Revealing the Impact of <i>g</i>-Tensor Anisotropy on the Charge Recombination in Donor–Acceptor Dyads Under High Magnetic Fields

Four new donor-acceptor dyads, featuring triarylamine donors and perylene diimide acceptors, were synthesized to investigate the influence of the <i>g</i>-tensor on the magnetic field-dependent spin dynamics of the resulting radical pairs. These pairs are characterized by the exchange interaction 2<i>J</i> being larger than the effective isotropic hyperfine coupling <i>a</i>_eff. To control the isotropic <i>g</i>-factor and <i>g</i>-tensor anisotropy of the radical anion generated via photoinduced electron transfer, the perylene diimides were functionalized with phenyl chalcogen ethers. In dyads containing oxygen, sulfur, and selenium ether substituents, not only was the characteristic 2<i>J</i>-resonance observed but also a pronounced high-field effect in the charge recombination kinetics, extending up to <i>B</i> = 10 T. Quantum dynamics simulations based on the stochastic Liouville equation revealed that this effect is primarily driven by <i>g</i>-tensor anisotropy-induced relaxation, which increases along the chalcogen ether series. Additionally, we derived an exact analytical solution describing the impact of <i>g</i>-factor differences and <i>g</i>-tensor anisotropy on spin relaxation in the high-field limit. These findings highlight the critical role of <i>g</i>-tensor-induced relaxation in radical pairs at high magnetic fields, offering new insights for the molecular design of materials with potential applications in quantum information science, where incoherent relaxation processes should be avoided.