Relativistic effects in spectroscopy and photophysics of heavy-metal complexes illustrated by spin–orbit calculations of [Re(imidazole)(CO)3(phen)]+

Baková, Radka; Chergui, Majed; Daniel, Chantal; Vlček, Antonı́n; Záliš, Stanislav

doi:10.1016/j.ccr.2010.12.027

Cited by 96 publications

(115 citation statements)

References 127 publications

(274 reference statements)

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“…One should rather classify the states as spin−orbit states, as described in ref 28. Of course, the lowest excited states will have a purer spin character because of less mixing, as witnessed by the long phosphorescence lifetimes one measures in luminescent metal complexes.…”

Section: Ultrafast Iscmentioning

confidence: 99%

Ultrafast Photophysics of Transition Metal Complexes

2015

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The properties of transition metal complexes are interesting not only for their potential applications in solar energy conversion, OLEDs, molecular electronics, biology, photochemistry, etc. but also for their fascinating photophysical properties that call for a rethinking of fundamental concepts. With the advent of ultrafast spectroscopy over 25 years ago and, more particularly, with improvements in the past 10-15 years, a new area of study was opened that has led to insightful observations of the intramolecular relaxation processes such as internal conversion (IC), intersystem crossing (ISC), and intramolecular vibrational redistribution (IVR). Indeed, ultrafast optical spectroscopic tools, such as fluorescence up-conversion, show that in many cases, intramolecular relaxation processes can be extremely fast and even shorter than time scales of vibrations. In addition, more and more examples are appearing showing that ultrafast ISC rates do not scale with the magnitude of the metal spin-orbit coupling constant, that is, that there is no heavy-atom effect on ultrafast time scales. It appears that the structural dynamics of the system and the density of states play a crucial role therein. While optical spectroscopy delivers an insightful picture of electronic relaxation processes involving valence orbitals, the photophysics of metal complexes involves excitations that may be centered on the metal (called metal-centered or MC) or the ligand (called ligand-centered or LC) or involve a transition from one to the other or vice versa (called MLCT or LMCT). These excitations call for an element-specific probe of the photophysics, which is achieved by X-ray absorption spectroscopy. In this case, transitions from core orbitals to valence orbitals or higher allow probing the electronic structure changes induced by the optical excitation of the valence orbitals, while also delivering information about the geometrical rearrangement of the neighbor atoms around the atom of interest. With the emergence of new instruments such as X-ray free electron lasers (XFELs), it is now possible to perform ultrafast laser pump/X-ray emission probe experiments. In this case, one probes the density of occupied states. These core-level spectroscopies and other emerging ones, such as photoelectron spectroscopy of solutions, are delivering a hitherto unseen degree of detail into the photophysics of metal-based molecular complexes. In this Account, we will give examples of applications of the various methods listed above to address specific photophysical processes.

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Section: Ultrafast Iscmentioning

confidence: 99%

Ultrafast Photophysics of Transition Metal Complexes

2015

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“…[40][41][42][43][44][45][46][47][48] Herein the electronic and geometrical structures of the ground state and lowest S n and T n excited states of bidentate complexes 1 and 2 and of terdentate complexes 3, 4 and 5 depicted in Scheme 1 and their absorption spectra are studied at the TD-DFT level, including solvent and SOC effects. Our goal is to compare and interpret the remarkable disparity in the emissive properties of these complexes, cyclometalated or not and representative of a wide class of square planar Pt(II) complexes investigated for their luminescence properties.…”

Section: Introductionmentioning

confidence: 99%

Spin–orbit effects in square-planar Pt(ii) complexes with bidentate and terdentate ligands: theoretical absorption/emission spectroscopy

Gourlaouen

Daniel

2014

Dalton Trans.

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The absorption and emission properties of five Pt(ii) planar complexes with bidentate ligands, namely [Pt(bpy)Cl2] (bpy = 2,2'-bipyridine) and [Pt(ppy)Cl2](-) (ppy = 2-phenylpyridine) , and terdentate ligands, namely [Pt(tpy)Cl](+) (tpy = 2,2':6',2''-terpyridine) , [Pt(phbpyR)Cl] (phbpy = 6-phenyl-2,2'-bipyridine; R = H) and [Pt(dpybR)Cl] (dpyb = 2,6-di(2-pyridyl)benzene; R = CH3) were investigated by means of density functional theory (DFT) and time-dependent DFT (TD-DFT) methods including solvent correction and spin-orbit coupling (SOC). The DFT optimized structures of the five complexes in the electronic ground state are in agreement with the experimental X-ray data and the theoretical absorption spectra reproduce quantitatively the main features of the experimental spectra. It is shown that the structures remain nearly planar in the low-lying singlet and triplet excited states of charge transfer character, metal-to-ligand (MLCT) or halide (Cl) to ligand (XLCT) whereas a significant distortion corresponding to the out-of-plane-bending of the Pt-Cl bond characterizes the geometry of the metal-centered (MC) states. In cyclometalated complexes , and this distortion is energetically unfavorable and not competitive with radiative decay via the low-lying MLCT and XLCT excited states. The absorption spectra of all complexes are significantly affected by spin-orbit coupling (red-shift and broadening), especially in the non-cyclometalated complexes and characterized by the presence of pure low-lying (3)MC states. The SOC effects are less important in the terpyridine complex the lowest part of its spectrum being contaminated by mixed (3)MLCT/(3)XLCT states. In the cyclometalated complexes and the presence of several LC states in the lowest part of the spectra is responsible for a small shift to the red as compared to the other complexes. The solvatochromism that characterizes the absorption of this class of molecules in the visible region is interpreted by the MLCT/XLCT mixed character of the excited states in this energy domain (400-450 nm). Indeed the solvent dependent XLCT contribution will control the magnitude of SOC in these excited states and will move the band to the red region when diminishing and to the blue region when increasing. As far as emission is concerned it is shown that strongly distorted non-radiative MC state's minima, situated below the charge transfer state's minima (ΔE = -0.3 eV to -0.8 eV) are easily accessible upon irradiation in the visible region in complexes and , and in to a lesser extent, leading to no or low luminescence at room temperature. In contrast, the minima of the emissive states of mixed MLCT/XLCT/LC character are efficiently populated in and . The luminescence of complex , cyclometalated in the axial position, is particularly efficient because the minimum of the lowest emissive state is well separated from those of the MC states (ΔE = +0.23 eV) in contrast to its analog, complex , cyclometalated in the lateral position where the emissive MLCT/LC state minimum is nearly degenera...

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“…We carried detailed fs optical fluorescence and transient absorption studies, which were combined with extensive quantum-chemical calculations. [21,24,25,63] Some of the remarkable findings of this study are the fact that the ultrafast ISC from singlet to triplet is significantly longer that in the above tris-bipyridine complexes, even though Re has a larger spin-orbit (SO) constant than Ru or Fe. Also, the ISC time increases [21] in the series Cl-Br-I (from ~100 to 150 fs), which is contrary to the expected trends considering the SO constant of the halogen atom.…”

Section: Rhenium(i)-halogen Carbonylbipyridine Complexesmentioning

confidence: 92%