Excited-State Relaxation in Luminescent Molybdenum(0) Complexes with Isocyanide Chelate Ligands

Diisocyanide ligands with a m-terphenyl backbone provide access to Mo0 complexes exhibiting the same type of metal-to-ligand charge transfer (MLCT) luminescence as the well-known class of isoelectronic RuII polypyridines. The luminescence quantum yields and lifetimes of the homoleptic tris(diisocyanide) Mo0 complexes depend strongly on whether methyl- or tert-butyl substituents are placed in α-position to the isocyanide groups. The bulkier tert-butyl substituents lead to a molecular structure in which the three individual diisocyanides ligated to one Mo0 center are interlocked more strongly into one another than the ligands with the sterically less demanding methyl substituents. This rigidification limits the distortion of the complex in the emissive excited-state, causing a decrease of the nonradiative relaxation rate by one order of magnitude. Compared to RuII polypyridines, the molecular distortions in the luminescent 3MLCT state relative to the electronic ground state seem to be smaller in the Mo0 complexes, presumably due to delocalization of the MLCT-excited electron over greater portions of the ligands. Temperature-dependent studies indicate that thermally activated nonradiative relaxation via metal-centered excited states is more significant in these homoleptic Mo0 tris(diisocyanide) complexes than in [Ru(2,2′-bipyridine)3]2+.

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Temperature Dependent Emission Properties of ReI Tricarbonyl Complexes with Dipyrido-Quinoxaline and Phenazine Ligands

Journal of the Brazilian Chemical Society ◽

10.21577/0103-5053.20210161 ◽

2022 ◽

Author(s):

Cristiane Ramos ◽

Fernando Prado ◽

Marcos Eduardo Carmo ◽

Giliandro Farias ◽

Bernardo Souza ◽

...

Keyword(s):

Excited State ◽

Quantum Yields ◽

Triplet States ◽

Solvent Mixtures ◽

Spin Orbit Coupling ◽

Temperature Dependent ◽

Emission Properties ◽

Luminescent Probes ◽

Ligand Charge Transfer ◽

Different Temperatures

In this work, the emission properties of fac-[Re(CO)3(NN)(py)]+, NN = 1,10-phenanthroline (phen), dipyrido[3,2-f:2’,3’-h]quinoxaline (dpq) and dipyrido[3,2-a:2’3’-c]phenazine (dppz); py = pyridine were investigated in different temperatures, ranging from 80 to 300 K, and in different solvent mixtures and in polymethyl methacrylate. The changes observed in the emission quantum yields were rationalized based on a two-level excited state model, in which the nonemissive upper state is thermally populated and decays faster than the lowest lying emissive state. fac‑[Re(CO)3(dpq)(py)]+ is a metal-to-ligand charge transfer (MLCT) emitter as the complex with phen but exhibits smaller emission quantum yields, being more sensitive to the solvent. This behavior was rationalized by quantum-mechanical calculations including the spin-orbit coupling matrix elements, revealing that intersystem crossing from the lowest singlet excited state in fac- [Re(CO)3(dpq)(py)]+ likely occurs to triplet states lying at higher energies. Similar behavior were observed for fac-[Re(CO)3(dppz)(py)]+, although the later exhibits intraligand emission that are strongly quenched in fluid solutions by low-lying MLCT states. The fundamental studies carried out here provide new insights on the excited state dynamics of ReI complexes with dipyridoquinoxaline and phenazine ligands and can contribute for further advances on their application as luminescent probes.

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Regioisomeric Effect on the Excited-State Fate Leading to Room-Temperature Phosphorescence or Thermally Activated Delayed Fluorescence in a Dibenzophenazine-Cored Donor–Acceptor–Donor System

10.26434/chemrxiv-2021-6672t ◽

2021 ◽

Author(s):

Takumi Hosono ◽

Nicolas Oliveira Decarli ◽

Paola Zimmermann Crocomo ◽

Tsuyoshi Goya ◽

Leonardo Evaristo de Sousa ◽

...

Keyword(s):

Excited State ◽

Room Temperature ◽

Delayed Fluorescence ◽

Quantum Yields ◽

Room Temperature Phosphorescence ◽

Thermally Activated Delayed Fluorescence ◽

Light Emitting ◽

Thermally Activated ◽

Donor Acceptor ◽

Emission Behavior

Exploring design principle for switching thermally activated dealyed fluorescecne (TADF) and room temperature phosphorescence (RTP) is a fundamentally imporant research in developing triplet-mediated photofunctional organic materials. Herein systematic studies on the regioisomeric and substituents effects in a twisted donor–acceptor–donor (D–A–D) scaffold (A = dibenzo[a,j]phenazine; D = dihydrophenazasiline) on the fate of the excited state have been performed. The study revealed that the regiosiomerism clearly affects the emission behavior of the D–A–D compounds. Distinct difference in TADF, dual TADF & RTP, and dual RTP were observed, depending on the host used. Furthermore, OLED organic light-emitting diodes (OLEDs) fabricated with the developed emitters achieved high external quantum yields for RTP-based OLEDS up to 7.4%.

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Evaluation of Luminescence Decay Measurements Probed on Pure and Doped Pt(IV) Hexahalogeno Complexes. II. Molecular Properties Obtained from Temperature Dependent Lifetime Curves

Zeitschrift für Naturforschung A ◽

10.1515/zna-1997-0513 ◽

1997 ◽

Vol 52 (5) ◽

pp. 447-456

Author(s):

Ingo Biertümpel ◽

Hans-Herbert Schmidtke

Keyword(s):

Excited States ◽

Ground State ◽

Energy Levels ◽

Decay Rates ◽

Rate Equations ◽

Temperature Dependent ◽

Lifetime Measurements ◽

Thermally Activated ◽

Ground State Energies ◽

Higher Excited States

Abstract Lifetime measurements down to nearly liquid helium temperatures are used for determining energy levels and transition rates between excited levels and relaxations into the ground state. Energies are obtained from temperature dependent lifetimes by fitting experimental curves to model functions pertinent for thermally activated processes. Rates are calculated from solutions of rate equations. Similar parameters for pure and doped Pt(IV) hexahalogeno complexes indicate that excited levels largely belong to molecular units. Some of the rates between excited states are only somewhat larger than decay rates into the ground state, which is a consequence of the polyexponential decay measured also at low temperature (2 K). In the series of halogen complexes, the rates between spinorbit levels resulting from 3T1g increase from fluorine to bromine, although energy splittings become larger. Due to the decreasing population of higher excited states in this series, K^PtFö shows a tri-exponential, K2PtCl6 a bi-exponential and FoPtBr6 a mono-exponential decay. In the latter case the population density of higher excited states relaxes so fast that emission occurs primarily from the lowest excited Γ3(3T1g) level. Phase transitions and emission from chromophores on different sites can also be observed.

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A density functional theory and spectroscopic study of intramolecular quenching of metal-to-ligand charge-transfer excited states in some mono-bipyridine ruthenium(II) complexes

Canadian Journal of Chemistry ◽

10.1139/cjc-2014-0155 ◽

2014 ◽

Vol 92 (10) ◽

pp. 996-1009 ◽

Cited By ~ 7

Author(s):

Shivnath Mazumder ◽

Ryan A. Thomas ◽

Richard L. Lord ◽

H. Bernhard Schlegel ◽

John F. Endicott

Keyword(s):

Density Functional Theory ◽

Excited State ◽

Charge Transfer ◽

Excited States ◽

Lower Energy ◽

Density Functional ◽

Dimethyl Sulfide ◽

Intramolecular Electron Transfer ◽

Functional Theory ◽

Ligand Charge Transfer

The complexes [Ru(NCCH3)4bpy]2+ and [Ru([14]aneS4)bpy]2+ ([14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane, bpy = 2,2′-bipyridine) have similar absorption and emission spectra but the 77 K metal-to-ligand charge-transfer (MLCT) excited state emission lifetime of the latter is less than 0.3% that of the former. Density functional theory modeling of the lowest energy triplet excited states indicates that triplet metal centered (3MC) excited states are about 3500 cm−1 lower in energy than their 3MLCT excited states in both complexes. The differences in excited state lifetimes arise from a much larger coordination sphere distortion for [Ru(NCCH3)4bpy]2+ and the associated larger reorganizational barrier for intramolecular electron transfer. The smaller ruthenium ligand distortions of the [Ru([14]aneS4)bpy]2+ complex are apparently a consequence of stereochemical constraints imposed by the macrocyclic [14]aneS4 ligand, and the 3MC excited state calculated for the unconstrained [Ru(S(CH3)2)4bpy]2+ complex (S(CH3)2 = dimethyl sulfide) is distorted in a manner similar to that of [Ru(NCCH3)4bpy]2+. Despite the lower energy calculated for its 3MC than 3MLCT excited state, [Ru(NCCH3)4bpy]2+ emits strongly in 77 K glasses with an emission quantum yield of 0.47. The emission is biphasic with about a 1 μs lifetime for its dominant (86%) emission component. The 405 nm excitation used in these studies results in a significant amount of photodecomposition in the 77 K glasses. This is a temperature-dependent biphotonic process that most likely involves the bipyridine-radical anionic moiety of the 3MLCT excited state. A smaller than expected value found for the radiative rate constant is consistent with a lower energy 3MC than 3MLCT state.

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Ten-Nanosecond Step-Scan FT-IR Absorption Difference Time-Resolved Spectroscopy: Applications to Excited States of Transition Metal Complexes

Applied Spectroscopy ◽

10.1366/0003702971940648 ◽

1997 ◽

Vol 51 (4) ◽

pp. 580-583 ◽

Cited By ~ 23

Author(s):

Pingyun Chen ◽

Richard A. Palmer

Keyword(s):

Excited State ◽

Excited States ◽

Signal To Noise Ratio ◽

Ir Absorption ◽

Decay Kinetics ◽

Time Resolved ◽

Ligand Charge Transfer ◽

Ft Ir ◽

Good Signal ◽

Nanosecond Time Resolution

Ten-nanosecond time resolution has been achieved with step-scan FT-IR absorbance difference spectroscopy (S2FT-IR Δ A TRS) and demonstrated by measuring Δ A spectra of fac-[Re(bpy)(CO)3Cl] and cis-[Os(bpy)2(CO)(4,4′-bpy)]2+ (bpy = 2,2′-bipyridine; 4,4′-bpy=4,4′-bipyridine) in CH3CN solution, following 355-nm laser excitation. In both complexes, the large shifts in (CO) to higher energy are consistent with the assignment that the lowest-energy excited states are metal-to-ligand charge transfer in nature. For [Os(bpy)2(CO)(4,4′-bpy)]2+, it is also possible to measure the excited-state decay kinetics, again with 10-ns resolution. In addition, Δ A bands are observed that are related to excited-state vibrations of the bipyridine ligands. Δ A spectra of good signal-to-noise ratio can be obtained for complexes with lifetimes as short as 10 ns.

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Temperature dependent iodide oxidation by MLCT excited states

Dalton Transactions ◽

10.1039/c4dt01683a ◽

2014 ◽

Vol 43 (47) ◽

pp. 17856-17863 ◽

Cited By ~ 6

Author(s):

Atefeh Taheri ◽

Gerald J. Meyer

Keyword(s):

Excited State ◽

Excited States ◽

Temperature Dependent ◽

Iodide Oxidation ◽

First Time

Temperature dependent excited state iodide oxidation by two heteroleptic Ru polypyridyl compounds was quantified for the first time.

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Photoacidity as a tool to rationalize excited state intramolecular proton transfer reactivity in flavonols

Photochemical & Photobiological Sciences ◽

10.1039/c7pp00334j ◽

2018 ◽

Vol 17 (2) ◽

pp. 231-238 ◽

Cited By ~ 22

Author(s):

Luís Gustavo Teixeira Alves Duarte ◽

José Carlos Germino ◽

Cláudia de Ávila Braga ◽

Cristina Aparecida Barboza ◽

Teresa Dib Zambon Atvars ◽

...

Keyword(s):

Excited State ◽

Proton Transfer ◽

Excited States ◽

Intramolecular Proton Transfer ◽

Flavonol Derivatives ◽

Proton Transfer Reactivity ◽

Electronic Ground

Determination of acidic strengths at the electronic ground and excited states of flavonol derivatives.

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Excited-state deactivation mechanisms of protonated and neutral phenylalanine: a theoretical study

RSC Advances ◽

10.1039/c5ra00630a ◽

2015 ◽

Vol 5 (37) ◽

pp. 29032-29039

Author(s):

Reza Omidyan ◽

Mitra Ataelahi ◽

Gholamhassan Azimi

Keyword(s):

Excited State ◽

Proton Transfer ◽

Excited States ◽

Theoretical Study ◽

Minimum Energy ◽

Bond Stretching ◽

Minimum Energy Paths ◽

Electronic Ground

Minimum energy paths (MEPs) of protonated phenylalanine (PheH+) at the electronic ground and S1 (1ππ*) excited states along the Cα–Cβ bond stretching coordinate, following proton transfer to the aromatic chromophore.

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Photodisproportionation of (1,5-Cyclooctadiene) copper(I) Hexafluoroacetylacetonate Induced by Metal-to-Ligand Charge Transfer Excitation

Zeitschrift für Naturforschung B ◽

10.1515/znb-2003-0717 ◽

2003 ◽

Vol 58 (7) ◽

pp. 704-707 ◽

Cited By ~ 2

Author(s):

Horst Kunkely ◽

Arnd Vogler

Keyword(s):

Excited State ◽

Charge Transfer ◽

Quantum Yields ◽

Long Wavelength ◽

Ligand Charge Transfer ◽

Elemental Copper ◽

Charge Transfer Excitation ◽

Reactive Excited State

The complex CuI(COD)(hfac) with COD = 1,5- cyclooctadiene and hfac = hexafluoroacetyl-acetonate shows two long-wavelength absorptions at λmax = 308 and 241 nm which are assigned to hfac intraligand (IL) and CuI →COD metal-to-ligand charge transfer (MLCT) transitions, respectively. The photolysis of CuI(COD)(hfac) in hexane leads to the release of the olefin and the subsequent disproportionation of CuI(hfac) to elemental copper and CuII(hfac)2 with the quantum yields Φ = 10−3 at λirr =313 nm and Φ = 3×10−3 at λirr = 254 nm. It is suggested that the reactive excited state is of the MLCT type.

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