DITFB/4-OH-TEMPO体系中卤键作用的19F DNP研究

卤键与氢键相似，是实现分子与分子非共价键连接的作用之一，其广泛地应用于工程材料和生命化学等领域．有关卤键相互作用的动态核极化（DNP）研究还未见报道．本文利用连续波-电子顺磁共振（CW-EPR）谱仪及自主研制的DNP实验平台对存在卤键相互作用的体系——1，4-二碘四氟苯（DITFB）/4-羟基-2，2，6，6-四甲基吡啶-1-氧自由基（4-OH-TEMPO）进行¹⁹F DNP研究，并与无卤键作用对照组——六氟苯（PFB）/4-OH-TEMPO的¹⁹F DNP增强效果进行了比较．结果发现，DITFB/4-OH-TEMPO较PFB/4-OH-TEMPO具有更窄的EPR线宽和更大的¹⁹F DNP增强．这表明自由基与DITFB卤键作用削弱了自由基之间的电子自旋-自旋相互作用，从而使自由基横向弛豫时间（T_2e）增加、线宽变窄，导致DNP饱和因子和增强倍数变大．因此，可以通过卤键调控自由基电子自旋相互作用，以改善核的DNP增强效果．

The Effect of Intermolecular Halogen Bond on 19F DNP Enhancement in 1, 4-Diiodotetrafluorobenzene/4-OH-TEMPO Supramolecular Assembly

Halogen bond, as hydrogen bond, is a non-covalent bond. Dynamic nuclear polarization (DNP) technique has been used previously to study hydrogen bonds-mediated intermolecular interactions. However, no study has been carried out so far to study the halogen bond-mediated intermolecular interactions with DNP. In this work, 19F DNP polarization efficiency of the halogen bonds existing in supramolecular assembling by 4-OH-TEMPO and 1,4-diiodotetrafluorobenzene (DITFB) was studied on a home-made DNP system. The formation of intermolecular halogen bonds appeared to increase 19F DNP polarization efficiency, suggesting that the spin-spin interactions among electrons were weakened by the halogen bonds, resulting in an increased T2e and a larger saturation factor.