Search results for "LUMO"
showing 10 items of 164 documents
Structural, electronic and energetic effects in heterocyclic fluorene derivatives fused with a fulvene unit
2019
Abstract A set of 36 heterocyclic (B, N and O) fluorene (C) derivatives fused in nine ways with fulvene ring have been analyzed by means of different local aromaticity criteria. Molecular geometry of analyzed compounds were optimized at B3LYP/6-311++G(2d,2p) level of theory. The evaluation of the local aromaticity has been carried out through the use of the geometry-based harmonic oscillator model of aromaticity (HOMA) and the magnetism-based zz‐component of the nucleus independent chemical shifts calculated 1 A above the ring center (NICS1zz) indices as well as one aromaticity index derived from the Quantum Theory Atoms in Molecules (QTAIM), i.e. the para-delocalization index (PDI). Additi…
Synthesis, reactivity and structural studies of carboranyl thioethers and disulfides.
2005
The equimolar reaction of 1-SH-2-R-1,2-closo-C2B10H10 (R = Me, H, Ph) with KOH in ethanol produces the thiolate species [1-S-2-R-1,2-closo-C2B10H10]−. These react with iodine to give the disulfide bridged dicluster (1-S-2-R-1,2-closo-C2B10H10)2 (R = H, Me, Ph) compounds as analytically pure, white and air-stable solids in high yield. Synthesis of monothioether bridged species is synthetically more difficult. In fact three procedures have been tested to obtain the thioether bridged dicluster compounds (2-R-1,2-closo-C2B10H10)2S (R = Me, H, Ph) but only (2-Me-1,2-closo-C2B10H10)2S was successfully synthesized and characterized. Attempts to produce mixed compounds (1-R-1,2-closo-C2B10H10)S(1-R…
[Ir(C^N)2(N^N)]+ emitters containing a naphthalene unit within a linker between the two cyclometallating ligands
2016
The synthesis of four cyclometallated [Ir(C^N) 2 (N^N)][PF 6 ] compounds in which N^N is a substituted 2,2’- -bipyridine (bpy) ligand and the naphthyl-centred ligand 2,7-bis(2-(2-(4-(pyridin-2-yl)phenoxy)ethoxy) ethoxy)naphthalene provides the two cyclometallating C^N units is reported. The iridium( III ) complexes have been characterized by 1 H and 13 C NMR spectroscopies, mass spectrometry and elemental analysis, and their electrochemical and photophysical properties are described. Comparisons are made with a model [Ir(ppy) 2 (N^N)][PF 6 ] compound (Hppy = 2-phenylpyridine). The complexes containing the naphthyl-unit exhibit similar absorption spectra and excitation at 280 nm leads to an …
Luminescent osmium(II) bi-1,2,3-triazol-4-yl complexes: photophysical characterisation and application in light-emitting electrochemical cells
2016
The series of osmium(II) complexes [Os(bpy)3-n(btz)n][PF6]2 (bpy = 2,2’-bipyridyl, btz = 1,1’-dibenzyl-4,4’-bi-1,2,3-triazolyl, 1 n = 0, 2 n = 1, 3 n = 2, 4 n = 3), have been prepared and characterised. The progressive replacement of bpy by btz leads to blue-shifted UV-visible electronic absorption spectra, indicative of btz perturbation of the successively destabilised bpy-centred LUMO. For 4, a dramatic blue-shift relative to the absorption profile for 3 is observed, indicative of the much higher energy LUMO of the btz ligand over that of bpy, mirroring previously reported data on analogous ruthenium(II) complexes. Unlike the previously reported ruthenium systems, heteroleptic complexes 2…
FT Raman and DFT Study on a Series of All-antiOligothienoacenes End-Capped with Triisopropylsilyl Groups
2009
minal a positions. These substituents aid in purification and solution processability, and can be removed under mild chemical conditions. For the first time, we have the opportunity to analyze a series of oligothienoacenes to gain insight into the fundamental structure–property relationships with respect to the addition of each ring. Furthermore, this series of compounds can be directly compared to other well-studied series of closely related oligomers, such as nonfused oligothiophenes and fully fused all-syn oligothienoacenes. [7] To gain precise insight into relationships between the structure and properties of a wide range of p-conjugated molecular Herein, we study the p-conjugational pr…
Crystal and molecular structure studies of (Z)-N-methyl-C-4-substituted phenyl nitrones by XRD, DFT, FTIR and NMR methods
2017
Abstract (Z)-N-methyl-C-4-substituted phenyl nitrones –O+N(Me)=C(H)R (Z-2a R = 4-ClC6H4, Z-2b R = 4-NO2C6H4, Z-2c R = 4-CH3OC6H4) were synthesized and characterized by elemental analyses, FTIR, 1H, 13C and DEPT-135 NMR spectroscopy and also by single crystal X-ray diffraction (in the case of Z-2a and Z-2b). The geometries of the nitrone molecules Z-2a, Z-2b and Z-2c and their E-isomers; (E)-N-methyl-C-4-chlorophenyl nitrone E-2a, (E)-N-methyl-C-4-nitrophenyl nitrone E-2b and (E)-N-methyl-C-4-methoxyphenyl nitrone E-2c were optimized using density functional theory (DFT) at the B3LYP/6-311++G(d,p) level of theory. The theoretical vibrational frequencies obtained by DFT calculations are in go…
Lowest triplet excited states of a novel heteroleptic iridium(III) complex and their role in the emission colour
2009
Abstract The [Ir(ppy-F 2 ) 2 Me 4 phen] +1 complex, where ppy-F 2 is 2-(2′,4′-fluorophenyl)pyridine and Me 4 phen is 3,4,7,8-tetramethyl-1,10-phenanthroline, has been theoretically investigated by means of DFT calculations. The molecular and electronic properties calculated for [Ir(ppy-F 2 ) 2 Me 4 phen] +1 are compared with those obtained for the simpler [Ir(ppy)(bpy)] +1 complex. The introduction of fluorine substituents in the ppy ligands and the use of phenanthroline instead of 2,2′-bipyridine as the diimine ligand increase the HOMO–LUMO energy gap and blue-shift the emission colour. The phenanthroline ligand causes the appearance of two nearly-degenerate LUMO orbitals of different symm…
Highly Stable and Efficient Light-Emitting Electrochemical Cells Based on Cationic Iridium Complexes Bearing Arylazole Ancillary Ligands.
2017
A series of bis-cyclometalated iridium(III) complexes of general formula [Ir(ppy)2(N∧N)][PF6] (ppy− = 2-phenylpyridinate; N∧N = 2-(1H-imidazol-2-yl)pyridine (1), 2-(2-pyridyl)benzimidazole (2), 1-methyl-2-pyridin-2-yl- 1H-benzimidazole (3), 2-(4′-thiazolyl)benzimidazole (4), 1- methyl-2-(4′-thiazolyl)benzimidazole (5)) is reported, and their use as electroluminescent materials in light-emitting electrochemical cell (LEC) devices is investigated. [2][PF6] and [3][PF6] are orange emitters with intense unstructured emission around 590 nm in acetonitrile solution. [1][PF6], [4][PF6], and [5][PF6] are green weak emitters with structured emission bands peaking around 500 nm. The different photoph…
Getting discriminant functions of antibacterial activity from physicochemical and topological parameters.
2001
Linear discriminant analysis has been demonstrated to be a very useful tool in the selection and design of new drugs. Up to now we have used it through the search of a topological pattern of activity. In this work our goal is to calculate a complete set of physicochemical parameters using semiempirical (quantum chemical) calculations as well as topological indices (TIs) and try to find out any discriminant function for antibacterial activity through the combined use of both types of descriptors. The physicochemical parameters, such as heat of formation, HOMO, LUMO, dipole moment, polarizability, hyperpolarizability, PM3 generated IR vibrational frequencies, etc., were calculated using PM3 H…
Theoretical study of new acceptor and donor molecules based on polycyclic aromatic hydrocarbons
2011
Functionalized polcyclic aromatic hydrocarbons (PAHs) are an interesting class of molecules in which the electronic state of the graphene-like hydrocarbon part is tuned by the functional group. Searching for new types of donor and acceptor molecules, a set of new PAHs has recently been investigated experimentally using ultraviolet photoelectron spectroscopy (UPS). In this work, the electronic structure of the PAHs is studied numerically with the help of B3LYP hybrid density functionals. Using the DELTA-SCF method, electron binding energies have been determined which affirm, specify and complement the UPS data. Symmetry properties of molecular orbitals are analyzed for a categorization and a…