Kabanova Victoria, Sander Mathias, Levantino Matteo, Kong Qingyu, Canton Sophie, Retegan Marius, Cammarata Marco, Lenzen Philipp, Lawson Latévi Max Daku, Wulff Michael
X-ray Photon Science, Uppsala, MB 516, Sweden.
Paul Scherrer Institute, 5232 Villigen, Switzerland.
Struct Dyn. 2024 Oct 23;11(5):054901. doi: 10.1063/4.0000254. eCollection 2024 Sep.
The structure and spin of photoexcited Fe(phen) in water are examined by x-ray scattering and x-ray emission spectroscopy with 100 ps time resolution. Excitation of the low-spin (LS) ground state (GS) to the charge transfer state MLCT leads to the formation of a high-spin (HS) state that returns to the GS in 725 ps. Density functional theory (DFT) predicts a Fe-N bond elongation in HS by 0.19 Å in agreement with the scattering data. The angle between the ligands increases by 5.4° in HS, which allows the solvent to get 0.33 Å closer to Fe in spite of the expansion of the molecule. The rise in solvent temperature from the return of photoproducts to the GS is dominated by the formation dynamics of HS, MLCT → HS, which is followed by a smaller rise from the HS → GS transition. The latter agrees with the 0.61 eV energy gap E(HS)-E(LS) calculated by DFT. However, the temperature rise from the MLCT → HS transition is greater than expected, by a factor of 2.1, which is explained by the re-excitation of nascent HS by the 1.2 ps pump pulse. This hypothesis is supported by optical spectroscopy measurements showing that the 1.2 ps long pump pulse activates the HS → MLCT channel, which is followed by the ultrafast return to HS via intersystem crossing. Finally, the spins of the photoproducts are monitored by the K emission and the spectra confirm that the spins of LS and HS states are 0 and 2, respectively.
通过具有100皮秒时间分辨率的X射线散射和X射线发射光谱，研究了水中光激发的Fe(phen)的结构和自旋。低自旋（LS）基态（GS）激发到电荷转移态MLCT会导致形成高自旋（HS）态，该态在725皮秒内回到GS。密度泛函理论（DFT）预测HS中Fe-N键伸长0.19Å，与散射数据一致。HS中配体之间的角度增加5.4°，这使得尽管分子膨胀，溶剂仍能比Fe靠近0.33Å。光产物回到GS导致的溶剂温度升高主要由HS的形成动力学主导，即MLCT→HS，随后是HS→GS跃迁导致的较小温度升高。后者与DFT计算的0.61eV能隙E(HS)-E(LS)一致。然而，MLCT→HS跃迁导致的温度升高比预期大2.1倍，这是由1.2皮秒泵浦脉冲对新生HS的再激发来解释的。这一假设得到了光谱测量的支持，测量表明1.2皮秒长的泵浦脉冲激活了HS→MLCT通道，随后通过系间窜越超快回到HS。最后，通过K发射监测光产物的自旋，光谱证实LS和HS态的自旋分别为0和2。
