Temperature dependence of relaxation time of a stable radical pair in SyPixD investigated by pulsed EPR

The temperature dependence of the spin–lattice relaxation of the radical pair of flavin and tyrosine in SyPixD was investigated by pulsed electron paramagnetic resonance (EPR) spectroscopy. Biphasic recovery with a fast component of the spin–lattice relaxation time, denoted as T1fast, and slow component of spin–lattice relaxation time, denoted as T1slow, was detected in the range of 4–80 K. Based on the temperature dependence of T1fast and T1slow below 16 K, the exchange coupling of the radical pair was estimated as 2J = 6–8 cm−1, defined as H = - 2 J S 1 ∗ S 2 .