Electron paramagnetic resonance (EPR) pulsed dipolar spectroscopy (PDS) using triplet states of organic molecules is a growing area of research due to the favourable properties that these transient states may afford over stable spin centers, such as switchability, increased signal intensity when the triplet is formed in a non-Boltzmann distribution and the triplet signal is used for detection, and high orientation selection, when the triplet signal is probed by microwave pulses. This arises due to the large spectral width at low fields, a result of the large zero field splitting, and limited bandwidth of microwave pulses used. Here we propose the triplet state of a substituted BODIPY moiety as a spin label in light induced PDS, coupled to a nitroxide, in a model peptide with a rigid structure. Orientation selection allows information on the relative position of the centres of the two labels to be obtained with respect to the nitroxide reference frame. Additionally, magnetophotoselection effects are employed to introduce optical selection and additional constraints for the determination of the relative orientation of the spin labels considering the reference frame of the triplet state.

中文翻译：

---

I2BODIPY 作为一种新的光开关自旋标记，用于利用磁光选择进行光诱导脉冲 EPR 偶极谱


使用有机分子的三重态的电子顺磁共振 （EPR） 脉冲偶极谱 （PDS） 是一个不断增长的研究领域，因为这些瞬态可能在稳定的自旋中心上提供有利的特性，例如可切换性、当三重态以非玻尔兹曼分布形成时信号强度增加，并且三重态信号用于检测， 以及当三重态信号被微波脉冲探测时，高取向选择。这是由于低场下的光谱宽度较大、零场分裂大以及所用微波脉冲带宽有限所致。在这里，我们提出了取代的 BODIPY 部分的三重态作为光诱导 PDS 中的自旋标记，与具有刚性结构的模型肽中的氮氧化物偶联。方向选择允许获得两个标签中心相对于氮氧化物参考系的相对位置信息。此外，磁光选择效应用于引入光学选择和附加约束，以确定考虑三重态的参考系的自旋标签的相对方向。