Real-Time Tracking of Photoinduced Metal-Metal Bond Formation in a d 8 d 8 Di-Iridium Complex by Vibrational Coherence and Femtosecond Stimulated Raman Spectroscopy
We report real-time dynamics of photoinduced metal-metal bond formation acquired from ultrafast time-resolved stimulated emission and femtosecond stimulated Raman spectra (FSRS) of [Ir (2,5-dimethyl-2,5-diisocyanohexane) ] (Ir(TMB)) in the region of low-frequency vibrations. Interpretation was suppo...
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| Vydáno v: | Journal of the American Chemical Society Ročník 147; číslo 11; s. 9810 |
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| Hlavní autoři: | , , , , , , , , |
| Médium: | Journal Article |
| Jazyk: | angličtina |
| Vydáno: |
United States
19.03.2025
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| ISSN: | 1520-5126 |
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| Shrnutí: | We report real-time dynamics of photoinduced metal-metal bond formation acquired from ultrafast time-resolved stimulated emission and femtosecond stimulated Raman spectra (FSRS) of [Ir
(2,5-dimethyl-2,5-diisocyanohexane)
]
(Ir(TMB)) in the region of low-frequency vibrations. Interpretation was supported by impulsive stimulated Raman experiments and time-dependent density-functional theory (TDDFT) calculations. The Ir-Ir stretching frequency doubled on going from ground to the lowest singlet excited state
dσ*pσ, from 53 to 126 cm
, demonstrating Ir-Ir bond formation. Spectral evolution during the first 4 ps after excitation showed extremely large-amplitude coherent oscillations of stimulated emission as well as FSRS signal intensities, which occurred with the excited-state Ir-Ir stretching frequency combined with frequencies of several deformation vibrations and the first Ir-Ir overtone. Corresponding vibrations were observed in FSRS directly but most of them vanished in the first 3 ps, indicating that they belonged to transiently populated hot vibrational states. Fourier transforms of intensity oscillations plotted against FSRS frequencies produced two-dimensional (2D-FSRS) maps with diagonal and off-diagonal features due to Franck-Condon-excited and anharmonically coupled vibrations, some of which acquired Raman intensity through coupling with the Ir-Ir stretch. We concluded that optical excitation impulsively shortens the Ir-Ir distance and increases its stretching force constant, assisted by a simultaneously excited network of coupled deformation modes. The electronically/vibrationally excited system then relaxes through periodic strengthening and weakening of the Ir-Ir interaction and changing conformations of the TMB ligand framework, forming a metal-metal bonded
dσ*pσ state after 4-5 ps. |
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| ISSN: | 1520-5126 |
| DOI: | 10.1021/jacs.4c18527 |