Bonn 2000 – wissenschaftliches Programm

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MO: Molekülphysik

MO 6: Spektroskopie II

MO 6.1: Vortrag

Dienstag, 4. April 2000, 14:00–14:15, HS VI

Triplet-state lifetime and spectroscopy of single molecules at room temperature — •Mark A Weber — PCI, Uni Siegen, Adolf-Reichwein-Str.2, 57068 Siegen

We have investigated the fluorescence of single molecules with a confocal laser-scanning-microscope. By means of a servo controlled scanning table we were able to observe individual molecules for a long period of time. The excitation intensity can be varied by an acousto-optical modulator within microseconds. The dependence of the fluorescence intensity on the excitation intensity was examined. We have observed saturation in the fluorescence intensity, which can be explained theoretically.

The time-resolution of the detectors allowed us to examine dark periods of the molecules. The statistical analysis of the data showed that most of the dark periods can be attributed to the triplet state. The results show that the triplet lifetime of a single rhodamine 6G molecule depends on its individual environment. The triplet lifetime of molecules at the glass-air-interface is clearly below the lifetime of molecules covered with a polymer film.

Sequences of single-molecule fluorescence spectra are presented with integration times as short as 50ms. By reducing averaging effects in the time domain, the vibronic bands appear better resolved, often with distinct bands instead of a shoulder in time averaged spectra. Furthermore it can be shown that the fluctuation of the intensity ratio of the vibronic bands can considerably contribute to room temperature spectral diffusion.