ³ 1 (0.0?kcal/mol) with a great kinetic stability of 54.1?kcal/mol. In addition, ring isomers CC-cCSSi ¹ 9 (19.8?kcal/mol), S-cCCCSi ¹ 12 (30.4?kcal/mol), S-cCCSiC ¹ 18 (9.4?kcal/mol), S-cSiCCC ¹ 21 (34.4?kcal/mol) and cage-like isomer cage-SiSCCC ¹ 23 (51.8?kcal/mol) also possess considerable kinetic stability (more than 10.0?kcal/mol). As a result, these six isomers are predicted to be possible candidates for future experimental and astrophysical detection. The bond natures and possible formation pathways in interstellar space of the SiCCCS are discussed. The predicted structure and spectroscopic properties for it are expected to be informative for the identification of SiC₃S and even larger SiC _n S species either in laboratory or in space.     

Coexistence of superconductivity and spin density wave orderings in the organic superconductor (TMTSF) 2 PF 6

The phase diagram of the organic superconductor (TMTSF)₂PF₆has been revisited using transport measurements with an improved control of the applied pressure. We have found a 0.8 kbar wide pressure domain below the critical point (9.43 kbar, 1.2 K) for the stabilisation of the superconducting ground state featuring a coexistence regime between spin density wave (SDW) and superconductivity (SC). The inhomogeneous character of the said pressure domain is supported by the analysis of the resistivity between T _SDW and T _SC and the superconducting critical current. The onset temperature T _SC is practically constant ( 1.20±0.01 K) in this region where only the SC/SDW domain proportion below T _SC is increasing under pressure. An homogeneous superconducting state is recovered above the critical pressure with T _SC falling at increasing pressure. We propose a model comparing the free energy of a phase exhibiting a segregation between SDW and SC domains and the free energy of homogeneous phases which explains fairly well our experimental findings. Received 3 September 2001 and Received in final form 9 November 2001     

Dimer dissociation energies of small odd-size clusters

The dimer dissociation energies of gold cluster ions Au ⁺ _n , n = 9, 11, 13, 15 have been determined with an extension of a recently developed model-independent method. Monomer-dimer decay pathway branching ratios provide the energy dependent process which is needed in this method. The measured values are D ₂ ( Au ⁺ ₉ ) = 3.66(8)(9) eV, D ₂ ( Au ⁺ ₁₁ ) = 4.27(11)(8) eV, D ₂ ( Au ⁺ ₁₃ ) = 4.50(9)(7) eV and D ₂ ( Au ⁺ ₁₅ ) = 4.29(10)(6) eV. Received 13 May 2002 / Received in final form 22 July 2002 Published online 24 September 2002 RID="a" ID="a"e-mail: manuel.vogel@uni-mainz.de     

Conformational analysis of <Emphasis Type="Italic">o</Emphasis>-allylphenol by density functional and IR spectroscopy methods

The two-dimensional cyclic potential energy surfaces for internal rotation of the allyl substituent and its vinyl fragment in o-allylphenol (o-APh) depending on the OH group orientation relative to the allyl substituent were constructed by a B3LYP/6-31G method. It is shown that o-APh exists in the gas phase as a mixture of eight non-planar rotamers (A, B, C, D, E, F, G, and H) and their eight optical isomers (A ₁, B ₁, C ₁, D ₁, E ₁, F ₁, G ₁, and H ₁). An intramolecular H-bond (IHB) O–H...π occurs only in four rotamers (A, B, A ₁, and B ₁). The content of such rotamers in the gas phase is 47.2% (as calculated by the B3LYP/cc-pVTZ method). Taking into account the solvation effect in the polarizable continuum model (PCM) for a solution of o-APh in cyclohexane decreases the total content of rotamers with an IHB (A and B) to 37.7%. The ratio of rotamers with OH groups bonded by an IHB and with free OH groups that is predicted theoretically agrees with the value measured experimentally from IR spectra of o-APH in CCl₄ solution.     

Photofragmentation of hydrated iron ions Fe(HO) () at 532, 355 and 266 nm

Photofragmentation of Fe(H₂O)n ⁺ clusters (n =1-9) is investigated at three different wavelengths, 532, 355 and 266 nm. Two fragmentation pathways are observed depending essentially on the photon energy, but also on the parent size n. The fragmentation products belong to two ion families, Fe(H₂O)m ⁺ and FeOH(H₂O)m ⁺ , which correspond to dehydration and intracluster dehydrogenation reactions respectively. The ion yields are studied as a function of the laser fluence in order to determine the number of photons implied in the photofragmentation process. This allows us to estimate that the D[(H₂O)_n-1Fe^+-(H₂O)] bond energy is ranging between 0.44 eV and 0.55 eV for .Photon absorption cross sections are also derived from the fluence experiments, and two different behaviors are observed: i) At 355 nm, far away from any transition, progressive solvation of the metal ion results in an increasing absorption cross section from n =2 to n =9. This can be attributed to a forbidden transition of bare , which becomes progressively allowed because of the interaction with more and more water ligands. ii) At 266 nm, close to several allowed transitions of bare , a distinct maximum is observed for the absorption of ion. It may be attributed to a change in the spin multiplicity when switching from and on one hand to Fe(H₂O) on the other. Received: 11 November 1997 / Revised: 18 February 1998 / Accepted: 22 April 1998     

Triangular antiferromagnetic order in the honeycomb layer lattice of

ErCl₃ crystallizes in the AlCl₃-type layer structure. The crystal structure was refined in the paramagnetic state by powder neutron diffraction. The monoclinic lattice parameters at 1.5 K are a = 6.8040(3)?, b = 11.7456(5)?, c = 6.3187(3)? and . The space group is C2/m. Short-range, predominantly in-plane, magnetic ordering occurs above 350 mK up to several Kelvin. Below mK a three-dimensional antiferromagnetic order with a propagation vector of sets in. The magnetic structure of ErCl₃ was determined by powder and single-crystal neutron diffraction at temperatures down to 45 mK. The Er³⁺ ions are located on two-dimensional honeycomb layers in the a–b plane. There are two antiferromagnetically coupled triangular sublattices which form right- and left-handed helices along the c-axis. The magnetic moments are oriented in the a–b plane and amount to 3.3(1) at saturation. From the temperature dependence of the integrated neutron magnetic peak intensity a critical exponent (2) was derived for the magnetic phase transition. Received 1 December 1999 and Received in final form 21 July 2000     

Experimental determination of spin-rotation and spin-spin magnetic interactions in by nuclear spin conversion

When a gas sample of ¹³CH₃F is prepared with a population of isomers (ortho and para forms) far from the equilibrium given by nuclear spin statistics, it relaxes towards this equilibrium with an exponential decay rate. This phenomenon called nuclear spin conversion is mainly governed by intramolecular spin-spin and spin-rotation interactions. In the quantum relaxation model [P.L. Chapovsky, Phys. Rev. A 43, 3624 (1991)], two pairs of ortho-para levels (J = 9, K = 3; J' = 11, K' = 1) and (J = 20, K = 3; J' = 21, K' = 1) are principally responsible for the conversion. The levels of the second pair are coupled by both spin-spin and spin-rotation interactions. The application of an electric field (up to 10 kV/cm) induces a crossing of the Stark components of this pair, which is observed for the first time. A specific experimental set-up based on an electric field of alternating triangular shape is used, which allows the determination of the strength of both interactions via the measurement of the spin conversion decay rates. This work yields the first experimental value for the electronic contribution to the spin-rotation interaction in ¹³CH₃F. Received 23 May 2002 / Received in final form 18 September 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: Patrice.Cacciani@univ-lille1.fr