Femtosecond internal conversion and reorientation of 5-methoxyindole in hexadecane

The femtosecond internal conversion (IC) of the tryptophan sidechain analog 5-methoxyindole (5MI) in hexadecane (HD) was observed using fluorescence upconversion. The time constant for internal conversion between 1La and 1Lb was estimated at 10–40 fs. A triple-exponential emission anisotropy decay, due to molecular reorientation, was also observed. The dependence of initial anisotropy upon excitation wavelength sets limits on 1La vs. 1Lb transition oscillator orientations.