Photo-magnetic properties and dynamics of multi-spin coupled systems

分子系统的自旋多重性在很大程度上影响其涉及电子态的动力学。在耦合自旋系统中，系统的总自旋多重数并不是简单地定义的，因为两个自旋并不总是耦合得足够强或足够弱以给出单个自旋多重数。特别是在适度耦合的三重态-双重态体系中，由于偶极相互作用的取向依赖性，基波函数的混合程度取决于磁场与分子轴之间的夹角。在p-联苯键的无铜基卟啉二聚体中，二聚体的最低电子激发态由游离碱的激发三重态和铜卟啉的基态二重态组成。在532 nm激光照射下，二聚体被激发，然后弛豫到最低电子激发态。该二聚体在甲苯中40K的时间分辨EPR谱表明，所观察到的激发态是一个适度耦合的三重态-双重态。部分取向样品在不同磁场位置的章动频率测量表明，系统的自旋多重性主要取决于共振磁场，也取决于分子相对于磁场的取向。

Spin multiplicity of the molecular system largely influences its dynamics involving electronic states. In coupled spin systems, the total spin-multiplicity of the system is not simply defined because the two spins are not always coupled enough strongly or weakly to give a single spin-multiplicity. Especially in moderately coupled triplet-doublet system, the degree of mixing of the basis-wavefunctions depends on the angle between the magnetic field and molecular axis due to orientation dependence of dipolar interaction. In a p-bipheyl-linked copper porphyrin-free base porphyrin dimer, the lowest electronic excited state of the dimer is composed of the excited triplet state of the free base and the ground state doublet of the copper porphyrin. Laser irradiation at 532 nm leads to the excitation of the dimer followed by the relaxation to the lowest electronic excited state. Time-resolved EPR spectra in toluene at 40K of this dimer suggest that the observed excited state is a moderately coupled triplet-doublet system. Nutation frequency measurements of partially oriented samples at different magnetic filed positions indicate that spin-multiplicity of the system largely depends on the resonance magnetic field and also the orientation of the molecule relative to the magnetic field.