Abstract

Radical (and polaron) pair recombination reactions play a role a wide variety of problems, ranging from why the electroluminescence of organic light emitting diodes changes in the presence of an applied magnetic field to how migratory songbirds detect the direction of the Earth’s magnetic field. The quantum mechanical Hamiltonian of a radical pair is straightforward to write down, but the resulting Schrödinger equation is extremely difficult to solve exactly for a radical pair containing a realistic number of hyperfine-coupled nuclear spins. We have developed both semiclassical and quantum mechanical methods to overcome this difficulty, derived the quantum master equations that account for radical pair recombination and electron spin relaxation processes, and performed a variety of benchmark radical pair spin dynamics calculations, including a recent exact quantum mechanical calculation of the spin dynamics of a carotenoid-porphyrin-fullerene complex that the Hore and Timmel groups have shown to provide a “proof of principle” for the operation of a chemical compass. This talk will review some of the highlights of our work in this area, starting with the problem that first motivated us to work on radical pairs and ending with a demonstration that the problem has now been solved.