Search results for "Triplet state"
showing 10 items of 118 documents
Temperature and excitation energy dependence of decay processes of luminescence in Ge-doped silica
2003
We report experimental results on the time decay of photoluminescence at 4.2 eV in Ge-doped silica. This optical emission is assigned to a singlet-singlet transition between electronic states localized on an oxygen deficiency nearby a Ge atom and its radiative decay rate is in competition with an intersystem crossing mechanism that populates an excited triplet state. We investigate the dependence of the lifetime of this photoluminescence on the temperature, in the 6--295 K range, and on the excitation energy, in the ultraviolet and vacuum ultraviolet region. The mean value of the decay time decreases on increasing the temperature, in agreement with the phonon-assisted nature of the intersys…
Exploring two-state reaction pathways in the photodimerization of cyclohexadiene.
2006
The ground- (S0) and lowest triplet-state (T1) pathways associated with dimerization of cyclohexadiene to give [2+2] and [4+2] cycloadducts have been theoretically studied at the UBLYP and UB3LYP levels of theory with the 6-31G* basis set. The DFT energies were validated by CCSD(T) single-point energy calculations. These cycloaddition reactions follow stepwise mechanisms with formation of bis-allylic biradical (BB) intermediates. In the S0 ground state, the interaction between two cyclohexadiene molecules with formation of BB intermediate IN(S0) has a large activation enthalpy of 32.0 kcal mol(-1). On the other hand, C-C bond-formation in the lowest triplet state (T1) leading to BB intermed…
Spin-Based Quantum Information Processing in Magnetic Quantum Dots
2005
We define the qubit as a pair of singlet and triplet states of two electrons in a He-type quantum dot (QD) placed in a diluted magnetic semiconductor (DMS) medium. The molecular field is here essential as it removes the degeneracy of the triplet state and strongly enhances the Zeeman splitting. Methods of qubit rotation as well as two-qubit operations are suggested. The system of a QD in a DMS is described in a way which allows an analysis of the decoherence due to spin waves in the DMS subsystem.
Synthesis of a labile sulfur-centred ligand, [S(H)C(PPh2S)2]−: structural diversity in lithium(i), zinc(ii) and nickel(ii) complexes
2016
A high-yield synthesis of [Li{S(H)C(PPh2S)2}]2 [Li2·(3)2] was developed and this reagent was used in metathesis with ZnCl2 and NiCl2 to produce homoleptic complexes 4 and 5b in 85 and 93% yields, respectively. The solid-state structure of the octahedral complex [Zn{S(H)C(PPh2S)2}2] (4) reveals notable inequivalence between the Zn-S(C) and Zn-S(P) contacts (2.274(1) Å vs. 2.842(1) and 2.884(1) Å, respectively). Two structural isomers of the homoleptic complex [Ni{S(H)C(PPh2S)2}2] were isolated after prolonged crystallization processes. The octahedral green Ni(ii) isomer 5a exhibits the two monoprotonated ligands bonded in a tridentate (S,S',S'') mode to the Ni(ii) centre with three distinctl…
Characterization of a sucrose/starch matrix through positron annihilation lifetime spectroscopy: unravelling the decomposition and glass transition p…
2010
The triplet state of positronium, o-Ps, is used as a probe to characterize a starch-20% w/w sucrose matrix as a function of temperature (T). A two-step decomposition (of sucrose, and then starch) starts at 440 K as shown by a decrease in the o-Ps intensity (I(3)) and lifetime (τ(3)), the latter also disclosing the occurrence of a glass transition. Upon sucrose decomposition, the matrix acquires properties (reduced size and density of nanoholes) that are different from those of pure starch. A model is successfully established, describing the variations of both I(3) and τ(3) with T and yields a glass transition temperature, T(g) = (446 ± 2) K, in spite of the concomitant sucrose decomposition…
Colour tuning by the ring roundabout: [Ir(C^N)2(N^N)]+ emitters with sulfonyl-substituted cyclometallating ligands
2015
A series of cationic bis-cyclometallated iridium(III) complexes [Ir(C^N)2(N^N)]+ is reported. Cyclometallating C^N ligands are based on 2-phenylpyridine with electron-withdrawing sulfone substituents in the phenyl ring: 2-(4-methylsulfonylphenyl)pyridine (H1) and 2-(3-methylsulfonylphenyl)pyridine (H2). 2-(1H-Pyrazol-1-yl)pyridine (pzpy) and 2-(3,5-dimethyl-1H-pyrazol-1-yl)pyridine (dmpzpy) are used as electron-rich ancillary N^N ligands. The complexes have been fully characterized and the single crystal structure of [Ir(2)2(dmpzpy)][PF6]·MeCN has been determined. Depending on the position of the methylsulfonyl group, the complexes are green or blue emitters with vibrationally structured em…
Regioisomerism in cationic sulfonyl-substituted [Ir(C^N)2(N^N)]+ complexes: its influence on photophysical properties and LEC performance
2016
A series of regioisomeric cationic iridium complexes of the type [Ir(C^N)2(bpy)][PF6] (bpy = 2,2'-bipyridine) is reported. The complexes contain 2-phenylpyridine-based cyclometallating ligands with a methylsulfonyl group in either the 3-, 4- or 5-position of the phenyl ring. All the complexes have been fully characterized, including their crystal structures. In acetonitrile solution, all the compounds are green emitters with emission maxima between 493 and 517 nm. Whereas substitution meta to the Ir-C bond leads to vibrationally structured emission profiles and photoluminescence quantum yields of 74 and 77%, placing a sulfone substituent in a para position results in a broad, featureless em…
A penetration depth study on the non-centrosymmetric superconductors Li2(Pd1−xPtx)3B
2008
Abstract We study the superconducting order parameter in the non-centrosymmetric compounds Li 2 (Pd 1− x Pt x ) 3 B ( x =0, 0.3, 0.7 and 1) by measuring magnetic penetration depth λ ( T ). The low temperature λ ( T ) shows a linear temperature dependence for x ⩾0.3, but follows exponential-like behavior for lower Pt contents. These findings suggest that a spin-triplet state might gradually develop with increasing x due to the broken inversion symmetry.
ChemInform Abstract: Relaxation Phenomena of a Triplet Spin Probe in Glassy and Crystalline o-Terphenyl.
2010
The authors used quinoxaline in its photoexcited triplet state as a spin probe in order to measure the spin-lattice relaxation rate in o-terphenyl glass as a function of temperature. They found a power law with an exponent close to 2. Since o-terphenyl can easily be crystallized, they investigated the crystal, too. Below 3.5 K the spin is highly polarized, contrary to the behavior in the glass, where it reaches thermal equilibrium down to the lowest temperatures of their experiment (1.4 K). Around 3.5 K the polarization in the crystal vanishes. Above it appears with opposite sign due to thermal equilibration.
A study of electron transfer in Ru(dcbpy)2(NCS)2 sensitized nanocrystalline TiO2 and SnO2 films induced by red-wing excitation.
2008
Excited state dynamics and electron transfer from the Ru(dcbpy)2(NCS)2 (RuN3) sensitizer to semiconductor nanoparticles were studied using time-resolved femtosecond absorption spectroscopy. We found that excitation of the red wing of the absorption spectrum of the sensitizer populates the (3)MLCT state directly, both in solution and attached on semiconductor nanoparticle films. Electron injection is slowed down and becomes gradually less efficient as excitation moves towards red from the absorption maximum at 535 nm. At 675 nm the injection is non-exponential and characterized by 5, 30 and 180 ps time constants. The non-exponential electron injection observed is assigned to injection from a…