Follmer Alec H, Ribson Ryan D, Oyala Paul H, Chen Grace Y, Hadt Ryan G
Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States.
J Phys Chem A. 2020 Nov 5;124(44):9252-9260. doi: 10.1021/acs.jpca.0c07860. Epub 2020 Oct 28.
Recent interest in transition-metal complexes as potential quantum bits (qubits) has reinvigorated the investigation of fundamental contributions to electron spin relaxation in various ligand scaffolds. From quantum computers to chemical and biological sensors, interest in leveraging the quantum properties of these molecules has opened a discussion of the requirements to maintain coherence over a large temperature range, including near room temperature. Here we compare temperature-, magnetic field position-, and concentration-dependent electron spin relaxation in copper(II) phthalocyanine (CuPc) and vanadyl phthalocyanine (VOPc) doped into diamagnetic hosts. While VOPc demonstrates coherence up to room temperature, CuPc coherence times become rapidly -limited with increasing temperature, despite featuring a more covalent ground-state wave function than VOPc. As rationalized by a ligand field model, this difference is ascribed to different spin-orbit coupling (SOC) constants for Cu(II) versus V(IV). The manifestation of SOC contributions to spin-phonon coupling and electron spin relaxation in different ligand fields is discussed, allowing for a further understanding of the competing roles of SOC and covalency in electron spin relaxation.
近期，人们对过渡金属配合物作为潜在量子比特（qubit）的兴趣，重新激发了对各种配体支架中电子自旋弛豫基本贡献的研究。从量子计算机到化学和生物传感器，利用这些分子量子特性的兴趣引发了一场关于在较大温度范围内（包括接近室温）保持相干性所需条件的讨论。在此，我们比较了掺杂在抗磁主体中的铜（II）酞菁（CuPc）和氧钒酞菁（VOPc）中，温度、磁场位置和浓度依赖的电子自旋弛豫情况。虽然VOPc在室温下仍能保持相干性，但尽管CuPc的基态波函数比VOPc更具共价性，其相干时间却随着温度升高而迅速受限。根据配体场模型的解释，这种差异归因于Cu（II）和V（IV）不同的自旋 - 轨道耦合（SOC）常数。文中讨论了SOC在不同配体场中对自旋 - 声子耦合和电子自旋弛豫的贡献表现，从而有助于进一步理解SOC和共价性在电子自旋弛豫中的竞争作用。
