Bayreuth 1998 – scientific programme

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CP: Chemische Physik

CP 17: Sondersymposium: Einzelmolekülspektroskopie

CP 17.1: Talk

Thursday, March 12, 1998, 09:10–09:30, H18

Time Resolved Spectroscopy for Single Molecules — •Taras Plakhotnik and Daniel Walser — Physical Chemistry Laboratory, Swiss Federal Institute of Technology, ETH Zentrum, CH-8092 Z"urich, Switzerland

Fluorescence excitation spectroscopy on single guest molecules in low-temperature solids is the most direct method for measuring the homogeneous line shape of optical transitions and for studying interactions affecting the line shape. Unfortunately, in all "guest-host" systems exploited to date, the recording time of a single molecule line cannot be shorter than 10 ms in the best case. A new method based on the calculation of autocorrelation functions for spectra measured at a high acquisition rate is developed to study fast spectral dynamics of single molecules. The technique allows for temporal resolutions down to the luminescence lifetime. The method was applied to investigate spectral diffusion in two-photon excitation spectra of diphenyloctatetraene single molecules in an n-tetradecane Shpol’skii system. The diffusion is light induced, and is absent in one-photon excitation spectra. Its step-like temporal behavior is different from the one observed in glasses and described by the standard two-level-system model. The new technique is promising to find a wide range of applications in the study of spectral dynamics of single quantum systems on time scales from microseconds to hours.