Search results for "Triplet state"
showing 10 items of 118 documents
Mechanism of triplet photosensitized Diels-Alder Reaction between indoles and cyclohexadienes: theoretical support for an adiabatic pathway.
2006
Diels-Alder reactions between indoles (InHs) and 1,3-cyclohexadienes (CHDs) were achieved by using aromatic ketones as photosensitizers. For instance, irradiation of deaerated dichloromethane solutions containing benzoylthiophene (BT, 1 mM), indole (20 mM), and phellandrene (40 mM), in the presence of an acylating agent, led to the N-acetylated Diels-Alder cycloadduct in 46% yield (endo:exo ratio of 1.8:1). Energy transfer from the BT triplet to the CHD gave rise to diene dimers as byproducts. Several combinations of CHDs, InHs, and aromatic ketones were tested; the Diels-Alder reaction was found to be a general process, except when the indole nucleus was substituted at position 2 or 7 and …
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…
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…
A theoretical study on the thermal ring opening rearrangement of 1H-bicyclo[3.1.0]hexa-3,5-dien-2-one: a case of two state reactivity
2009
The molecular mechanism of the thermal rearrangement of singlet 1H-bicyclo[3.1.0]hexa-3,5-dien-2-one to give triplet 4-oxocyclohexa-2,5-dienylidene has been investigated using density functional theory (B3LYP and M05-2X functionals) as well as ab initio CASSCF and CASPT2 multiconfigurational methods. The reactant has a singlet ground state while the product can be found in three low lying electronic states P((3)B(1)), P((1)B(1)), and P((1)A'). Therefore, the molecular mechanism of this ring opening rearrangement may involve up to three different potential energy surfaces of two spin multiplicities: two singlet (closed shell, CS, and open shell, OS) and one triplet. The stationary points on …
Triplet‐State Position and Crystal‐Field Tuning in Opto‐Magnetic Lanthanide Complexes: Two Sides of the Same Coin
2019
Lanthanide-complex-based luminescence thermometry and single-molecule magnetism are two effervescent fields of research, owing to the great promise they hold from an application standpoint. The high thermal sensitivity achievable, their contactless nature, along with sub-micrometric spatial resolution make these luminescent thermometers appealing for accurate temperature probing in miniaturised electronics. To that end, single-molecule magnets (SMMs) are expected to revolutionise the field of spintronics, thanks to the improvements made in terms of their working temperature-now surpassing that of liquid nitrogen-and manipulation of their spin state. Hence, the combination of such opto-magne…
Resonance Raman Studies of Bis(terpyridine)ruthenium(II) Amino Acid Esters and Diesters
2009
Resonance Raman (rR) spectroscopy in combination with DFT calculations was used to elucidate the nature of the 1metal-to-ligand charge-transfer states (1MLCT) of ester derivatives of homo- and heteroleptic bis(terpyridine)ruthenium(II) complexes [RuII(tpy–COOC2H5)(tpy–R)](PF6)2 with R = NH2 (1a), R = COOC2H5 (1b) and R = NHCOCH3 (1c). The rR spectra provide evidence that the 1MLCT states of 1b and 1c are well described by the expected 1[(“t2g”)5{π*(tpy–COOC2H5)}1] electron configuration, while the 1MLCT state of the donor/acceptor-substituted complex 1a also involves the amine-substituted terpyridine ligand. The excited state of 1a can be described by a 1[{dyz/π(tpy–NH2)}1{π*(tpy–COOC2H5)}1…
A theoretical insight into the photophysics of psoralen
2006
Psoralen photophysics has been studied on quantum chemistry grounds using the multiconfigurational second-order perturbation method CASPT2. Absorption and emission spectra of the system have been rationalized by computing the energies and properties of the low-lying singlet and triplet excited states. The S1 ππ* state has been determined to be responsible of the lowest absorption and fluorescence bands and to initially carry the population in the photophysical processes related to the phototherapeutic properties of psoralen derivatives. The low-lying T1 ππ* state is, on the other hand, protagonist of the phosphorescence, and its prevalent role in the reactivity of psoralen is suggested to b…
Hybrid functional study of structural, electronic and magnetic properties of S-doped ZnO with and without neutral vacancy
2013
Abstract The structural and electronic properties of S-doped ZnO are investigated by density functional theory (DFT) and empirical pseudopotential method (EPM). Using the Heyd–Scuseria–Ernzerhof (HSE) hybrid functional with an adjusted mixing coefficient α , we obtain a good agreement on lattice parameters and band gap energy with the available experimental data. We have also investigate the Zn-vacancy effects on the electronic and magnetic properties of S-doped ZnO. Our calculations demonstrate that S impurity prefers to be close to the cation vacancy in the apical position. The magnetic analysis with the HSE functional shows a triplet state character with a total magnetic moment of 1.81 μ…
Azole-containing cationic bis-cyclometallated iridium(iii) isocyanide complexes: a theoretical insight into the emission energy and emission efficien…
2019
Using a density functional theory approach, we explore the emission properties of a family of bis-cyclometallated cationic iridium(iii) complexes of general formula [Ir(C^N)2(CN-tert-Bu)2]+ that have tert-butyl isocyanides as neutral auxiliary ligands. Taking the [Ir(ppy)2(CN-tert-Bu)2]+ complex (Hppy = 2-phenylpyridine) as a reference, the effect of replacing the pyridine ring in the cyclometallating ppy ligand by a five-membered azole ring has been examined. To this end, two series of complexes differing by the nature of the atom (either nitrogen or carbon) linking the azole to the phenyl ring of the cyclometallating ligand have been designed. Each series is composed of three molecules ha…
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…