scholarly journals Photoluminescence of Ni(II), Pd(II), and Pt(II) Complexes [M(Me2dpb)Cl] Obtained from C‒H Activation of 1,5-Di(2-pyridyl)-2,4-dimethylbenzene (Me2dpbH)

Molecules ◽  
2021 ◽  
Vol 26 (16) ◽  
pp. 5051
Author(s):  
Lukas Kletsch ◽  
Rose Jordan ◽  
Alicia S. Köcher ◽  
Stefan Buss ◽  
Cristian A. Strassert ◽  
...  
Keyword(s):  
Glassy Matrix ◽  
No Emission ◽  
Perfect Agreement ◽  
Long Wavelength ◽  
Oxidation Potentials ◽  
Ligand Charge Transfer ◽  
Td Dft ◽  
Lowest Unoccupied Molecular Orbital ◽  
Type Character ◽  
Highest Occupied Molecular Orbitals

The three complexes [M(Me2dpb)Cl] (M = Ni, Pd, Pt) containing the tridentate N,C,N-cyclometalating 3,5-dimethyl-1,5-dipyridyl-phenide ligand (Me2dpb−) were synthesised using a base-assisted C‒H activation method. Oxidation potentials from cyclic voltammetry increased along the series Pt < Ni < Pd from 0.15 to 0.74 V. DFT calculations confirmed the essentially ligand-centred π*-type character of the lowest unoccupied molecular orbital (LUMO) for all three complexes in agreement with the invariant reduction processes. For the highest occupied molecular orbitals (HOMO), contributions from metal dyz, phenyl C4, C2, C1, and C6, and Cl pz orbitals were found. As expected, the dz2 (HOMO-1 for Ni) is stabilised for the Pd and Pt derivatives, while the antibonding dx2−y2 orbital is de-stabilised for Pt and Pd compared with Ni. The long-wavelength UV-vis absorption band energies increase along the series Ni < Pt < Pd. The lowest-energy TD-DFT-calculated state for the Ni complex has a pronounced dz2-type contribution to the overall metal-to-ligand charge transfer (MLCT) character. For Pt and Pd, the dz2 orbital is energetically not available and a strongly mixed Cl-to-π*/phenyl-to-π*/M(dyz)-to-π* (XLCT/ILCT/MLCT) character is found. The complex [Pd(Me2dpb)Cl] showed a structured emission band in a frozen glassy matrix at 77 K, peaking at 468 nm with a quantum yield of almost unity as observed for the previously reported Pt derivative. No emission was observed from the Ni complex at 77 or 298 K. The TD-DFT-calculated states using the TPSSh functional were in excellent agreement with the observed absorption energies and also clearly assessed the nature of the so-called “dark”, i.e., d‒d*, excited configurations to lie low for the Ni complex (≥3.18 eV), promoting rapid radiationless relaxation. For the Pd(II) and Pt(II) derivatives, the “dark” states are markedly higher in energy with ≥4.41 eV (Pd) and ≥4.86 eV (Pt), which is in perfect agreement with the similar photophysical behaviour of the two complexes at low temperatures.

Spectroscopic trends in a series of Re(I) α-diimine complexes as a function of the antenna/photoisomerizable ligands: a TD-DFT and MS-CASPT2 study

2014 ◽  
Vol 92 (10) ◽  
pp. 979-986 ◽  
Author(s):  
Megumi Kayanuma ◽  
Chantal Daniel ◽  
Etienne Gindensperger
Keyword(s):  
Excited States ◽  
Electronic Structures ◽  
Density Functional ◽  
Time Dependent ◽  
Functional Theory ◽  
B3lyp Level ◽  
Ligand Charge Transfer ◽  
Td Dft ◽  
Energy Domain ◽  
Diimine Complexes

The absorption spectra of 11 rhenium(I) complexes with photoisomerizable stilbene-like ligands have been investigated by means of density functional theory (DFT). The electronic structures of the ground and excited states were determined for [Re(CO)3(N,N)(L)]+ (N,N = bpy (2,2′-bipyridine), phen (1,10-phenanthroline), Me4phen (3,4,7,8-tetramethyl-1,10-phenanthroline), ph2phen (4,7-diphenyl-1,10-phenanthroline), or Clphen (5-chloro-1,10-phenanthroline); L = bpe (1,2-bis(4-pyrydil)ethylene), stpy (4-styrylpyridine), or CNstpy (4-(4-cyano)styrylpyridine)) at the time–dependent (TD) DFT/CAM-B3LYP level of theory in vacuum and acetonitrile to highlight the effects of both antenna N,N and isomerizable L ligands. The TD-DFT spectra of two representative complexes, namely [Re(CO)3(bpy)(stpy)]+ and [Re(CO)3(phen)(bpe)]+, have been compared with MS-CASPT2 spectra. The TD-DFT spectra obtained in vacuum and acetonitrile agree rather well both with the ab initio and experimental spectra. The absorption spectroscopy of this series of molecules is characterized by the presence of three low-lying metal to ligand charge transfer (MLCT) states absorbing in the visible energy domain. The nature of the isomerizable ligands (bpe, stpy, or CNstpy) and the type of antenna ligands (bpy, phen, and substituted phen) control the degree of mixing between the MLCT and intraligand excited states, their relative energies, as well as their intensities.

scholarly journals Towards Iron(II) Complexes with Octahedral Geometry: Synthesis, Structure and Photophysical Properties

Molecules ◽  
2020 ◽  
Vol 25 (24) ◽  
pp. 5991
Author(s):  
Mohamed Darari ◽  
Antonio Francés-Monerris ◽  
Bogdan Marekha ◽  
Abdelatif Doudouh ◽  
Emmanuel Wenger ◽  
...  
Keyword(s):  
Excited States ◽  
Photophysical Properties ◽  
Octahedral Geometry ◽  
Ligand Field ◽  
Unexpected Result ◽  
Quintet State ◽  
Dft Modeling ◽  
Ligand Charge Transfer ◽  
Td Dft ◽  
Polypyridine Complexes

The control of ligand-field splitting in iron (II) complexes is critical to slow down the metal-to-ligand charge transfer (MLCT)-excited states deactivation pathways. The gap between the metal-centered states is maximal when the coordination sphere of the complex approaches an ideal octahedral geometry. Two new iron(II) complexes (C1 and C2), prepared from pyridylNHC and pyridylquinoline type ligands, respectively, have a near-perfect octahedral coordination of the metal. The photophysics of the complexes have been further investigated by means of ultrafast spectroscopy and TD-DFT modeling. For C1, it is shown that—despite the geometrical improvement—the excited state deactivation is faster than for the parent pseudo-octahedral C0 complex. This unexpected result is due to the increased ligand flexibility in C1 that lowers the energetic barrier for the relaxation of 3MLCT into the 3MC state. For C2, the effect of the increased ligand field is not strong enough to close the prominent deactivation channel into the metal-centered quintet state, as for other Fe-polypyridine complexes.

Substitution effects and electronic properties of the azo dye (1-phenylazo-2-naphthol) species: a TD-DFT electronic spectra investigation

2015 ◽  
Vol 93 (5) ◽  
pp. 509-517 ◽  
Author(s):  
Lakhdar Mansouri ◽  
Bachir Zouchoune
Keyword(s):  
Electronic Spectra ◽  
Geometry Optimization ◽  
Energy Difference ◽  
Point Of View ◽  
Substitution Effects ◽  
Spectral Position ◽  
Full Geometry Optimization ◽  
Small Energy ◽  
Perfect Agreement ◽  
Td Dft

DFT/B3LYP and ab initio Hartree–Fock calculations with full geometry optimization have been carried out on hydrazo and azo forms of 1-phenylazo-2-naphthol and their substituted derivatives. The predicted geometries show that a small energy difference of 1.8 kcal/mol might tune the equilibrium between both forms. Depending on the electron donating and electron accepting of the different used substituents (CF3, NH2, CH3, Cl, and NO2), the various obtained isomers show small energy differencies between meta and para substitution except for the NH2 one, indicating the coexistence of the tautomers in solution. The ortho(C12) position was found to be the less favored substitution in all cases, while the second ortho(C16) position for different substituents provides isomers competing with the most stable meta and para ones. The obtained results suggest that a judicious choice in the substituents’ use on the phenyl ring should lead to stabilization. The TD-DFT theoretical study performed on the optimized geometry allowed us to identify quite clearly the spectral position and the nature of the different electronic transitions according to their molecular orbital localization, hence, reproducing the available UV-Vis spectra. The increase in the wavelength values is in perfect agreement with red shifts and the ΔE (ELUMO – EHOMO) decreasing. Thus, from the point of view of both substitution and the used solvent, the obtained electronic spectra appear to behave quite differently.

Preparation, Photophysical, Electrochemical, and Ion-Binding Properties of Ru(II) Polypyridyl Complexes Containing a Crown Ether Unit

2011 ◽  
Vol 66 (9) ◽  
pp. 923-929 ◽  
Author(s):  
Feixiang Cheng ◽  
Ning Tang ◽  
Jishu Chen ◽  
Fan Wang ◽  
Longhai Chen
Keyword(s):  
Glassy Matrix ◽  
Ion Binding ◽  
Electrochemical Studies ◽  
Binding Properties ◽  
Binding Ability ◽  
Polypyridyl Ligands ◽  
Ligand Charge Transfer ◽  
Hyperchromic Effect ◽  
The Stability ◽  
Absorption And Emission Spectroscopy

Two polypyridyl ligands, 4`-(4,5-diazafluoren-9-ylimino)benzo-15-crown-5 (L1) and 4` -(4,5-diazafluoren- 9-ylimino)benzo-12-crown-4 (L2), and their Ru(II) complexes [(bpy)2RuL1](PF6)2 and [(bpy)2RuL2](PF6)2, respectively, have been synthesized and characterized. The two complexes display metal-to-ligand charge transfer absorptions at around 444 nm in CH3CN solution at r. t. and emission at around 573 nm in an EtOH-MeOH (4 : 1, v/v) glassy matrix at 77 K. Electrochemical studies of the complexes show one Ru(II)-centered oxidation at around 1.33 V and three ligandcentered reductions. The binding ability of the complexes with Na+ and Li+ has been investigated by UV/Vis absorption and emission spectroscopy and electrochemical titrations. Addition of Na+ and Li+ to solutions of the complexes results in a progressive quenching of the emission, a hyperchromic effect of the UV/Vis absorption, and a progressive cathodal shift of the Ru(II)-centered E1/2 potential. The stability constants for the stoichiometric 1 : 1 ratio of the complexes and the cations have been obtained by UV/Vis absorption titration.

Luminescence properties and optimized structural conformations of the S0, S1 and T1 states of a tetranuclear formamidinate complex based on AuI and AgI metal ions

2019 ◽  
Vol 75 (7) ◽  
pp. 985-989
Author(s):  
Wayne Hsu
Keyword(s):  
Metal Ions ◽  
Excited States ◽  
Ground State ◽  
Density Functional ◽  
Metal Salts ◽  
Time Dependent ◽  
Functional Theory ◽  
Planar Conformation ◽  
Ligand Charge Transfer ◽  
Td Dft

N,N′-Bis(pyridin-4-yl)formamidine (4-pyfH) was reacted with AuI and AgI metal salts to form a novel tetranuclear complex, tetrakis[μ-N,N′-bis(pyridin-4-yl)formamidinato]digold(I)disilver(I), [Ag2Au2(C11H9N4)2] or [Au x Ag4–x (4-pyf)4] (x = 0–4), 1, which is supported by its metallophilicity. Due to the potential permutation of the coordinated metal ions, six different canonical structures of 1 can be obtained. Complex 1 shows an emission at 501 nm upon excitation at 375 nm in the solid state and an emission at 438 nm upon excitation at 304 nm when dispersed in methanol. Time-dependent density functional theory (TD-DFT) calculations confirmed that these emissions can be ascribed to metal-to-ligand charge transfer (MLCT) processes. Moreover, the calculations of the optimized structural conformations of the S0 ground state, and the S1 and T1 excited states are discussed and suggest a distorted planar conformation for the tetranuclear Au2Ag2 complex.

A new heteroleptic phosphorescent cuprous complex supported by a BINAP ligand: synthesis, structure, luminescence properties and theoretical analyses

2020 ◽  
Vol 76 (2) ◽  
pp. 177-185
Author(s):  
Dan-Dan Wang ◽  
Jian-Teng Wang ◽  
Li Song ◽  
You-Yu Wang ◽  
Wen-Xiang Chai
Keyword(s):  
Charge Transfer ◽  
Density Functional ◽  
Low Cost ◽  
Complex Cation ◽  
X Ray Diffraction ◽  
Ligand Charge Transfer ◽  
Td Dft ◽  
Powder Samples ◽  
Phosphorescence Emission ◽  
Cuprous Complex

Luminescent cuprous complexes are an important class of coordination compounds due to their relative abundance, low cost and ability to display excellent luminescence. The heteroleptic cuprous complex solvate rac-(acetonitrile-κN)(3-aminopyridine-κN)[2,2′-bis(diphenylphosphanyl)-1,1′-binaphthyl-κ2 P,P′]copper(I) hexafluoridophosphate dichloromethane monosolvate, [Cu(C5H6N2)(C2H3N)(C44H32P2)]PF6·CH2Cl2, conventionally abbreviated as [Cu(3-PyNH2)(CH3CN)(BINAP)]PF6·CH2Cl2, (I), where BINAP and 3-PyNH2 represent 2,2′-bis(diphenylphosphanyl)-1,1′-binaphthyl and 3-aminopyridine, respectively, is described. In this complex solvate, the asymmetric unit consists of a cocrystallized dichloromethane molecule, a hexafluoridophosphate anion and a complete racemic heteroleptic cuprous complex cation in which the cuprous centre, in a tetrahedral CuP2N2 coordination, is coordinated by two P atoms from the BINAP ligand, one N atom from the 3-PyNH2 ligand and another N atom from a coordinated acetonitrile molecule. The UV–Vis absorption and photoluminescence properties of this heteroleptic cuprous complex have been studied on polycrystalline powder samples, which had been verified by powder X-ray diffraction before recording the spectra. Time-dependent density functional theory (TD-DFT) calculations and a wavefunction analysis reveal that the orange–yellow phosphorescence emission should originate from intra-ligand (BINAP) charge transfer mixed with a little of the metal-to-ligand charge transfer 3(IL+ML)CT excited state.

scholarly journals Thiophene-forming one-pot synthesis of three thienyl-bridged oligophenothiazines and their electronic properties

2016 ◽  
Vol 12 ◽  
pp. 2055-2064 ◽  
Author(s):  
Dominik Urselmann ◽  
Konstantin Deilhof ◽  
Bernhard Mayer ◽  
Thomas J J Müller
Keyword(s):  
Cyclic Voltammetry ◽  
Helical Structure ◽  
Quantum Yields ◽  
Absorption Bands ◽  
One Pot ◽  
Fluorescence Quantum Yields ◽  
Oxidation Potentials ◽  
Td Dft ◽  
Lower Oxidation ◽  
Stokes Shifts

The pseudo five-component Sonogashira–Glaser cyclization synthesis of symmetrically 2,5-diaryl-substituted thiophenes is excellently suited to access thienyl-bridged oligophenothiazines in a one-pot fashion. Three thienyl-bridged systems were intensively studied by UV–vis and fluorescence spectroscopy as well as by cyclic voltammetry. The oxidation proceeds with lower oxidation potentials and consistently reversible oxidations can be identified. The Stokes shifts are large and substantial fluorescence quantum yields can be measured. Computational chemistry indicates lowest energy conformers with sigmoidal and helical structure, similar to oligophenothiazines. TD-DFT and even semiempirical ZINDO calculations reproduce the trends of longest wavelengths absorption bands and allow the assignment of these transitions to possess largely charge-transfer character from the adjacent phenothiazinyl moieties to the central thienyl unit.

scholarly journals Photophysical and Electrocatalytic Properties of Rhenium(I) Triazole-Based Complexes

Inorganics ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 22
Author(s):  
Adrian Comia ◽  
Luke Charalambou ◽  
Salem A. E. Omar ◽  
Paul A. Scattergood ◽  
Paul I. P. Elliott ◽  
...  
Keyword(s):  
Molecular Orbital ◽  
Energy Gap ◽  
Cyclic Voltammograms ◽  
Reduction Wave ◽  
Peak Potential ◽  
Diimine Ligands ◽  
Highest Occupied Molecular Orbital ◽  
Catalytic Wave ◽  
Ligand Charge Transfer ◽  
Lowest Unoccupied Molecular Orbital

A series of [Re(N^N)(CO)3(Cl)] (N^N = diimine) complexes based on 4-(pyrid-2-yl)-1,2,3-triazole (1), 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (2), and 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (3) diimine ligands were prepared and their photophysical and electrochemical properties were characterized. The ligand-based reduction wave is shown to be highly sensitive to the nature of the triazole-based ligand, with the peak potential shifting by up to 600 mV toward more positive potential from 1 to 3. All three complexes are phosphorescent in solution at room temperature with λmax ranging from 540 nm (1) to 638 nm (3). Interestingly, the complexes appear to show inverted energy-gap law behaviour (τ = 43 ns for 1 versus 92 ns for 3), which is tentatively interpreted as reduced thermal accessibility of metal-centred (3MC) states from photoexcited metal to ligand charge transfer (3MLCT) states upon stabilisation of the N^N-centred lowest unoccupied molecular orbital (LUMO). The photophysical characterisation, supported by computational data, demonstrated a progressive stabilization of the LUMO from complex 1 to 3, which results in a narrowing of the HOMO–LUMO energy gap (HOMO = highest occupied molecular orbital) across the series and, correspondingly, red-shifted electronic absorption and photoluminescence spectra. The two complexes bearing pyridyl (1) and pyrimidyl (2) moieties, respectively, showed a modest ability to catalyse the electroreduction of CO2, with a peak potential at ca. −2.3 V versus Fc/Fc+. The catalytic wave that is observed in the cyclic voltammograms is slightly enhanced by the addition of water as a proton source.

BIS(BIPYRIDYL)-RU(II)-1-BENZOYL-3-(PYRIDINE-2-YL)-1H-PYRAZOLE AS POTENTIAL PHOTOSENSITISER: EXPERIMENTAL AND DENSITY FUNCTIONAL THEORY STUDY

2017 ◽  
Vol 79 (5-3) ◽  
Author(s):  
Wun-Fui Mark-Lee ◽  
Febdian Rusydi ◽  
Lorna Jeffery Minggu ◽  
Takashi Kubo ◽  
Mohammad Kassim
Keyword(s):  
Density Functional Theory ◽  
Electronic Properties ◽  
Density Functional ◽  
Energy Levels ◽  
Spectroscopic Techniques ◽  
Functional Theory ◽  
Injection Process ◽  
Highest Occupied Molecular Orbital ◽  
Ligand Charge Transfer ◽  
Td Dft

Ru(II) complexes, [Ru(bpy)2(m-R-L)](PF6)2 where bpy = 2,2’-bipyridyl and  m-R-L= 1-(meta-R)-benzoyl-3-(pyridine-2-yl)-1H-pyrazole derivatives (R = H, CH3 and Cl) abbreviated as RuL, Ru(m-CH3-L) and Ru(m-Cl-L) complexes, respectively, were synthesized and characterized with spectroscopic techniques namely, infrared, UV-Vis and nuclear magnetic resonance (NMR), photoluminescence and mass spectroscopy. Density functional theory (DFT) and time-dependent (TD) DFT calculations were carried out to study the structural and electronic features of the molecules. These Ru(II) complexes exhibit photo-electronic properties required for a photosensitiser in a TiO2-catalysed photoelectrochemical (PEC) cell. In-depth understanding of the R-L fragment functionality is important to tune the photo-electronic properties of the Ru(II) complex. The highest-occupied molecular orbital (HOMO) is mainly localized at the Ru(II) centre, while the LUMO is dominantly spread across the R-L ligand. The Ru(II) complexes showed favourable metal-to-ligand charge transfer (MLCT) energy levels, which are comparably higher than the conduction band of TiO2 to facilitate electron injection process. Among the Ru(II) complexes, Ru(m-Cl-L) comparatively possesses the highest photoluminescence quantum yield and has the potential to be applied as photosensitiser in PEC systems.

Tuning the Carrier Type and Density of Monolayer Tin Selenide via Organic Molecular Doping

2021 ◽  
Author(s):  
Yu Jie Zheng ◽  
Qi Zhang ◽  
Omololu Odunmbaku ◽  
Zeping Ou ◽  
Meng Li ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Organic Molecules ◽  
Single Layer ◽  
Conduction Band Edge ◽  
Shallow Acceptor ◽  
Tin Selenide ◽  
Lowest Unoccupied Molecular Orbital ◽  
Molecular Doping ◽  
P Type ◽  
Highest Occupied Molecular Orbitals

Abstract Utilizing first-principles calculations, charge transfer doping process of single layer tin selenide (SL-SnSe) via the surface adsorption of various organic molecules was investigated. Effective p-type SnSe, with carrier concentration exceeding 3.59×1013 cm-2, was obtained upon adsorption of tetracyanoquinodimethane (TCNQ) or 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ) on SL-SnSe due to their lowest unoccupied molecular orbital (LUMO) acting as shallow acceptor states. While we could not obtain effective n-type SnSe through adsorption of tetrathiafulvalene (TTF) or 1,4,5,8-tetrathianaphthalene (TTN) on pristine SnSe due to their highest occupied molecular orbitals (HOMO) being far from the conduction band edge of SnSe, this disadvantageous situation can be amended by the introduction of an external electric field perpendicular to the monolayer surface. It is found that Snvac will facilitate charge transfer from TTF to SnSe through introducing an unoccupied gap state just above the HOMO of TTF, thereby partially compensating for the p-type doping effect of Snvac. Our results show that both effective p-type and n-type SnSe can be obtained and tuned by charge transfer doping, which is necessary to promote its applications in nanoelectronics, thermoelectrics and optoelectronics.

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