PICOSECOND RESOLUTION OF INDOLE ANISOTROPY DECAYS AND SPECTRAL RELAXATION BY 2 GHz FREQUENCY‐DOMAIN FLUOROMETRY

We used frequency‐domain fluorescence spectroscopy to measure rotational diffusion and time‐resolved emission spectra of indole in methanol on the picosecond timescale. The indole emission was quenched by acrylamide to allow measurements to the instrumental limit of 2 GHz and to eliminate emission from the longer‐lived indole molecules, which can no longer provide information on the picosecond (ps) processes. The resolution was adequate to measure rotational correlation times as short as 8 ps at 80†C, and spectral relaxation times as short as 16 ps at 5†C.