Dataset of "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 supported by impulsive stimulated Raman experiments and 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 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.本研究报道了[Ir₂(2,5-二甲基-2,5-二异氰己烷)₄]²⁺（Ir(TMB)）在低频振动区域的超快时间分辨受激辐射与飞秒受激拉曼光谱（FSRS）数据，以此揭示光诱导金属-金属键形成的实时动力学过程。本研究的光谱解析得到脉冲受激拉曼实验与含时密度泛函理论（TDDFT）计算的佐证。从基态跃迁至最低单重激发态¹dσ*pσ时，Ir-Ir伸缩振动频率从53 cm⁻¹翻倍至126 cm⁻¹，证实了Ir-Ir键的形成。激发后最初4 ps内的光谱演化过程显示，受激辐射与FSRS信号强度均呈现幅度极大的相干振荡，其振荡频率由激发态Ir-Ir伸缩振动频率、若干变形振动频率以及一级Ir-Ir泛频共同构成。上述振动模式可直接在FSRS中观测到，但其中绝大多数在最初3 ps内便消失，表明它们属于瞬态占据的热振动激发态。以FSRS频率为横坐标、强度振荡的傅里叶变换结果为纵坐标作图，得到二维飞秒受激拉曼光谱（2D-FSRS）图谱，其特征包含对角峰与非对角峰，这源于弗兰克-康登激发振动与非简谐耦合振动；部分振动模式通过与Ir-Ir伸缩振动耦合获得拉曼强度。综上，光激发会通过同时激发耦合变形振动网络，使Ir-Ir键长被脉冲式缩短并提升其伸缩力常数。随后，电子与振动均处于激发态的体系通过Ir-Ir相互作用的周期性增强与减弱，以及TMB配体骨架构象的变化实现弛豫，并在4~5 ps后形成具有金属-金属键的¹dσ*pσ激发态。