Electron spin coherence for the magnetoreception of radical pair systems

The radical pair mechanism is widely recognized as the origin of electrons and spin polarization in photochemical reactions, but in recent years it has also been proposed as a candidate mechanism for magnetoreception of animals. In radical pair formation, the spin multiplicity (S or T) of the precursor excited state is conserved. Furthermore, spin multiplicity selectivity during radical pair recombination renders spin dynamics within the radical pair critically important. Whilst it is well established that spin dynamics within these radical pairs are coherent, direct observation remains exceptionally challenging. Direct observation is particularly difficult when this coherence is not artificially created by phenomena such as magnetic resonance used for spin observation. In the present study, we are progressing two spectroscopic techniques two-step laser irradiation and transient absorption detected external magnetic fields switching techniques, which are to investigate the origin of low-field effects in radical pairs. Both techniques are are accessible to coherent spin dynamics of RPs and give us the capability of the time-resolved measurements of the S-T mixing process in the low-field region.