Abstract
A fast, sensitive differential calorimeter is described which permits the observation of heating caused by the relaxation of the lowest triplet states of organic molecules formed by flash excitation. From the ratio of slow to total heating after flash excitation, we calculate Φt, the quantum yield of triplet formation. The detection of the small amounts of heat involved (∼10−5 cal) is accomplished by means of a capacitor microphone transducer which measures volume changes caused by the heating. The response time (∼100 μsec) is determined by the lowest cavity resonance of the sample cell. At room temperature we find for anthrance in ethanol Φt=0.66, while for acridine orange in glyerol Φt=0.23.
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