Electron Spin Decoherence due to Hindered Rotation in Donor-Bridge-Acceptor Linked Molecules

Extraordinarily broad line widths for the magnetic field effects (MFEs) on radical pair recombination in rigid oligoaromatic donor-bridge-acceptor molecules have been successfully simulated by the full-hybrid Monte Carlo (MC) MD simulation, in which modulation of the exchange coupling due to hindered rotation is directly calculated. It has been demonstrated that the single-site Liouville equation gives nearly identical results at general diffusional rotation times (< a few nanoseconds) if the effective exchange coupling and singlet–triplet dephasing rate constants are estimated from the electron-only MC simulation of spin coherence. Furthermore, the single-site model is applicable to multinuclear simulations of the so-called low-field effect, which is due to the coherent superposition of the degenerate zero-field eigenstates. These findings ensure MD-assisted spin dynamics simulations with high accuracy and fewer computational resources.