Low-magnetic field effect and electrically detected magnetic resonance measurements of photocurrent in vacuum vapor deposition films of weak charge-transfer pyrene/dimethylpyromellitdiimide (Py/DMPI) complex

Photogenerated carrier dynamics of TIPS-pentacene films as studied by photocurrent and electrically detected magnetic resonance

The carrier generation process and spin dynamics through photoexcitation in the vacuum vapour deposition film of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pn) were investigated by temperature dependence measurements of photocurrent and electrically detected magnetic resonance (EDMR). The EDMR signal was constructed from two components and showed a maximum at approximately 200 K. The temperature dependence was analysed using quantum mechanical simulation, assuming the carrier dynamics of the weakly coupled electron-hole pair (e-h pair). In addition, the analytical formula of photocurrent generation and EDMR signal intensity were also derived based on classical rate equations and used to understand the carrier dynamics. Through phase-shift analysis in quadrature detection of the EDMR signals, one of the two components was well analysed by using a narrow Lorentzian shape, and the other was by using a broad Gaussian.

Spin relaxation in radical pairs from the stochastic Schrödinger equation

We show that the stochastic Schrödinger equation (SSE) provides an ideal way to simulate the quantum mechanical spin dynamics of radical pairs. Electron spin relaxation effects arising from fluctuations in the spin Hamiltonian are straightforward to include in this approach, and their treatment can be combined with a highly efficient stochastic evaluation of the trace over nuclear spin states that is required to compute experimental observables. These features are illustrated in example applications to a flavin-tryptophan radical pair of interest in avian magnetoreception and to a problem involving spin-selective radical pair recombination along a molecular wire. In the first of these examples, the SSE is shown to be both more efficient and more widely applicable than a recent stochastic implementation of the Lindblad equation, which only provides a valid treatment of relaxation in the extreme-narrowing limit. In the second, the exact SSE results are used to assess the accuracy of a recently proposed combination of Nakajima-Zwanzig theory for the spin relaxation and Schulten-Wolynes theory for the spin dynamics, which is applicable to radical pairs with many more nuclear spins. We also analyze the efficiency of trace sampling in some detail, highlighting the particular advantages of sampling with SU(N) coherent states.