Real-Time Tracking of Photoinduced Metal-Metal Bond Formation in a d8d8 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 [Ir2(2,5-dimethyl-2,5-diisocyanohexane)4]2+ (Ir(TMB)) in the region of low-frequency vibrations. Interpretation was sup...
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| Published in: | Journal of the American Chemical Society Vol. 147; no. 11; p. 9810 |
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| Main Authors: | , , , , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
06.03.2025
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| ISSN: | 1520-5126, 1520-5126 |
| Online Access: | Get more information |
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| Summary: | 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 [Ir2(2,5-dimethyl-2,5-diisocyanohexane)4]2+ (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 1dσ*pσ, from 53 to 126 cm-1, 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 1dσ*pσ state after 4-5 ps.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 [Ir2(2,5-dimethyl-2,5-diisocyanohexane)4]2+ (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 1dσ*pσ, from 53 to 126 cm-1, 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 1dσ*pσ state after 4-5 ps. |
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| Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 1520-5126 1520-5126 |
| DOI: | 10.1021/jacs.4c18527 |