Search results for "Triplet"
showing 10 items of 159 documents
Photophysical properties of the triangular [Au(HNCOH)]3 complex and its dimer
2020
Rate constants for radiative and non-radiative transitions of the [Au(HNCOH)]3 complex and its dimer were calculated within the Herzberg–Teller approximation based on quantum mechanical principles. A high triplet quantum yield was estimated for the monomer. Internal conversion (IC) was found to be the major competing process to the intersystem crossing (ISC) from the lowest excited singlet state (S1) to the lowest triplet state (T1). ISC and IC from the spin-mixed 1 state also dominate the triplet relaxation process resulting in a negligible phosphorescence quantum yield for the monomer. The IC and ISC rate constants of the dimer are considerably smaller due to much lower Franck–Condon fact…
Spin state, electronic structure and bonding on C-scorpionate [Fe(II)Cl2(tpm)] catalyst: An experimental and computational study
2020
Abstract The Fe(II) spin state in the condensed phase of [Fe(II)Cl2(tpm)] (tpm = [tris(pyrazol-1-yl)methane]; 1) catalyst has been determined through a combined experimental and theoretical investigation of X-Ray Absorption Spectroscopy (XAS) at the FeL2,3-edges and NK-edge. Results indicated that in this phase a mixed singlet/triplet state is plausible. These results have been compared with the already know Fe singlet spin state of the same complex in water solution. A detailed analysis of the electronic structure and bonding mechanism of the catalyst showed that the preference for the low-spin diamagnetic ground state, strongly depends upon the ligands, the bulk solvent and the interactio…
Luminescent copper(i) complexes with bisphosphane and halogen-substituted 2,2′-bipyridine ligands
2018
Heteroleptic [Cu(P^P)(N^N)][PF6] complexes, where N^N is a halo-substituted 2,2'-bipyridine (bpy) and P^P is either bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9- dimethylxanthene (xantphos) have been synthesized and investigated. To stabilize the tetrahedral geometry of the copper(I) complexes, the steric demands of the bpy ligands have been increased by introducing 6- or 6,6'-halo-substituents in 6,6'-dichloro-2,2'-bipyridine (6,6'-Cl2bpy), 6-bromo-2,2'- bipyridine (6-Brbpy) and 6,6'-dibromo-2,2'-bipyridine (6,6'-Br2bpy). The solid-state structures of [Cu(POP)(6,6'-Cl2bpy)][PF6], [Cu(xantphos)(6,6'-Cl2bpy)][PF6].CH2Cl2, [Cu(POP)(6-Brbpy)][PF6] and [Cu(xantp…
All-organic fast intersystem crossing assisted exciplexes exhibiting sub-microsecond thermally activated delayed fluorescence
2021
A novel strategy is presented towards acquisition of exciplex systems exhibiting thermally activated delayed fluorescence (TADF) with a high reverse intersystem crossing (RISC) rate (exceeding 107 s−1). This approach involves constructing exciplex donor–acceptor molecular pairs, where the acceptor molecule possesses the ability to undergo fast and efficient intersystem crossing (ISC). With the use of 6-cyano-9-phenylpurine (PCP) acceptor and carbazole-based donor molecules, exciplexes were obtained, where the excitation is contained on PCP and undergoes fast ISC to form a local excited triplet state (3LEA). The controlled excitation transfer to the 3LEA level provides an optimal reverse int…
Diindeno-fusion of an anthracene as a design strategy for stable organic biradicals
2016
The consequence of unpaired electrons in organic molecules has fascinated and confounded chemists for over a century. The study of open-shell molecules has been rekindled in recent years as new synthetic methods, improved spectroscopic techniques and powerful computational tools have been brought to bear on this field. Nonetheless, it is the intrinsic instability of the biradical species that limits the practicality of this research. Here we report the synthesis and characterization of a molecule based on the diindeno[b,i]anthracene framework that exhibits pronounced open-shell character yet possesses remarkable stability. The synthetic route is rapid, efficient and possible on the gram sca…
Experimental and Theoretical Studies on Magnetic Exchange in Silole-Bridged Diradicals.
2006
International audience; Five bis(tert-butylnitroxide) diradicals connected by a silole [2,5-R2-3,4-diphenylsilole; R = Me3CN(®O.bul.)Z; Z = p-C6H4 (7a), p-C6H4C6H4-p (7b), 1,4-naphthalenediyl (7c), m-C6H4 (7d)] or a thiophene [2,5-R2-thiophene; R = p-Me3CN(®O.bul.)C6H4 (12)] ring as a coupler were studied. Compd. 12 crystallizes in the orthorhombic space group Pna21 with a 20.752(5), b 5.826(5), and c 34.309(5) .ANG.. X-ray crystal structure detn., electronic spectroscopy, variable-temp. EPR spectroscopy, SQUID measurements and DFT computations (UB3LYP/6-31+G*) were used to study the mol. conformations and electronic spin coupling in this series of mols. Whereas compds. 7b, 7c, and 7d are q…
Hyperpolarized 1H long lived states originating from parahydrogen accessed by rf irradiation
2013
Hyperpolarization has found many applications in Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI). However, its usage is still limited to the observation of relatively fast processes because of its short lifetimes. This issue can be circumvented by storing the hyperpolarization in a slowly relaxing singlet state. Symmetrical molecules hyperpolarized by Parahydrogen Induced Hyperpolarization (PHIP) provide a straightforward access to hyperpolarized singlet states because the initial parahydrogen singlet state is preserved at almost any magnetic field strength. In these systems, which show a remarkably long 1H singlet state lifetime of several minutes, the conversion of t…
Photoreactivity of Furocoumarins and DNA in PUVA Therapy: Formation of Psoralen−Thymine Adducts
2008
The mechanism of the [2 + 2] cycloaddition photoreaction of psoralen and a DNA nucleobase, thymine, cornerstone of the furocoumarin-based PUVA (psoralen + UVA radiation) phototherapy, has been studied by the quantum-chemical multiconfigurational CASPT2 method. Triplet- and singlet-mediated mono- and diadduct formations have been determined to take place via singlet-triplet crossings and conical intersections, correlated with the initially promoted triplet or singlet states in different possible reactive orientations. Pyroneside monoadducts are suggested to be formed in the triplet manifold of the system, and to be less prone to yield diadducts because of the properties of the monoadduct low…
Theoretical Insight into the Spectroscopy and Photochemistry of Isoalloxazine, the Flavin Core Ring
2006
The electronic singlet-singlet and singlet-triplet electronic transitions of the isoalloxazine ring of the flavin core are studied using second-order perturbation theory within the framework of the CASPT2//CASSCF protocol. The main features of the absorption spectrum are computed at 3.09, 4.28, 4.69, 5.00, and 5.37 eV. The lowest singlet (S1) and triplet (T1) excited states are found to be both of pi character with a singlet-triplet splitting of 0.57 eV. On the basis of the analysis of the computed spin-orbit couplings and the potential energy hypersurfaces built for the relevant excited states, the intrinsic mechanism for photoinduced population of T1 is discussed. Upon light absorption, e…
On the Intrinsic Population of the Lowest Triplet State of Thymine
2007
The population of the lowest triplet state of thymine after near-UV irradiation has been established, on the basis of CASPT2//CASSCF quantum chemical calculations, to take place via three distinct intersystem crossing mechanisms from the initially populated singlet bright 1pipi* state. Two singlet-triplet crossings have been found along the minimum-energy path for ultrafast decay of the singlet state at 4.8 and 4.0 eV, involving the lowest 3npi* and 3pipi* states, respectively. Large spin-orbit coupling elements predict efficient intersystem crossing processes in both cases. Another mechanism involving energy transfer from the lowest 1npi* state with much larger spin-orbit coupling terms ca…