Spectral hole burning of the primary electron donor state of Photosystem I

Persistent photochemical hole burned profiles are reported for the primary electron donor state P700 of the reaction center of PS I. The hole profiles at 1.6 K for a wide range of burn wavelengths (λ_B) are broad (FWHM∼310 cm^-1) and for the 45:1 enriched particles studied exhibit no sharp zero-phonon hole feature coincident with λ_B. The λ_B hole profiles are analyzed using the theory of Hayes et al. [J Phys Chem 1986, 90: 4928] for hole burning in the presence of arbitrarily strong linear electron-phonon coupling. A Huang-Rhys factor S in the range 4-6 and a corresponding mean phonon frequency in the range 35-50 cm^-1 together with an inhomogeneous line broadening of∼100 cm^-1 are found to provide good agreement with experiment. The zero-point level of P700^* is predicted to lie at∼710 nm at 1.6K with an absorption maximum at∼702 nm. The hole spectra are discussed in the context of the hole spectra for the primary electron donor states of PS II and purple bacteria.