A REVERSIBLE PHOTOCHEMICAL REACTION OF CHLOROPHYLL a WITH I2

Abstract
Abstract— Chlorophyll a and I2 form a 1:1 addition compound, which exhibits a strong absorption maximum at about 360 nm. When dissolved in anaerobic methanol, this compound can be reversibly bleached by illumination with red light. Prolonged illumination at low temperatures (˜– 75°C) or intense illumination at room temperature reduces the height of the red absorp tion maximum to about half of its normal value. Since the thermal back reaction is negligibly slow at – 75°C, presumably the chlorophyll‐I2 complex is converted completely to its bleached form, when illuminated under those conditions. This assumption leads to a simple mechanism which is consistent with the experimental data.

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