Polychromatic femtosecond fluorescence studies of metal–polypyridine complexes in solution

Bräm, Olivier; Messina, Fabrizio; El‐Zohry, Ahmed M.; Cannizzo, Andrea; Chergui, Majed

doi:10.1016/j.chemphys.2011.11.022

Cited by 87 publications

(79 citation statements)

References 39 publications

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“…2b). It is also worth noting that the short-lived far-ultraviolet emission is roughly the mirror image of the CTTS band, as expected immediately after excitation 26 . The second process (t 2 ) leads to the disappearance of the broad VIS signal.…”

Section: Resultsmentioning

confidence: 89%

“…Indeed, CTTS transitions are strongly dipole-allowed (the integrated intensity of the first CTTS band yields a radiative lifetime of B1 ns), therefore their fluorescence at early times, before complete electron-iodine separation, should be detectable. Indeed, with our fluorescence up-conversion setup, we detected short-lived emission (o50 fs) from molecular states with an order of magnitude longer radiative lifetimes 26 . Here, using the ultraviolet extension of our setup, we report the observation of the CTTS dynamics in real time.…”

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confidence: 99%

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Real-time observation of the charge transfer to solvent dynamics

et al. 2013

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Intermolecular electron-transfer reactions have a crucial role in biology, solution chemistry and electrochemistry. The first step of such reactions is the expulsion of the electron to the solvent, whose mechanism is determined by the structure and dynamical response of the latter. Here we visualize the electron transfer to water using ultrafast fluorescence spectroscopy with polychromatic detection from the ultraviolet to the visible region, upon photo-excitation of the so-called charge transfer to solvent states of aqueous iodide. The initial emission is short lived (B60 fs) and it relaxes to a broad distribution of lower-energy charge transfer to solvent states upon rearrangement of the solvent cage. This distribution reflects the inhomogeneous character of the solvent cage around iodide. Electron ejection occurs from the relaxed charge transfer to solvent states with lifetimes of 100-400 fs that increase with decreasing emission energy.

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Section: Resultsmentioning

confidence: 89%

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confidence: 99%

Real-time observation of the charge transfer to solvent dynamics

et al. 2013

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“…As mentioned in the Introduction, there is ample evidence 17,21,37 that the ISC times generally do not scale with the strength of the spin−orbit constant of the metal atom and that the density of states, the molecular structure and the photoinduced structural dynamics play an important role in the ISC dynamics, providing, respectively, the system with a pool of accepting states or allowing it to reach a favorable molecular configuration for ISC to occur. In the present case, the two complexes have quite similar molecular structures, but their electronic structures are nonetheless significantly different (Figure 1), with Os2 having a higher density of states than Os1.…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, in both complexes we observe a ∼10% contribution of a slower fluorescence decay of 1.5 ps and 150 fs. By analogy to ruthenium complexes, such as [Ru-(dcbpyH) 2 (NCS) 2 ] 2+ (N719), 21 this could arise from the lower energy part of the 1 MLCT manifold of states undergoing slower ISC to the triplet manifold.…”

Section: Discussionmentioning

confidence: 99%

“…9−19 The relaxation of the electronic states of metal−polypyridine complexes from and through the 1 MLCT states down to the triplet metal-to-ligand charge transfer ( 3 MLCT) states is characterized by an ultrafast cascade of internal conversion (IC), intramolecular vibrational redistribution (IVR), and intersystem crossing (ISC) events in tens to hundreds of femtoseconds. 15,20,21 In sensitization by the commonly used Ru−polypyridine complexes, electron injection is known to occur on two different time scales: a short one, from the initially excited nonthermalized 1 MLCT state(s) within a few femtoseconds, 22−24 and a slower one, from the thermalized 3 MLCT states on the picosecond to nanosecond time scale. 25−28 The overall injection quantum yield is close to 100%.…”

Section: Introductionmentioning

confidence: 99%

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Ultrafast Relaxation Dynamics of Osmium–Polypyridine Complexes in Solution

Bräm¹,

Messina²,

Baranoff

et al. 2013

J. Phys. Chem. C

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We present steady-state absorption and emission spectroscopy and femtosecond broadband photoluminescence up-conversion spectroscopy studies of the electronic relaxation of Os(dmbp) 3 (Os1) and Os(bpy) 2 (dpp) (Os2) in ethanol, where dmbp is 4,4′-dimethyl-2,2′-biypridine, bpy is 2,2′-biypridine, and dpp is 2,3-dipyridyl pyrazine. In both cases, the steady-state phosphorescence is due to the lowest 3 MLCT state, whose quantum yield we estimate to be ≤5.0 × 10. For Os1, the steady-state phosphorescence lifetime is 25 ns. In both complexes, the photoluminescence excitation spectra map the absorption spectrum, pointing to an excitation wavelength-independent quantum yield. The ultrafast studies revealed a short-lived (≤100 fs) fluorescence, which stems from the lowest singlet metal-to-ligand-charge-transfer ( 1 MLCT) state and decays by intersystem crossing to the manifold of 3 MLCT states. In addition, Os1 exhibits a 50 ps lived emission from an intermediate triplet state at an energy ∼2000 cm −1 above that of the long-lived (25 ns) phosphorescence. In Os2, the 1 MLCT− 3 MLCT intersystem crossing is faster than that in Os1, and no emission from triplet states is observed other than the lowest one. These observations are attributed to a higher density of states or a smaller energy spacing between them compared with Os1. They highlight the importance of the energetics on the rate of intersystem crossing.

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Ultrafast Studies of the Light‐Induced Spin Change in Fe(II)‐Polypyridine Complexes

Chergui¹

2013

Spin‐Crossover Materials

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Polychromatic femtosecond fluorescence studies of metal–polypyridine complexes in solution

Cited by 87 publications

References 39 publications

Real-time observation of the charge transfer to solvent dynamics

Real-time observation of the charge transfer to solvent dynamics

Ultrafast Relaxation Dynamics of Osmium–Polypyridine Complexes in Solution

Ultrafast Studies of the Light‐Induced Spin Change in Fe(II)‐Polypyridine Complexes

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