用于指导仲氢诱导核极化状态保存的己烯分子中五自旋的单重态制备和寿命研究

仲氢诱导核极化（PHIP）技术能极大地增强核磁共振（NMR）信号的灵敏度，已被应用于磁共振成像、原位化学反应监测等领域．除了不断提高不同分子极化后的灵敏度外，延长和保存高极化度状态对PHIP技术的应用也至关重要，其中将极化后的状态制备成核自旋单重态是目前被研究较多的一种方法．本文以能被PHIP技术极化的己烯分子为研究对象，通过设计优化控制脉冲，对分子中的一个五自旋体系进行操控，制备了多种核自旋单重态，结果表明：己烯分子的碳-碳双键上存在三种不同的核自旋单重态，它们的寿命均长于仲氢极化后产生的初始态的寿命，可以作为延缓极化度衰减的一种中间态；通过对比单重态的寿命与相应自旋的纵向弛豫时间发现，将极化后己烯的状态转化为纵向磁化可能也是一种保存极化度的有效方法．

Preparation and Lifetime Studies of the Singlet State of Five Spins in Hexene Molecules Used to Guide the Preservation of the Parahydrogen-induced Nuclear Polarization State

Parahydrogen-induced polarization (PHIP) technique can greatly enhance the sensitivity of nuclear magnetic resonance (NMR) signals, and has been applied in the fields of magnetic resonance imaging, in situ chemical reaction monitoring, etc. In addition to improving the sensitivity of different molecules in the PHIP, it is also crucial to extend and preserve the high polarization state. To achieve this, a possible approach is to transfer the polarized state into a nuclear spin singlet state. Here, we focus on the singlet states preparation in hexene molecule that can be polarized by PHIP. By designing optimal control pulses, a five-spin system in hexene molecule was manipulated, and various quantum states were prepared respectively. Our results show that three different nuclear spin singlet states could be prepared with the group CH₂=CH- in hexene. The three different nuclear spin singlet states have longer lifetime than that of the initial state polarized by PHIP, and thus can be utilized as the intermediate states to delay the decay of the polarization state. By comparing the lifetime of the singlet state with the longitudinal relaxation time of the corresponding spin, it is deduced that converting the state of the polarized hexene to longitudinal magnetization may also be an effective way to preserve the polarizability.