Highly Efficient Spectral Hole-Burning in Oxygen-Evolving Photosystem II Preparations

We present the first report of highly efficient persistent spectral hole-burning in active (oxygen-evolving) Photosystem II (PSII) preparations. Samples are poised in the S1 state of the Kok cycle, with the primary quinone (QA) either neutral or photoreduced to QA - via a low-temperature pre-illumination. Remarkably efficient hole-burning is observed within the chlorophyll Q y (0,0) absorption envelope in the wavelength range of 676−695 nm. The hole-burning action spectrum of a sample poised in the S1(QA -) state is dominated by a narrow feature (∼40 cm-1) at 684 nm, where hole depths of 30% are attainable. The photoproduct for spectral holes burnt in this region is distributed across the ∼50 cm-1 absorption feature centered at 683.5 nm, independent of the excitation wavelength within this band. Saturated hole-burning experiments indicate weak electron−phonon coupling near 684 nm but stronger coupling for holes burnt near 690 nm. Selective excitation near 690 nm of samples in the S1(QA) state also results in efficient QA - formation. Negligible hole-burning activity is observed at higher energies (