Search results for "Singlet"
showing 10 items of 352 documents
Variation of the ground spin state in homo- and hetero-octanuclear copper(II) and nickel(II) double-star complexes with a meso-helicate-type metallac…
2011
Homo- and heterometallic octanuclear complexes of formula Na₂{[Cu₂(mpba)₃][Cu(Me₅dien)]₆}-(ClO₄)₆·12H₂O (1), Na₂{[Cu₂(Mempba)₃][Cu(Me₅dien)]₆}(ClO₄)₆·12H₂O (2), Na₂{[Ni₂(mpba)₃]-[Cu(Me₅dien)]₆}(ClO₄)₆·12H₂O (3), Na₂{[Ni₂(Mempba)₃][Cu(Me₅dien)]₆}(ClO₄)₆·9H₂O (4), {[Ni₂(mpba)₃][Ni(dipn)(H₂O)]₆}(ClO₄)₄·12.5H₂O (5), and {[Ni₂(Mempba)₃][Ni(dipn)-(H₂O)]₆}(ClO₄)₄·12H₂O (6) [mpba = 1,3-phenylenebis(oxamate), Mempba = 4-methyl-1,3-phenylenebis(oxamate), Me₅dien = N,N,N',N'',N''-pentamethyldiethylenetriamine, and dipn = dipropylenetriamine] have been synthesized through the "complex-as-ligand/complex-as-metal" strategy. Single-crystal X-ray diffraction analyses of 1, 3, and 5 show cationic M(II)₂M'(I…
X‐ray Absorption Spectra of Cu II and Cu III Complexes of N , N ′ ‐1,2‐Phenylenebis(2‐mercapto‐2‐methylpropionamide)
2005
The X-ray absorption spectra of Cu I I and Cult complexes of N,N'-1,2-phenylenebis(2-mercapto-2-methylpropionamide) were recorded and analysed in solid phase. The EXAFS spectra of the two samples were refined with full multiple scattering path. Geometry optimisations on the Cu I I and Cu I I I complexes were performed by the B3LYP density functional method, with the 6-31G(d,p) basis set, considering different spin multiplicities. The singlet state of the Cu I I I complex was shown to be more stable than the triplet state, and a good agreement between the calculated and the corresponding experimental structure was found. Further single-point calculations on the optimised geometry were carrie…
Analyse und Optimierung von Gasphasen‐Reaktionen, 18 1,2) Die Pyrolyse von Methylazid
1981
Die PE-spektroskopisch analysierte Pyrolyse von Methylazid verlauft bei 850 K und liefert als Hauptprodukt Methanimin, welches nach einer MNDO-Singulett-Hyperflache betrachtlich stabiler sein sollte als das tautomere Methylnitren. Analysis and Optimization of Gasphase Reactions, 181,2) The Pyrolysis of Methyl Azide The PE spectroscopically analyzed pyrolysis of methyl azide occurs at 850 K and yields as main product methanimine, which according to a MNDO singlet hypersurface should be considerably stabilized relative to the tautomeric methyl nitrene.
Slow and Fast Singlet Energy Transfers in BODIPY-gallium(III)corrole Dyads Linked by Flexible Chains
2014
Red (no styryl), green (monostyryl), and blue (distyryl) BODIPY-gallium(III) (BODIPY = boron-dipyrromethene) corrole dyads have been prepared in high yields using click chemistry, and their photophysical properties are reported. An original and efficient control of the direction of the singlet energy transfers is reported, going either from BODIPY to the gallium-corrole units or from gallium-corroles to BODIPY, depending upon the nature of the substitution on BODIPY. In one case (green), both directions are possible. The mechanism for the energy transfers is interpreted by means of through-space Förster resonance energy transfer (FRET).
Antenna effects in truxene-bridged BODIPY triarylzinc(ii)porphyrin dyads: evidence for a dual Dexter–Förster mechanism
2014
The antenna process from an energy donor (BODIPY; 4′,4′-difluoro-1′,3′,5′,7′-tetramethyl-4′-bora-3a′,4a′-diaza-s-indacene) in its singlet state to two acceptors (two zinc(II) 5,15-p-tolyl-10-phenylporphyrin) bridged by a central truxene residue (5′,5′′,10′,10′′,15′,15′′-hexabutyltruxene), 5, has been analysed by means of comparison of the energy transfer rates with those of a structurally similar β-substituted BODIPY-(zinc(II) 5,10,15-p-tolyl-porphyrin), 6, where no conjugation is present between the donor and the two acceptors using the Forster resonance energy transfer (FRET) approximation. It is estimated that the energy transfer in 5 operates mostly via a Dexter mechanism (>99%), and th…
Tuning the photophysical properties of anti-B18H22: efficient intersystem crossing between excited singlet and triplet states in new 4,4'-(HS)2-anti-…
2013
The tuning of the photophysical properties of the highly fluorescent boron hydride cluster anti-B18H22 (1), by straightforward chemical substitution to produce 4,4'-(HS)2-anti-B18H20 (2), facilitates intersystem crossing from excited singlet states to a triplet manifold. This subsequently enhances O2((1)Δg) singlet oxygen production from a quantum yield of ΦΔ ∼ 0.008 in 1 to 0.59 in 2. This paper describes the synthesis and full structural characterization of the new compound 4,4'-(HS)2-anti-B18H20 (2) and uses UV-vis spectroscopy coupled with density functional theory (DFT) and ab initio computational studies to delineate and explain its photophysical properties.
The Iron Hydrido Complex [FeH(dppe)2]+: Solution and Solid-State Reactivity with Dinitrogen
2006
The blue compound [FeH(dppe)2]BPh4 (1) (dppe = 1,2-bis(diphenylphosphino)ethane) is investigated by optical absorption, vibrational, NMR and Mossbauer spectroscopy as well as magnetic susceptibility measurements. In the solid state, 1 is found to be paramagnetic (S=1) whereas in tetrahydrofuran (thf) solution it is diamagnetic. Importantly, 1 reacts with dinitrogen in thf solution and in the solid state to give the yellow and green dinitrogen complexes 2a and 2b, respectively, both of which have the formula [FeH(N2)(dppe)2]BPh4. Apart from their colour and optical spectroscopic properties, the dinitrogen compounds 2a and 2b also differ in their magnetic, Mossbauer and vibrational properties…
Photochemie elektronenreicher 1,3‐Distyrylbenzole
1988
Die 1,3-Distyrylbenzole 3 mit bis zu sieben Alkoxygruppen werden der oxidativen Photocyclisierung unterworfen. Bei der Bildung der Produkte 6, 7 und 8 konnen als Konkurrenz- bzw. Folgeprozesse die Abspaltung von Methanol (3bb 7bb, 3bf 7bf) und die Chinonoxidation (3cf 8) auftreten. Die eigensensiblisierte Erzeugung von Singulettsauerstoff kann bei 6bf zur Endoperoxidbildung fuhren (6bf 11). Photochemistry of Electron-Rich 1,3-Distyrylbenzenes The 1,3-distyrylbenzenes 3, containing up to seven alkoxy groups, are subjected to the oxidative photocyclization. Elimination of methanol (3bb 7bb, 3bf 7bf) and quinone oxidation can occur as competitive or consecutive reactons in the formation of the…
The Low-Lying Excited States of 2,2′-Bithiophene: A Theoretical Analysis
2004
The low-energy region of the singlet →singlet, singlet →triplet, and triplet→triplet electronic spectra of 2,2'-bithiophene are studied using multiconfigurational second-order perturbation theory (CASPT2) and extended atomic natural orbitals (ANO) basis sets. The computed vertical, adiabatic, and emission transition energies are in agreement with the available experimental data. The two lowest singlet excited states, 1 1 B u and 2'B u , are computed to be degenerate, a novel feature of the system to be borne in mind during the rationalization of its photophysics. As regards the observed high triplet quantum yield of the molecule, it is concluded that the triplet states 2 3 A g and 2 3 B u ,…
Corrigendum: An Unusually Small Singlet-Triplet Gap in a Quinoidal 1,6-Methano[10]annulene Resulting from Baird's 4n π-Electron Triplet Stabilization.
2016
Within the continuum of π-extended quinoidal electronic structures exist molecules that by design can support open-shell diradical structures. The prevailing molecular design criteria for such structures involve proaromatic nature that evolves aromaticity in open-shell diradical resonance structures. A new diradical species built upon a quinoidal methano[10]annulene unit is synthesized and spectroscopically evaluated. The requisite intersystem crossing in the open-shell structure is accompanied by structural reorganization from a contorted Mobius aromatic-like shape in S0 to a more planar shape in the Huckel aromatic-like T1. This stability was attributed to Baird’s Rule which dictates the …