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PHOTOPHYSICAL PARAMETERS OF CHLOROPHYLLS a AND b·FLUORESCENCE AND LASER‐INDUCED OPTOACOUSTIC MEASUREMENTS

Abstract— The quantum yields of internal conversion (energy loss) of the photoexcited chlorophylls a and b in ethanol at 24°C have been determined by measuring the quantum yields of the competing radiative (fluorescence) and non‐radiative (intersystem crossing) deactivation processes (which lead to energy storing species) by means of emission and laser‐induced optoacoustic spectroscopy, respectively. The values for internal conversion of chlorophyll a are 10% and 14% in the presence and absence of molecular oxygen, respectively. The corresponding yields for chlorophyll b are negligibly small. The internal conversion in chlorophyll a is attributed to vibronic coupling with the substituents of the porphin system, since internal conversion was found to be substantially reduced for unsubstituted Mg‐porphin in ethanol and for chlorophyll a when dissolved in a viscous medium.