A study on the energy-dependent quenching of chlorophyll fluorescence by means of photoacoustic measurements.

The mechanism of energy-dependent quenching (qE) of chlorophyll fluorescence was studied employing photoacoustic measurements of oxygen evolution and heat release. It is shown that concomitant to the formation of qE the yield of open reaction centers φp decreases indicating that qE quenching originates from a process being competitive to fluorescence as well as to photochemistry. The analysis of heat release (rate of thermal deactivation) shows: 1. The competitive process is not given by a still unknown energy storing process. 2. If the competitive process would be a futile cycle the life-times of the involved intermediates had to be faster than 50 μs.The results of the photoacoustic measurements are in line with the idea that qE quenching originates from an increased probability of thermal deactivation of excited chlorophylls.