Multiparameter Spectroscopy of Single Molecules

Multidetector TCSPC can be used to obtain several spectroseopie parameters simultaneously from a single molecule [108, 154, 155, 295, 419, 500]. The optical setup used in [419] is shown in Fig. 5.129. 

The molecules to be investigated are embedded in polymethylmathacrylate (PMMA). An image of the sample is obtained by scanning and assigning the photons to the individual pixels by their macro time. Based on this image, appropriate molecules are selected for further investigation. 

These molecules are then brought into the focus and time-tag data are acquired. From the macro times of the recorded photons traces of the emission intensity of a single molecule are built up. The traces show bright periods, when the molecule cycles between the ground state and the excited singlet state, and dark periods, when the molecule is in the triplet state (Fig. 5.130). 

The intersystem crossing yield is obtained from a histogram of the number of photons in the bright periods. The histogram of the dark periods reflects the triplet decay and delivers the triplet lifetime. The fluorescence lifetime is obtained by building up the fluorescence decay functions from the micro times. 

The histogram of the photon numbers in the bright periods, the histogram of the dark periods, and the histogram of the micro times are shown in Fig. 5.131. 

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