Phelps Ryan, Agapaki Eleftheria, Brechin Euan K, Johansson J Olof
EaStCHEM School of Chemistry, University of Edinburgh David Brewster Road EH9 3FJ Edinburgh UK
Chem Sci. 2024 Jun 27;15(30):11956-11964. doi: 10.1039/d4sc00145a. eCollection 2024 Jul 31.
Octahedral Mn(iii) ions predominantly exhibit an axially elongated Jahn-Teller (JT) distortion, which is responsible for their large uniaxial magnetic anisotropy. As a result, they are often used in the synthesis of single-molecule magnets (SMMs). Modulation of the JT distortion using femtosecond laser pulses could offer a route to controlling the magnetisation direction, and therefore is promising for the development of data storage devices that work on ultrafast timescales. Photoinduced switching of the distortion from an axially elongated to an axially compressed structure has been demonstrated for various Mn(iii) complexes. However, the dynamics around the region of the conical intersection for the photoinduced JT switch remains unclear. Here, ultrafast transient absorption spectra were recorded for solutions of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)manganese(iii) (Mn(dpm)) in ethanol to further explore the dynamics of the photoinduced JT switch. We observe the generation of a vibrational wavepacket on the excited state surface, which has a frequency of approximately 155 cm and encompasses a JT-active vibrational mode. This coherent motion is maintained after passage through the conical intersection back to the ground state, which launches wavepackets along the ground state potential energy surface (PES) with frequencies of approximately 180 and 110 cm that we assign to the elongated and compressed state, respectively. Inspection of the relative phases of the frequencies reveals phase shifts that are consistent with a one-mode reaction coordinate, and passes through the conical intersection at 1/4 and 3/4 of the excited state vibrational period. Our results provide direct insights into the non-adiabatic dynamics of Mn(iii) complexes, which can be used to guide the synthesis of optically controlled SMMs.
八面体三价锰离子主要表现出轴向拉长的 Jahn-Teller（JT）畸变，这是其大的单轴磁各向异性的原因。因此，它们常用于单分子磁体（SMM）的合成。使用飞秒激光脉冲调制 JT 畸变可以提供一种控制磁化方向的途径，因此对于开发在超快时间尺度上工作的数据存储设备很有前景。对于各种三价锰配合物，已经证明了畸变从轴向拉长结构到轴向压缩结构的光致开关。然而，光致 JT 开关的锥形交叉区域周围的动力学仍然不清楚。在这里，记录了三（2,2,6,6-四甲基-3,5-庚二酮基）锰（III）（Mn(dpm)）在乙醇溶液中的超快瞬态吸收光谱，以进一步探索光致 JT 开关的动力学。我们观察到在激发态表面上产生了一个振动波包，其频率约为 155 cm，包含一个 JT 活性振动模式。这种相干运动在穿过锥形交叉回到基态后得以维持，基态沿着基态势能面（PES）发射波包，其频率分别约为 180 和 110 cm，我们分别将其归因于拉长态和压缩态。对频率的相对相位的检查揭示了与单模反应坐标一致的相移，并在激发态振动周期的 1/4 和 3/4 处穿过锥形交叉。我们的结果为三价锰配合物的非绝热动力学提供了直接的见解，可用于指导光控 SMM 的合成。
