Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, F-91405 Orsay, France.
Phys Chem Chem Phys. 2020 May 28;22(20):11498-11507. doi: 10.1039/d0cp01127d. Epub 2020 May 12.
We report a comprehensive study of the structures and deactivation processes of protonated adrenaline through cryogenic UV photodissociation spectroscopy. Single UV and double-resonance UV-UV hole burning spectroscopies have been performed and compared to coupled-cluster SCS-CC2 calculations performed on the ground and first electronic states. Three conformers were assigned, two lowest energy gauche conformers along with a higher energy conformer with an extended structure which is indeed the global minimum in solution. This demonstrates the kinetic trapping of this high energy gas phase conformer during the electrospray process. At the band origin of all conformers, the main fragmentation channel is the C-C bond cleavage, triggered by an excited state proton transfer to the catechol ring. Internal conversion leading to the water loss channel competes with the direct dissociation and tends to prevail with the increase of excess energy brought by the UV laser. Picosecond time-resolved pump-probe spectroscopy was performed to measure the excited state lifetimes of the three conformers of AdH, which decay with the increase of excess energy in the ππ* state, from 2 ns at the band origin down to few hundreds of picoseconds 0.5 eV to the blue. Finally, about 0.8 eV above the band origin, the πσ* state is directly reached, leading to the opening of the H-loss channel.
我们通过低温 UV 光解光谱法对质子化肾上腺素的结构和失活过程进行了全面研究。进行了单 UV 和双共振 UV-UV 烧孔光谱学研究，并与在基态和第一电子态上进行的耦合簇 SCS-CC2 计算进行了比较。分配了三种构象，两种最低能量的 gauche 构象以及一种具有扩展结构的更高能量构象，该构象实际上是溶液中的全局最小值。这表明在电喷雾过程中，这种高能气相构象被动力学捕获。在所有构象的带原点处，主要的断裂通道是 C-C 键的断裂，这是由激发态质子转移到儿茶酚环引发的。导致水损失通道的内部转换与直接解离竞争，并随着 UV 激光带来的过剩能量的增加而趋于占主导地位。进行了皮秒时间分辨泵浦探测光谱学研究，以测量 AdH 的三种构象的激发态寿命，这些寿命随着ππ态中过剩能量的增加而增加，从带原点的 2 ns 下降到 0.5 eV 处的几百皮秒。最后，在带原点上方约 0.8 eV，直接达到πσ态，导致 H 损失通道打开。
