Absorbance-detected electron spin echo spectroscopy of non-radiative triplet states in zero field: An application to the primary donor of the photosynthetic bacterium rhodobacter sphaeroides R-26

Abstract Electron spin echoes of triplet states in zero field were optically detected using the singlet ground-state absorbance. The technique has been applied to reaction centers of the photosynthetic bacterium Rhodobacter sphaeroides R-26. The spin-spin relaxation time T 2 of the triplet state of the primary electron donor P (a bacteriochlorophyll dimer) was 1.16±0.05 μs, independent of temperature in the range 1.2–2.1 K.